Principles of Smoke Management

PRINCIPLES OF SMOKE MANAGEMENT

This publication was made possible by funds from ASHRAE research.

Principles of Smoke Management by John Klote and James Milke is an exhaustive treatment of smoke management, including pressurized stairwells, pressurized elevators, zoned smoke control, and smoke management in atria and other large spaces. Recent advancements include heat release rate, toxicity of smoke, natural atrium venting, plugholing, minimum depth of an atrium smoke layer, smoke stratification, smoke detection, tenability systems, and computer analysis. The book includes numerous example calculations. Methods of analysis include equations, network flow models, zone fire models, scale modeling, and hazard analysis. Computational fluid dynamics (CFD) is also addressed. The book includes a CD of computer software for ar~alysisof smoke management systems.

This publication was prepared under ASHRAE Research Project 1122. Cognizant TC: TC 5.6, Fire and Smoke Control.

ABOUT THE AUTHORS John H. Klote, DSc., P.E., Fellow ASHRAE, is a consulting engineer specializing in the design and review of smoke management systems, as well as code consulting and teaching private smoke management courses. He conducted research for 19 years at the National Institute of Standards and Technology (NIST) and has published over 80 papers and articles on smoke management and other aspects of fire protection. Dr. Klote headed the Building Fire Physics Group at NIST, which conducted research in smoke niovement in buildings. The tools used for this research included full-scale fire experiments, scale model fire experiments, network airflow models, zone fire models, and computational fluid dynamics (CFD). Klore acted as a consultant in the area of smoke movement for the investigations of the MGM Grand fire and the First Interstate Bank fire. Klote's research was the basis of the 1997 revision to the NFPA Life Safety Code (section 5-2.13), allowing elevators to be used as a second means of egress from towers. In 1986, he earned a Doctor of Science degree in mechanical engineerins from George Washington University. He is a member of the National Fire Protection Association (NFPA). a fellow of SFPE, and a fellow of ASHRAE. He has extensive participation in ASHRAE and NFPA committees, including being a past chairman of ASHRAETC 5.6, Fire and Smoke Control. Dr. ~ l o t is e a registered professional engineer in the District of Columbia, North Carolina, California, and Delaware. James A. Milke, Ph.D., is an associate professor and associate chair of the Department of Fire Protection Engineering at the University of Maryland. Dr. Mike has been a member of thefaculty and staff of the department since 1977. He received his Ph.D. in aerospace engineering from the University of Maryland, with an emphasis in structures. He received an M.S. degree in mechanical engineering and a B.S. degree in fire protection engineering, both from the University of Maryland. In addition. he has a B.S. degree in physics from Ursinus College. Dr. Mike has served as a research fire prevention engineer at the Building and Fire Research Laboratory, National Institute of Standards and Technology, as the fire protection engineer for Fairfax County, Virginia, and as,a consultant to numerous organizations. Dr. Milke is a fellow of the SFPE and is a member of the National Fire Protection Association. the International Association of Fire Safety Science. and the American Society of Civil Engineers. He is the chairman of the NFPA Technical Committee on Smoke Management Systenis and the ASCWSFPE committee on Structural Design for Fire Conditions. He ser\.es on the Fire Council of Underwriters Laboratories.

PRINCIPLES OF SMOKE MANAGEMENT

John H. Klote 0

James A. Milke

American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc.

Society of Fire Protection Engineers

ISBN 1-883413-99-0

02002 American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc. 1791 Tullie Circle, N.E. Atlanta, GA 30329

AI1 rights reserved. Printed in the United States of America

ASHRAE has compiled this publication with care, but :W-IRAE has not investigated, and ASHRAE expressly disclaims any duty to investigate, any product, service, process, procedure, design, or the like that may be described herein. The appearance'of any technical data or editorial material in .this publication does not eonstitute endorsement, warranty, or guaranty by ASHRAE of any product, service, process, procedure, design, or the like. ASHRAE docs not warrant that the information in the publication is free of errors, and ASHRAE does not necessarily agree with any statement or opinion in this publication. The entire risk of the use of any information in this publication is assumed by the user. No part of this book may be reproduced without permission in writing from ASHRAE, except by a reviewer who may quotc brief passaees or reproduce illustrations in a revicw with appropriate crcdit; nor may any part of this book be reproduced, stored in a retrieval system, or transmitted in any way or by any means--electronic. photocopying. recording, or other-without permission in writing from ASHRAE.

ASHRAE STAFF

Mildred Ceshwiler Editor

Erin Howard Assistant Editor

Barry Kurian

manager Jayne Jackson Pi-od~ictioi~ Assistant

Christina Johnson Editorial Ass b r n / ~ t

PUBLISHER W. Stephen Cornstock

DEDICATION This book is dedicated to the memory of George T. Tamura, who conducted pioneering research in smoke control at the National Research Council of Canada.

TABLE OF CONTENTS Chapter

Page

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X Chapter I-Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l Chapter 2-Fire and Heat Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Chapter 3-Smoke and Tenability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Chapter &Evacuation

Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

Chapter 5-Effective Areas and Smoke Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Chapter &-Principles

of Smoke Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Chapter 7-Air Moving Equipment and Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

111

Chapter 8 . 4 omputer Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

119

Chapter 9-Hazard Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

129

Chapter 10-Stainvell Pressurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Chapter 1 l-Elevator Smoke Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

157

Chapter 12-Zoned Smoke Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

171

Chapter 13-Fundamental Concepts for Atria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

181

Chapter 14-Atrium Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

199

Chapter 15-Physical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

217

Chapter 16-Computational Fluid Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Chapter 17-Commissioning and Routine Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

243

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

247

Appendis A-Units of Mcnsurcmcnt and Physical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

vii

AppendixB-Bibliography .................................................................... 271 Appendix C-Calculation of Elevator Evacuation Time

............................................. 277

Appendix D-Application of CONTAMW ........................................................ 289 Appendix E-ASMET Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

321

Appendix F-ASET-C: A Room Fire Program for Personal Computers .................................

329

Appendix G-Data and Computer Output for Stairwell Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 Appendix H-Data and Computer Output for Zoned Smoke Control Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 Appendix I-Inspection Procedures for Smoke Control Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 Appendix J-Test Procedures for Stairwell Pressurization Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 Appendix K-Test Procedures for Zoned Smoke Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 Appendix L-Inspection Procedures for Atria Smoke Exhaust systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 Appendix M-Test Procedures for Atria Smoke Exhaust Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

PREFACE In 1983, ASHRAE published Design of Smoke Control Systems for Buildings, written by myself and John Fothergill. This book was the first attempt to consolidate and present practical information about smoke control design. Judging by the many favorable comments and suggestions about this first book, I feel that it was a success. The first publication was limited to systems that control smoke by means of the physical mechanisms of pressurization and airflow. In 1992, ASHRAE and SFPE jointly published Design of Smoke Management System written by myself and James Milke. The term smoke management was used in the title of this publication to indicate that the physical mechanisms were expanded from pressurization and airflow to include compartmentation, dilution, and buoyancy. Based on heightened concerns about supplying combustion air to the fire, a caution was added about the use of airflow for smoke management. This new publication addresses the material of the two earlier books plus people movement in fire, hazard analysis, scale modeling, and computational fluid 'dynamics. In addition, the material about tenability and atrium smoke management has been extensively revised. As with the other books, this new book is primarily intended for designers, but it is expected that it will be of interest to other professionals (code oficials, researchers, etc.). This book and its predecessors are different from other design books in a number of respects. This book is written in both English units (also called IP, for inch-pound) and S1 units so that it can be used by a wide audience. To the extent practical, equations are accompanied by derivations and physical descriptions of the mechanisms involved. The physical descriptions are worked into the text as simple explanations of how particular mechanisms, processes, or events happen. The goal of the derivations and physical descriptions is to provide information and understanding so that readers can apply the material of this book in creative and insightful ways. As with the first two publications, I hope that this book is of value to the engineering community. Further, I invite readers to mail their suggestions and comments to me at the address below: John H. Klote, D.Sc., P.E.

I I I I Carper Street McLean, VA 22 l0 l

ACKNOWLEDGMENTS This project would not have been possible without the support of the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE). Acknowledgment is made to the members of the ASHRAE Smoke Control Monitoring Committee for their generous support and constructive criticism. The members of this subcommittee are: Williarn A. Webb, Chairman (Performance Technology Consulting, Ltd., Lake Bluff, Ill.) John A. Clark (Eagan, Minn.) Dave Elovitz (Energy Economics, Inc., Natick, Mass.) Gary Lougheed (National Research Council Canada, Ottawa, Ontario) The support and advice of the staff of the Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., was invaluable. Particular appreciation is expressed to Richard Bukowski, Glen Fomey, and Richard Peacock. Special thanks are due to Daniel Madrzykowski for his advice regarding oxygen consumption calorimetry and heat release rate. The authors are indebted to Kevin McGrattan of BFRL for his valuable advice and constructive criticism regarding computational fluid dynamics. Richard Gann and Barbara Levin of N E T and Emil Braun of Hughes Associates, Baltimore, Md., provided valuable information and insight concerning the evaluation of the effects of toxic exposures. Creg Beyler of Hughes Associates provided constructive criticism in a number of areas. Special thanks are due to Gary Lougheed for his constructi\-e criticism and for tlie body of relevant research conducted by him and his associates at the National Research Council of Canada. Students of fire pro~ectionengineering at the University of Maryland have provided insightful comments on drafts of several chapters of this book In particular, the students Suzelte Hartmann and Julie Naviaser developed the information about CONTAMW that is included as Appendix D. The content of this book is heavily dependent upon tlie work of many researchers, design engineers, and other professionals around the world. So many of these people have provided experimental research results, system concepts, and analytical methods that it is impossible to thank them all individually. Appreciation is expressed to all those u h o have contributed to the advancement of smoke managemen1 technology directly or indirectly by their contributions to fire science and fire protection engineering.

CHAPTER 1

Introduction moke is recognized as the major killer in fire situations. Smoke often migrates to building locations remote from the fire space, threatening life and damaging property. Stairwells and elevator shafts frequently become smoke-logged, thereby blockin,0 evacuation and inhibiting rescue and fire fighting. The MGM Grand Hotel fire (Best and Demers 1982) is an example of the smoke problem. The fire was limited to the first floor, but smoke spread throughout the building. Some occupants on upper floors were exposed to smoke for hours before rescue. The death toll was 85, and the majority of the deaths were on floors far above the fire.

S

The MGM Grand is not unique in this respect, as is illustrated by the fires at the Roosevelt Hotel (Juillera~t 1964) and Johnson City Retirement Center (Steckler et al. 1990). All of these fires were located on the first floor, but the majority of deaths were on upper floors (Figure 1.l).'

l , During the intensive activity of fire fighting and rescue, the locations of some of the bodies are not recorded. Thus Figure 1.1 is limited to the deaths for which the locations were known.

L

23 22 21 20 19 18 17

g E

Retirement Center Fire Johnson City. TN Dec 24,1989

8 7

4 1

2 I 0 1 2 3

MGM Grand Hotel Fire Las Vegas, NV Nov 21,1980

Deaths

Note: Floors Renumbered for 2 I 0

1 2 3 4 5 6 7 8 9101112131415161718

Deaths

L.,-I

0 1 2 3 4 5 6 7 8

Deaths

Figure I .I Deaths byjloor for three fires where rhefire was locn~ed017 rile firsrjloot:

Chapter l - Introduction

Figure l .2 Floor plan of the Health Care Test Faciliy at the ArIST Annex. The general public is unaware of how fast a fire can grow and of how much smoke can be produced by a fire. This unawareness extends to many designers and other related professionals. Because such an awareness is necessary to the evaluation of design parameters for smoke management systems, the following example is provided. This example is fire test N-54, performed at the Health Care Test Facility at the National Institute of Standards and Technology Annex in Gaithersburg, Md. For technical details of this unsprinklered fire test, the reader is referred to a report by O'Neill et al. ( 1 980). The floor plan of the test facility is shown in Figure 1.2. In this test, various fabrics representing common clothing materials were hung on wire coat hangers and arranged loosely in a wooden wardrobe. A cardboard box containing crumpled newspaper was placed on the floor of the wardrobe. The test started when the crumpled newspaper was ignited by a match. Following ignition, the left-hand door of the wardrobe was closed tightly while the right-hand door was left partially open resulting in a 3 in. (76 mm) opening along the vertical edge of the door. At one second after ignition, no flame or smoke was visible. At 80 seconds, flames were visible flowing from the top of the wardrobe, a layer of smoke was covering the ceiling of the burn room, and smoke had flowed into the corridor forming a one-foot-thick layer just below the corridor ceiling. At 110 seconds, flames were flowing from the top two-thirds of the wardrobe opening, and the smoke flowing out of the burn room doorway had increased significantly. At 120 seconds after ignition, flames were flowing from the entire opening of the wardrobe door, and the layer of smoke in the corridor and lobby had descended to approximately 4 ft (1.2 m) below the ceiling.

Such very rapid fire growth and accompanying smoke production represent a real possibility in .actual wardrobe fires and perhaps even closet fires. Many other fire scenarios are possible. For example, a latex or a polyurethane filled mattress ignited by an adjacent wastebasket fire would reach about the same stage of development in six minutes that wardrobe test N-54 reached in two minutes. Full-scale fire tests by Bennetts et al. (1997) and Lougheed et al. (2000, 2001) have shown that successfully sprinklered fires can continue to bum and produce enormous amounts of dense buoyant smoke after sprinkler activation. While it appears this smoke production is greatest for fires that are shielded from sprinkler spray, some unshielded fires still produced considerable amounts of buoyant smoke. The concept of smoke management has developed as a solution to the smoke migration problem.2 Smoke movement can be managed by use of one or more of the following mechanisms: compartmentation, dilution, airflow, pressurization, or buoyancy. These mechanisn~s are discussed in detail in Chapter 4. The use o f pressurization produced by mechanical fans is referred to as snloke control by NFPA 92A (NFPA 2000). By this definition, stairwell pressurization (Chapter 7), elevator pressurization (Chapter 8), and zoned smoke control (Chapter 9) are all types of smoke control systems. The primary emphasis of this book is on systems that cse pressurization produced by mechanical fans. The use of pressurization to control the flow of undesired airborne matter has been practiced for at least 50 years. For example, it has been used in buildings, such as experimental laboratories, where there is danger of 2. As discussed later in "Preliminary Design Considerations," smoke management is only one of many techniques available to h e protection engineers.

Principles of ~ m o k ~ ~ a n a ~ e m e n t

poison gas, flammable gas, or bacteriological material migrating from one area to another; it has been used to control the entrance of contaminants where a dust-free environment is necessary; it has been used wheremdiation migration and contamination could occur; and it has been used in hospitals to prevent the migration of bacteria to sterile areas. However, the use of airflow and pressurization to control smoke flow from a building fire is a fairly recent adaptation.

INTENT The primary intent of this book is to provide practical state-of-the-art infoimation to engineers who have been charged with design of smoke management systems. The book is also intended to provide information for the review of designs and development of codes and standards,. This chapter contains general background informati6n; Chapter 2 deals with fire development and the heat :release rate of fires. Chapter 3 discusses the nature of:s.moke, including toxicity, heat exposure, and visibility through smoke. Chapter 4 ciiscusses people movement during- fire evacuation. Chapter 5 is devoted to smoke movement in buildings, and the individual driving forces of smoke movement are discussed in detail. Chapter 6 contains a fimdamental discussion of topics that are essential for the design of systems to manage smoke movement. It discusses the mechanisms of compartmentation, dilution, airflow, pressurization, and buoyancy, which are used by themselves or in combination to manage smoke conditions in fire situations. Background information is provided about ducts, fans, fire dampers, smoke dampers, and fan-powered ventilation systems in Chapter 7. Chapter 8 is a description of the computer programs that are used for the analysis of smoke management systems. Chapters 9 through 14 address hazard analysis, stairwell pressurization, elevator smoke control, zoned smoke control, and atrium smoke management. For applications for which these conventional methods are inappropriate, the methods of scale modeling and computational'fluid dynamics (CFD) can be used (Chapters 15 and 16). Chapter 17 addresses the important topic of commissioning and routine testing. It may be noted that pressurized corridors have been omitted. The principIes presented in this book can bz applied to pressurized corridors in a manner similar to their application to other pressurization systems. The . concern with pressurized corridors is that if a fire room door is blocked open, the corridor pressurization system can force smoke into other rooms off the corridor. For this reason, pressurized corridors are not generally recommended except for applications where practical '

~

methods are employed to minimize the possibility of doors being propped open. While advances in tenability analysis have made engineering analysis of smoke shafts feasible, these systems are not included in this book. The idea of smoke shafts is that smoke flows up the shaft due to bgoyancy where the smoke flows away from the building, but the authors have concerns about the fundamental effectiveness of smoke shafts. Further, there seems to be little interest in smoke shafts. The stair systems known as "smokeproof' towers are misnomers, in that there is nothing about them that ensures no smoke migration into stairs. Originally, these towers were separate from the building and were connected to it only by walkways open to the outside. Some versions of these towers used relatively small openings in exterior vestibule walls in place of the separate walkways. In the absence of an engineering analysis of these systems, it can only be stated that the benefits of these systems are questionable. For these reasons, separated stair towers are not included in this book, and it is recommended that the term "smokeproof' towers not be wed.

EQUATIONS AND UNITS OF MEASUREMENT Considering that this book is primarily intended for design, it seems most appropriate that units should be specified for every equation. However, the topic of smoke management is relatively new, and there is no test to refer to for the derivation of many of the equations used. Further, it was desired that the text be in both Inch-Pound (IP) units and the International System (S[) units. It would be unacceptably cunlbersome to present derivations using both commonly used English units and S1 units. The equations used for derivations are dinlensionally homogeneous, and they can be used with the S1 system, the slug pound system, and the pound mass poundal system (Appendix A). These dimensionally homogeneous equations are easily identified because no units are specified for them in the text. Howe\;er, all of the equations t h a ~the reader is IikeIy to use for design analysis are given in both English and S1 units. These equations are easily identified because the appropriate units for the equation are specifically indicated in the text.

~

HISTORY OF SMOKE VENTING

-

Smoke venting has been used extensively to manage smoke flow during theater fires. The acceptance of such venting resulted from several major theater fires, including those at the Brooklyn theater, which killed 283 in 1877; the Vienna Ring theater. which killed 449

Chapter l -Introduction

A

ServiceTower

Are Areas 2 and 4 on Floor 10

Experimental Tower

I

m

............. ....... m

. m . m

m

............ :::::.--p ..... ........... ............ ............m m............

iiilial:l

m

. m . Fire Area 3 on Floor l 0 n

m

m

I n

3 Smoke Shafl 4 ElwatorlSiau Lobby Supply

Figure 1.3 Typical floor plan of the office building at 30 Church Street.

Figure 1.4 Typicalfloor plan of 117e NRCC exper-hen-

in 188 1; the Theater Royal, which killed 186 in 1887; and the Iroquois theater, which killed 571 in 1903. All of these fires started on the theater stage and resulted in major loss of life in the audience. The Palace theater fire in Edinburgh in 1911 was an exception. In this fire, smoke venting through the stage roof was credited for helping to prevent any loss of life. The buoyancy of the hot smoke forced the smoke flow through the vent openings, and this venting is called natural venting or gravity venting. Over the past few decades, fan-powered smoke exhaust has become the standard for almost all atria in North America. In other areas, such as Europe, Australia, and New Zealand, both natural venting systems and fan-powered exhaust systems have become common for atria. Modem atria smoke management designs are based on engineering analysis developed over the last few decades. These analytical methods are primarily based on research in smoke plumes andzone fire modeling. Information about these analytical methods is provided in Chapters 13 and 14.

klered fires. The term "smoke free" is used to mean essentially free of smoke, with the possibility of such insignificant amounts of combustion products that tenability is maintained. Other full-scale fire tests also demonstrated that pressurization could provide "smoke free" exits during large unsprinklered fires (Koplon 1973a, 1973b; Butcher et al. 1976). Cresci (1973) describes visualization experiments using a model of the stair shaft at the Church Street building, where stationary vortices \\.ere observed at open doonvays. These vortices are the reason that the flow coefficient through an open stainvell door is about half of what it \i.ould be otherwise. This significant effect on airflow is discussed in Chapter 6. The Research Tower near Ottawa (Figure 1.4) was used for a joint National Institute of Standards and Technology (NIST) and National Research Council Canada (NRCC) study of elevator smoke control. Again, i t was demonstrated that pressurization could control smoke from large unsprinklered fires (Tamura and Klote 1987a, 1987b, 1988; Klote and Tamura 1986a, 1986b, 1987). In the spring of 1989, NIST conducted a series of experiments of zoned smoke control at the Plaza Hotel in Washington D C , as shown in Figure 1.5 (Klote 1990). A zoned smoke control system is a system that uses pressurization to restrict smoke migration to the zone of fire origin. Once again, it was demonstrated that pressurization could control smoke from large unsprinklered fires. An analysis based on first principles of engineering was made of the pressure differences produced by the smoke control'system during the fires at the Plaza Hotel. As is done with zone fire modeling, the pressures n.ithin rooms were considered hydrostatic. The general trends of calculated values were in agreement with the msasurements (Figure l h ) , and this indicates a levc.1 of

HISTORY OF PRESSURIZATION SMOKE CONTROL The idea of smoke protection by pressurization systems is .to restrict the movement of smoke from a building fire. To study the effectiveness of pressurization smoke control, the Brooklyn Polytechnic Institute conducted a series of fire experiments at a 22-story office building at 30 Church street in New York City (DeCicco 1973). This building was scheduled for demolition. Materials representative of fuels that would be in an office were burned on floors 7 and 10, as shown in Figure 1.3. This project demonstrated that pressurization could provide "smoke free" exits during large unsprin-

talfire tower.

Principles of Smoke Management

applicability of zone fire modeling for analysis of pressurization smoke control systems. OBJECTIVES O F SMOKE MANAGEMENT Some objectives of a smoke management system are to reduce deaths and injuries from smoke, reduce property loss from smoke damage, and to aid firefighters. Many designers feel that life safety is the primary objective of smoke management; however, systems have been built with the primary objective of protecting property--especially high-value equipment. Regardless of the objective, the methods of design analysis presented in this book are applicable. Theoretically, a smoke management system can be designed to provide a safe escape route, a safe refuge area, or both. However, a pressurization (smoke control) system can meet its objectives even if a small amount of smoke infiltrates protected areas. For this book, pressurization systems are designed on the basis that no smoke infiltration will occur. Hazard analysis (Chapter 9) can be used for the design of systems that maintain tenability even when people come into contact with some smoke. PERFORMANCE-BASED DESIGN In recent years, performance-based codes have become a topic of considerable attention. Traditional codes prescribe requirements, while performance-based codes require a level of performance. A perforrnancebased design is developed to meet the level of performance stipulated in the code. This book uses a performance-based approach, where the kind of performance is based on the type of system. Pressurization smoke control systems are designed to maintain specific levels of pressurization at

barriers, such as partitions and closed doors. Atrium smoke exhausts often are designed to keep smoke from descending below a specific level. Further, various types of smoke management systems can be designed to maintain tenable conditions within specific spaces. PRELIMINARY DESIGN CONSIDERATIONS Smoke management should be viewed as only one part of the overall building fire protection systems. Two basic approaches to fire protection are to prevent fire ignition and to manage fire impact. Figure 1.7 shows a simplified decision tree for fire protection. The building occupants and managers have the piimary role in preventing fire ignition. The building design team may incorporate features into the building to assist the occupants and managers in this effort. Because it is impossible to prevent fire ignition completely, managing fire impact has assumed a significant role in fire protection design. Compartmentation, suppression, control of construction materials, exit systems, and smoke management are examples. The NFPA Fire Protection Handbook (NFPA 1997), SFPE Handbook of Fire Protection Engineering (SFPE 2002), and NFPA 550 (NFPA 1995) contain detailed information about fire safety.

0'

S

l0

l5

20

25

3;

i7me (minutes)

(a) Pressure Difference Near Ceiling

0

00

5

10 15 20 lime (minutes)

25

30

(b) ~ressureDierence Near Floor

Figure 1.5 Secot7djloor-plnt~oJthe Plnzn Ho~el.

Figure 1.6 Co117par-isotio/ tneaszrt-ed and calczrlated ~ I ~ S I I dI f -i t~s n c e s ji-ot~l Plaza Hotel tests.

Chapter 1-introduction

Objectives

Ignition

Impact

TlTl.m/l Heat-Energy

Source-Fuel

Sources

Interactions

Threat'

Exposure'

'Note: Smoke management is one of many fire protection tools that can be used to help manage the threat of fire and manage the exposure of fire.

~ i g u r e1.7 Sin~plifiedfir.eprotectiondecision tree.

Many factors will affect the design of a slnoke management system. Before the actual mechanical design of the system can proceed, the potential constraints on the system should be determined and the design criteria established. This section introduces some considerations peculiar to smoke management system design, some of which are merely listed below, since detailed discussion is beyond the scope of this book. However. published works on some of these subjects are cited in the bibliography in Appendix B. Occupancy type and characteristics Evacuation plan Refuge areas Distribution of occupant density Human life support requirements Form of detection and alarm Fire service response-to-alarm cliaracteristics Fire suppression system characteristics Type of heating, ventilating, and air-conditioning (HVAC) system Energy ~na~iagement system Building security provisions Controls Status of doors during potential fire condition Potential lirc threats Internal compartmentation and arcliitectr~ralcharacteristics Bu~ldmgleakage paths Exterior temperatures Wind vcloc~ty

FLEXIBILITY A N D RESILIENCY To help ensure smoke management system performance, the approaches of flexibility and resiliency can be employed. The concept of flexibility consists of using design features that allow for easy adjustment of a smoke management system in order to achieve acceptable performance. A resilient system is one that resists serious adverse effects due to pressure fluctuations. During the design of a new building, the leakage paths throughout the building can only be estimated. Therefore, the smoke management design calculations constitute only an approximate representation of the pressures and airflows that will occur as a result of the smoke management system in the actual building. The introduction of flexibility into a smoke management system allows for variations in leakage from the originally estimated values. Because it is difficult to measure leakage paths in existing buildings, the concept of flexibility is also useful for retrofit of smoke management in existing buildings. In many systems, flexibility can be achieved by the use of fans with sheaves3 to allow several flow rates, a variable flow fan for the same purpose, or by dampers that can be manually adjusted to obtain desired pressure differences. Pressure fluctuations often occur during a fire when doors are opened and closed and when windows are opened, closed, or broken. To resist such fluctuations, resiliency can, be incorporated in a system by use o f 3. A sheave is tlic whcel with a groovcd rim, sonieti~ncscallcd a bclt whecl. By exchanging a sheave for onc of anothcr dinmetcr. thc rotational spced of the fan and its flow ratc are changed.

Principles of Smoke Management

automatic control to reduce the pressure fluctuations. For example, in pressurized stairwells, automatic control can be used in the supply fan bypass system to reduce the effect of opening and closing stairwell doors. An alternative is.to keep the exterior stairwell door open during pressurization. This eliminates what is probably the major source of fluctuations; that is, the opening and closing of the exterior stairwell door. The concepts of flexibility and resiliency are discussed further where they apply to specific smoke management applications. /

SAFETY FACT0RS

/

W'

a

9,

Smoke management is still a relatively new field, and it should come as no surprise that there is no CO sensus concerning safety factors, which are commonly used in many branches of engineering to provide a level of assurance of system performance. Further, the topic of safe@ factors has attracted little attention in smoke control design. Safety factors for sizing fans of pressurization systems are very different from those intended to maintain a tenable environment in an atrium or other application based on a hazard analysis. If a pressurization fan is undersized, it will not maintain acceptable pressure differences. This should be apparent and corrected during commissioning. Ideally, an analysis of a system intended to maintain a tenable environment would be based on detailed and accurate capabilities of simulating smoke transport, physiological effects of fire-related exposures, human response to fire, and evacuation analysis. However, this technology is not so advanced, and these calculations are of necessity based on a number of conservative assumptions with conservative design parameters. It can be argued that such conservative calculations may result in conservative designs even in the absence of any safety factors. The specifics of the design and the meth06s of analysis would be expected to have a significant impact on any approach to safety factors. ~ e & u s eof the absence of any accepted approaches to safety factors, this topic is not included in the methods of analysis of this book. FIRE SUPPRESSION SYSTEMS Automatic suppression systems are an integral part of many fire protection designs, and the efficacy of such systems in controlling building fires is well documented. However, it is important to recognize that while the functions of fire suppression and smoke management are both desirable fire safety features, they should not be readily substituted for each other. One of the best ways to deal with the smoke problem is to stop smoke production. To the extent that a suppression system

slows down the burning rate, it reduces the smoke problem. From fires that are suppressed rather than extinguished, smoke is produced. This smoke can move through the building due to various driving forces discussed in Chapter 5. OII the other hand, well-designed smoke management systems can maintain tolerable conditions along critical egress routes but will have little effect on the fire. In addition to the fact that the systems perform different functions, it is important that the designer consider the interaction between smoke management and fire suppression. For example, in the case of a h l l y sprinklered building, the pressure difference needed to control smoke movement is probably less than in an unsprinklered building, due to the likelihood that the maximum fire size will be significantly smaller than in an unsprinklered building. A pressurization (smoke control) system can adversely affect performance of a gaseous agent (such as halon, CO2, or NZ)suppression system when the systems are located in a common space. In the event that both systems are activated concurrently, the smoke exhaust system may exhaust the suppressant gas from the room, replacing it with outside air. Because gas suppression systems commonly provide a single application of the agent, the potential arises for renewed growth of the fire. A general guideline would be that the gaseous agent suppression system should take precedence over the smoke control system. An extremely desirable feature in such spaces would be the ability to purge the residual smoke and the suppressant gas after the fire is completely extinguished and to replace them with fresh air. This ability to replace the atmosphere in these spaces in the post-fire period is very important from a life-safety viewpoint, since some gas suppressants are asphyxiants at normal design concentrations. ENERGY CONSERVATION The smoke management system must be designed to override the local controls in a variable air volume HVAC system so that the air supply necessary to pressurize nonfire spaces is supplied. Also, if there is an energy management system or a 24-hour clock system, the designer must ensure that the smoke management system will take precedence over the local control system so that the necessary air is supplied or exhausted according to the design approach. It is a good general rule that smoke management should take precedence over energy conservation features in both new designs and retrofits.

Chapter l - Introduction

SYSTEM ACTIVATION System activation is probably the major area of disagreement in the field of smoke control. Primarily, this disagreement is about automatic activation versus manual activation. In the early days of smoke control, there was general agreement that activation of "pressure sandwich" systems should be automatic upon alarm from smoke detectors. Automatic activation by smoke detectors located in building spaces has the clear advantage of fast response. Some building designers and fire service officials began to realize that smoke detectors could go into alarm on a floor far away fiom the fire. Thus, automatic activation by smoke detectors could result in pressurization of the zone in which the fire occurred. This would result in the opposite of the desired operation; that is, smoke would be forced into other zones. As a result, a vocal minority of officials feel that smoke control should only be activated manually by fire fighters after they are sure of the fire location. However, many involved professionals are concerned that such manual activation could be so late in the fire development that significant hazard to life and damage to property would result. Such delayed activation can suddenly transport a body of smoke that is highly charged with unbumed hydrocarbons, carbon monoxide, and other toxic gases and depleted of oxygen to remote locations. This can result in a wave-like movement of toxic gases or flame to remote areas. The most recent view on the subject is that zoned smoke control should be automatically activated by an alarm from either heat detectors or sprinkler water flow. This can only be accomplished if the detector or sprinkler zones are compatible with the smoke control zones. Using heat detector or sprinkler flow signals for activation increases the likelihood of proper identification of the fire zone. For smoldering fires, this approach would result in a significantly longer response time, and smoke detectors would probably be better suited for applications where smoldering fires are of particular concern. However, for flaming fires, it is believed that the response time with this approach would be short enough so that significant benefit would be realized by the operation of the smoke control system. It is hoped that advances in smoke detector technology and application will significantly improve the ability of these detectors to positively identify the fire zone. Throughout all of this controversy, there has been complete agreement that zoned smoke control should not be activated by alarms from manual stations (pull boxes). The reason can be illustrated by the scenario ofa man who, while observing a fire on an upper floor of a building, decides that the first thing he should do is to

get out of the building. On the way down the stairs, he thinks of his responsibility to the other occupants. He stops on a lower floor long enough to actuate a manual station. If that alarm activated the smoke control system, the wrong zone would be identified as the fire zone. Because of the long response time and the maintenance problem of clogging with airborne particles, it is generally agreed that smoke detectors located in HVAC ducts should not be the primary means of smoke control system activation. A means of activation of higher rellability and quicker response time is needed. However, an alarm from a duct-located detector can be used in addition to such a primary means of activation. A signal fiom only this secondary means might be unusual, but it should be able to activate the smoke control system. Most stairwell pressurization systems operate in the same manner regardless of where the fire is located. Therefore, it generally is agreed that most stairwell pressurization systems can be activated by the alarm of any fire alarm-initiating device located within the building. A possible exception to this is large buildings with horizontal separations, such that smoke is not expected to have an impact on some stairwells remote from the fire. It is recommended that zoned smoke control systems be equipped with a remote control center from which the smoke control system can be manually overridden. This center should be easily identifiable and accessible to the fire department. Such a remote control center allows fire fighters to change the mode of smoke control system operation in addition to system shutdown. Activation of smoke management systems for atria and other large spaces is addressed in Chapter 10. RELIABILITY O F S M O K E MANAGEMENT The intent of this section is to provide insight into the need for acceptance testing and routine testing and the relative importance of system simplicity: The following should not be thought of as an exhaustive treatment of smoke management reliability. Due to the difficulty of obtaining data about the reliability of components of smoke management systems, the simple calculations that follow are only very rough estimates. However, it is believed that the insight gained justifies this treatment despite these limitations. Further, the same reliability concerns that apply to smoke management systems apply to all life safety systems, and the following discussion may be of general interest beycnd smoke management. The discussion is limited to series systems, which are systems that operate only if all the components operate, as is true of many smoke management system designs. Redundancies (such as backup power) are not included in this analysis. The reliability, R, o i a series

Principles of Smoke Management'

Table 1.1: Estimated System Reliability for New Smoke Management System That Has Not Been Commissioned

System 1 2

3 4 5

No. of HVAC System Fans 3

0 3 5 5

No. of Other Components

Reliability1 of New System

Mean Lifez of Commissioned

Before Commissioning

0 3 9 18 54

0.97 0.83 0.56 0.31 0.03

System (months) 1 16

46 14 8 3

System reliabilities calculated from Equation (1.1). For purposes of these calculations, the reliabiliti&of fans ofa forced air HVAC system were taken as 0.99, and other components were taken as 0.94. 2. Mean lives calculated from Equation (1.3). For purposes of these calculations. the failure rates of fans of a forced air HVAC system were taken as 104 per hour, and other components were taken a s I O - ~per hour. 1.

system is the product of the reliabilities, Ri,of the.components. .-:

Usually, discussions of reliability progress from this point with the assumption that all components operate initially and that failures occur with time after system installation. For this assumption to be appropriate, a program of acceptance testing and defect correction is necessary. Such commissioning must include an installation check of all components, tests of system performance during all modes of operation, repair of defects, and retesting until all defects are corrected. Current construction practices are such that system commissioning is not always this exhaustive. For this reason, attention is first given to reliability of systems without commissioning followed by a discussion of reliability of systems for which all components operate after commissioning.

RELIABILITY BEFORE COMMISSIONING For newly installed components, the reliability can be thought of as the likelihood that the component will both be installed properly and be in good working condition when it is delivered to the construction site. There are an enormous number of errors that can occur during manufacture, transportation, storage, and installation that can cause a component to fail to operate. Problcms such as motors wired for the wrong voltage, motors not connected to power, dampers failing to close, fans running backward, holes in walls, and automatic doors failing to close have been observed in newly built smoke management systems. Based on experience \\lit11 tield testing of smoke management systems, it is estimated that the reliability of components i n noncommissioned systems is 0.90 or highcr. An imporlant consideration regarding the reliabilily of a component in a noncorn-

missioned system is if that component is part of an HVAC system. In hot or cold weather, building occupants demand that the HVAC system provide comfort conditions. Thus, for a new building in extreme weather, it can be considered that the reliability of the HVAC system fan will approach unity. Based on field observations, it is believed that other components will have a lower reliability. The following reliabilities were chosen for example calculations for new systems that have not been commissioned: Fans of a forced air HVAC system 0.99 Other components 0.94 These values were arbitrarily selected, but the relative values between them are based on the discussion above. Table I. 1 lists calculated reliabilities of such systems made up of many components. It can be observed from this table that the more components a system has, the less likely the system is to operate before it has been commissioned. The most reliable new system would be one that only uses the HVAC system fans. A large complicated system consisting of many components (Table 1.1, system 5) has very little chance of operating before commissioning. The trend of lower reliability for complicated systems agrees with observations of the author during nunixous field tests of systems of various degrees of complexity. Probably the most important point to be made from this discussion is the need for commissioning of new systems.

MEAN LIFE OF COMMISSIONED SYSTEMS For this discussion, all system components are considered to operate-at the end of the commissioning process. A commonly used relation for the reliability of components is the exponential distribution, R; = exp(-),,r)

.

(1.2)

Chapter l - Introduction

I II

"

I

Circuit Breakers DistrobutionTransfomen

Mechanical

I 1 /

Large I Electronic Valve Eq P"U"~""'"S""

Figure 1.8 Typical ranges offailure rates (adaptedfioni Lees [ I 9801).

where ki is the failure rate of the component. The mean life, L, of a system is

selected for example calculations, but their relative values are based on the above discussion: Fans of a forced air I-[VAC system 1 o - per ~ hr Other components

Some typical ranges of failure rates of some coniponents and systems are shown in Figure 1.8. It can be seen that failure rates vary over large ranges and that failure rates vary considerably with equipment type. It seems that the failure rate of HVAC system fans would be lower than those of other components. If these fans fail, building occupalits desiring heating o r cooling tend to put pressure on maintenance personnel to get fans repaired quickly. Smoke management systems are only needed for a short time over the life of a building. Thus, when an HVAC system fan is called uron for smoke management duty, it seems that it will be more likely to operate than other components. To account for this, the effective failure rate of HVAC system fans can be thought of a s being much smaller than other components. The following failure rates were arbitrarily

Io-' per hr

Table 1.1 shows mean lives of systems composed of various numbers of components. It can be observed that systems composed of a few components have long mean lives, while those made up of very many components have short lives. This tends to support the view that simple systems are more reliable, and this view is supported by obsenations in the field. However, it should be cautioned that systems should not be overly simple; that is, they should have the features needed to achieve desired performance at likely conditions during a fire. Further, the above simple analysis did not include the beneficial effects of redundancies. However, it is safe to conclude that unnecessary system complexities should be avoided. The mean lives listed in Table 1 .l also indicate that routine testing and repair of smoke management systems is needed so that the systems will probably be in good working order when they are needed. A similar statement can be made concerning all life safety systems.

CHAPTER 2

Fire and Heat Release

ky 1 robably the most important aspect of a building fire is the heat release rate (HRR). The temperature and amount of gases produced by a fire are directly related to the HRR, and predictive computer models use the HRR as input. When talk about the size of a fire or how big a fire is, they almost always are referring to the HRR. Other indicators of fire size are the fire area and fire perimeter, but neither of these is commonly used to depict how big a fire is in the predictive models that have gained a high level of acceptance in recent years. For these reasons, the term jr-e size is used in this book to mean HRR. The intent of this chapter is to provide basic information about fire size and development that should be helpful concerning evaluation and deterniination of design fires. A design fire is the challenge that a smoke management system is designed to withstand. Because the presence of sprinklers often plays a role in the determination of a design fire, sprinklers are also included. The design fire can be a steady fire or an unsteady one. While the steady fire is not physically realistic, it can result in very conservative designs and it can simplify design analysis.

P

i l

I

8

(

quences of a fire after ignition but not with the causes of Ignition. Growth: After ignition, fire growth is determined by the material burning, with little Or no influence from the compa*ment. This stage is characterized by an bundance airafor the fire. 2.2 showschair an office fire 2 startingofin corner of Figure an upholstered and growing until it spreads to other objects. As the fire grows, the temperature in the room rises. A fire with sufficient combustion air is called a fuel confrolled fire, and such a fire is also referred to as burning infr-ee air. Flashover: In engineering, most processes of interest consist of gradual changes, but flashover is an exception. Flashover is a sudden change from an apparent steady fire confined to a relatively small space to a fire that involves a much larger space, such as the entire room. For the office fire of Figure 2.2 (c), materials throughout the room are subject to thermal radiation from the Flames and the smoke layer under the ceiling. When this radiation is sufficiently high, some of these materials ignite. This is followed by other materials

I

STAGES O F FIRE DEVELOPMENT

I

I I

Fires in rooms or other compartments are often described in terms of the stages of fire development, shown in Figure 2.1. These stages are useful in discussing fires, but many fires do not go through all of these stages due to lack of fuel or the action of a suppression system. Ignition: Ignition is the period during which the fire begins. Smoke management deals with the conse-

I

l f--

Gr~wth

Il II II

Post Flashover

II

I

l1

I

I

I

Dewy

Time

Figure 2. l

The stages offwe developn7etzf.

Chapter 2- Fire and Heat Release

(a) Fire restricted to inside corner of chair and resulting in smoke layer under ceiling

Principles of Smoke Management

Table 2.1: Approximate Values of CO Yield for Room ~ i r e s *

7

Measure Temperature, Flow Rate, & Gas Concentrations.

CO yield**

Flaming fires in "free air" Fully involved fire (in a room without cellulosic materials on ceiling or upper portion of walls)***

0.04

0.2

These estimates are based on Pit&(1994). Mulholland (2002), and Tewarson (2002). ** Keld is in Ib CO produced per Ib of fuel burned (or g o f CO produced per g of fuel burned). *** Fully involved fires in rooms with cellulosic materials (wood, paper, cardboard, etc.) on ceiling or upper ponion o f walls are expected to have CO yields several times higher (Pi- 1994).

Figure 2.3 Open air calorimeter: igniting, and then the entire room is involved in fire. Once a fire gets to the stage depicted in Figure 2.2 (c), it only takes a few seconds for a room to flashover. In a very large room, such as an open office floor plan, only a portion of the room may flashover. The smoke layer temperature at which flashover occurs is generally in the range of 930°F to 1300°F (500°C to 700°C). The criteria for flashover is sometimes taken to be a smoke layer temperature of 1100°F (600°C) or a radiant heat flux of 1.8 ~ t u l f st (20 ~ kw/m2) at the floor of the fire r o a n (Peacock et al. 1999). Fully Developed Fire: This stage of fire development has the highest temperatures. For small and medium rooms, the HRR of a fully developed fire depends on the amount of air that reaches the fire. Such a fully developed fire is ventilation cotztt-olled. In a ventilation controlled fire, more volatile gases are produced by the burning materials than can be bumed in the room with the oxygen available, and the fire can be characterized by flames consisting of burning volatile gases extending from open doonvays of the fire room. For very large rooms, as in an open office floor plan, the fire may not ever become ventilation controlled. Fully developed fires are characterized by inefficient combustion and high production of CO (Table 2.1). Decay: As the fuel is consumed, the HRR of the fire and the temperature of the room drop. The fire may change from ventilation controlled to fuel controlled. Strictly speaking, the term post-flashover fire includes both fully developed and decay stages, but the term is often used to mean a fully developed fire.

MEASUREMENT OF HEAT RELEASE RATE In the early days of fire research, determination of the HRR during a fire was very crude. Typically, materials were burned on a load cell (scale), and the HRR was estimated from the mass loss and the heat of combustion of the material. If the load cell became too hot, tlie mass

measurements would be meaningless. Various schemes . to keep the load cell from heating up were devised, but they all interfered to some extent with the measurements. The situation was even worse when pieces of burning material would fall from the load cell. To further exacerbate the difficulties with such HRR determinations, many items burned are composites of several different materials, each with its own heat of combustion. For example, a desk might be made of wood, fiberboard, sheet plastic and molded plastic doors, and drawer fronts. Not only do these materials have different heats of combustion, but they burn at different times during the course of a fire. For these reasons, an HRR estimated from measured mass losses is often unreliable.

Oxygen Consumption Calorimetry In the 1980s, fire research laboratories around the world worked to develop a method of calorimetry that was not subject to the problems of the old method discussed above. The new method is based on the osygen used up in the fire and is called oxygetz conszrt?zptioncaloritnetty (and sometimes oxygetz depletion calorinzetry). While oxygen consumption calorimeters often have load cells, the measurements from these cells are for sepante information and not for calculation of the HRR. The key to this technology is that the heat released per unit oxygen consumed is almost a constant for most materials. Huggctt (1980) found that this heat release constant is 5,630 Btu per Ib of oxygen consunled (13.1 MJ per kg of oxygen consumed). For most materials involved in building fires, this constant has an uncertainty of about 6%. Figure 2.3 shows a calorimeter where furniture is burned under a hood connected to an exhaust, such that all the smoke is drawn into the exhaust. From measurements of the mass flow of exhaust and the O2 content of

Chaptei 2 - Fbe and Heat Release

Measure Temperature. Flow Rate, and Gas Concentrations.

Smoke Plume Front View

Section View

Figure 2.4 Room calorimeter: the exhaust, the time rate of O2 consumption can be calculated. From this, the HRR can be calculated. Because some of the O2 is not completely consumed, gas measurements also include CO and CO2 Parker (1982) presents equations for calculation of the HRR, for various applications. Oxyzen consumption calorimeters are calibrated by burning a gaseous fuel (methane, propane, etc.) at a measured flow rate. The uncertainty of the calorimeter depends on the uncertainties of (1) the operation of the calorimeter, (2) the calorimeter calibration process, and (3) the heat release constant. Calorimeter operation is not always as intended. Some of the smoke may not be captured by the hood, or burning materials may fall off the fire and away from the calorimeter. With such unintended operation, uncertainties in excess of 20% could result. For a well-calibrated calorimeter operated as intended, the uncertainty of measured HRR may be in the neighborhood of 10%. For more information about the uncertainty of ovygen consumption calorimeters, see Stroqp et al. (2000). Open air calorimeters (Figure 2.3) are sometimes called furniture calorimeters because they are often used for furniture. However, they can be used for any fuel package provided that ( l ) all of the smoke from the fire is collected, and (2) the heat released does not damage the calorimeter including the pollution control equipment. Typically, these calorimeters are located indoors to protect the fire from the wind. The hoods are usually l0 to 20 ft (3 to G m) square, but the size is only constrained by the practicalities of construction. Other types of Oz consumption calorimeters are the room calorimeter and the cone calorimeter. The room calorimeter (Figure 2.4) is used when the effects of the walls and ceiling on the HRR are thousht to be signifi-

Time (S)

Figure 2.5 Three kiosk fires iIIzcstrate iypical repeatabiIiry of burni~~g materials (data Ji-onl MifIer-[I 9961). cant. The cone calorimeter is a "bench scale" laboratory instrument developed at NIST (Babrauskas 1990).

HRR OF SOME OBJECTS When duplicate objects are burned, there are deviations in HRR as illustrated with the three kiosk fires of Figure 2.5. These kiosks are for selling T shirts. The deviations of HRR are due to a number of factors, including (I) minor variations in arrangement of the Tshirts, (2) variations in composition of T-shirts, (3) variations in the dimensions of the kiosk, (4) variations in materials of the kiosk, and (5) variations in the air currents near the kiosk. However, the shapes and peak HRRs of kiosk curves are similar. Figures 2.6 to 2.19 show HRRs of other objects. The peak HRR of Scotch pine Christmas trees burned by Stroup et al. (1 999) were in the range of' 1800 to 5000 Btu1 S (1900 to 5300 kW), as shown in Figure 2.6. Ahonen et

P r i i p l e s of Smoke Management

al. (1984) burned smal!er spruce trees, and the peak HRRs were in the range ofabout 40 to 620 Btds (42 to 650 kW). All of these Christmas tree fires had rapid growth stages followed by decay as the tree was burned up. Data for a burning dresser (Figure 2.7) and bunk bed (Figure 2.8) were obtained by Mitler (2000). Like the Christmas tree fires, the dresser had rapid growth

Time (S)

Figure 2.6 Scotch pine Chrislrnas tree (adapledfi-orn S~roupet al. [ l 9991).

O 'V

Figure 2.7

300

600

960 l ~ O O 1&0 Time (S)

0 1/00

Wooder? dresser- fda/n ji-on? hfitler[2000]).

5000

..-.

4C30

m 2000

3000

-

3000

z 5

2000 I 1OGO

IL

I

1000 '0

Figure 2.9 Innerspring tnat~ressfilled wilh polyurelhane foam (dala fvom Lawson et al. [ I 9841).

5000

4000

-$

stages followed by decay. Many other objects b u m 4 under an open air calorimeter will show the same type of rapid growth followed by decay as the material burns UP. Lawson et al. (1984) burned an assortment of furnilure (Figures 2.9 to 2.16). In general, all these curves are of the s a n e generd shzpe as the proceeding HRR curves, with the exception of one of the chairs. The upholstered chair of Figure 2.1 1 has two HRR peaks: (1) 950 Btds (1000 kW) at 240 s and (2) 570 Btuls (600 kW) at 400 S. The wardrobe of Figure 2.15 is an even more pronounced example of multiple peaks: (1) 3500 Btuls (3700 kW) at 120 s and (2) 3100 BWs (3300 kW) at 360 S. For objects with two HRR peaks, the second peak is due to material or materials in the object that bum differently from those responsible for the first peak. Also, a fire consisting of a number of objects would be expected to have more than one peak, as in Example 2.2. Madrzykowski and Vittori (1992) burned workstations. These workstations are simulated offke workspaces, including a chair, shelves or a desk, paper, personal computer, and dividers separating the worksta-

300

600

900 1200 Time (S)

0 1500 1800

Figure 2.8 HEN/1-eleasc rn/cjur- b~rnkbed (dalnfiani Miller- [2000]).

0

3

6 0

9 0 1 Time (S)

0

1&0

0 l&

Figure 2.10 M C I ~ fi-ame I chair wilh polyurethane foani-filled cushions (dalafi-on7 Lawson er al. [1984]).

Chapter 2-Fire and Heat Release

l ooc

l

4 l000

1.

' 360

660 >OO lime

1;00

1;00

0 18fOO

(S)

Figure 2.11 Upholstered chair with polyurelhanefoa~n padding and weighing 25 lb (11.5 kg) (datafroni Lawson et al. [1984]).

0 0

300

600

900 lime

Figure 2.14 Metal wardrobe w'th cotton andpolyesrer garments (data from Lawson cl al. [1984]).

1200 1500 1800 Time (S)

(S)

Figure 2.1 2 Upholsfered chair ~ Y t polytrerhn~~e h foam padding and weighing 62 IB (28.3 kg) (dnia.f,.otn Lauson et al. [l 9841).

Figure 2.15 Wardrobe of 0.5 in. (12.7 I ~ Ip!~-~t~ood ) wirh cotton nnd po!~wtet-garnienrs (dnro ,/ram Lnwson et al. [l 9841).

8000

.

-Unfinished

6000 -

Fire Retardant

A

In

Paint:

1

g 4000 - 'i :.:.: :.

1 Coat 2 Coats

.8000 6000

- 4000

U

2S K I

K

. 1

,

2000 S;

8.

. lime (S)

.foam padding Figure 2.13 Sofa wit/? po~v~tretl~at~e (datafi-0171 Laws017 et al. [19S4]).

Figure 2.16 War-drobeof 0.125 in. (3.2 ~mnjp11.1t~ood ~ d t hcotton a ~ i dpol~:este~garnze~its(darn ,from Lnwson et al. [1984]).

Principles of Smoke Managemerit

20W

2000

.

; ;1500

1500

m 1000 ,

l000

I

I

500

OO

F E

500

6W

1200 1800 2400 lime (S)

0

3000 3600

Figure 2.17 Two-divider workstation with conventional desk and credenza (data from Madrzykowski and Vettori [1992]).

Time (min)

Figure 2.19 Automobiles (data from Joyeux [1997]).

lime (S)

Figure 2.18 Three-divider wo~kstationwith an open work top and shelf (data from Madrzykm~skia17dVettori [l 9921).

Figure 2.20 Crib made of geometrically arranged sticks.

tion from other spaces. The two-divider workstation (Figure 2.17) has a peak HRR of 1700 Btuis (1800 kW) at 140 S. The three-divider workstation (Figure 2.18) has a peak HRR of 6400 Btuis (6800 kW) at 550 S. A major reason for the higher HRR of the three-sided workstation is probably the increased radiation feedback from the additional divider and the shelves. For further information about the HRRs of workstations, readers are referred to Madrzykowski (1998).

was used for tests of the smoke management system at the Plaza Hotel (Klote 1990). This crib was made of 144 wood sticks, 1 .S in. (38 mm) by 1.5 in. (38 mm) by 2 ft (0.61 m) long, and it had a peak HRR of aboet 1400 Btuls ( l 500 kW) when burned in free air. The stack of nine wood pallets shown in Figure 2.2 1 has a peak HRR of about 3,500 Btu% (3,700 kW) when burned in free air. Gross (1 962), Block (197 l), and Walton (1988) have burned wood cribs of various sizes and stick spacings. Babrauskas (2002) provides heat release data of cribs and pallets.

Figure 2.19 shows HRR data of automobiles measured by Joyeux (1 997). Joyeux showed that cars made in the 1990s had a higher HRR than those made earlier, and this may be due to increased use of polymers and other nonnletallic materials. -Because of these higher HRRs, a car fire in a parking garage can ignite an adjacent car. Cribs and piles of wood pallets are used in research and testing when reproducible solid fuel fires are needed (Figures 2.20 and 2.21). Cribs are geometrically arranged piles of sticks. The crib shown in Figure 2.20

VENTILATION-CONTROLLED FIRES

; A,!i = area of ventilation opening from i = 1 to n,

ft2

(m').

This is illustrated for two openings in Figure 2.23. Door Width (ii;;

Figure 2.22 HRR ofafully developedfire it1 a sinall 01-

medium-sizedroomofnot-tnalconstr~rction.

For openings with the same top and bottom elevations. A, = A,,, + A w 2 .

Figure 2.2 1 Stack o f 17ine/~a//cts.

Figure 2.23 Combining vet7tilariotl openings for esrimate of the size o f a-firl(pckvelo~~ed~fit~e.

Principles of Smoke Management

'HRR DECAY D U E TO SFRINKLERS A constant HRR after sprinkler actuation is a conservative estimate for many applications. Fire decay after sprinkler actuation is more realistic. Fire decay can be expressed as

where

Q

I

Conservative Estimate of Constant HRR

=

HRRat sprinkler actuation, kW (Btuls);

=

to,,

(a) Sprinklers Overpowered by Fire

post sprinkler actuation HRR, kW (Btuls);

time from ignition, s (S); = time of sprinkler actuation, s (S);

t

Time

=

r

= time constant of fire suppression, s (S). For a number of fuel packases likely to be found in offices, Madrzykowski and Vettori (1992) conducted sprinklered fire experiments with a spray density of 0. I0 gpm/ft2 (0.07 m d s ) of water. They determined that a fire decay curve with a time constant of 435 s had a higher HRR than most of the sprinklered fires (Figure 2.25). Evans (1993) used these data and data for wood crib fires with sprinkler spray densities of 0.06 gpm/ft2 (0.041 mmls) and 0.097 gprn'ft2 (0.066 mmls) from Tamanini (1976) to develop the following correlation:

Time (b) Conservative Estimate of Constant

HRR After Sprinkler Activation

where r v = spray density, gpmlf? (mnds);

C,

=

6.15 (3.0).

While Equation (2.4) has not been experimentally verified, it does allow us to adjust the decay time for sprinkler densities other than those of Madrzykowski and.Vettori.

Sprinkler Response Time (c) Fire Decay After Sprinkler Activation

Figure 2.24 Interaction between fire and sprinklers.

flame height is typically less than the ceiling height, and room air entrainnient cools the gases in the w o k e plume. Methods of calculating the plume temperature are in Chapter 13. If the sprinklers do activate, the spray could evaporate before the droplets reach the fuel.

While the information in this section is primarily about sprinklers, it also applies to vents actuated by fusible links and fixed temperature heat detectors. The responsiveness of sprinklers is tested by the plunge test, where a sprinkler is "$mgedWinto a heated oven in which heated air is circulated. The nnalysis of the plunge test is mathematically the sanie as that of a small piece of hot metal suddenly quenched in a cool fluid, as described in heat transfer texts (Kreith 1965: Incropera and DeWitt 1985). This analysis is based on the assumptions that ( I ) the internal resistance of the sprinkler is negligible, (2) the sprinkler is instantaneously put ill the oven, (3) the convective heat transfer coefkient is constant, (4) the gas temperature i n the

Chapter 2-Fire and Heat Release

oven is constant, and (5) the only heat transfer is from the sprinkler to the gas. The temperature of the sprinkler increases exponentially, as shown in Figure 2.26. The time constant, r, of the sprinkler is

calculated from Equation (2.6). The RTI of standsrd sprinklers varies from about 140 to 280 fill2 s1I2 (77 to 155 m'I2 sln), and the RTI of quick-response sprinklers (QRS) varies from about 50 to 100 fill2 slR (28 to 55 ,lR ,lR). The response time index does not account for conductive heat transfer from the sprinkler. To account for conduction, a virtual RTI can be calculated as

where =

time constant, s (S);

m

=

mass of the sprinkler, Ib (kg);

C

=

specific heat of the sprinkler, Btuflb"F (Jkg "C);

h,

=

convective heat transfer coefficient, ~ t d f t s2 "F

CRTI

'+1/2 where RTI, = virtual RTI, fill2 slR (m1' slR);

(w/m2 "C); A

=

-RTI --

RTI, =

Z

surface area of the sprinkler, ft2 (m2).

CRTI= conductivity factor, f i l n / s " ~(m'l2 IS'").

The time constant, r, is the time at which the temperature of the sprinkler has reached 63% of the way to the gas temperature. The convective heat transfer coeficient varies with velocity, so that the time constant also varies with the velocity at which it is measured. The response time index (RTI) was developed as a measure of sprinkler responsiveness that is independent of velocity.

.

.

: I

where u is the velocity, Ws (mds). In the plunge test, the time to actuation and the gas velocity are measured. Then the time constant can be calculated from the time to actuation, and the RTI is

'I: is time constant

Time Figure 2.26 Temperatutasfot~n spr-ir~kler-plztr?ge test

'

.

-

Paper Cart Fuel Package -.--.Secretarial Desk Fuel Package o Executive Desk Fuel Package ---- Office II Fuel Package Office I Fuel Package - - - Sofa Fuel Packdge Work Station I Fuel Package - - - Work Station I I Fuel Package Wood Cribs

-

. X

0

200

400

Time, t -

600

t,,

.

800

(S)

Figure 2.25 Filr decuj' due to spri~ikleraclio/i n.ill7 a spruj, derisi@of 0.10gpn/ f? (0.07 /ii/ii/s)(adupledfiori~Mad-zykowski and kllori [ l 9921).

.

Principles of Smoke Management

S~rinklerActuation Actuation depends on gas temperature and velocity near the sprinkler. In a fire, a jet of hot gases flows radially from where the smoke plume intersects the ceiling. Computer programs have been developed that use correlations for such a ceiling jet to predict actuation time. The program DETACT-QS (Evans and Stroup 1986) assumes that the thermal device is located in a relatively large area, that only the ceiling jet heats the device, and that there is no heating from the accumulated hot gases in the room. The required program inputs are the height of the ceiling abo:!e the fuel, the distance of the thermal device from the axis of the fire, the actuation temperature of the thermal device, the response time index (RTI) for the device, and the rate of heat release of the fire. The program outputs are the ceiling gas tkmperature and the device temperature, both as a function of time and the time required for device actuation. DETACT-T2 (Evans et al. 1986) is similar to DETACT-QS, except it is specifically for t-squared fires. Several zone fire models (such as FAST, LAVENT, and JET) are capable of calculating ceiling jet temperatures and predicting actuation (Chapter 8).

DESIGN FIRES A design fire curve is the description of the development of a design fire that can be used in a fire scenario. The curve is for HRR as a function of time. This curve can be as simple as a constant, and it can also be a simple function of time. The design fire curve can also be a complicated sequence of lesser cunles for some or all of the stages of tire development described at the beginning of this chapter. A fire scenario includes more than just the design fire curve. The word sce17nrio means an outline of events, as in a play or other theatrical production. A fire scenario can be thought of as the outline of events and conditions that are critical to detemiining the outcome of alternative designs. In addition to the HRR and fire location, a scenario could include the type of materials burned, airborne toxicants and soot produced, and people movement during fire.

In many spaces, the fuel loading is severely restricted with the intent of restricting fire size. Such spaces are characterized by interior finishes of metal, brick, stone, or gypsum board and furnished with --. objects made of similar materials plus plants. Even for such a /ire1 reswicmf space, there can be an almost unlimited number of combustiblc objects that are in the space for short periods. Such combustible materials that

are not intended to be located in the space are referred to as tramientfuels. A few examples of transient fuels are Christmas decorations, paint and solvents in stairwells during redecorating, unpacked foam cups in cardboard boxes after delivery, cut up cardboard boxes awaiting removal, and closely stacked upholstered furniture after delivery. Sometimes, transient fuels remain in place for long periods. Some examples are (1) a number of polyurethane mattresses delivered to a dormitory and waiting for distribution in the next school year, (2) automobiles on display in a shopping mall, (3) boats and campers on display in an arena, and (4) a two-story colonial house built for display inside a shopping mall. Transient fuels must not be overlooked when selecting a design fire. One approach to incorporating transient fuels in a design fire is to consider the fire occurring over 100 ft2 (9.3 m2) of floor space with a heat release rate density of 20 Btuls ft2 (225 kw/m2). This amounts to an allowance for transient h e l s of 2000 Btuls (2100 kW).

Steady Fires It is the nature of fires to be unsteady, but the steady fire is a very useful idealization. Steady fires have a constant heat release rate. In many applications, use of a steady design fire can lead to straightforward and conservative designs.

HRR per Unit Area Morgan (1979) suggests a typical rate of heat release per unit floor area for mercantile occupancies of 44 Btuls ft2 (500 kw/m2). Fang and Breese (1980) determined about the same rate of heat release for residential occupancies. Morgan and Hansell (1987) and Law (1982) suggest a heat release rate per unit floor area for office buildings of 20 Btds f? (225 kw/m2). For smoke management applications, a heat release rate per floor area of 20 Btuls ft2 (225 kw/m2) is suggested for restricted fuel spaces, and 44 Btuls ft2 (500 kw/m2) is suggested for spaces with furniture, wood, or other combustible materials. A firc occurring over 100 ft2 (9.3 m2) of floor space would result in 2000 Btuls (2100 kW) for restricted fuel space and 4600 kW (4400 Btuls) for a space with combustibles. The heat release densities of Table 2.2 can be useful in determining design fires.

Unsteady Fires Fires frequently proceed through an incubation period of slow and uneven growth, followed by a period of established growth as illustrated in Figure 2.27 (a). Figure 2.27 (b) shows that established growth- is often

Chapter 2-Fire and Heat Release

Table 2.2: Heat Release Density of Some Materials Heat Release Density, q kwlrn2 Btuls f$

Material Burned I. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. I . 16. 17. IS. 19. 20. 21. 22. 23. 24.

Wood pallets, stacked 0.46 m (1.5 h) high (6-12% moisture) Wood pallets, stacked 1.52 m (5 ft) high (6-12% moisture) Wood pallets, stacked 3.05 m (10 ft) high (6-12% moisture) Wood pallets, stacked 4.88 m (16 ft) high (6-12% moisture) Mail bags, filled, stored 1.52 m (5 fi) high Cartons, compartmented, stacked 4.57 m (15 fi) high PE letter trays, filled, stacked 1.52 m (5 ft) high on cart PE trash barrels in cartons, stacked 4.57 m ( l 5 ft) high PE fibeglass shower stalls in cartons, stacked 4.57 m (15 ft) high PE bottles packed in item 6 PE bottles in cartons, stacked 4.57 m (15 ft) high PU insulation board, rigid foam, stacked 4.j7 m (l5 ft) high PS-jars packed in item 6 PS tubes nested in cartons, stacked 4.27 m ( l 4 ft) high PS toy parts in cartons, stacked 1.57 m (l5 ft) high PS insulation board, rigid foam, stacked 4.27 m (14 ft) high PVC bottles packed in item 6 PP tubes packed in item 6 PP & PE film in rolls, stacked 4.27 m (14 ft) high Methanol pool, 0.16 m (0.52 ft) diamcter Methanol pool, 1.22 m (4.0 ft) diameter Methanol pool, 1.74 m (5.7 ft) diameter Methanol pool, 2.44 m (8.0 ft) diamc~er Methanol pool. 0.97 tu (3.2 ft) square

25.

Silicone transfornler fluid pool, 1.74 m (5.7 fr) diameter

26.

Silicone transformer fluid pool, 2.44 m (8.0 ft) dianletcr

90

8

27.

Hydrocarbon transformer fluid pool. 1.22 nl (4.0 ft) diameter

940

83

.

1400 4,000 - 6,800 10,000 400 1,700 8,500 2,000 1,400 6,200 2,000 1,900 . 14,000 5,400 2,000 3,300 3,400 4,400 6,200 2,000 400 400 420 745

125 350 .600 900 35 150 750 175 125 550 175 170 1,250 475 180 290 300 390 550 I SO 35 35 37 66

90

8

28.

Hydrocarbon transformer fluid pool, 1.74 m (5.7 ft) diameter

900

80

29.

Heptane pool, 1.22 (4 ft) diameter

3.000

270

30.

Heptane pool, 1.74 (5.7 ft) diameter

3.200

280

Nn~rc.

I . Abbreviations are: PE = polytl~ylenc.PS = polyslyrsnc. PVC 2. Items I tlirough I 0 frorn~fl'~ 4 2 0 (2000). 3. ltenis10 tl~rdugh30 rrolii Hcskcs~ad(IYS4). 4. ltcms 25 tlirot~gli28 arc proprietary products

=

pulyvinyl cliloride. PP = polypropylene. P U = polyurethane.

represented by an idealized parabolic equation (Heskestad 1984).

where Q

=

heat rclcasc rate of fire, kW (Btuls);

a

=

firc growth coefficient, k w k 2 ( ~ t u l s ~ ) ;

1

=

time aficr ignition, S;

=

cfl'cc[ivc ignition time,

* 20. Figure 2.29 Point source radiation model. where The point source radiant model is appropriate provided that the distance from the center of the flame is greater than twice the diameter of the fire (R > 20). The radiant heat release of the fire is

where Q

=

heat release rate of the fire, Btu/s (kW);

X,.

=

radiative fraction.

Heat transfer from a flame is by conduction, convection, and radiation. For most fires, conductive heat transfer from the flame is negligible. The radiant fraction can be expressed as

where X , is the convective fraction. The radiative fraction depends on the material burned and the diameter of the fire, and the radiative fraction varies from about 0.1 to 0.6. Low sooting fuels, such as methanol, have low radiative fractions, and high sooting materials, such as gasoline and polystyrene,

RSD

=

separation distance from the center of the fire to a target, ft (m);

qi.

=

intensity of thermal radiation needed for nonpiloted ignition, ~tu/ft2S (kw/m2).

Fuel items less than RSD away from the fire would be expected to ignite, and fuel items farther than RsD away would not be expected to ignite. The radiant flux needed for nonpiloted ignition varies from about 0.9 13tu/ft2S (10 k ~ l m ' ) for thin easy-to-ignite materials to ~ kw/rn2) for thick materials. 1.8 ~ t u / f St (20 For a fire, the heat release rate, Q,..;, that results in ignition of an object at a distance of R away is

For radiant heat transfer where R is less than twice the diameter of the fire, a method other than the point source model is needed. Several texts have general information about radiant heat transfer (Siege1 and Howell 1992; lncropera and DeWitt 1985; Kreith 1965). For information about radiant heat transfer of fire, readers are referred to Quintiere (1998), Drysdale (1985), and Mudan and Croce (1995).

Principles of Smoke Management

11

1)

1

'".-Ruarnnle 'r-- 2.2 ---

-

a

-

Race Fuel --- Packaoe m-

- - "v

The fuel load in a large atrium consists of the polyurethane foam-filled sofas and chairs shown in Figure 2.30. The a i l i n g of the atrium is sufficiently high so that successful sprinkler suppression is not anticipated. The HRR of the sofas is the same as that of Figure 2.13, and its peak HRR is 2960 Bhds (3 120 kW). The HRR of the chairs is the same as that o f Figure 2.1 2, and the peak HRR is 20 l 0 Bhds (21 20 kW). How many sofas and chairs make up the base fuel package, and what is the HRR of the base fuel package?

Part I: Initial Estimate of Base Fuel Package

I(11

Use a radiant flux for nonpiloted ignition of qr,

For the sofq Q, =

= 0.3(2960) = 888

= 1.8

~tu/ft' s (20 kw/rn2).

Bhds (937 kW).

11 From Equation'(2.14), the separation distance from the burning sofa is This shows that a fire on sofa I would not be expected to ignite sofa 2, but it would be expected to ignite chair I . Because fires are often off center, the center of the fire is taken as the "+" on the side near the chair. This is conservative in that ignition of the chair would be sooner than if the center of the fire were farther away. For the chair, Q,. = X r = ~ 0.3 (2010) = 603 Bhds (636 kW)

1l

From Equation (2.14), the separation distance from the burning sofa is

I1

I

1l

7

This shows that the fire of chair I would be expected to ignite sofa 2. Because sofas 3 and 4 are at least 18 ft (5.5 m) away from sofas I and 2, ignition of sofas 3 and 4 would not be expected. For now the base fuel package will be considered to consist ofsofas I and 2 and chair I.

Part 11: Calculate HRR Base Fuel Package On Figure 2.30, the distance from the center of the fire on sofa I is R , = 3.6 ft ( l . l m). The heat release rate that results in ignition at R , can be calculated from Equation (2.15)

This means that when the fire ofsofa I reaches 293 Btds (309 kW), the chair would be expected to ignite. Because R , = R1, ignition of s kW). sofa 2 is expected when the chair I fire also reaches 293 B t ~ d(309 Calculations of the HRR are done graphically on Figure 2.3 1: (a) The HRR of sofa I is taken from Figure 2.13. The ignition time ofehair I is determined at the intersection of the sofa 1 curve and 293 Btds (309 kW). (b) The HRR of chair I is taken from Figure 2.12. (c) The ignition time of sofa 2 is determined in a manner similar to step (a), and the HRR curve for sofa 2 also is taken rrom 2.13. (d) T'le curves for sofas I and 2 and chair I are added to obtain the cunTefor the base fuel package. It should be noted that adding the HRR curves as in step (d) assumes that the objects will bum as they would in frce air under a calorimeter and neglects any effect of radiation from other burning objects.

)IPart

111: Check Bare Fuel Package

This part checks to see if the-base fuel package will ignite other materials. The highest peak of the HRR curve of Figure 2.3 1 (d) is at 3600 Btds (3800 kW).

1

For the base fuel package,

8,. =

%,.Q = 0.3 (3600) = 1080 Btds (l 140 kW).

From Equation (2.30). the separation distance from the b a r fuel packaee is

-

The other items in Figure 2.30 are I S It (5.5 m) lion1 the base fuel package, so ignition ol'these items wo~tldnot be expected. So the base fuel package and its HRR curve can be ~lscddirectly for a design analysis, or a simplified design llRR curvs can be adapted rrom it. Ifthere were fuel items \\ ithin this separation distance. these items would have to be added to the base rue1 package, and a new HRR cunre would have to be determined.

Chapter 2 - F i e and Heat Release

time (S) (a) Draw curve for sofa 1, and locate ignition point of chair 1.

. .

time (S)

(b) Draw wrve for chair 1.

Sofa 3

Sofa 4 Chair 2

7 7 4000

Note:

R, = R ,= 3 . 6 f t ( l . i m) Figure 2.30 Arrangemen! offurni~urein the aft-iutnof Example 2.2.

Time (S) (c) Locate ignition point and draw curve for sofa 2

Time (S) (d) Get base fuel package by adding the 3 other curves

Figure 2.31 Graphic delem-minafion of [he base file1 package oof Examnple 2.2.

CHAPTER 3

Smoke and Tenability n this book, the term srnoke is used in accordance .with the definition of NFPA 92A (2000) and NFPA 92B (2000), which states that smoke consists of the airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion, together with the quantity of air that is entrained or 0therwise mixed into the mass. The products of combustion usually include particulates, unburned fuel, water vapor, carbon dioxide, carbon monoxide, and some other toxic and corrosive gases. As smoke moves through a building, air mixes into the smoke mass and the concentration of combustion products in the smoke decreases. Including air that is entrained or othenvise mixed facilitates discussions about fire smoke management in atriums and other iarge spaces. Generally. smoke is thought of as being- visible, but the above definition includes "invisible smoke" produced by burning of materials that produce little or no particulate matter, such as hydrogen, natural gas, and alcohol. Information about smoke hazards is useful in evaluating'the effects of small quantities of smoke migrating into "protected spaces," and it is useful in evaluating the consequences of smoke migration without smoke protection. This chapter concentrates on smoke hazards due to toxicity, temperature, and smoke obscuration. The hazards of temperature consist of hear exposwe, which can occur when a person comes into bodily contact with hot gases, and thermal racliafiot~e-vposur-e, n.hich can occur when a person receives thermal radiation from flames or hot smoke that are some distance away from the person. Exposure to toxic gases, heat. and thermal radiation can be a direct hazard to life, and reduced visibility due to smoke obscuration can be a significant indirect haz-

I

ard. Frequently, people become disoriented in fire situations because they cannot see through heavy smoke. If they remain in the building too long, they fall victim to exposure to toxic gases or elevated temperatures. Further, in buildings with balconies, smoke obscuration can result in fatal falls. Smoke management systems can be designed with the objective of providing a tenable environment in the means of egress or at other locations during evacuation. Such a tenability system needs to be designed to meet tenability criteria. Such criteria need to include exposure to toxic gases, heat, and thermal radiation. Further, the criteria often include visibility. As discussed at the end of this chapter, th-e criteria for a tenability design depend on the specific application.

oBSCURAT1oN Many different methods of expressing smoke obscuration are used in fire science and fire protection engineering, and this section discusses the common methods. There is a lack of uniformity concerning smoke obscuration, and some engineering publications use different terminology or have different mathematical definitions for the same terms. These differences could result in significant errors, and readers are cauticned to take care to verify the exact meanings of obscuration terms used in other publications. The terminology that follows was selected with the intent of being consistent with most technical publications in this field. The fraction of light transmitted through the pathlength of smoke is called the transniittance and is written as

Chapter 3-Smoke and Tenability

p--

Photo

tight

Source

where T = transmittance, dimensionless; I, = intensity of light at the beginning of the pathlength; I, = intensity of light remaining after it has passed through the pathlength. The units for light intensity are arbitrary, and such units are unnecessary for discussions of smoke obscuration and even for measurements of smoke obscuration. Transmittance is measured by monitoring the extinction of a beam of light passing through a pathlength, X, of smoke as illustrated in the light meter of Figure 3.1. Strictly speaking, the discussion jn this section applies to light composed of only one wavelength, such as a laser beam, but light meters using less exotic light sources (such as incandescent bulbs) have been used extensively for fire tests. When the atmosphere is "smoke free," the intensity of light remaining after it has passed through' the pathlength is almost exactly the same as the intensity at the beginning of the pathlength, and the transmittance is almost exactly one. It follows that the transniittance of a beam passing tliroi~ghL L ~ i ~ ismoke" b l e is less than one. Neutral density tiltcrs, wliich allow only a specific fraction of the light to pass through, are used to calibrate light meters. Thus, the voltage (or current) output of the photo cell can be calibrated to give transmittance directly. O/~fical de17xitj:,6is delined as

+- Li9hiBe,=!?-

-+- - - -

I

Wlres To Power Source and Data Acquisition System Figure 3.1 Smoke meter used to measure smoke obscuration. Wires From

Power Source

where a is the extinction coefficient per unit distance in units of ft" (m-'). The extinction coefficient is sometimes called the attenuation coefficient. Percentage obscut-ation is occasionally used and is defined as

where R is the dimensionless percentage obscuration. The specifc optical dens@ is measured in some laboratory smoke tests and is defined as

where

6,

=

specific optical density (dimensionless);

6

=

optical density per unit distance, ft-' (m-');

I/, =

volume of the smoke test chamber, ft3 (m3);

Substituting Equation (3.1) and rearranging results in an equation for optical density in terms ol'transmittance,

A

decomposed surface area of the test sample burned ft2 (m2).

where

The specific optical density is a practical measurement of smoke obscuration only when the decomposed area of the sample is well defined. For laboratory tests where the mass loss of the sample is measured, the mass optical densiry is an appropriate measure of obscuration. The mass optical density is detined as

6 T

optical density per unit distance. K' (m-'); = transmittance. dimensionless; X = distance of light travel or the pathlength, ft (m). Thc e.vti17ctiori co@cit'rit pcr unit distance is defined as =

=

where

Substituting E q i ~ a t i o(3. ~ ~l ) and rearranging yiclds

4,

=

mass optical density, ft2/lb (ni2/S);

d

=

optical density pcr unit distance, K ' (m-');

Principles of Smoke Management

Table 3.1: Comparison of Different Methods of Expressing Smoke Obscuration

Transmittance

Pathlength

Optical Density

Extinction

X

6

Coefficient a

Percentage Obscuration

V,

=

volume of the smoke test chamber, ft3 (m3):

AM

=

mass loss oftest saniple, Ib (g).

The mass concentration of fuel burned in the test chamber is

AM

- / ' - VC

nl

cern that a disoriented person could fall from a balcony. Because a person falling 5 ni (16 ft) has about a 50% chance of fatality, falls are a serious concern for buildings with balconies. Based on the work of Jin (1974, 1975, 1985), the relation between visibility and smoke obscuration is

(3.9)

where nyis the mass concentration of fuel burned in units ). this density into Equation of lb/ft3 ( g / ~ ~ 3Substituting (3.8) yields

K a

S = -

where S = visibilitj, fi (m);

a K

Table 3.1 lists some values of optical density, extinction coefficient, and percentage obscuration for different path lengths. Equations for conversion between differefit smoke obscuration terms are listed in Table 3.2.

VISIBILITY T H R O U G H S M O K E When people cannot see because of smoke from a building fire, they walk slowl!.. \vhich can significantly lengthen evacuation time, and they can become disoriented and lost, thus prolonging their exposure to toxic gascs. In atrium fire situations. there is the added con-

(3.11)

extinction coefficient ft-l (m-'); = proportionality constant (Table 3.3). The visibility is the obscuration threshold, which is the distance at which an object c,n just be seen. The proportionality constant is dependent on the color of smoke, the illumination of the object. the intensity of background illumination, and visual acuity of the observer. Jin conducted tests determining visibility of light-emitting and -reflecting signs. Signs in a smokefilled chamber were observed from outside through a glass window, and the results for illuminated signs are shown in Figure 3.2. White smoke \\as produced by smoldering fires, and black smoke \\.as produced by flaming tires. Visibility through the \vhite smoke was less, probably due to higher light scattering. It is well =

Chapter 3- Smoke and Tenability

'

Table 3.2: Conversion Equations for Smoke Obscuration Convert To

From

Optical Density

Extinction Coefficient

6 = 0.4343 a

Optical Sensity

Percentage Obscuration

6 = - log,, (1 - A1100)

Optical Density

Specific Optical Density

Optical Density

Mass Optical Density

Extinction Coefficient

Optical Density

Extinction Coefficient

Percentage Obscuration

Equation

6 = 6,mf

a = 2.303 S a = -log, ( l - A / 100) X

Extinction Coefficient

Specific Optical Density

Extinction Coefficient

Mass Optical Density

Percentage Obscuration

Optical

Percentage Obscuration

Extinction Coefficient

Percentage Obscuration

Specific Optical Dznsity

Percentaze Obscuration

Mass Optical Density

Specific Optical Density

Optical Density

Specific Optical Density

Extinction Coefficient

Specific Optical Density

Percentage Obscuration

ensi it^

a = 2.3036,,m,

2. = 100(1- 10-~")

6, = 6 v , / A

6 =-

K Io&~(I-A/100) Ax

Specific Optical Density

Mass Optical Density

Mass Optical Density

Optical Density

Mass Optical Density

Extinction Coefficient

Mass Optical Density

Percentase Obscuration

Mass Optical Density

Specific Optical Density

6, = 6,,,m

lA

S,,, = 6 /.m,

6

6 A

=A

,,l

m/ V C I.

Norncnclnturc: 6 =oplical densiiy pcr unit distance. rt-l (n1.l): a = extinction coellicient per unit distnncc. fi-' (ni-l); 1 = percentage obscurntion (diiilcnsio~iless): ? = is specific optical dcnsity (din~cnsionlcss):& = mass optical density, liZllb (n121g): 1; = volumic oflhe snloke tssr chambcr, lij (111'): :\.V

= nixrs

loss ortcst uorplc, Ih (g): A = decomposed arca ot'thc tea mmplc burned. li' (m'):

m') [ m ,

h.tl! 1;

I:

-

.Y

=

distancu of'lipht m x c l or lllc ~;IL.I;

li(111).

,U,-= ni,ass concentration

ol.l'uel burned. lblli' (g:

~ r i n c i ~ lof e sSmoke Management .

Table 3.3: Recommended Proportionality Constants for Visibility Based on Research of Jin (1974,1975, and 1985) Situation Illuminated signs

K 8

Reflecting signs

3

Building components in reflected light

3

Brightness of S i n

a 2000 cdlm' a!

SO0 cdlm'

0 2000 c d d

0 Mo cdlm2

-

Example 3.2 Visibility of Doors and Walls In Example 3.1, what is the visibility of walls and doors? From Table 3.3, K = 3. Extinction coefficient = 0.207 m-'. From Equation (3.12), S= 31.207 = 14 ft or 4.3 m.

0 Irritating Smoke a NonirritatingSmoke

Kind d Smhe Black Smoke Black Smoke Whde Smoke Whmte Smoke

E > OWOQ

>

I

0.4

op 4 I

0.5

0.7

I

I

1 1.5 Ednction Coefficient,a (lh)

I

21

2

0.2

I

,

,

I

I

I

I

1.5 2 Extinction Coefficient, U (llm)

0.3

0.5 0.7

1

l

3

Figure 3.2 Relatiomhip between the visibility of lightemitting signs and smoke obscuration (adaptedfi-on7Jiu [l 9Sj1).

Figure 3.3 Relationship between visibility of liglitemitting signs ar7d smoke obscuratioi7 forir-r-itating and 17onir-r-itating smoke (adaptedfiotn Jin [ l 9851).

known that scattering of background lighting can significantly reduce visibility of lighted signs, but quantitative data about the effect of background illumination are needed. Jin found that the proportionality constant ranged from 5 to 10 for light-emitting signs. For reflecting signs, the constant ranged from 2 to 4 . Jin indicates that the minimum value of visibility for reflecting signs may be applicable for the visibility of other objects, such as walls, floors, doors, and stairs. Based on Jin's research,.the values of K are listed in Table 3.3.

The above information about visibility does not take into account the irritating effects of smoke on the eyes. Jin (1985) conducted tests correlating the visibility and walking speed of subjects exposed to irritating smoke with the extinction coefficient. There are shortcomings with correlating pl~ysiologicaleffects with an optical property of smoke since the effects would seem to be primarily caused by chemical components of smoke. However, the effects of eye irritation are so significant that Jin's work on the topic is discussed below.

Example 3.1 Visibility of an illuminated

1

Fro:

Table 3.3, K = S.

I

11 Extinction coelficient is a=2.303 d so a=7.303(.09) = 0.207 11 From Equation (3.1 1 ), S = 81.207 = 39 li (1 2 m). the distance

Figure 3.3 shows the relation between visibility and obscuration for irritating and nonirritating smoke for a light-emitting sign. The irritating smoke was white smoke produced by burning wood cribs; the less irritating smoke was produced by burning kerosene. The visibility relationships of Equations (2. i l) and (2.12) are not appropriate when subjects are exposed to irritating smoke. In thick irritating smoke, subjects could not keep their eyes open long enough to read the sign. Figure 3.4 shows the relation between smoke obscuration and \valking speed of people walking down a corridor in irritating and nonirritating smoke. Both eye irritation and smoke density affect walking speed. Walking speed decreases with cxtinction coefficient for both smokes,

Chapter 3-Smoke and Tenability

but it is much worse for irritating smoke. For an extinction coefficient of 0.4 m-', the walking speed through irritating smoke was about 70% of that through nonirritating smoke. For extinction coefficients greater than 0.5 m-', the walking speed decreased to about 1 ttlsec (0.3 &S)--the speed of a blindfolded .person. The drop in walking speed was because subjects could not keep their eyes open, and they walked in a zigzag or went step-bystep as they held the side wall. Jin (1985) developed an empirical relation for visibility in irritating smoke: K S = -(Cs- 1.471og,,a) a

(3.12)

{only for a 2 0.076 ft-' (0.25 m-' ) where

a = extinction coefficient, fi-l (m-'); S- = visibility, ft (m); K = proportionalityconstant (Table 3.3); CS = -0.6255 (0.133).

chapters on compartrnentatioridesign and atrium design. For laboratory smoke test chambers and simple room calculations, the mass concentration of particulate, my can be calculated from Equation (3.9). The extinction coefficient can be expressed as

where

a

=

extinction coefficient, fi-' (m-');

a,

=

specific extinction coefficient, f&lb (m2tg);

rnp = mass concentration of particulate 1b/ft3(g/m3).

The specific extinction coefficient depends on size distribution and optical properties of :he particulates. Seader and Einhorn (1976) obtained values for a,,, of 2.1 x 104 ft2/lb (4.4 m21g) for smoke from pyrolysis of wood and plastics and 3.7 X lo4 ft2/lb (7.6 m2/g) for smoke froc: flaming combustion of these same materials. Substituting Equation (3.14) into Equation (3.1 1) results in

the smoke were initating? From Table 3.3, K = 8. where Extinction coefficient = 0.207 A-'.

S

=

visibility, fi (m);

From Equation (3.12),

K = proportionality constant (Table 3.3):

S = -[-S

a,,, = specific extinction coeflicient, ft2/lb ( n ~ ' / ~ ) ;

.207

.6255 - 1.47 log(.207)] = 15 ft (1.6 m)

An alternate approach to calculation of visibility from the mass concentration of particulate is obtained from combining Equations (3.10) and (3.1 l ) with the conversion from optical density to extinction coefficient (Table 3.2).

n7/,

=

mass concentration of particulate lb/fi3 (glm3).

Equation (3.15) relates visibility to the mass concentration of particulate. The comment concerning the utility of Equation (3.13) also applies to Equation (3.15).

0 Irritating Smoke Non~mtatingSmoke

where S = visibility, fi (m); K = proportionality constant (Table 3.3);

S,,,

=

inass optical density, ft2/lb(m2/&;

=

mass concentration of fuel burned lb/ft3(g/m3) I

Mass optical densities for some wood and plastics are in Table 3.4. Equation (3.13) can be useful because the mass concentration of fuel burned can be calculated from a smoke transport model as discussed later in the

0

0.2

0.4

0.6

0.8

1.0

1.2

Extinction Coefficient, a (m")

Figure 3.4 I+hlking spcctl it7 irrim1it7got7d not7it-rila1i17gs117oke(crthp!ed.fi-orxJir~[I9S5]).

Principles of Smoke Management

Table 3.4: Mass Optical Densities (adapted from Mulholland2002) Mass Optical Density, - 4"

Material

ft%b

m21g

Sample Combustion Conditions

Natural Materials: Plywood Wood (Douglas fir) Cotton

Flaming1

Cotton

Flaming2

Pyrolysis Pyrolysis

Synthetic Materials: Pyrolysis

Polymethylrnethacrylate (PMMA; ~ l e x i ~ l a s ~ ~ ) Polyvinylchloride Polyvinylchloride (with plasticizer) Neoprene Polypropylene

Flaming 1

Polyethylene

Flaming1

Paraffin wax

Flaming1

Polystyrene

Flaming1

Styrene

Flaming1

Polyvinylchloride

Flaming1

Pyrolysis Pyrolysis Pyrolysis

Polyurethane

Flaming1

Polyurethane

Flaming2

Latex

Flaming 1

Latex

Flaming2

Neoprene

Flaming1

Neoprene

Flaming2

Polystyrene

Flaming1

Polystyrene

Flaming3

Polystyrene foam

Flaming1

Polystyrene foam

Flaming3

Acrylonitrile-butadiene-styrene (ABS)

Flaming1

Acrylonitrile-butadiene-styrene (ABS)

Flaming3

1. Samples in horizontal conliguration (0.005 m'). 2. The sample is a mattress. 3. The sample is a plastic utility table. The use of trade names implies neither recommendation nor endorsement ofany product by the authors or

publ~sher.

Thickness in. cm 0.24 0.24

0.6 0.6

Chapter 3 -Smoke and Tenability

Tiie airborne particulates produced by a fire consist primarily of soot, and the production of particulates can be estimated as

where

MP = mass of particulates produced, Ib (g);

My

=

mass of he1 consumed, Ib (g);

yp

=

particulates yield (dimensionless).

Values ofyp are listed in Table 3.5 from small-scale experiments of turbulent flaming combustion for a number of materials. While it is expected that particulate production will vary with the size of the fire and the orientation of the fuel, the data of Table 3.5 are rccommended h the absence of data from the kind of large fires for \vhicli smoke management systems are designed. Considering a \veil rnixed space, the mass concentration of the pa~ticulatesis

Example 3.4 Visibility Due to a Pillow Fire If smoke from the burning of a 0.50 Ib (230 g) polyurethane ' foam pillow were uniformly mixed in a 20 ft (6.1 m) square, 10 ft (3.05 m) high room, what would be the visibil. ity of a lightemitting sign?

Approach 1: From Table 3.5, the particulate yield of flexiblt polyurethane foam is 0.1 88. From buation (3.16), the mass 0) airborne particulate is

From Equation (3.17), the mass concentration of the particulates is

Using a, = 3 . 7 1~o4 fiZAbfor flaming combustion and K = 8 Fable 3.3), visibility is calculated fi.orn Equation (3.15) as

visibility of a light-emitting s i y . 4pproach 2: The mass concentration of fuel burned is calcu!ated from Equation (3.9): where

I/,

=

volume of: h c smoke in the space, li3 (11i3).

Equation (3.17) can be used for a laboratory test where l/,. is [he volume of the test chamber. This equation also can be used for a tire in a room or atrium where VC is the volume of tlie smoke layer. In both cases, the smoke volume is considered to be well mixed so that the smoke properties are uniform throughout the volume. For a h e wit11 a constant heat release rate, the mass of fuel consuliied by a fire can be expressed as

From Tablc 5.4, the mass optical densiy 4,.of polyurethmc Foam from a flaming mattress fire is 1600 ft'nb (0.33 m' g). Visibility is calculated from Equation (3.13):

kibility of a light-emitting sign.

WCsee that this is different from !he 9 fr (7.7 m) estimated in ~pproachI, and this is indicative ofthe limitati~nsof this techiology, including availability of a," and d,,, data.

EXPOSURE T O GASES

where M/

=

mass of Cue1 consumed, Ib (g);

=

total heat rdcase rats Gtuis (kW);

AHch

=

chemical hcat of cornbustion Btullb (klkg);

1

=

timc li.om ignition, S (S);

K/-

=

1 (1000).

Values of' I'or some materials are listed in Tablc 3.5. Iri tires. combustion is never complete. Combustion efficicnc is the ratio of tlie chemical heat of combustion LO the ncl Iieat of combustion. Using AH,.,, eliminates thc nccd to consider conibustion efliciency.

I n the following sections, information about human responses to exposures to toxic gases applies to an a w r age person. A person's response to an exposure to toxic gases primarily depends on age, metabolism, health history, and respiratory rate. Carbon monoxide (CO) poisonin,o accounts for the majority of total fire fatalities (.Berl and Halpin 19SO; Harland and Woolley 1979). Table 3.6 lists toxicity dsta for several gases, but only a few gases have been incorporatcd in predictive toxicity models. The toxic efficts of CO are probably the most well known, but some o h e r gases included in toxicity models are hydrogcn cyanide (HCN), hydrogen chloridc (HCI), and hydrogsn bromide (HBr).

Principles of Smoke ~ a n a ~ e m & t

Table 3.5: Particulate Yield of Heat of Combustion for Well-VentilatedFires of Solid ~ u e l s '

Material

Particulate. Yield Yp

Chemical Heat of Combustion, AHch Btulib

Natural Materials: Wood (red oak) Wood (Douglas fir)' Wood (hemlock) Fiberboard* Wool 100% @ntlretic materials: Acrylonitrile-butadiene-styrene(ABS) Polymethylmethacrylate (PMMA; plexiglasTM) Polypropylene Polystyrene Silicone ~o~~este? Nylon Silicone mbber Poly~lrethaneFoam (Flexible)) Polyurethane Foam ( ~ i ~ i d ) ) Polystyrene ~ o a m ) Polyethylene ~ o a m ) Phenolic Foam Polyethylene (PE) PE with 25% chlorine PE with 36% chlorine PE with 48% chlorine Polyvinylchloride (PVC) PVC 1 (L01 = 0.50) PVC 2 (L01 = 0.50) PVC (L01 = 0.20) PVC (L01 = 0.25) PVC (L01 = 0.30) PVC (L01 = 0.35) Ethylenetetrafluoroethylene (ETFE; TcfzelTM) Perfluoroalkoxy (PFA; TenonTM) Fluorinated polyethylene-polypropylene(FEP; TenonTM) Tetrafluoroethylenc (TFE; ~ e f l o n ~ " ) 1.

Data from Tewarson (2002) except as othenvise noted.

2. Paniculate yield data from Mulllolland (2002). 3. Values listed are an average o f a nurnhcr ol'd~lTerent nialerials under this general name. '"The use o f trade n a n m irnplics neithcr reconimendation nor endorsenient o f any product by [lie authors or puhlishcr.

kJ/kg

Chapter 3-Smoke and Tenability

Table 3.6: Lethal Concentration of Some Gases Gas Co2 C2H40 C2H402

NH3 HCI CO HBr NO COS H2S HF C3H4N COF2 NO2 C3Hj0

carbon dioxide acetaidehyde acetic acid

LCS0for 30-Minute Exposure (ppm) ,

470,000

ammonia hydrogen chloride carbon monoxide hydrogen bromide nitric oxide carbonyl sulfide hydrogen sulfide hydrogen fluoride acrylonitrile carbonyl fluoride nitrogen dioxide acrolein

fonnaldeliyde hydrogen cyanide HCN C9H602N2 toluene disocyanate phosgene COCl, perfluoroisobutylene CAFX CH20

Hyperventilation due to carbon dioxide (COz) exposure will increase the rate of intake of CO. Oxygen ( 0 2 ) deprivation is a special case, and the reduction in the amount of O2 available for tissue respiration is referred to as hypoxia. Because of the interaction of these gases, exposure effects discussed below consider the combined effects of these gases. The effect of exposure to toxic gases on a specific individual depends on the physiological characteristics of the individual.

due to building fires tend to change with time. Thus, Haber's rule has limited use for tenability calculations. In the past few decades, tenability limits have been expressed in terms of time integrated values. Time integrated values account for the effect of exposure to a changing concentration of a particular gas over a period of time rather than an instantaneous exposure. The E parameter in Haber's rule can be considered a time integrated value with a constant gas concentration. If the concentration is variable in time, then an integration must be conducted to obtain the area under the concentration-time curve in order to determine a time integrated value.

FED from Animal Test Data While most animal toxicity tests have been conducted on rats, other animals include mice, guinea pigs, hamsters, and rabbits. Because of concern for animal rights, the toxicity research programs used the minimum of animals, and most laboratories stopped animal testing near the end of the 20th century. These tests determine the concentration of airborne combustion products that is lethal to 50% of the test animals exposed for a specified time, and this lethal concentration is referred to as the LCjo. The specified time for animal tests is usually 30 minutes, and the number of fatalities consist of animals that die during the test and during a post-exposure time, usually 14 days after the test. Using extrapolated animal test data, the fractional effective dose is

where FED = fractional effective dose (dimensionless);

C

=

f

=

concentration, 1blft3( & I ~ ) ; exposure time (min);

Exposure and Time

LCf 50 = lethal exposure dose from test data, Ib ftJ min

Haber (1924) proposed that the effect of an exposure to a gas is related to the product of the gas concentration and time duration of the exposure. Haber's rule is expressed as

(g m'3 rnin). An FED greater than or equal to one indicates fatality. The concentration, C, is the density of materials that started as fuel that have accumulated at a location at time I. This concentration has units of mass of the material burned per unit volume. The lethal exposure dose, LCI ,o, is the product of the LCso and the exposure time. Table 3.7 lists some values of LCfSOfor a number of common materials. The above equation is the time-integrated form of the FED equation. For most applications, the time functional relationship of concentration is not known, and the following expression can be used for discrete pairs of concentration and time intervals.

where E = effect of exposure (ppm-min), C = concentration (ppm), and I = duration of exposure (rnin). This elementary equation assumes a constant ingestion rate of the tosin. The effects of some gases do not follow Haber's rulc, and concentrations of toxic gases

Principles of Smoke ~ a n a ~ e m e ' * t

Table 3.7: Approximate Lethal Exposure Dose, LCtSO, for Common Materials (adapted from Purser 1995) -

Material

Nonflaming Fire min g m-3 min

Ib

Cellulosics C, H, 0 plastics PVC WooVNylon (low N2)

0.046 0.03 1 0.03 1 0.03 1

730 500 500 500

Flexible Polyurethane Rigid Polyurethane

0.042 0.0039 0.0 10

680 63 160

~odacrvlicl~~~' I.

('Fuel-Controlled Fire

f lb-ft-3 n i n- 0.19

\

g md min)i

d

-3120

Fully Developed Fire lb ff3 min g m-3 min

0.075 0.0 19 0.057

1200 300 920

0.047 0.033 0.012 0.0044

750 530 200 70

0.087 0.0062 0.0087

1390 100 140

0.012 0.0034 0.0028

200 54 45

PAN is polyacr).lonitrile.

Example 3.5 Calculation of FED Would a 20-minute exposure to atmosphere in a room resulting !?om burning 6 Ib of flexible polyurethane foam in the room be expected to be fatal? The size ofthe room is 8 R by 12 R by 8 fi (2.44 m by 3.66 m by 2.44 m). where Ci Afi

=

LCf

=

n

=

concentration for time interval I, lb/ft3 (eJni3);

= time interval i, min (rnin);

lethal exposure dose from test data, Ib

Flexible polyurethane foam would be expected to bum very rapidly compared to the 20-minute exposure time, so the concentration in the room can be considered constant.

rnin

C =

(g m-' min);

6 mass of fuel burned volume of space - (8)(12)(8)

number of discrete concentration time pairs.

When the concentration is constant, Equation (3.2 1) written as Cr FED = LCt50

From Table 3.7, LCt 50 = 0.087 Ib ft-3 rnin (1390 g m-3 min) for a fuel-controlled fire. Because the concentration is constant, the FED is calculated as

(3.22)

Many references use the term corzcentrafion rime pmdzicf, Cf, to mean the integral term of Equation (3.22), and this meaning of Cf will be used for the rest o f this book. The question arises, should incapacitation or fatality be used as the design criterion for gas exposure. A person who is incapacitated due to exposure to toxic gases will continue to be exposed to those gases. Unless the person is rescued or the gas concentrations improve dramatically, such exposure will result in fatality. Incapacitation often is used to mean the condition that self-evacuation is very difficult or impossible. Usually an incapacitaling dose is less than a fatai dose, but this is not always the case. It is possible that a person could walk out of the smoke-filled environment only to die some time later. While a FED of one indicates fatality, Bukowski et al. (1 989) state that an FED of 0.5 can be considered an approximation to the incapacitaling dose. I L is possible that this approximation is a conservative criterion for smoke nnanage~ncntdesign analysis.

= l Ct FED = - - 0.0078(20) LC,,, 0.087

,

This indicates that fatality would be expected.

Table 3.8: Components of Air constituent' Nitrogen (Nz) Oxygen (01) Carbon Dioxide (CO2) Argon (Ar) Trace Gases (He, Kr, Xe, H?,CH,, and N20) 1.

O h

by Volume 78.084 20.946 0.033 0.9?4 0.003

Handhook oj Clrerrrisr~)~ alrd Plryics (CRC 1985)

Components of Air Calculations using predictive toxicity gas models involve the components o f air, and these components are listed in Table 3 3 . The small concentration of CO2 is essential to control normal breathing, but it does not have a significant impact on toxicity calculations.

Chapter 3-Smoke and Tenability

For the fire protection purposes of this book, the small quantities of CO2, argon (Ar), and the trace gases are neglected, and air is considered to be composed of 20.9% O2 and 79.1% NZ by volume. Some sources use 21% 0 2 and 79% N2 by volume, which also yields useful engineering results. :

CO and CO2 Exposure to CO results in carboxyhemoglobin uptake (COHb) in the blood, which results in decreased oxygen-carrying capacity of the blood. Stewart et al. (1973) conducted a series of experiments on humans and, based on this research, C O H b uptake can be expressed as

is seen for any time. In the former case, this would represent such physiological effects as breath holding and the time required for the gas to be transferred to the blood and then to the tissues. In the latter case, this represents an exposure concentration for which the equilibrium concentration of carboxyhemoglobin (COHb) in the blood is below the level that causes lethality (Levin et al. 1987). Following the work with CO, the effect of CO2 on the observed CO toxicity was studied. The result of this work was the observation that the "effective toxicity" of CO increases with increasing CO2 concentration, doubling at a level of about 5% (50,000 pprn), as shown in Figure 3.6. The physiological effects of the CO2 are to increase the respiration rate and reduce the blood pH, producing a metabolic acidosis. The interaction beh~.een

where CCOHb = concentration of COHb in the blood%;

CCo

=

concentration of COHb in the blood at time zero,%; concentration of CO in air, pprn;

V

=

volume of breathed air per minute, Llmin;

Ati

=

exposure time interval, min.

CCOHb,O=

Equation (3.23) does not include the effects of oxygen depletion, increased breathing rate due to CO2 exposure, or exposure to other toxic gases. The volume of breathed air, V , is called the respiratory minute volume (RMV). The typical RMV of a 150 Ib (70 kg) person at rest is about 8.5 Llmin. O'Neill et al. (1980) used a higher RMV of 18 Llmin to account for activity and. CO2 exposure, but this approach can significantly underestimate toxic effects, as is discussed later. For calculations, a value of CCONb,O = 0.75% can be used, and incapacitation and lethality are approximately 25% COHb and 50% COHb, respectively. However, calculation of the COHb level from Equation (3.23) is not a reliable indication of toxicity Lr incapacitation because it does not include the effects of other gases commonly present in smoke (see Example 3.8). In the development of predictive toxicity gas models for fire applications, the first pure gas to be studied was CO. Rats were exposed to varying concentrations of pure CO for various times, and the concentrations necessary to produce deaths of 50% of the exposed animals (the LC50)for each exposure time was determined. The plot of these data (Figure 3.5) shows that the curve has two asymptotes-an exposure time (about I minute) below wliich no cl'fect is seen for any concentration and a concentration (about 1700 ppm) below which no effect

1 I I

Asymptote l minute

-

Asymptote 1700 ppm

-

"0

10

3350 PPm

* - - - - - -at-60_min_ ___

20

30

40

50

Time (minutes)

Figure 3.5 Carbori I I I O I I O S I ~COI~C~I~II-a1io11 ~ VS. time to letlinlitj~($SO% of exposed rate (odnyied

..

0

l

0

,

1000

.

. 2000

..&&-EL. ,, Deaths

I

1

, . 3000

I

..?E%

'.'..,.."-.m

4M)O

5003

E

Carbon Monodde (ppm)

Figure 3.6 Dearlls,fi.o~ne.vposi~reto CO alone and CO p1zr.s COz (udoptcd ,%.on7 Lcvin er ul. ( 1 9s 71).

. . .,... . .;,:A;:

>.

.

CO and CO2 is apparent from the formulations of the Ngas and FINmodels that follow.

N-Gas Model The N-gas model was developed at the National Institute of Standards and Technology (NIST) and relates fatality with animal test data of exposures to pure gases and mixtures of gases (Levin 1996; Levin et al. 1995; Babrauskas et al. 1991). For mixtures of gases, including NO2, the N-gas model can be stated as

and for mixtures not including NO2, the N-gas model can be stared as NGas =

,,,[CO] [ C O 2 ]- b

[HCN] + LC,,(HCN)

+

+

20.9 - [ 0 2 1 20.9 - L C p ( 0 2 ) ,

[HCf] LC,,(HCf)

+

[HBI-] LC,,(HBr)

Principles of Smoke ~ a k g e m e * t

.

The model incorporates the ~ncreasedbreathing rate due to CO2 exposure. It is apparent that there is a unique interaction between HCN and NO2. For many of the gases, the contribution to lethality is expressed as the ratio of the gas exposure to the LCS0. This is how O2 is treated, except that it is in terms of oxygen depletion. The toxicity of CO2 is not included in the N-gas model because fire-generated atmospheres do not contain toxic concentrations of CO,. The LCso of CO, is 47% and the maximum concentration of CO2 in a fire atmosphere is 20.9% if all of the oxygen in the air is converted to CO2. For animal tests, it was found that when the NG,, value was approximately I, some of the animals died. For values below 0.8, there would be no fatalities, and for values above 1.3, all of the animals would be expected to die. The time-integrated average exposure to CO is 1 ' -1 Ccodf ,=o =

(3.25)

where N ~ a ~=

N-Gas model indicator (dimensionless);

n7

=

-18 for CO2 S 5% and 23 for CO2 > 5%;

B

=

122,000 for COz < 5% and -38,600 for CO, > 5%;

[CO] =

fe

where I, is the exposure time. The other time-integrated averages can be expressed in a similar manner. For discrete concentratio11data, the time-integrated average can be written as follows:

2 Cco, ;At;

1

[CO] = f

LCSO(OZ) = lethal concentration of 0 2 % ; LCjo(HCN)= lethal concentration of HCN, ppm;

l..

e

i: l

LCS0(NOZ)= lethal concentration of NO2, ppm; LCSO(HCI)= lethal concentration of HC1, ppm; LCSO(HBr)= lethal concentration of HBr, ppm; [CO]

=

[CO?]

=

time-integrated average exposure to CO, PPm; time-integrated average exposure to COz,

L021

=

PPm; time-integrated average exposure to O-,,

[HCW

=

[NOz]

=

[HCI]

=

W);

[I-IBr]

=

time-integrated average exposure to HCN, PPm; time-integnted average exposure to NOZ, PP'T time-integrated average exposure to HCI, ppm; time-intcgrated average exposure to H Br, ppm.

I [HBr] = l'>

2 C,,,.,

i= l

;Ati

&apte; 3 -Smoke and Tenability

Cco,i

=

concentration of CO, pprn;

CCm,i

=

concentration of CO2, ppm;

C02,i

=

concentration of 02,%;

CHCNi = concentration of HCN, ppm; Cm,,

=

concentration of NO2, ppm;

CHCISi= concentration of HC1, ppm; CHB,+ = concentration of HBr, ppm; fe

=

exposure time, min;

At

=

time interval i, min;

n

=

number of concentration values for each gas and time interval.

Equation (3.27) can be used where the time intervals are either uniform or nonuniform. For uniform intervals, the time-integrated average terins of these equations become mean averages. When the concentration of any of the gases other than 0 2 is zero, the contribution of that gas to the NW value is also zero. This is to be expected, but it is not so for the fractional incapacitating dose method discussed later. Equations (3.24) and (3.25) apply when the exposure time is the same as the duration of the LCS0data. Example 3.6 demonstrates the use of the N-Gas model for four gases, but Table 3.9 has LCSo values for all of the gases in this model for many exposure times. For exposure times between those listed in this table, LC50 values can be interpolated.

Example 3.6 Using the N-Gas Model

. .

.

lalculate /VGrrsfor a 20-minute exposure to the mixture of gases listed below. Time

C0.i

I

(m in)

0

0

Yo 20.90

CCOZ.; .

GO. i

PPm 0

PPm 0

c ~ ci ~ ~ . PPm 0

I

2

20.72

5SO

40

2

2

4

20.30

1900

60

3

3

6

19.80

3200

120

6

4

8

19.70

3600

120

6

5

10

19.60

3800

I60

8

6

I2

19.60

3800

500

25

7

14

19.60

3800

600

30

S

I6

19.60

3800

600

30

9

IS

19.60

3800

600

30

10

20

19.60

3800

600

30

The time-integrated avcragc exposures can be calculated from Equation (3.27). Bccausc the intervals are unifomi, the timeintegrated average ternis are mean averages of the concentrations as listed below. [CO] = 340 [02]= 19.8 1 [CO,] = 3208

[HCN J

=

17

Bccausc rhcl-e is no exposure to HCI and H&, Equation (3.25) becomes

Bccausc COz is less than 5% (50.000 ppm), t11 = -1 8 and b = 122,000. For a 70-minute exposure. lethal concentrations from Table 3.9 are LCS0(02)= 5.2% and LCjO(HCN)= 170 pprn.

This exposure ii'ould not be expected to cause fatalitv.

Principles.of Smoke Management

'

Table 3.9: Lethal Concentration, LCSO,of Various Gases Exposure Time min

HCN PP"'

Oz

1 2

3000 1600

-

5 10 15 20 25

570 290 230 170 160

4.0 4.8 5.0 5.2 5.3

15900 8400 6900 6400 5900

30 45

150 120

5.4 5.6

3800 3300

3000 2600

200 150

60

90

5.8

2800

2200

100

I.

HCI PP"' -

'

HBr PP"' -

NOz PP"'

-

1450

12600 6600 5400 5100 4700

830 510 380 320 290

FIO,i

=

hction of an incapacitating dose of ~ O W -

oxygen hypoxia per unit time (min-l); FImSi = hction of an incapacitating dose of CO2 per unit time (min-l); Ati = exposure time interval i (min);

n

number of concentration values for each gas and time intervals. The following terms are calculated as =

Note: LC50 values based on data from Levin et al. (1988 and 1989). Levin (1996). Levin (2000). and Hanzell et al. (1990) except for HBr. Because o f the chemical similarities o f HCl and HBr, they are expected to have similar toxicological effects, and most o f the above LC50 values for HBr were extrapolated from those o f HCI.

Fractional Incapacitating Dose Purser (2002) developed a model to calculate a fractional incapacitating dose for exposures to CO, HCN, CO2, and reduced Oz. The notation in this section has been modified from that of Purser to facilitate computer programming.

whichever is greater, where

FIN

=

fractional incapacitatingdose of all narcotic gases (dinlensionless);

FIco,;

=

fraction of an incapacitating dose of CO per

=

=

1. for zero CO, Flco,i has a value of zero;

unit tinie (min-l);

2. for zero HCN, FICjV,, has a value of about 0.0045 nii11-l; and

fraction ofan incapacitatingdose of HCN per

3. for zero 20.9% O1, FIO,,has a value of about 0.002 1

unit time (min-l);

Vcoz,,

where Cco,; = concentration of CO (ppm); CHC.\r; = concentration of HCN (ppm); CC02,; = concentration of CO2 (percent); Co., = concentration of Oz (percent). A value of FlIr of I or more indicates incapacitation. and the incapacitation time based on can be taken as the time it takes for FINto become I. Equation (3.29) represents incapacitation due to the toxic effects of COz, and this equation was included for completeness. As previously stated, fire-generated atmospheres do not contain toxic concentrations of COz Equation (3.29) may be useful for fire scenarios that include sources of CO? other than the fire. For applications where there are no nonfire sources of CO1, Equation (3.28) should be used for the calculation of F/,,,. As previously stated, the FINmethod is based on air composed of 20.9% 0 2 . Any combustion calculations or test measurements that are used for input to calculations of F/,, should be consistent with this O2 concentration. Examination of Equation (3.30) sho\vs that

factor for CO1-induced hyperventilation;

For item I , it would be expected that a zero concentration of CO would result in a zero contribution to the

Chapter 3-Smoke and Tenability

FIN. However, items 2 and 3 were unexpected. A z e r o concentration of HCN results in a positive contribution to the FIN,and no oxygen depletion ( 0 2 = 20.9%) also results in a positive contribution. For the short exposure times characteristic of most fire protection applications, these positive contributions are small and should not be of concern. some are measured in hours as was the case for the World Trade Center explosion. From Equation (3.28) and (3.30), an incapacitation time of

-

.

about 3.3 hours can be calculated for exposure to an atmosphere of normal 0 2 and zero concentrations of CO2, CO, and HCN. This exposure can be thought o f a s breathing normal air, and no such exposurewould result in incapacitation. This indicated that the FIN approach is inappropriate for long exposures. However, the FED and the N-gas model are based predominantly on test data with 30-minute exposure times, and applying these models for long exposure times is also questionable.

Example 3.7 Using the F[,,, Model For the gases of Example 3.6, calculate the FIN Use Equations (3.28) and (3.30) to calculate the table below. Remember for FIN, CO2has units of percent. i

Time (min)

FICO.i

0

0

NIA

l

2

0.00 13

2

4

0.00 19

3

6

0.0039

4

8

0.0033

0.0052 1

1.115

0.000563

0.072

5

10

0.0053

0.00545

1.119

0.000594

0.097

6

12

0.0 1 73

0.00806

1.119

0.000594

0.155

7

14

0.0209

0.00904

1.119

0.000594

0.223

S

16

0.0209

0.00904

1.119

0.000594

0.291

9

18

0.0209

0.00904

1.119

0.000594

0.359

10

20

0.0209

0.00904

1 119

0.000594

0.427

'~02,;

Floei

NIA

NIA

NIA

0.00475

1.053

0.000325

0.013

0.00486

1.080

0.000407

0.029

0.0052 1

1.107

0.000534

0.050

F ~ ~ ~ . i

FIN

0

At 20 minutes of exposure, the FIj,,is about 0.43. This indicates that this exposure is not expected to cause incapacitation.

Example 3.8 Comparison of To~icitvhlodels For the gas concentrations listed below, calculate NG,,, FIAi,and COHb.

Part

Time

c~?,i

Cc02.i

Cc0.i

i

(min)

%

PP"'

PP111

0

0

20.90

0

0

0

1

2

20.18

2320

320

8

2

4

18.50

7600

480

12

3 4

6 8

16.50 16.10

12800 14400

960 960

24 24

5

10

15.70

15200

1280

32

6

12

15.70

15200

4000

100

7

14

15.70

15200

4800

120

S.

16

15.70

15200

4800

120

0

IS

15.70

1 5700

4800,

120

10

20

15.70

15200

4800

120

I: In thc snnic manner as Example 3.6, Nh

from rh~scsposurc.

C ~ i ~ ~ . i

PP"'

= 1.1 is calculated. This means fatality \\xiuld he expected

Principles of Smoke Management

Example 3.8 (Continued) Comparison of Toxicity Models Part 11: Calculations of FIN are similar to those of Example 3.7. Time (min)

i

I

F l ~i ~ ,

F ~i N/A

~

0

0

N/A

I 2 3

2 4 6

0.0109 0.0166 0.0340

0.00545 0.00598 0.00788

4 5

8 10

0.0340 0.0458

0.00788 0.00947

~

vN ~ ~ 2 . i

Flo.i N/A

0.000

1.OS8 1.203 1.328

0.00043 0.00 108 6.00317

0.036 0.093 0.210

1.369 1.390

0.00393 0.00488

0.333 0.496

N/A

At F,,,.,,= 1, incapacitation is expected. From the above table, incapacitation is expected at about 12 minutes. Part 11: COHb in the blood is calculated from Equation (3.23);where 11

= 3.3 I 7 X

A C ~

- 1.036 . . I O-'CCO, lfAt and CCoHh= CCOHb,o +

ACCOHb.l i= l

c'

=

18 Urnin; At = 2 rnin: CCOH&,= 0.75%. Time

I/

CCO.:

(min)

* .;,

0 2 4

0.0Oil 0.032 0.048

ACco~b.i

%

c,,,, O/a

0.00000 0.7500 0.00003 0.7500 0.00005 0.750 1 G 0.096 0.000 1 1 0.7502 S 0.096 0.7503 0.000 1 1 10 0.12s 0.000 14 0.7504 12 0.400 0.00046 0.7509 14 0.450 0.00056 0.75 15 16 0.4SC1 0.00056 0.7520 18 O.IS(:I 0.00056 0.7526 20 0.480 0.00056 0.753 1 This lcvcl of COlib is below hat \vhich would resuit in either incapacitation or fatality, and these calcularams sl~ow[hat C@!{!, c~lculakdl h ~ Equation n (3.23) is not a reliable indication of incapacitation or fatality.

EXPOSURE T O HEAT Exposure to elevated temprl.ratul-e atmospheres can lead to skin burns and hypenhermia (heat stroke). A temperature limit of 250°F (1 2 1 'C) for d ~ air y is used as a rule of thumb to dctermins \\.hicl1 of thcse two possible efl'cc~swill dominate. Generally, to hcatcd . csposure . dry a i r a, a ,empcratllrc less approximately 2jO"F (121°C) lcads only to Iiypmhc.rmia. Pain from skin

burns can be expected to be the dominant effect for d q air temperatures greater than 250°F (1 21°C). The effect o.f esnosure to elevated tem~eratures depends on the of the a i r and the type and extent of clorhing worn. Physiologically, exposure to an elevated tcrnperature environment Can cause an increase in body or blood temperatuce. Also affecting the thermal

Chapter 3-Smoke and Tenability

tenability limits is the presence of clothing. Perspiration is a key mechanism used by humans to resist the effects of exposure to a high-temperature environment. However, clothing may inhibit the efficiency of this natural cooling process. Conversely, clothing provides insulation from high-temperature environments to protect the skin from becoming burned. Thus, at temperatures in excess of 250°F (121°C), where pain from skin burns is the dominant effect, the presence of clothing can be considered to be beneficial. However, at the lower temperatures, where hyperthermia is the dominant effect, clothing is detrimental. As in the case of exposure to toxic gases, consideration of the time duration of exposure is necessary to accurately assess thethreat. A limit of approximately 300°F (150°C) is often stated for exposure durations of five minutes. The thermal tolerance of humans at rest, naked, with low air movement is shown in Figure 3.7. Purser recommends the following relationhip for time to incapacitation based on averaging the time to incapacitation for exposures to huniid air arid dry air:

Exposure Time (minutes) . Figure 3.7 Ther-~nal~olerance for humans at rest, nnked, with low air movement (adapted fi-on7 Blockley [1973]).

The cumulative dose is the sum of the doses for each of the intervals:

where where 1~1,

=

F1,ll = total cumulative dose (dimensionless);

time to incapacitation due to thernial exposure, F,,,,, =

min;

sionless).

C,

=

5.670 (5.185);

C2

=

0.0 152 (0.0273);

T

=

temperature of air, "F ("C).

Incapacitation would be expected for FI,l, greater than or equal to one. Substituting Equations (3.31) and (3.32) into Equation (3.33) yields

Equation (3.3 l ) applies when the teniperature is not changing witli time. To deal witli changing temperatures, the same concept of a fractional incapacitating dose that was used for gases can be applied to heat exposure (Purser 2002). During any one time step, the incapacitating dose is given as G

Flrh

A/; = -

(3.32)

=

incapacitating dose for the time interval (di~nensionless);

Ati

=

exposure time intcrval i, min;

tlh,,

=

timc to incapacitation for tcmpcralureof'intenral i, min.

whcrc Fl,/,

=

total cumulative dose (dini~nsionless);

Ati

=

cxposure time interval i, n:in;

=

temperature of air in interval i, "F ("C);

C,

=

5.670 (5.185):

C?

=

0.0 157 (0.0373).

[/A. i

where F

incapacitating dose for time interval i (dinien-

Equation (3.34) is in a forin uscful for calculation with lcmpc'raturcs ~ I - O ~ L I by C Ca~smoke transport model or tcmpcrarurcs f.1-on1 lire tcsls 1,ccorded with a data acq~risitiorl?.stem.

Principles of Smoke Managemelit - --

Example 3.9 Cumulative Exposure to Heat

1

Determine if incapacitation would be expected for a petson exposed to a smoke layer where the average smoke layer temperature during the first minute is 125°F(52°C). During each ofthe next four minutes, the smoke layer temperature increases 25°F (14°C).

I in the following table, t f i , ,Fldl ,.,and Fit,, were calculated from Equations (3.31), (3.32), and (3.33). I

C

1111,i

min

"F

min

F I Ii ~

Ft~h

125 43 0.02 2 l50 30 0.03 3 175 20 0.05 4 200 14 0.07 5 225 9 0.11 Since the total F,,,, is well below 1.0, incapacitation would nor be expected. 1

0.02 0.06 0.11 0.18 0.28

EXPOSURE TO THERMAL RADIATION Thermal radiation can cause pain, blistering. and burning of exposed skin. Exposure to thermal radiation is often not addressed in discussions of tenability for smoke control applications because of the limited smoke temperatures for such designs. Gas temperatures that are tenable for contact with skin are also tenable with respect to thermal radiation. Stoll and Chianta (1969) show that the exposure time to pain and blistering can be represented by

observers be able to approach the fire? From Chapter 2, the separation distance for nonpiloted ignition due to thermal radiation can be adapted for the separation distance to prevent skin pain as

where Q, = radiant heat release of the fire, Btuls (kW);

RsD = separation disrance from the center of rhe fire to a person, fi (m); q,, = limit of radiant flux to prevent pain, ~ t d f t 's (kW1

III

Ill2).

Calculare Q,

where =

exposure time to pain, s (S);

;,,h

=

exposure time to blister, s (S);

qr

=

intensity of thernial radiation, ~ t u &s ( k ~ l m ' ) :

C,:,

=

3.20 (85);

C,,

=

8.39 (223).

I,:[,

The above relationships are shown in Figure 3.S. .A value of q): = 0.22 ~ t u l f t 's (2.5 kwlrn2) is often used as the value that can be tolerated for a few minutes \vithout unbearable pain.

RsD

=

=

1000 (0.3) = 300 Btds (320 kW), and use

1'0" -= 10 ft (3 m) separation distance.

d4d.22)

I

TENABILITY AND PERFECT DILUTION It is cornnion to encounter situations where the dilution necessary to meet some visibility criterion results in sucn ION gas concentrations that toxicity. is not an issue. Generally, such dilution also results in smoke temperatures so low that heat exposure and thermal radiation exposure are not issues. However, this is not so for fuels that produce low amounts of soot.

Chapter 3-Smoke and Tenability

Radiant Flux (kW/m2)

In Equatiorl(3.22), the concentration C is the same as the mass concentration of fuel burned, mj So that equationcan be written as

where FED

=

fractional effective dose (dimensionless);

m/

=

mass concentration of fuel burned, l b l g (g/

f

- exposure time (min); and

m3); LCt 5, = lethal exposure dose from test data, Ib ftJ min (g m-3 min). Without heat transfer, the smoke temperature will be Radiant Flux (Btuk fi2) Figure 3.8 Tolerai7ce of humat1 skin to thermal radiant J11u (adapted fj-otn Stoll a17d Chianta [l 9691).

Klote (1 999a) developed equations based on perfect dilution that allow relative comparison of visibility, toxicity, and temperature for a particular fuel. This section presents a similar but more straightPonvard approach. The analysis considers that the products of conibustion (particulates, gases, and heat) are diluted by air. This analysis neglects smoke panicle aging (agglomeration and deposition), reduction of specific gases, and heat transfer. These are all conservative assumptions in that they result in higher predicted levels of dilution to meet tenability criterion. Further, almost all smoke transport calculations neglect smoke particle aging and reduction of specific gases. This analysis consists of putting visibility, the effect of toxic esposure, and smoke temperature in terms of a common variable so comparisons can be made. The variable selected is the mass concentration of fuel burned, 11.;: Equation (3.13) already has visibility in such terms:

visibility. ft (m); proportionality constant (Table 3.3); mass optical density, li2/lb (m2/%); mass concentration of furl burned 1b/ft3(g/rn3).

where

Tg

=

smoke temperature, "F ("C);

To

=

ambient temperature, "F ("C);

Q = heat release rate of fire, Btu (Id); M, = mass of smoke, Ib (kg); Cp = specific heat ofsmoke, 0.24 BtuAb "F (I .O I d k g "C);

The follo\ving equations are needed in order to get the desired expression for the smoke temperature:

where Mj = mass of fuel bumed, Ib (g); AHc11=

chemical heat of combustion, Btu4b (kJ/kg);

PS

=

density of smoke, lb/fi3 (kg/m3);

i"2 R

=

ambient pressure, lb/$ (Pa);

=

gas constant of smoke, 53.3 ft Ibfllbm O R (287 JI

C7.

=

kg K); 460 (273);

=

volume of smoke, h3(m3);

=

1 ( 1000).

v, 9

Substitu~ingEquations (3.39) into Equation (3.38) and rearranging yields

Principles of Smoke Management

+ T,=- CT

l-a

where a =

m

Rmch L .

K/ CpPa

(3.40)

Equations (3.36), (3.37), and (3.40) are in terms of the mass concentration of fuel burned, m/:Equation (3.36) can be solved for mass concentration of fuel burned:

The design criterion for visibility can be put into Equation (3.41) to get the maximum value of the mass concentration of fuel burned to meet the visibility ciiterion, and Equations (3.37)-and (3.40) can be used to calculate the upper limits of the FED and T, resulting from this mass concentration of-fuel burned. This approach is used in Example 3.1 1.

Example 3.11 Evaluation of Toxicitv and Heat Exposure from Visibilitv Criterion

)/

For a visibility criterion of being able to see an illuminated exit si.p 30 fi (9.1 m) away, are toxicity and heat exposure calculation needed in addition tovisibility calculations? The fuel ispolyurethane. .

I

Part I: Calculate m/ From Table 3.4, the mass optical density, ,a , is 1600 f&lb (0.33 m'@. From Table 3.3, K = 8 for an illuminated sign. Visibility, S, is 30 fi (9.1 m). From Equation (3.41),

11 This is the mass concentration of fuel burnedthat satisfies the visibility criterion.

1

Part 11: Calculate FED Use an exposure time of 20 minutes. From Table 3.7, the lethal exposure dose from test data. LCI jo, is 0.087 Ib fYz tiiin (1 390 g m-' min). From Equation (3.37),

I

I

This is an upper limit on the FED in that it is at the highest value of mass concentrarion of fuel burned.

Part 111: Calculate

T,

From Table 3.5, the chemical heat of combustion, AHd,. is 7570 Btdlb ( I 7,600 kJkg). P,= 14.7 (144) = 2120 lb/ft2. To = 75 "F (24 "C). From Equation (3.40),

This temperature is the upper limit for the smoke based on dilution, aud it is not a s o n c a n wirh regard to heat exposure. This example shows that calculations for esposure to toxic gases and heat exposure arc not necessary. provided that the systcm \\as designed to meet the visibility criterion. Because heat exposure is not an issue. exposure to thernial radiation is also not an issue.

Chapter 3 -Smoke &d ~ e i a b i l i t ~

TENABILITY CRITERIA In the most general sense, the criterion for all tenability systems could be stated as: tenable conditions are to be maintained in spaces where people are expected to be for the expected duration of their time in those spaces. However, such a criterion is too general to be useful for design applications, and more specific criteria are needed. More detailed criteria deal with one or more of the following: exposure to toxic gases, exposure to heat, exposure to thermal radiation, and visibility through smoke. It is the nature of such detailed criteria that it depends on the specific application. The time for exposures can be mandated in codes, and Chapter 4 provides information about people movement that can be used to calculate this time. For the conditions of Example 3.1 1, the exposures to toxic gases, heat, and thermal radiation are insignificant provided that the system was designed to meet the visibility criterion. For such insignificant exposures, detailed tenability criteria have no real purpose. Whenever possible, this approach can sgnificantly simplify design analysis. For applications where exposure to toxic gases is significant, it might seem that the tenability criterion should be based on prevention of both incapacitation and fatality. Because a person who is incapacitated will

remain in the toxic environment until fatality or rescue, it seems that the criterion should at a minimum be based on incapacitation. Exposures to some gases (for example HC1 and HBr) can result in post-exposure fatality, such that a person might not be incapacitated while being exposed but die some time after exposure. Considering both the dominance of CO among toxic fire gases and that CO does not result in post-exposure fatalities, incapacitation could be a sufficient criterion for most applications.

The visibility distance for exit signs depends on the distance between the exits in a specific building. The visibility distence for seeing balcony walls and railings might be taken as two or three times the width of the balcony. In many applications, the criterion for seeing the exit signs wodd be expected to be the more stringent of the two. For additional material about survival of exposure to fire produced environments, see Gann (2001).

CHAPTER 4

Evacuation Analysis his chapter presents information about evacuation analysis for application to smoke management systems. In hazard analyses, evacuation behavior needs to be assessed to estimate the time duration in which an individual is exposed to a particular environment. The evacuation time is composed of at least the following three periods of time: Becoming aware of the tire Preparing for movement Movement to an exit Generally, an evacuation analysis considering only these three steps assumes that the individual's only action is to evacuate. In addition to evacuating. an individual [nay investigate, attempt extinguishment, assist others, call the fire department, etc. An evacuation analysis could account for many of these other actions in the "preparing for movement" step. During building fires, elevators are almost always taken out of service and vertical evacuation is by stairs. In a few situations, elevators are used for e\.acuation. For information about calculating evacuation time by elevators, see Appendix C.

THE MYTH OF PANIC Often, movies, television. and the press present the unrealistic image that panic bchavior in fire situations is common. However, extensi\.t. research supports the conclusion that panic behavior in fire situations is \.cry rare. Even in large building fires resul~ingin multiple deaths, people experiencing fear still usually act in pi~rposeful ways.

Quarantelli (1979a) provides the following statement concerning behavior in fire incidents: Overall my point has been that in both absolute and relative terms, human behavior in disasters in modem, industrial societies is fairly good by any reasonable criteria one could use. There is little evidence beyond anecdotal stories, and none of a systematic, comparative and quantitative nature that suggests that behavior under stress is any more illogical, irrational or dysfunctional than everyday behavior. Part of the problem is that sometimes the behavior under stress is compared not with everyday behavior, but with an idealized conception of behavior. Of course along that line it does not come out well. But this is a match of real disaster behavior with the ideal, when the honest comparison should be between real disaster behavior and actual everyday behavior. If the last kind of match is made, there is not that much difference between the two. While panic is perceived by nontechnical individuals to occur quite frequently in fires, it actually occurs very infrequently. As noted by Quarantelli (1979b) and confirmed by Bryan (2002) and Keating (1982), most commonly people respond adaptively to the fire incident and are often altruistic in their behavior. In Wood's (1971) study of human behavior in fires. he noted that peoplz acted to increase their level of risk in only 5% of all fire incidents. According to a panel convened to address panic, the characteristics of panic behavior include the following: Acute fear Perception ofxrisis Fear of separation (exceeds that of self-preservation) Confusion

Chapter 4-Evacuation Analysis

Table 4.1: Types of Fire Alarm Signals Used in Drills in London Subway Station Type Bell only Staff

Description Alarm bell rung, no staff or PA Alarm bell rung, two staff members gave PA announcement to "evacuate station"and then directed evacuation Each 30 seconds, PA announcement said twice, "please evacuate the station immediately" PA announcement instructing people to leave via trains or exits, with staff directing people following the directions of the announcement Same as stafffPA,except occupants were also told about the type (fire) and location of the incident

Public Address Staff + Public Address Directions + Public Address

Table 4.2: Comparison of Response to Various Fire Alarm Signals

Evacuation Alarm Bell Only Staff investigates, makes PA announcement. directs evacuation Plain "recorded" PA announcement. repeated every 30 seconds PA directive + staff directing evacuation P;\ directive plus status

-

Time (min, S) to Start Time (min, S) to Start to Move From to Move to Bottom of Concourse Escalator Comments 8:15 9:OO Delayed or no evacuation 2:15 3:OO Occupants directed to concourse . 1:15 7:40 Occupants stood at bottom of escalator 1:15 1 :30 Occupants evacuated 130 1:00 Occupants evacuated

Extreme frustration Chaotic/antisocial behavior Entrapment Flight Contagion

The panel indicated that all nine characteristics may not be evident for every individual who does engage in panic type behavior (Quarentelli 1979b). However, they also caution against quickly labeling any particular action as panic behavior that has only a few of these characteristics. B E C O M I N G A W A R E O F T H E FIRE Bryan (2002) discusses several ways that occupants become aware of'a fire. In most cases, the initial cues of a fire are ambiguous, involving a different odor, a slight haze, or strange noises. In some cases occupants may observe the flames. In still others, occupants may be alerted by an alartii system. Evaluating the rime to become aware o f the tire via an audible or visual fire alarm signal actuated by a fire detector or sprinkler waterflow switch may involve an analysis of the response time of automatic detection equipment or sprinklers. Several computzr models discussed in Chapter 8 are capable of calculating sprinkler dctection. In contrast. manual detection is ~iiuchmore

difficult to estimate reliably, being a function of the fire scenario, building characteristics (compartmented versus open-plan), and thc proximity, alertness, and mental abilities of the occupants. PRE-MOVEMENT Interpretation o f t h e alarm signal as an indication of a threatening fire by building occupants is dependent on the type of signal provided by the alann system (Ramachandran 1991; Proulx and Sime 1991; Prouls and Fahy 1997). Bells and horns arc often ignored, being considered to indicatc a drill, test, or false alarm. In a laboratory exercise, Ranlachandran found that only 13% of 96 individuals considered bells to signal an actual alarm. Similarly, Pauls' survcv of occupants of office buildings indicatcd that only 17% of occupants responded to traditional fire alann signals in high-rise office build1r:gs. The response of people to various types of fire alarm signals was observed by Prouls and Sime in drills at mid-afternoon in a London subway station. Cameras recorded the responses of the individuals, with interviews conducted to supplement the video recording. The five types of alarms used in thc study are described in Table 4.1. Alarms were initiated tivc seconds after a train arrived at the station. It can be seen from Table 4.2 that pre-movcment ~ i r n ewas as much as nine minutes

Principles of Smoke Management

for an alarm bell only, but the pre-movement time was much less with verbal. announcements. For guidance on the use of verbal announcements, see Keating and Loftus (1977). Given the predominance of ambiguous cues during the early stages of a fire, building occupants often investigate these cues or ignore the initial cues completely, thereby delaying initiation of evacuation. Pre-movement time may also be dependent on the time of day. Proulx and Fahy measured the pre-movement time to be up to 10 minutes long in a mid-rise apartment fire drill during the day. During an early morning high-rise apartment fire, the pre-movement time was 15 minutes for numerous occupants and up to five hours for others.

EVACUATION TIME ANALYSIS There are three principal approaches for estimating the evacuation time for a building: I . ~&&ical correlation of total evacuation time for building. 2. Model movement applying hydraulic analogy, simulating people as fluid particles. 3. Model movement applying hydraulic analogy, with consideration of the behavioral aspects of the people.

Empirical Correlations The first method consists of correlations that were developed from a regression analysis of evacuation data from 50 fire drills in high-rise office buildings ranging from 8 to 15 stories in height. The two correlations developed by Pauls (1980) (one from a linear regression analysis and the other from a nonlinear regression analysis) are

Evacuation Analysis Using Hydraulic Analogy Evacuation analysis using the hydraulic analbgy assumes that people follow a directed route of travel to their destination, which is typically outside or an area of refuge. As such, the occupants are assumed to travel along a route where the distance to the destination is continuously decreasing, neglecting the possibility of traveling in circles, proceediag in the "wrong" direction, and retracing steps, etc. Consequently, an "efficiency" factor may be applied to evacuation times estimated using this approach to account for the possibility of an evacuation process where the occupants may divert from a directed route. Evacuation modeling following the hydraulic analogy requires information on the people movement characteristics of velocity, flow rate, and specific flow.

-

Veloci~: rate of travel along a corridor, ramp, stak4 Flow rate: number of persons passing a particular segment of the egress system per unit time (for example, persons per unit time passing through a doorway or over an imaginary line drawn across a corridor). Specificflow: flow rate per unit width of the egress component (for example, per unit time per unit width through a doorway).

The movement of people has been examined for travel on stairs (mostly downward travel), in corridors, and through doonvays. Virtually all of the information on people movement has been collected from observations of fire drills or normal movement. Population per Effective WidM (plm)

and

where . T = evacuation time (win); C, = constant, 0.193 (0.08 1 ); Cz

= =

W

=

-

constant, 0.0394 (0.01 2);

population using the stair (p); effective width of stair, ft (m) (see discussion on efective width later in this section). The unit of population above is persons, and the symbol used in this chapter for persons is p. The predictions of Equations (4.1) and (4.2) are very close to each other, as shown in Figure 4.1. Becausc Equation (4.2) is the simpler form, i~ is IUOI-c commonly uscd. P

Equations: - - - (4.1) (4.2)

"0

50

190

150

200

250

Population per Effective Width (plft)

Figure 4.1 Estinlared evncmtion time jor- high-rise buildings (Pauls 1980). 4.

Thc v c l o c i r on stairs rcSers to the rate o f ~ r a v calong l p;trh obtaincd by con~wctingthe tips ofthc stairs.

;I di;lgonal

Chapter 4-Evacuation Analysis

Considering that people tend to move faster in emergencies than they do in fire drills (Figure 4.2), it might seem that evacuation time estimates based on fire drill data would be conservative. However, this does not account for the possibility of exit routes being blocked by smoke or fire. An "efficiency" factor also may be applied to account for blocked exits routes.

Velocity The velocity has been shown to be a function of the density of the occupant flow, type of egress component, and mobility capabilities of the individual (Gwynne et al. 1999; Nelson and MacLennan 2002; Predtechenskii and Milinskii 1978). Nelson and MacLennan propose correlations of velocity for mobile individuals considering the available data collected by numerous researchers. For a density greater than 0.05 1 p/ft2 (0.55 p/m2),

For densities less than 0.05 1 p/ft2 (0.55 p/m2), other occupants do not interfere with the walking speed of an individual. The maximum walking velocity for level walkways and stairways is

v = 0.85k

where v = velocity, @m (mk); a = constant, 2.86 (0.266); k = velocity factor, fpm (mls); and

-D = density of occupant flow, @/m2). Equations (4.3) and (4.4) apply to flow on horizontal surfaces and on stairs. For horizontal surfaces and the stair tread and riser types listed in Table 4.3, the velocity factors are listed in Table 4.4. On stairs, the distance of travel is the diagonal of the stair (Figure 4.3), which is

where

LD Lv

=

diagonal distance of the stairs, ft (m);

=

vertical distance of travel, ft (m);

B = angle of the stairs. The dependence of the velocity on density, as predicted by Equations (4.3) and (4.4): is presented in Figure 4.2. The velocity correlations prejznted in Equations (4.3) and (4.4) principally relate to adult, mobile individuals. Prouls (1995) indicates that the mean velocity for children and the elderly is on the order of 90 fpm (0.45 d s ) . The velocity for an "encumbered" adult is in the range of 45 to 155 fpm (0.22 to 0.79 rnls), which is Table 4.4: Velocity Factor, k

Area Density. 6

Figure 4.2 Cornpar-ison o f nor-nzal velociq and velocity during emergencies (P,-edtechenskii and Milirukii 1978).

Egress Component Corridor, aisle, ramp, doorway Riser and Tread Type 7.5110 711 1 6.5112 6.511 3

Table 4.3: Dimensions of Stair Risers and Treads Riser, LR

Riser and Tread Type 7.5110

in. 7.5

Tread, LT

mm

in.

190

10

mm 254

Stair Angle, 8

Sin, Q

36.9"

0.600

k (fpm) 275

k (mls)

196 212 229 242

1 .OO 1 .08

1.40

1.16 1.23

~ r i n c i ~ l e s 'Smoke of Management

Figure 4.3 Stair geometry. also appreciably less than the maximum velocity noted in Equation (4.4).5 Table 4.5 lists mean velocities for impaired individuals.

Density,., Density is the ratio of the number of people in a group in an egress component divided by the total floor area occupied by the group (including the area between individuals). This can be expressed as

tions because emergencies can happen during unusually crowded conditions. The number of people expected to occupy a particular space is dependent on the use oftthe space. The number of people expected to occupy a space can be estimated for design purposes based on occupant load factors, which are included in the U.S. building codes (ICC 2000; ICBO 1997; BOCA 1999; SBBCI 1999) and the NFPA Life Safety Code (2000). The occupant load factors included in each of the referenced codes are similar and these occupant load factors represent average maximum density of occupants. Occupant load factors from the NFPA Life Safety Code are listed in Table 4.6. Predtechenskii and Milinskii use a definition of density based only on areas. rea density &e ratio of the floor area occupied by each individ~ualperson in the group divided by the tdal floor area occupied by the gouk(including the area between individuals). This can be expressed as

where where P = population, p (p); 7

7

total floor area occupied by the group, ti- (m-). Typical densities of people nlovenlent range from 0.1 to 0.2 p/ft2 (1.0 to 2.0 p/n~2)(Predtechenskii and Milinskii 1978; Frantzich 1996; Pauls 2002; Fruin 1987). The. normal occupant loading may not be considered an appropriate population for evacuation calcula-

A

=

5. An encumbered adult is an individual c a v i n g packages, luggage, o r a child.

S

=

area density (dimensionless);

A,,

=

average area occupied by an individual, ft- (m-).

7

The average area occupied by an individual includes the floor area directly under the individual and the floor space around the individual. The relationship between these two density tenns is

For the areas that people occupy. see Tables 4.7 to 4.9.

Table 4.5: Mean Velocity for Impaired Individuals (Shields et al. 1996) - - .. lnipairment Electric wheelchair Manual wheelchair Crutches Walking stick Walking fialne Rollator No aid No disability

Level Walkway fpni nits

260 200 280 160 100 I10 I S0 2-10

0.89 0.69 0.94 0.8 1 0.5 1 0.6 1 0.93 1.24

7

Stairs down f ~ m nils

Stairs up fpni nils

43 63

0.22 0.32

43 67

0.22 0.3

65 140

0.33 0.70

SI I40

0.4 l 0.70

Chapter 4-Evacuation Analysis

Table 4.6: Occupant Load ~actors' Occupant Load ~ a c t o ? Space Use Assembly Less concentrated use without fixed seating Concentrated use without fixed seating Waiting space Library-stack areas Library-reading areas Mercantile Street floor and sales basement Multiple street floors Other floors Storage, shipping Educational Classroom area Shops Daycare centers Business (offices), industrial Hotel and apartment Health care Sleeping departments In-patient treatment departments Detention and correctional

perslf?

pers/m2

15 net 7 net 3 net l00 gross 50 net

1.4 net 0.65 net 0.28 net 9.3 gross 4.6 net

30 gross 40 gross 60 gross 300 gross

2.8 gross 3.7 gross 5.6 gross 27.9 gross

20 net 50 net 35 net l00 gross 200 gross

1.9 net 4.6 net 3.3 net 9.3 gross 18.6 gross

120 gross 240 gross 120 gross

I l . l gross 22.3 gross 11.1 gross

l. Data from Table A-S-3.1.l of NFPA l01(2000). 2. The populalion of a space is the product o f [he load factor and the net area or gross area oftha! space as indicated above.

Table 4.7: Area Occupied b y people1 .

10 to 15 2

Walking

Standing

Female Male All All ,411'

I . Data are from Kendik (IYSj). 2. Wih coats

ft 1.36 1.3 1 1.33

Age

15 to30 m= 0.126 0.122 0.124

Crcater than 30

ft' 1.63 1.78 1.72 1.57

m2 0.151 0.165 0.160 0.146

2.00

0.186

ft2

.,l

2.08 1.87

0.192 0.174

Principles of Smoke Management

Table 4.8: Area Occupied by People in IP units1 Horizontal projection2

Shoulder Breadth

Body Depth

Adult Youth Child

1,I-1.4

1.5-1.6

0.92-1.1

Encumbered ~ d u l t ~

2.5-8.9

1.6-3.6

1.3-2.6

Person Type

I . Data are from Predtechenskti and Milinskii (1978). 2. The horizontal projection is dctcrmined by representing the body shape by an ellipse. 3. An encumbered adult is an individual c a v i n g a child, l u a a g e . or packages.

Table 4.9: Area Occupied by People in SI units1 Horizontal projection2

Person Type Adult Youth Child

Shoulder Breadth

Body Depth

m2

m

m

0.10-0.13

0.46-0.50

0.28-0.32

Encumbered ~ d u l t ~ Data are from Predtcclienskii and klilinskii (1978). The horizontal projection is dctenninsd by representing the body shape by an ellipse 3. An encumbsrsd adult is an individual canyin: a child, luggage. or packages. I.

2.

Densily ( p h i ) 1

3 0 0 ° ,

I

2 I

I

3 I

,

,

Density (plrn')

:d

Stair Riser and Tread Type:

0

1.50

- 1.00

3

4

16

- 25

='5 0 -

- 0.50 3 - 0.25 -0

0.4

Velocir!.ns a/imction o f densip.

Specific Flow

Stair Riserand Tread Type:

= $

12

C

- 20 15

0.8

U

0 c

3 10 a

m

F a Z

a

0

W

0.4

5 0 0

Density ( p l f f )

Figure 4.4

2

30

- 0.75 .$

50 -

1

0.1

0.2

0.3

0.4

0

Density ( P I U )

Figure 4.5

Spec~$cflowas afilnction o f d e n s i ~ .

F,. = DV = ( 1 -aD)kD

(4.10)

The specific tlo\v, F,, is analogous to the mass flux in hyd;dillic systems. As such. the specific flow is defined as the product of the velocity and density of the flow,

\\.here F, = specific flow, plmin-ft (pls-m).

Expr-essions Ibr thc specific flow as a function of density call o n l y be obtained by for [he velocity 1.1-0111Equations (4.3) and (4.4). FOI-a dcnsity yeatcr than 0.05 i p/li2 (0.55 p!m2),

The specific flow predicted by Equations (4.10) and (4.1 1) is presented in Figure 4.5. The width referenced in the units for the specific flow equations relates to the ..effective width" as defined by Pauls (2002). The con-

For densities less than 0.05 1 p/ft2 (0.55 p/m2),

Chapter 4- Evacuation ~ n a l ~ s ~ i s

Flow

cept of effective width is based on the observation that people do not generally occupy the entire width of an egress component, staying a small distance away from the walls or edge of the component. Nelson and MacLennan refer to this small distance as a "boundary layer," in keeping with the hydraulic analogy for people movement. The width of the boundary layer for the variety of egress components is presented in Table 4.10. The boundary layer and effective width are illustrated in Figure 4.6.

Nelson and MacLennan (2002) present a method to obtain a first order approximation of the egress time in buildings. The method involves determining the maximum flow rate for each of the egress components in the egress system. For a density greater than 0.051 p/ff2 (0.55 p/m2), the flow rate for a particular egress component is given as

Maximum Specific Flow

where

Considering that Equation (4.10) is a quadratic function, a maximum specific flow is achieved at a density of

Because a is indenendent of the type of egress component, according to this correlation. the specific flow is maximized at the same density for all types of egress components. Predtechenskii and Milinskii provide data that indicate differences in the density where the specific flow is inaxinlized for different types of egress components.

F,

=

flow rate p/min, @/S);

w

=

effective width, ft (m).

For a density less than 0.051 p/ft2 (0.55 p/m2), the flow rate for a particular egress component is given as

The maximum flow rate occurs when the specific flow is maximized (i.e., where D,,,, occurs (see Equa-

L I l

4

Effective

-;

width

I

/ Boundary

Layer

Generally, evacuation of a building requires that building occupants traverse several egress components. For example, for an individual located in a room on an upper floor, evacuation involves travel along aisles or through an open space in the room, through the room doorway into a corridor, along a corridor to the stair doon\.ay, down the stairs, and through the exterior door to the outside. / Boundary

Table 4.10: Boundary Layer Width

Component Theater chairs, stadium benches Railings, handrails' Obstacles Stainvays, doors, archvays Corridor and ramp walls I.

Boundary Lager in. mn! 0 0 S9 3.5 -1 100 6 l50 S 200

\Vllcrc Ilandr;~itsarc present. Nelson and I I x L c ~ l n msug:cst that the boundxy laycr a-id111i'or Iwndr:~ilsshould he used i i d i c Iwundary laycr \r id111lirr 11;lndrailsis Ics; [ h ~ n 1 1 1 Ibr ~ 111c egress C(III~(IOIISIIIwlicrc I ~ I C Iiandrail i s prcrtxl.

Layer

Water 'cooler

Effective

Width?

Principles of Smoke Management

Table 4.11: Maximum Specific Flow Maximum Specific Flow,

Fs,m, Egress Component Corridor, aisle, ramp, doorway Riser and Tread Type 7.5110 711 1 6.5112

Figure 4.7

Comti-ained flow ir7 evacuotion of a fivestory building.

tion (4.12)). Maximum specific flow, F,,,,,,w, for a variety of egress components is provided in Table 4.1 1. Tlie controlling egress coniponent is tlie component with tlie smallest maximum flow rate, relating to where a queue is expected to form if D,,,, occurs ill an upstream component.

EVACUATION TIME

Constrained Flow Approach The constrained flow approach is based on the assumption that there is a point along the egress system where a queue forms. Tlie evacuation flow envisioned when applying this type ofevacuation model is depicted in Figure 4.7 where the egress system is funneled into a particular point, such as an exterior doorway, before the evacuees depart from the building or affected area. Assuming that all occupants start their evacuation simultaneously at time zero, the niodeled evacuation time using the constrained flow approach can be estimated as

where nodel led evacuation time for an egress route.

I,,,

=

f,

=

time for first person to arrive at constraint,

I,

=

I,

=

time for population to pass through constraint. time for first person to travel fi-om constraint and proceed to outside (or area of'reli~ge).

plmin-ft 24.0

pls-m 1.32

17.1 18.5 20.0

0.94 1.01 1.09

For a particular egress system composed of several components, the maximum flow rate, F,, of each comThe flow time ponent can be determined as FS,,w. associated with each component is P/FS,,,,w, where P is the population passing through the component. The is component with the greatest value of P/Fs,,,,,w defined as the controlling element where the constraint is expected. In many situations, the point of constraint can be identified easily. For example, consider a stainvell discharging directly to the outside that has doors of only 0r.e width (see Figure 4.7). For staiiwell and door widths designed to comply with the Life Safety Code or model building codes in the US., the minirnuni flow will be associated with the doorways. Tlie entire population using this stainvell would have to pass through this exterior door. Because the interior stainvell doors on the upper floors would only serve a fraction of this population, they would be less congested. The exception is the stair that is used for evacuation of only one floor, and this stair would have constraints at both stairwell doors, provided that both doors are of the same width. In such a case, the evacuation analysis could be conducted witli the constraint at either location. When the exterior stairwell daor is the constraint in tlie egress system, the modeled evacuation time becomes

Example 4.1 illustrates tlie constrained flow approach. This example is appropriate for situations where a queue is expected to form at the exterior stairwell door. Generally this happens when an appreciable number of people occupy tlie area of the building being niodeled. Conversely, in buildings with low occupant loads, a queue is unlikely. In cases with low occupant loads, a more complex analysis is needed to examine the occupant flow on a component-by-co~iiponent basis. These analyses also may be applied to provide a more accurate assessment in cases whcre queuing is likely.

Chapter 4- Evacuation Analysis

Example 4.1 Evacuation Time Determine the evacuation time for a five-story building with the following characteristics (see Figure 4.8): There are 200 people on each floor. Each floor is served by two 44 in. (1.12 m) wide stairways. The doors leading into and from the stairway are 32 in. wide (0.81 m). The stair riser and tread type was 7/11. The floor-to-floor distance is 12 ft (3.7 m) and the landing behveen floors is 4 X 8 ft (1.22

X

2.44 m). Handrails are provided on both sides of the stairways.

Solution: Component

Effective Width

Door into stairway

ft (m) 1.67 (0.51)

Stairway Landing Door from stainvay

Specific Flow plft-rnin (plm-S)

Flow Rate ptmin @/S)

3.08 (0.94)

24.0 (1.32) 18.5 (1.01)

40 (0.67) 57 (0.95)

2.67 (0.82) 1.67 (0.5 1)

24.0 (1.32) 24.0 (1.32)

65 (1.08) 40 (0.67)

Time for population to move out of exterior stair door: The controlling component is selected as the door leading from the stairway The time required for the half of the buildmg occupants on the upper floors (400 persons) to pass through this doorway is estimated to be 400140 = 10 minutes. Time to travel down one flight of stairs: The time required for the first person traveling at a velocity associated with the maximum density is given by the time ro travel do\vn one flight of stairs and two landings. The vertlcal distance of the stairs is 12 ft (3.7 m). From Table 4.3, sin 0 is 0.537 for 711 1 stairs. From Equation (4 S), the diagonal distance along the stairs is LD = Lr,/sin0 = 12/0.537 = 22.3 ft (6.8 m). The density on the stairs is taken at D,,,,. From Equation (4.12), D,,

2

= 0.175 p!ft

(1.88 plm2).

From Table 4.4, k is 21 2 fpm ( l .08 rnls). From Equation (4.3), v = X-- akD = 212 - 2.86(212)(0.175) = 106 fpm (0.539 1~1s) . The length of travel along each of two landings is 8 ft (2.4 m) (assuming an average length oftravel on the middle of the landing). Because thc velocity on a stairway is less than that for a horizontal component, such as a landing, the velocity on the landing is limited to that achieved on the stainvay. As such, the length of travel on the landing can be added to that for the stairway, giving a total length of travel of 38.3 ft (11.7 m). The time required to traverse this distance at the velocity achieved on the stairways is 38.31106 = 0.36 min (22 s). This is roundsd up to 0.4 min (24 s). Total evacuation time: The total evacuation rime is 10 + 0.4 = 10.4 min (624 S).

Principles of Smoke Management

-

(a) Elevation View

Figure 4.9 Merging egress,flows.

I '

I

'(b) Plan Mew

Figure 423 Diagram o f building for- Esati7ple 4.1.

Component-by-Component Analysis The component-by-component analysis involves a determination of the time for the population to traverse each egress component. In this case, the density of the flow along each egress component must be determined so that the velocity and floiv rate can be determined. The starting point of such an analysis is to assume an initial density of the population. If such a calculation is to be done using algebraic equations (instead of one of the computer nlodels described in the last section of this chapter), a reasonable assumption is to consider all building occupants on a particular floor to be uniformly distributed in the corridors. As the population starts to move, the density of the people may change as a result of t'lree types of transitions: mergers o f flows at corridor intersections or where people entering a stair merge with people traveling in the stairs from other floors, changes in the widtl; of the egress component, changes in specific flan,, resulting in a transition from one type of egress component to another, e.g., a corridor to a stair. The new density after a transition may be determined by applying one of the following principles. The combined flow rat< of people entering an intersection equals the flo!!, rate of people from the intel-section (see Figure 4.9).

If the conibined flow rate of egress components leading to the intersection is greater than the capacity of the f l o n rate for the egress component leading from the intersection, a queue is expected to form. If a queue forms, the analysis can continue, considering that the flow rate in component #3 is equal to the maximunl capacity of the component. Questions are often asked concerning the composition of the queue relative to the incoming flows (i.e., does any one group have a "right-of-way" while most or all of the other group stops). The total evacuation time of the building is not dependent on which group has the right-of-way. Alternatively, if the intent of the analysis is to determine the time required to clear a particular floor level and the merger is nith people from another floor level, then the right-of-nay decision will impact the results. Unfortunately, there is no technical support for establishing any rules co~lcerningthe right-of-way or proportion of the tlorvs from the entering streams that Gccurs at a merger. Ho\ve\,er. given the observation from human behavior studies that people tend to react altruistically, it is reasonable to expect that people traveling from other floor levels nould yield to people leaving the fire floor. Where the \vidth o f the egress component changes, as indicated in Figure 4. IOa and 4.10b, the density of the flow also changes. The flow rate of people entering the egress component equals that leaving it:

For converging flow. as illustrated in Figure 4.IOb, a queue might be espected to form at the transition. When there is a queue, the flow downstream from the transition is equal 1.0 the ~llasi~nurn capacity of the component. When a queue forms \\.it11converging flow of Figure 4. lob, the density ofa tlow ofoccupants proceeding away fiom a transition isdetermined by solvingeither Equation

-

Chapter 4-Evacuation Analysis

(4.13) or (4.14). Where Equation (4.13) applies, solution of the quadratic equation results in two possible solutions for the density. The lesser value for density should be selected as the correct value. The lower density is correct for reasons indicated in the following example. If an occupant flow at the maximum density was approaching a widening comdor (Figure 4.10a), the solution of Equation (4.13) would yield one density greater than the maximum and one less. However, in the case of a widening corridor, it's unreasonable to expect the density to increase (and velocity to decrease) when proceeding from the narrow to the wide corridor. In either of these types of analyses where multiple egress paths are available to a group of occupants, some

(a) Diverging Flow

(b) Converging Flow Figure 4.10 T,-ansiliorzin egress componcrit.

assumption needs to be made of the distribution of occupants among the available paths. Often; an equal proportion of the group is assumed in each of the available paths. Alternatively, the distribution may be determined in propxtion to the respective capacities or other characteristics of the available paths (Predtechenskii and Milinskii 1978; Murosaki et ai. 1986). The following model can be applied if the order of evacuation is arbitrarily determined to proceed from highest floor to lowest floor. At time zero, all people move to the stairs on all floors and travel to the next floor level. If the stairwell capacity is exceeded as a result of the merger, then the maximum flow proceeds in the stairwell with the right-of-way given to the occupants on upper levels. (The total evacuation time is independent of whether people from upper floors have or surrender the right-of-way.) Consequently, the merged flow in the stairwell is composed predominantly of people from the upper level, supplemented by additional people from the next floor to provide the maximum permitted flow rate for the stairwell. Occupants on all other floor levels stop their movement into the stair as a result of the stairwell having achieved maximum capacity Once the last occupant from the upper floor reaches the Icvel below the upper floor, the flow from this next floor is increased to its maximum value. The component-bycomponent approach is illustrated in Example 4.2.

Principles of Smoke Management

Example 4.2 Evacuation Time Determine the evacuation time for the same five-story building as in Example 4.1 (see Figure 4.8):

Solution: Assume that all occupants initiate movement simultaneouslyand half of the building occupants are located in the corridor at a distance of at least 100 R (15.2 m) fiom the stair door. Other occupants are in the spaces adjacent to the corridor and are assumed to join the people in the corridor promptly upon notificaiion. Assume an equal number of occupants use the two stairs. (1.35 p/m2). The density of the people in the corridor is 0.125 Given this density, the specific flow of the people in the corridor is 22 p/ft-min (1.20 p/m-S) < F,. The velocity in the corridor is 177 @m(0.90 &S). The flow rate in the corridor is 58.7 p/min (0.98 p/s). Time to reach stainvay is 100/177= 0.56 rnin (339 S). The maximum specific flow of the door leading into the stainvay is 40 p/min (see example 4.1) (0.67 PIS). As such, a queue forms at the doorwa~,given that the flou. in the corridor toward the door is 58.7 p/min (0.98 p/s). The queue builds at a rate of 18.7 p/min (0.3 1 p/s). (1.07 p/m2). Given flow of 40 p/min (0.67 p/s) in stairway, density is 0.099 lea\-ingthe fifth floor approaching the fourth floor is 152 @m (0.77 m/s). The vel&ity in the stair for Time to cave1 38.4 ft (11.7 m) to reach fourth floor is 0.25 min ( l 5 S).

-

-,

At this point, flows from the fourth and fifth floors merge at the landing of the fourth floor, as well as every other floor level. The total time required for the last person from the fifth floor ro enter the stair at that floor level is 2.79 rnin (167 S). The time required for the last person from the fifth floor to reach the 4th floor is 3.04 rnin (182 S). With a flow proceeding down the stain From the fifth floor of 40 p/min (0.67 p/s) and 40 p/min (0.67 p/s) entering the stairway ffom the 4th floor, the outflow from the point of merger would be 80 p'niin (1.33 p/s) if no queue occurs. However, since the flow capacity in the stainvay is 57 p/min (0.95 p/s), the flo\v in the stain\-ay \\-ill be limited to 57 p/min (0.95 p/s). Priority of flow in the stairway is given to occupants from the top floor Ie\.el. Thus, prior to the queue fonning in the stainvay (i.e., 031 rnin [19 S]),32 people exited from the second, third, and fourth floors. Because the flow capacity in the stain\a!. is limited to 40 plmin (0.67 p/s), the flow ffom all lower floors is stopped. Once the last person from the fifthtloor reaches the founh floor. the flow of the GS remaining people from the fourth floor recommences. The time required for the last person from the fourth floor to enter the stair at that floor level is 4.74 rnin (284 S). The time required for the last person from the fourth floor to reach the third floor is 4.99 rnin (299 S).

I

I

Similarly: The time required for the last person frotn the third floor to enter the stair at thzt floor lcvel is 6.69 min (40! S). The time required for the last person from the third floor to reach the second floor is 6.94 rnin (4 16 S). The time required for the last person from the second floor to enter the stair at that floor level is 8.64 rnin (5 18 S). The time required for the last person from the second floor to reach the first floor is 8.89 rnin (533 S).

COMPUTER-BASED EVACUATION MODELS The lbllowing three types of e\ acuation models are available: Sh~lation Optimization Risk assessment Si~nulatio~, modcls predict 1n0\sment and bella\.ior of occupants by assessing the t l o ~disrribution among

paths (where choices are available). The flow distribution between multiple paths may be determined by occupant behavior considerations. Optimization models minimize the evacuation time by considering an optimal distribution of occupants among multiple flow paths. The current optimization models neglect behavioral considerations. The risk assessment models quantify the risk posed to building occupants by conducting a fire Ilazard analysis, combined with an elementary evacuation analysis. The risk assessment models need to be

Chapter 4- Evacuation Analysis

applied numerous times to address the probability of various scenarios and their outcomes. The characteristics of existing evacuation models are described in a review by Gwynne and Galea (1999). A summary of the chakcteristics of the evacuation models is indicated in Figure 4.11. Building spaces may be represented as coarse or fine networks. A coarse network usually uses a single node to represent each space. Additional nodes are used only for large rooms or rooms that have connections to several other rooms. In the coarse network approach, rooms (or nodes) are connected by arcs. Coarse networks assume unifonn conditions on each node and a constant traversal time along arcs. Alternatively, fine networks divide each room into several small sections. In some cases, a small grid is created over the entire building space where the size of a particular area may be as small as the area occupied by an individual. Theevacuation models assess movement of the building occupants by two perspectives. A global perspective tracks the occupants anonyn~ously. In this approach, the iiiodel does not distinguish which individual leaves the room or building at a particular time. The global perspective models assume uniform characteristics for the entire building population. In contrast, models with the individual perspective track each person, identifying where any particular person is during the evacuation period. The models with the individual perspective consider individual traits (e.g., mental and physical capabilities, tolerance to smoke, and group interactions). Behavioral characteristics included in the models may be done by several methods (e.g., deterministic equations [functional analogy], pre-established behavioral patterns, and iflthen rules, \vhich may or may not be subject to change by the user). One principal area of concern with the evacuation models relates to the reliability of input parameters. People movement characteristics need to be provided. Where a constant velocity is required, the results of the analysis will be dependent on whether the mean or maximum velocity is included. Some of the niodels require personal characteristics of building occupants (e.g., as

Figure 4.11 Evacuation models (adapted Gwynne and Galea 1999).

from

"patience" and motivation factors) be entered. Justification of such input is subject to much debate. Most of the models assume that occupants only become engaged in evacuation behavior. Neglecting the variety of nonevacuation behavior that occurs will result in a smaller evacuation time, perhaps substantially, than if such behavior is considered. None of the models currently considers the possibility of two-way flow in a corridor, either as the result of emergency personnel or some building occupants moving opposite to the evacuating occupants. As a prerequisite to any evacuation analysis, the number of people in the building must be established. The location of the occupants also needs to be specified, though at varying levels of detail, depending on the model. Location of individual occupants can be "placed" at a specific point for applications involving fine network niodels. For the coarse network models, people only need to be located in a room or floor of a building. When using a first-order approach with hand calculations, the calculations become very tedious when placing people in individual rooms. As such, for firstorder estimates, people may be placed in a queue at the esit door from the floor or large section of the floor to simplify the calculations. The loss of accuracy with this assun~ptionrelates to the time for people to travel from their respective starting points to fonn a queue at the door. In many buildings, this time is relatively short.

CHAPTER 5

Effective Areas and Smoke Movement n building fires, smoke often migrates to locations remat; from the fire space. Stairwells and elevator shafts can become smoke-logged, thereby blocking evacuation and inhibiting fire fighting. In this chapter, several of the driving forces of smoke movement are discussed, methods of determining the neutral plane Ere provided, and some general comments are made conceming smoke movement. The information in this chapter is also applicable to the migration of other airborne matter, such as hazardous gases, bacteriolog~calmatter, or radloactlve matter in laboratories, hospitals, or indugtrial facilities. However, the discussion in this chapter is pr~marilyaimed at smoke movement. The concept of_ ettectlve flow areas is quite usehl for analysis of smoke movement and of smoke control systems, and this topic 1s addressed next.

I

-

m

m

The total flow, vT,from the space is the sum of the flows through the leakage paths:

The effective area, A,, for this situation is that which results in the total flow,

vT.Therefore, the total

flow can be expressed as

EFFECTIVE FLOW AREAS The paths in a system can be in parallel with one another, in series, or in a combination of parallel and series paths. The effective area of a system of flow areas is the area' that results in t h e s a m d o w as the system when it is shbjected to the same pressure difference over the total sistem of flow paths. This is analogous to the flow of electric current through a system of electrical resistances. The following analysis is for the same flow coefficients for each flow path and for constant air temperature. Variations in flow coefficients and temperature are addressed later. 7

Parallel Paths Three parallel leakage areas from a pressurized space are illustrated in Figure 5.1. The pressure difference, Ap, is the same across each of the leaka,oe areas.

Figure 5.1

Flowpafhs in parallel.

Chapter 5-Effective Areas and Smoke Movement

where

vT =

volumetric flow rate through the path, c h (m3/s);

m

=

mass flow rate through the path, Ibis (kgk);

C

=

dimensionless flow coefficient;

A, = effective flow area (or leakage area),

ft2 (m2);

Ap = pressure difference across path, in. H 2 0 (Pa); p

=

density gas in path, lb/@ (kg/m3);

K,

=

776. (1.00).

The flow

PI through area A , can be expressed as Figure 5.2 Flow paths is series.

The flows V* and v3 can be expressed in a similar manner. Substituting the expressions for PI, V * , and V3 into Equation (5.1) and collecting like terms yields

The effective area for flow paths in series is the flow area that results in the flow V for a total pressure difference of Apr. Therefore, the flow V can be expressed as

Compari~~g this with Equation (5.2) yields

Solving Equation (5.8) for ApT yields

The above logic can be extended to any number of flow paths, and it can be stated that the effective area of 17 individual leakage paths in parallel is the sum of the individual flow areas.

The pressure difference across A , can be expressed as

In Figure S. l. if A I is 1.08 R* (0.10 ni') and A? and A3 are both 0.54 ft' (0.05 m*),what is the effective flow area ofthe system?

I Fro111Equation (SS),

A , = 2.16 R' (0.20 m').

The pressure differences Ap2 and Ap3 can also be expressed in a similar manner. Substituting Equation into Equa(5.9) and the expressions for ApI, Apz,and tion (5.7) yields anexpression for the effective flow area.

Series Paths Three leakage paths in series from a pressurized space are illustrated in Figure 5.2. The flow rate. l', is the same through each of the leakage areas. The total pressure difference, Ap7, from the pressurized space to the outside is the sum of the pressure differences Ap ,. Ap?, and Apj across each of the respective flow areas. .-l ,,A?, and Aj:

(5.11) AJ.

This same reasoning can be extended to any number of leakage areas in series to yield

Principles pf Smoke Management

where n is the number of leakage areas,

Ai,in series.

In

smoke control analysis, there are tiequently only two paths

These two effective flow areas are in series with A , . Therefore, the effective area of the system is given by

in series, and the effective flow area for this case is

1

Example 5.2 Two Equal Series Paths Calculate the effective leakage area of two paths of 0.22 (0.02 m2) in series.

following flow areas: AI =A2 = A3 = 0.22 = A ~ = A ~ = o 9(0.01 .II m2).

ftL

From the equations above, A23, = 0.44 ft2 (0.04 m2), A4& = 0.33 9 (0.03 m2), and A, = 0.17 9 ( 0 316 m2).

For two equal flow areas (A = AI = A?), Equation (5.13) becomes A, = 0.707, A = 0.707 (0.22) = 0.156 9(0.0145 m').

11

I

Example 5.3 Two Unequal Series Paths Calculate the effective flow area of two paths in series, where the flow areas are AI = 0.100 ft2 (0.00929 m') and A2 = l .OO f;(0.0929 m2). ..-

From Equation (5.13), A,

= 0.0995

(0.00924 m2).

This example illustrates that, when two areas are in series and one is much larger than the other, the effective area is approsimately equal to the smaller area. P -

9 (0.02 m2) and A4

Effects of Temperatures and Flow Coefficients

II

I/ I

For most calculations involved in smoke control, the a&umptions o f constant temperature and unifomi flow coefficient are appropriate, but it may be desired in some cases to consider the effects of these parameters. For parallel and series flow paths, the equations for effective flow area are

P

Example 5.4 Effective Flow Area of Four Series P:tths Calculate the effective flow area of the folln\\ Ing areas that are

for parallel patlis and

From Equation (5.13), A, = 0.0704 liZ(0.00651 m2).

for series patlis where

Combination of Paths in Parallel and Series

l

The method of developing an effective area for a system of both parallel and series paths is to combine, systematkally, groups of parallel paths and series paths. The system illustrated in Figure 5.3 i s analyzed as an .. example: ' This figure shows that A2 and A3 arc parallel; therefore, their effective area is

Areas A+ As, and A6 are also in parallel, so their effective area is

Figure 5.3 Cornbina/ion qf/low p / h s in parallel a d series.

Chapter 5-Effective Areas and Smoke Movement

A, = effective flow area o f system, fl? (m2);

T,

=

absolute temperature in effective flow path, "R Q;

C,

=

flow coefficient for effective path, dimensionless;

=

absolute temperature in path i, "R (K);

=

flow area of path i, fl? (m2);

Ai

W: Arrrrws indicate direc(rmof air movement

Ci = flow coefficient of path i, dimensionless. For the case of two areas in series with the same flow coefficients, the effective area is

-

. ,. ,.;

,..'

. ,.:,;.<

.

. 7 ,.

.<

,.

,,

Normal S@& Effed

,?,; ,#, :,,;c y,f..?.,9.,>;$...'.;,9 Reverse Stack Effect

Figure 5.4 Air movement due to no/-nlaland reverse slack effect.

1. What'is the effective area of nvo paths in series, both of 0.22

ft? (0.02 m ' ) area with one at 70°F (21°C) and the other at

100°F (3S°C)? Use

I

c of 70°F (21°C).

From Equation (5.19),A, = 0.153 9 (0.0 142 m'). With both temperatures the same, the effective area of this system is 0.156 ft2 (0.0145 m"). as calculated in Example 5.2. Considering the degree of uncertainty associated wit11 flow areas; adjustment of the effectiie flow area is unnecessary. 2. What is the effectix area above if the elevated temperature is 1000°F (538"C)?

I

From Equation (5.19). A , = 0.1 I1 @ (0.0105 m').

DRIVING FORCES OF SMOKE MOVEMENT The driving forces of smoke movement include naturally occurring stack effect, buoyancy of combustion gases, expansion of combustion gases, the wind effect, fan-powered ventilation systems, and elevator piston effect. This section discusses these driving fcrces and, in particular, addresses smoke movement due to the stack effect process, either naturally occurring or that of combustion gases. Generally, each driving force is discussed here as acting alone in order to facilitate discussion and lead to an understanding of smokc transport.

Stack Effect Frequently, when it is cold outside, there is an upward movement of air within building shafts, such as stainvells, elevator shafts, du~nbwaitersshafts, rnechanical shafts, and mail chutes. Air in the building has a buoyant force because it is warmer and therefore less dense than outside air. The buoyant force causes air to rise within building shafts. This phenomenon is callzd by various names, such as stack effect, stack action. and chimney effect. These names come from the colnparlson with the upward flow of gases in a smoke stack or chimney. However. a downward flow of air can occur in airconditioned buildings when it is hot outside. For this manual, the upward flow will be called normal stack effect and the downward flow will be called re\srse stack effect as illustrated in Figure 5.4. Most building shafts have relatively large crosssectional areas and, for most flows typical of those induced by stack effect, the friction losses are negligible in comparison with pressure differences due to buoyancy. Accordingly, this analysis is for negligible shaft friction. but shafi friction is specifically addressed later. Pressure within a shaft is due to fluid static forces and can be espressed as

where = air pressure inside the shall, g

=

z

=

acceleration of gravity, elevation.

=

gas density inside the shafi.

For the ele\.ations relltvant to buildings, the accslsration of gravity can bc considered constant. For constant density. Equation (5.70)can hc integrated to yield

..

Principles of Smoke Management

Appendix A. Substituting Equation (5.24) into Equation (5.23) and rearranging results in the following equation. where p, is the pressure at z = 0. To simplifL the analysis, the vertical coordinate system was selected such that p, = p, at z = 0. In the absence of wind effects, the outside pressure,po, is

where p, is the density outside the shaft Pressures inside the shaft and outside the building are graphically illustrated in Figure 5.5 for normal stack effect. This figure also shows the pressure of the building spaces, and methods of calculating this are presented later in this section. The pressure difference: 4,:from the inside to the outside is expressed as

where To

=

absolute temperature of outside air,

T,

=

absolute temperature of air inside the shaft.

Because i~ariationsin pressure within a building are very small compared to atmospheric pressure, atmospheric pressure, p,,,,,, can be used in calculating gas density from the ideal gas law.

Equation (5.25) was developed for a shaft connected to the outside. The neutral plane is a horizontal plane located at z = 0, where the pressure inside equals that outside as stated above. If the location of the neutral plane is known, this equation can be used to determine the pressure difference from the inside to the outside regardless of variations in building leakage or the presence of other shafts. Methods of determining the location of the neutral plane are discussed later. Tables 5.1 and 5.2 are comparisons of pressure differences due to various driving forces. For standard atmospheric pressure of air, Equation (5.25) becomes

where

where =

pressure difference from shaft to outside, in. H 2 0

To

=

(Pal; absolute temperature of outside air, "R (K);

T,

=

absolute temperature of air inside shaft, "R (K);

h

=

distance above neutral plane, ft (m);

K,

=

7.64 (3460).

Aps0

p

=

air density.

p,,,,,

=

absolute atmospheric pressure,

R

=

gas constant of air,

T

=

absolute temperature of air.

Values for the gas constant and of standard atmospheric pressure for several systems of units are given in

Building Pressure.p,

Pressure

Figure 5.5

Pirsswcs nt~dpresszoadiJZwlices dut-ing normal stack efecf

Chapter 5-Effective Areas and Smoke Movement

Table 5.1: Comparison of Pressure Differences Due to Various Driving Forces (IP Units)

Driving Force Stack effect,

Location of'Ap Shaft to outside

CoriciiCions For all stack effect examples, T,= 70 "F and To= 0 "F:

7

(in. H20)

Equation (5.26)

Buoyancy of combustion Fire room to adjacent gases, room at ceiling Equation (5.3 l) Wind effect, Equation (5.34)

Across building (windward to leeward wall)

h=30ft h=30Oft . For Tf= 1600 "F and To= 70 "F:

0.07 0.7

h = 5 ft

0.05

h = 10 ft

0.1 1

For all wind examples, p = 0.75 lblf?, C,,z = 4 . 3 :

c,,

= 0.8,

and

U H = 15 mph

0.12

UH= 30 mph

0.48

Ventilation systems

Across barrier of Note: Values based on experience. smoke control system . Elevator piston effect, Elevator lobby to For all the examples of the upper limit of pressure differbuilding ence due to elevator car motion, p = 0.75 lb/ft3, A,, = 1.60 Equations (5.41) to (5.43) ft', A, = 0.42 ft', A,; = 0.54 ft':

0.05 to 0.35

For a single-car shaft with C, = 0.83, A, = 60.4 ft', and A, =

19.4 ft2:

U = 700 fprn For a double-car shaft with C,

= 0.91,

U = 700 fpm

A, = 120.8 ft2, and

0.05

Principles of Smoke Management

Table 5.2: Comparison of Pressure Differences Due to Various Driving Forces (S1 Units)

&(Pal

Driving Force

Location of Ap

Conditions

Stack effect,

Shaft to outside

For all stack effect examples, T,= 21 "C and T, = -18 "C:

Equation (5.26)

Buoyancy of combustion gases,

For Tf=870 OC and To = 21 OC:

Fire room to adjacent room at ceiling

h = 1.5m

Equation (5.3 1) Wind effect, Equation (5.34)

Ventilation systems Elevator piston effect, Equations (5.41) to (5.43)

h=3m the (windward to leeward wall)

Across barrier of smoke control system Elevator lobby to building

For all wind examples, p = 1.20 kg/m3, Clp2= - 0.3:

'

c,,

= 0.8

and

U H =14 m/s

130

Note: Values based on experience.

12 to90

For all the examples of the upper limit of pressure difference due to elevator car motion, p = 1.20 kg/m3, A, = 0.149 m2,

For a single-car shaft with Cc = 0.83, A,

= 5.61

m2, and A,

=

= 11.22

m2, and A,

=

2

1.80 m :

U = 2.03 m/s U = 3.56 m/s

For a double-car shaft with Cc= 0.94, A, 2

7.41 m :

Chapter 5-Effective Areas and Smoke ~ o v e m & t

Example 5.7 - Stack Effect in a Tall Building

The neutral plane is located at mid-height of a 600 ft (185 m) tall building with inside and outside-temperatures of 70°F (21°C) and 0°F (-18°C). What is the pressure difference at the top of the building?

Because of the neutral plane location, h = 300 ft (91.4 m). Using Equation (5.26), the pressure difference due.10 stack effect is 0.66 in. H20 (164 Pa) from the top of the shaft to the outside. Note: Figure 5.6 can also be used for this calculation. In using this figure, the term Apso l h is positive for normal stack effect and it is negative for reverse stack effect. Outside Temperature. To?F)

For the building illustrated in Figure 5.5, all of the vertical airflow is in the shaft. Of course, the floors of -real buildings have some leakage and there is some airflow through these floors. The discussion of stack effect to this point has been general and it applies to buildings with o r without leakage through floors. To analyze the pressure differences on building floors, an idealized building model is used that has no leakage between floors. For nonnal buildings, airflow through floors is much smaller than that through shafts. The following analysis develops some useful equations based on this zeroji'oor- leakage idealizatiot~. For the system of flow paths illustrated in Figure 5.5, the effective flow area per floor is

where A, = effective leakage area between the shaft and the outside, fi2 (ni2); A,; = per floor leakage area between the shaft and the building, ft2(m2); A;,

=

per floor leakage area between the building and the outside, ft' (m').

The mass flow rate, ril , for a floor can be expressed ' / ' , C is a by the orifice equation as C A , ( ~ ~ A , L I ~ , ) where dimensionless flow coeficient that is generally in the range of 0.6 to 0.7. For paths in series, the pressure difference across one path equals the pressure difference across the system times the square of the ratio of the effective area of the system to the flow area of the path in question. Thus, the pressure difference from the shaft to the building space is A / J , =~ ~A p , , , ( A , / . - l , i ) - . By sub-

-ro

-30

- 20

-10

o

10

10

so

4)

50

Outside Temperature. To('C)

Figure 5.6 Graph of pressure difference due to stack effect. stituting Equation (5.27) into this relation and rearranging, the effective area is eliminated.

In general, the ratio A,;/A,, varies from about 1.7 to 7. The pressure differences from a shaft to the building space are much less than those from the shaft to the outside, as can be seen from the examples listed in Tables 5.1 and 5.2. In the event that many windows on the fire floor break due to the fire, the value of A,, becomes very larse on the fire floor. When this happens, the ratio A;;/ Aio becomes very small, and Q,; approaches Thus, when a large number of windows break on the fire floor, the pressure from the shaft to the building is almost the same as that from the shaft to the outside. The development of Equation (5.28) considered the pressure difference uniform with height at each floor, which introduces an error-the maximum value of which can be calculated by Equation (5.26) for a value of /7 equal to the distance between floors. In the examples of Tables 5.1 and 5.2, if the floors were l0 ft (3. I m) apart, the maximum error of Equation (5.28) is about 0.01 in. H 2 0 (2.5 Pa). In general, this error is not significant. Equation (5.2s) can be rcwritkn for the pressure, p,. at the building space.

Principles of Smoke Management,

The series flow approach to determining building pressures described above can be used for buildings with multiple shafts if all the shafts are at the same pressures and if all the shafts have the same starting and ending elevations. Pressure measurements on several buildings (Tamura and Wilson 1966, 1967a, 1967b) verify the stack effect theory presented above for conditions encountered in the field. Further, these studies show that the zero floor leakage idealization is generally appropriate for determining pressure differences on building floors due to stack effect. Additionally, Igmura and Klote (1988) have conducted full-scale stack e;Fect experiments at the Canadian ten-story Fire Research Tower near Ottawa, which verified the stack effect theory for a'iange of temperatures and of leakage conditions they considered r-presentative of most buildings. Figure 5.7 shows comparisons of measured and calculated pressure differences due to stack effect for outside temperatures of 12°F (-I 1"C), 27°F (-3°C). and 45°F (7°C). Figure 5.8 shows comparisons of measured and calculated pressure differences for ratios A,, /A,, of 1.7. 2.4, and 7. Further, this stack effect theory provides a useful approximation for buildings in which all of the shafts do not have the same starting and ending ele\ations.

In unusually tight buildings with exterior stairwells, reverse stack effect has been observed even with low outside air temperatures (Klote 1980). In this situation, the exterior stairwell temperature was considerably lower than the building temperature. The stairwell was the cold column of air and the other shafts within the building were the warm columns of air. Smoke movement from a building fire can be dominated by stack effect. During normal stack effect (Figure 5.4), smoke from a fire below the neutral plane moves with the building airflow into shafts and up the shafts. This upward smoke flow is enhanced by anv buovancy forces on the smoke due to its temperature. Once - above the neutral plane, the smoke flows out of the shafbinto theupper floors of the building, as illustrated in Figure 5.9b. As discussed in Chapter 1, this kind of smoke flow can have fatal conseauences. as in the fires at the MGM Grand and other buildings. Leakage between floors ..-results in smoke flow to the floor above the fire floo~.If lkakage between floors is negligible, the floors below -the neutral plane+xcept for the fire floor-will be &sentially smoke-free. For significant leakase b e t w e e ~ flls, s x e floor will be much greater than to other floors below the kutral plane, as is shown in Figure 5.9h For a fire above the neutral ,lane. the buildinn airtlo\vs due to normal stack effect tend to restrict the extent of smoke flow. Airflow from the shafts to the fire floor can prevent smoke infLLtdQnafihasahafts ( ~ i g ure 5.9c), but leakage between floors can result in some smoke movement. If the buoyancy forces of the hot

-

U

>

Pressure Difference (in H,o) -.l2

-.cd

0

.cd

.08

.l2 28

24

20

16

g s

.-m 12

Note: Solid lines are calculated valuas.

8

4

-30

-20

-10

-

U

0

10

Pressure Difference (Pa)

20

0 30

q

2 '

Chapter 5 --Effective Areas and Smoke Movement

Pressure Dierence (in Y O )

Inside Temperature 72 OF(22 DC) Outside Temperature

27 O F (-3%) 7

Neutml Plane

,

-15

-10

I -5

Note: Solid lines are calculated values.

0

I

I

1

5

10

1s

Pressure Difference(Pa)

Figure 5.8 Presszwe differences across outside wall of the Canadiarl Reseal-c11 Tower for different bltildjtig leakages ladapiedflmn Tamura and Klote [l 9881).

Figure 5.9 Air- atid smoke movement it? a high-rise brrildiug h e to slack e#ec/: (U) oit:j'Io~i.due /a s/ack effect. (0) jir-Ebelow the ne~rtralpla~ie, (c)fire above /he neutt-a1plane. a d (d).fir-e above 111e~ieirlt-c11 plam 11i1h smoke entering a sliafl due to b u o p q ~ .

Principles of Smoke Management

Figure 5.10 Pressure during afully involved compartment fire.

smoke overcome the stack effect forces at the shafts on b e fire floor, smoke can infiltrate the shafts and flow to upper floors (Figure 5.9d). The air currents of reverse stack effect (Figure 5.4) . tend to affect the movement of relatively cool smoke in the reverse of normal stack effect. In the case of hot smoke, buoyancy forces can be so great that smoke can flow upward even during reverse stack effect. Further information about smoke flow due to stack effect and other driving forces is presented by Klote (1989).

Buoyancy of Combustion Gases High-temperature smoke from a fire has a buoy-ancy force due to its reduced density. The pressures occurring during a fully involved compartment fire are illustrated in Figure 5.10, and these pressures can be analyzed in the same manner as pressures due to stack effect. In the same manner as Equation (5.26) was developed for stack effect, the foIlowing equation for the pressure difference Apfi from the fire compartment to its surroundings can be developed:

perature. For standard atmospheric pressure, the above relation becomes

where =

pressure difference from fire compartment to surroundings, in. H 2 0 (Pa);

To

=

absolute temperature of outside air, OR (K);

Tf

=

h IS

=

absolute temperature of gas inside fire compartment, OR (K); distance above neutral plane, ft (m); 7.64(3460).

=

Fang (1980) has studied pressure differences caused by the stack effect of a room fire during a series of full-scale fire tests. During these tests, the maximum pressure difference reached was 0.064 in. H 7 0 (163a) across the bum room wall at the ceiling. Observation of Tables ..5.1. and 5.2 can pro_~~.@e insight on conditions for which buoyancy, as opposed to s%ck effect,iFTikeTy. to be the dciffiiitlriving force. \ ~ ~ f j j o k ~f,ao-G~s;-th~e~ - w i bbU.oyan.c wi lr-di,-iriinxe -

-

-.

where To = absolute temperature of gases surrounding the fire compartment; Tj = absolute temperature gas \vithin the fire compartment; h = distance above the neutral plane. The neutral plane is a horizontal plane where the pressure inside the fire compartment equals that outside. Equation (5.30) is for a constant fire-compartment tem-

f@rlarge values of As; /Aio at almost any location from at locations the neutral olane. For low values of-A~/d;, a. fa_rfrom the neutral plane,>&ck effect can dominats even when windows are unbroken. When windows are broken, stack~effectis even more likely to dominate. Stack effect p can.only be the dominant driving-forcedur-ing times of significant inside-toloutside temperaxe di tlerence. ------Much larger pressure differences are possible for tall fire compartments where the distance, h, from the neutral plane can be larger, as illustrated by the follow-. ing example. S"

,

Chapter 5- Effective Areas and Smoke Movement

II

I

l

Example 5.8 Buoyancy Pressure in a

Fire ~o&ar&ent For a firecompartment temperature of 1470°F (800°C), what is the buoyant; pressure difference at 6 It (1.83-m) above the neutral plane?

11

-

l

11 Using Equation (5.3 l), the buoyancy pressure difference is 0.06 1)

1 in. H20(15 Pa). Figure 5. I I can also be used forthis .-.-p

1

1)

11

Example 5.9 Buoyancy Pressure Difference for Very Tall Fire Compartment if the fire compartment temperature is 1290°F (700°C),what is the pressure difference at 3 5 R (10.7 m) above the neutral plane?.

I Fire CunpmenlTfmw&m

I(

IOC

2w

300

U10

SM

WO

(TJ 700

800

900

Fire C-Temperahrre(T)

Figure 5.11 Graph of pressures dueio buoyancy.

l

)I

Using Equation (5.3 1) or Figure 5.11, bbis 0.35 in. H 2 0 (88 Pa). This represents an extremely large fire that is probably unrealistic for most applications, but it was included to illusrrarr the exr-nt to which Equation (5.31) can be applied. .

I

I(

Expansion of Combustion Gases In addition to buoyancy, the energy released by a fire can cause smoke movement due to expansion. In a fire compartment with only one opening to the building, air will flow into the fire compartment and hot smoke will flow out of the compartment. Neglecting the added mass of the fuel, which is small compared to the airflow, and considering the thermal properties of smoke to be the same as those ofair, the ratio of the volumetric flows can be simply expressed as a ratio of absolute ternperatures.

v,,,,, v;,, -

Wind Effect Wind can have a pronounced effect on smoke movenient. The pressure, p,,, that wind exerts on a wall of a building can be expressed as

where

TO,/,

p,,. = wind pressure, in. H20(Pa);

Tit,

C,,. = dimcnsionless pressure coefficient;

where

ire,,,

pressure difference across these openings due to expansion is negligible because of the large flow areas involved. However, for a fire space without open doors or windows, the pressure differences due to expansion may be important, provided there is suficient oxygen to support combustion for a significant time. Gas expansion in such a closed space subject to the exhaust o f zoned smoke control, is addressed in Chapter 12.

p,

= volumetric flow rate of smoke out of the fire

=

U / , = wind velocity at the upwind wall of height H, rnph

compartment, cftn (rn3/s);

,

= volumetric flow rate ofair into the fire compart-

ment, chm (m3/s); To,, = absolute temperature of smoke leaving the fire conipartnient, "R (K); T,, = absolute temperature of air entering the fire compartment, "R (K). For a smoke temperature of I 1 10°F (600°C), the gas will expand to about three tinies irs original volume. For a tire conlpartnlcnt with open doors or windows, the

outside air density, lb/$ (kgh3);

K,,.

=

(mfs); 0.0 129 (1 .OO).

I t is thc nature of wind to be variable with peak values &at can be two or three times that of the average. The peak values arc important for structural loads, but --___theX5aTaverage wind-velocity is more appropriate for . - . . -. the calculation OS smoke transport and evaluation-- of smOEnlanagenlent s y ~ e r n In ~ . this discussion of wind . .-effects, the tern1 \*cloci~yi s ~ u s e dto indicate the nreo,~ --

-W--

-

-

Principles of Smoke Management

The pressure coefficient depends on building geometry and local wind obstructions. For a low-rise building without local wind obstructions, a typical distribution of the pressure coefficient is shown in Figure 5.12. Because the wind is blowing directly at one of the walls, the distribution of the pressure coefficients is symmetrical, and the pressure coefficients only need to be shown for half of the building. It can be seen that the pressure coefficients are positive for the windward wall and negative for the other walls. For a tall building without local wind obstructions, typical distribution of the pressure coefficient is shown in Figure 5.13. As with Figure 5.12, distribution of these Pressure coefficients is also symmetrical. Values of oressure coefficient C.... averaged over the wall area. are li$ed in Table 5.3for rectangular buildings, which are free of local obstructions. An approximation of the overall pressure difference from one side of a building to another due to wind effect can be obtained from

__

L

.v

-

U

L

Figure 5.12 Typical distribution ofpressure coefficient over a low-rise building free of local obstructions. W2d

where

C,",

-

L' -0.6

=

average pressure coefficient for windward wall;

Clu2 = average pressure coefficient for leeward wall. Above the surface of the earth, the wind velocity increases until it reaches the gradient winds. This layer of increasing wind speed is referred to as the wind boundary layer. In the absence of local obstructions to the wind, the relationship between velocity and height in the boundary layer is often approximated by the power law equation,

I

where U

=

wind velocity, @m ( d s ) ;

U.

=

velocity at reference elevation, @m ( d s ) ;

z

=

elevation of velocity, U, ft (m);

zo =

reference elevation, ft (m);

/ \\\\\\\ Side

Front

Some general values of the wind exponent, a , are

Figure 5.13 q ~ i c adistribution l ofpressure coefficient over a tall buildingj.ee of local obstt-uclions.,

edge of a large city center could be considered terrain category 1 (Figure 5.14) for winds from the direction of

the city center and category 2 (Figure 5.14) for winds Trom the opposftedirection. I nere has been a la%of consistency among authors regarding recommended val-

a = wind exponent, dimensionless.

-

Chapter 5 -Effective Areas and Smoke Movement

Table 5.3: Average Pressure Coefficients for Walls of Rectangular Buildings Free of Local Obstructions (adapted from MacDonald [1975]) Building Height Building Plan Ratio Ratio Elevation

Wind Angle Plan

a

c,,,for Surface A

B

C

Note: h = height to eaves or parapet P = length (greater horizontal dimension of a building); (lesser horizontal dimension of a building).

W

D

= width

Principles of Smoke Management,

-

Terrain Category 1: Large City Center 50% of Buildings Higher Than 70 ft (21 m); Over at Least 6600 ft (2000 m) Upwind

n

Terrain Category 2:. . Urban, Suburban, Wooded Areas & Other Areas With Closely Spaced Obstructions Compared tc or Laps: Than Single Family Homes; Over at Least 6600 fi (2000 m) Upwind

~

~

~p

~

~~

Terrain Category 3: Open Terrain with Scattered Obstacles Generally Less Than 33 ft (10 m) High

Terrain Category 4: Flat, Unobstructed Areas Exposed to Wind Flowing Over a Large Body of Water; No More Than 1600 fi (500 m) Inland

m

-7

-

rc

-7

Wind Velocity Profile

a = 0.10 6 = 7OOft (210m)

Note: a is the the wind exponent, and 6 is the wind boundary layer thickness. Figure 5.14 bl4ricl frlwiri cofegor-ies.

Chapter 5-Effective Areas and Smoke Movement

ues of wind exponent, and the values of Figure 5.14 were chosen to be consistent with those o f the 1997 ASHRAE Handbook-Fundamentals, Chapter 6, "Airfl;w Around Buildings." Using Equation (5.35) with z = H (where H is t h e upwind height of the wall of a building), the average velocity of the gradient wind can be expressed as

For building and wind measurement sites that are near each other, the velocities of the gradient winds are equal. Equating Equations (5.36) and (5.37) and rearranging results in Smet 'H

=

'met met

H

(:)

a

(5.38)

Substituting this into Equation (5.33) yields where

UgeH= velocity of the gradient wind above the building, fpm (&S); = wind velocity 2t the top of the wall, fpm (&S); UH = upwind height of the wall, fi (m); H 6 = boundary layer height in the vicinity of the building, ft (m); a = wind exponent in the vicinity of the building, dimensionless. General values o f boundary layer height, 6, are listed inFigure 5.14 for the terrain categories. and these were also chosen to be consistent with those of ASHRAE Fundamentals. The weather service measures wind data at airports and other locatio~is,typically at 33 ft (10 m) above the ground. The average velocity of the gradient wind can also be expressed as

where

Ug,,,,,, = velocity of the gradient wind above the wind anemometer, fpm ( d s ) ; U,, = measured wind velocity, fprn ( d s ) ; H,,,,, = height of wind measurement, ft (m); 6,,,,, = boundary layer height in the vicinity of the wind anemometer, ft (m); = wind exponent in the vicinity of the wind anea;,1et mometer, dinlensionless.

where

It can be seen that Equation (5.39) has the advantage in that it can be used to calculate wind pressures based on measured design wind data. The above discussion is for buildings without large local obstructions. For buildings with such obstructions, specialized wind tunnel tests are needed to determine the pressure coefficients due to the wind. Such tests are routinely conducted for structural analysis of large buildings. For both structural and smoke management purposes, the wind flow around buildings is fully developed turbulent flow, and the flow coefficients are independent of the Reynolds number. Thus, the flow coefticients obtained from wind tunnel tests for structural analysis are applicable for smoke management analysis. While the tern~inologyof a wind tunnel test report may ditkr from that o f this section, the results are applicable to smoke management analysis. For tnforniation about wind and smoke management, readers are referred to Kandola (1986a, 1986b) and Klote (1995). For additional information about wind pressures on buildings see Aynsley (19S9), Shaw and Tamura (1977). and Kandola ( 1 9 8 6 ~ ) .Several civil engineering tests provide useful information about wind engineering-for example, Dyrbye and Hansen (1997); Liu (1 99 I): MacDonald (1 975); and Simiu and Scanlan ( I 996).

Example 5.10 Wind Pressure in a Suburban Area A building is located in the center of a large suburban area. and the design velocity from measurements at a nearby airport is 22 mph (&S). Tlie i~eightof the windward wall is 120 fr. the wind coetticient is 0.8, and tlie outside air density is 0.075 lb/m3 (1.2 kg;lm3). Calculate the wind pressure.

From Figure 5.14, the city center is terrain category 2 with a = 0 . 2 and 6 = 1200 FI (370 IN),a ~ l dthe airport is temain catcgory 3 with ,,,,= 0.14 and 6,, = 900 fi (270 ni). The height of the wind anemometer is H,,,,,= 33 ti (l0 m).

a,

Note: Da~nliom R u i n d t w ~ n e ltest would be more accurate than rhcse calculations. and such wind tunnel daL1 should bc used wlm available.

Principles of Smoke Management

III

Example 5.11 Wind Pressure in an Urban Area For the conditions of Example 5.10, what is the wind pressure if the building were located in a large city? From Figure 5.14, the urban area is terrain category 1 with o = 0.33 and 6 = 1500 ft (460 m). time, 2amct 2a g00 2(0.14) 120 2(0.33) From Equation (5.40), C = = 0.476. h - Hme 6 33 l500 From Equation (5.39),pWis 0.09 in. H 2 0 (22 Pa). Note: As with Example 5.10, data from a wind tunnel test would be more accurate than these calculations, and such wind tunnel data should be used when available.

(-,

11

(9 (-1

(-1

11

II

Forced Ventilation Systems Heating, ventilating, and air-conditioning (HVAC) systems frequently transport smoke during building fires. When a fire starts in an unoccupied portion of a building, the HVAC system can transport smoke to a space where people can smell the smoke and be alerted to the fire. 'Upon detection of fire or smoke, the HVAC system shbuld be designed so that either the fans are shut down'or the system goes into a special smoke control mode of operation. The advantages and disadvantages of these approaches are complex, and no simple consensus has been reached regarding a preferred method for various building types. However, if normal HVAC operation continues, the HVAC system will transport smoke to every area the system serves. As the fire progresses, smoke in these spaces will endanger life, damage property, and inhibit fire fighting. Although shutting down the HVAC system prevents it from supplying oxygen to the fire, system shutdown does not prevent smoke movement through the supply and return ducts, air shafts, and other building openings due to stack effect, buoyancy, or wind. Installation of smoke dampers can help inhibit this smoke movement. A third alternative fire mode for HVAC systems consists of continued HVAC operation, while dumping return air to the outside in an attempt to minimize smoke transport throughout in the building by the HVAC system. While this third approach has not been experimentally or theoretically verified, it seems that it may have the potential to minimize smoke transport through the HVAC system. Computer 'simulation of smoke movement through HVAC systems is discussed by Klote (1987).

Elevator Piston Effect When an elevator car moves in a shaft, transient pressures are -produced. A downward-moving elevator car forces air out of the section of shaft below the car and into the section of shaft above the car, as illustrated in Figure 5.15. Klote and Taniura (1986) developed the following analytical equation for the pressure difference, 41,,,due to elevator piston effect from the outside to the elevator shaft above the car:

Machinery Room

Lobby

+-

Building Space

4--

+-

'

" //

/v h'

/'/

/< h' I L '

//

L

Note: Arrows indicate the direction of flow. /,y// ,b

Figure 5.15 Airflow due to the downward moveinenf of an elevator cal:

where P

=

air density within the shaft, lb/ft3 (kg/m3);

A,

=

cross-sectional area of shaft, ft2 (m2);

U

=

velocity of elevator car, Fpm (mls);

N,

=

number of floors above the car, dimensionless;

Nb

=

number of floors below the car, dimensionless;

C

=

flow coefficient for building leakage paths, dimensionless;

A,

=

effective flow area per floor batween the shaft and the outside,

c,

=

(m2);

flow coefficient for flow around the car, dimensionless;

Chapter 5-Effective Areas and Smoke Movement

A, = free flow area in shaft around car, or cross-sectional area of shaft less cross-sectional area of the car, I? (m2);

bp,- = pressure difference h m the building to the lobby, in. H20 (Pa);

dp,, = pressure difference from the outside to the shaft, in. H20 @a);

Kpe= 1.66x10~(1.00). The coefficient C, was cvzluated at 6.94 for a twocar shaft with only one car moving and at 0.83 for a twocar shaft with both cars traveling side-by-side together. The value for the two cars moving together is believed to be appropriate for obtaining approximations of pressures produced by the motion of a car in a single car shaft. For the sake of simplicity in the analysis leading to Equation (5.41), buoyancy, nind, stack effect, and effects of the heating and ventilating system were omitted. Omitting stack effect is equivalent to stipulating that the building air temperature and the outside air temperature are equal. For the system of three series flow paths from the shaft to the outside illustrated in Figure 5.15, the effective flow area, A,, per floor is

where A, = effective flow area, ft2(m2): A,, = leakage area behveen the lobby and the shaft, li?

A,

=

effective flow area between shaft and the outside,

ti? (m2); Air

=

leakage area between the building and the lobby,

rt' (m2). This series flow path analysis does not include the effects of other shafts, such as stairwells and dumbwaiters. Provided that the leakage of these other shafts is relatively small compared to AOi, Equation (5.42) is appropriate for evaluation of A, for buildings with open floor plans. Further, Equation (5.43) is appropriate for closed floor plans, provided all the flow paths are in series and there is negligible vertical flow in the building outside the elevator shaft. The complicated flow path systems probably require case-by-case evaluation, which can be done by using the effective area techniques presented later in this manual. To test the above theory, experiments were conducted in a hotel in Toronto, Ontario, Canada. Figure 5.16 shows measured pressure differences across the top floor elevator lobby while a car was descending. Also shown is the calculated pressure difference, which is in good ageement with the measurements. This experiment is described in detail by Klote and Tarnura (1986).

A;,. = leakage area between the building and the lobby,

A,, = leakage area between the outside and the building,

ft' (m'). A detailed discussion of effective flow areas is provided later in this text. in a similar manner to the development for stack effect, the pressure difference from the lobby to building interior can be expressed as Time (S)

where

Figure 5.16 Pressure difference across elevator- lobby of a Toronto hotel due to piston effect.

Principles of Smoke Management

Example 5.12 Pressures Due to Moving Elevator Car What pressure differences are produced by a downward-moving elevator car with a velocity of 600 fpm (3.05 mls) in a singleshaft? The shaft is 20 stories high and the car is on the 18th floor (No= 2 and Nb = 17). The areas are

f? (m2) A, area between lobby and shaft 1.60 (0.149) Ai,, area between building and lobby 0.42 (0.039) 0.54 (0.050) AOi,area between outside and building 60.4 (5.61) As, cross-sectional area of shaft 19.4 (1.80) A,, free flow area around car Use C = 0.65, C, = 0.83, and p = 0.075 1b/ft3@/m3). From Equation (5.42), the effective area is 0.325 f?(0.302 m'). From Equation (5.26), the pressure difference kom the outside to the shaft, Apso,is 0.30 in. H20 (75 Pa). From Equation (5.43), the pressure difference kom the building to the lobby is 0.18 in. H20 (45 Pa). The pressure difference, Mri, cannot exceed the upper limit of

where (Wri),

'

=

=

upper limit of the pressure difference from the building to the lobby, in. HzO (Pa); air density within the shaft, 1b/ft3(kg/m3);

2 = cross-sectional area of shaft, ft' (m ); =

effective flow area per floor between the shaft

=

and the outside, ft2 (m2): velocity of elevator car, fpm (rnls);

=

free flow area in shaft around car, or cross-sectional area of shaft less cross-sectional area of

Air

=

the car, ft2 (m2); leakage area between the building and the

=

lobby, ft2 (m2); flow coefficient for flow around the car, dimensionless;

K,,

= 1.66

X

I O -(1.00). ~

This relation is for unvented tlevator shafts o r shafts for which the vents are closed. The pressure difference, (M,;),,,is strongly dependent upon U, As, and A,. For example, Figure 5.17 shows the calculated relationship k t w e e n (W,;),, and U due to one car moving in a single-car shaft, a double-car shaft, and a quadruplecar shaft. As expected, (Wri), is much greater for the single-car shaft. It follows that the potential for smoke problems due to piston effect in single-car shafts is h h i g r e X e X i ~ i ~ E ~ a r S L f t J . C b X p a r i s O nf < stack effect induced pressure differences indicates that they -- can be larger than those of other driving forces(Tables 5.1 and 5.2). a

Operation of- .elevators , --. . -- --by the fire ssrvice during a fire can result in smoke being pulled into the elevator shaft by piston effect. It seems a safe rzconmendation -that fire fighters should favor the-"se o f elevators in mult~ple-carshafts over ones in singe-car shafts. Klote -(1988) developed another analysis of piston effect. including the influence of elevator smoke control, and experiments conducted by Klote and Tamura (1987) were in good agreement with this theop.

-

Chapter 5-Effective Areas and Smoke Movement

Example 5.13 Upper Limit of Pressure Due to Elevator Motion 1. What is the uppcr limit of the pressure difference produced by the moving elevator car in a singlecar shaft fiom Example 5.6? The

values used in #is calculation a&

U, car velocity C, flow coefficient for flow around elevator car

600 fpm (3.05 d s ) 0.83 lb/@ (1.20 kg/m3) 0.075 p, air density in shaft 0.325 ft2(0.0302 m2) A,, effective area between shaft and outside Ai, area between building and lobby 0.42 ft2 (0.039 m2) A,, cross-sectional area of shaft 60.4 ft2 (5.6 1 m2) A,, free flow area around car 19.4 ft2 (1.80 m2) From Equation (5.44), the upper limit of pressure difference fi-orn the building to the lobby is 0.19 in. H20(47 Pa). 2. What would be the upper limits of pressure difference if the car were in a double-car shall ora quadruple-carshaft? For multiple-car shafts, C, = 0.94 is used. The areas for these shafts are: For double-car shaft A,, cross-sectional area of shaft A,, free flow area around car

120.8 ft2 (1 1.22 m') 79.8 ft2 (7.41 m')

For cyadru~le-carshaft A,, cross-sectional area of shaft A,, free flow area around car

241.5 ft2 (22.44 m ' ) 200.5 ft2 (1 8.63 m') From Equation (5.44), tlie upper limits of pressure difference from the building to the lobby are:

For the double-car shaft: 0.035 in. H20(9.0 Pa). For the quadruple-car shaft: 0.022 in. H20 (5.5 Pa).

IPressure differences, (Ap,.;),,,for other car velocities are sho\vn on Figure 5.17. o.2or

Car Velocity (rnls) 2 3

; , ,

1

l,

1

,

4

l

5, 50 40

Single Car Shaft

these neutral plane locations, the flowv rates and pressures can be evaluated.

-

g

Quadruple Car Shaft Double Car Shaft

Q

ioo

n

200

400

600

800

1000

Car Velocity (fpm)

Figure 5.17 Calczclated q m r limit ofpi-esszcre d(lj^eretice,Ji.onithe elevator lobby to the buildi~lg due to pis1017effect.

Shaft with a Continuous Opening The flow and pressures of normal stack effect for a single shaft connected to the outside by a continuous opening of constant width from the top to the bottom of the shaft is illustrated in Figure 5.18. The following analysis of this flow, and the resulting location of the neutral plane, \\.as developed by McGuire and Taniura (1975). The pressure difference from the shaft to the outside is expressed by Equation 15.25). The mass flow\. rate, dm;,,, through tlie differential section, tlh. of the shaft below the neutral plane is

LOCATION OF NEUTRAL PLANE In this section, methods of determining the location

where

o f the neutral plane arc described for a single shaft connected to the outside only. The methods of effective area can be uscd to extend this analysis to buildings. Using

A' = area ot'thc opening pcr unit hcight

Principles of Smoke Management

Example 5.14 Location of Neutral Plane with Uniform Leaka~e Calculate the location of the neutral plane for a 100 tt (30.5 m) tall building of uniform floor-to-floor leakage. The inside temperature is 72°F (22"C), and the outside temperature is 0°F (-18°C).

II

From Equation (5.48), the neutral plane is located at a height of 48.8 ft (14.9 m) above the bottom of the building. This is slightly different from the generally accepted approximation of

Figure 5.18 Nonnal stack effect betweett a single shaft

comected to the olrtside opening.

a continzro~rs

To obtain the mass tlow rate into the shaft, this equation can be integrated from the neutral plane ( h = 0) to the bottom of the shaft (It = - H,,). Pressure ~iiference.Ap,, Figure 5.19 Nortnal stack G e c t for a single shafr with

In a similar manner. an expression for the mass flow sate from the shaft can be developed, where H is the total height of the shaft.

hvo openings.

Shaft With Two Vents

For steady flow, the mass flow rate into the shaft equals that leaving it. Equating Equations (5.46) and (5.47), canceling like terms, rcarrangins. and substituting, Equation (5.24) yields I H,, -H l+(T~/T0)""

(5.45)

Normal stack effect for a shaft with two openings is illustrated in Figure 5.19. The pressure difference from the shaft to the outside is expressed by Equations (5.25) and (5.26). To simplify analysis, the distance? H , between the openings is considered much greater than the hzight of either opening. Thus, the variation of pressure \\h11 height for the openings can be neglected, and the mass flow rate into the shaft can be expressed as

where

H,,

=

distance from the bolt0111of the shaft to the neutral

and the mass flow rate out of

is

plane, ft (m);

H = height ol'shal't. fi (m); Ty

r,

=

absolute temperature of air in shaft. "R ( K ) ;

=

absoluw temperature ofoutside air. "R ( K ) .

c,~,,I-)

~ j l ~= , , ~

(5.50)

where A , and A* are the areas above and below the neutral plane. Equating these two flo\vs as was done above yields

Chapter 5-Effective Areas and Smoke Movement

small in comparison to the shaft height, H. Thus, a constant pressure difference can be used to describe the flow through the vent. The mass flow out of the shaft is the sum of the flow out of the continuous opening, expressed as Equation (5.47), plus the flow out of the vent of area A, located a t an elevation of H, above the shaft bottom. .

where

H,

=

distance from the bottom of the shaft to the neutral plane, ft (m);

H

=

heightofshaft, ft(m);

T,

=

absolute temperature of air in shaft, "R (K);

T,

=

absolute temperature of outside air, "R (K);

A,

=

area above neutral plane, ft2 (m2);

Ab - = area below neutral plane,

The conservation of mass equation for the shaft can be written as

ft2(m2).

The location of the neutral plane is highly dependent on the ratio Ab/A,. For Ab /A, that approaches zero, H, approaches H. This means that if the area at the b d tom is very small compared to the area at the top, then the neutral plane is at or near the top area. Equation (5.5 l ) is a strong function of the flow areas and a weak function of temperature.

1

Example 5.15 Location of Neutral Plane with Two Equal Openings What is the location of the neutral plane in a l00 ft (30.5 m) tall shaft with hvo equal leakase areas (Ah = A,) at the shaft top and bottom? The inside temperature is 72°F (22°C). and the outside temperature is 0°F (-l 8°C).

As would be expected, this equation reduces to Equation (5.48) for A,. = 0. Equation (5.54) can be rearranged as

From Equation (5.5 l), the neutral plane is located 46.4 fi (14.1 m) above the bolton1area. This is only a little less than Example 5.14 with the continuous opening (48.8 ft [14.9 m]).

1

Example 5.16 Location of Neutral Plane with Two Unequal Openings What is the location of the neutral plane in a 100 ft (30.5 nil tall shafi with a 4 ft2 (0.37 m') opening at the top and a I ft2 (0.093 m') opening at the bononl? The inside temperature is 72'F (22"C),and the outside temperature is 0°F (-I 8°C).

1

Canceling like terms and incorporating Equation (5.53) results in

l

From Equation (5.5 1). the neutral plane is located 93.3 fi (28.4 m) above the bottoni area. This illustrates the extent to which nonunifoml leakaze areas can cause the ncutral plane to be h r f r m the building's mid-height.

Vented Shaft The flow and pressures of normal stack ellkcl lor a shaft connected to the outside by a vent and a continuo u s opening are shown in Figure 5.20. The tbllowing analysis is tor a vcnt above the neutral plane, but a similar one can be madc I'or a vent below the neutral plane. This analysis is an extension of one by McGuire and Talnura (1 975) for a top \-ented shali. The mass flow into the shaft is expressed by Equation (5.46). For simplicity of analysis, the height of the vent is considered

Neutral Plane

-

Principles of Smoke Management

much greater than the area of the continuous opening (A'H). As with Equatibn (5.51), the above equation is a strong function of the flow areas and a weak function of temperature.

For relatively large vents, the ratio A1H/AV approaches zero. As A1H/AVapproaches zero, the first and third terms in the above equation approach zero, and the equation is reduced to H, = H , Thus, the neutral plane is at or near the vent elevation, for a vent area very

Regardless of whether the vent is above or below the neutral plane, the neutral plane will be located between the height described by Equation (5.4) for an unvented shaft and the vent elevation, H , Further, the larger the value of A, /ArH, the closer the neutral plane will be to H ,

CHAPTER 6

Principles of Smoke Management he term "sn~okemanagement," as used in this manual, includes all methods that can be used singly or in combination to modify smoke movement for the benefit of occupants or firefighters or for the reduction of property damage. The use of barriers, smoke vents, and smoke shafts are traditional methods of smoke management. The effectiveness of barriers is limited to the extent to which they are free of leakage paths. The effectiveness of atrium smoke vents and smoke shafts is limited to the extent that smoke must be sufficiently buoyant to overcome any other driving forces that could be present. Fans are used with the intent of providing smoke protection by means of pressurization. The mechanisms of compartmentation, dilution, pressurization, airflow, and buoyancy are used by themselves or in combination to manage. smoke conditions in fire situations. These mechanisms are discussed in the sections below.

SMOKE MANAGEMENT

Compartmentation Barriers with sufficient fire endurance to remain effective throughout a fire exposure have a long history of providing protection against fire spread. In such fire compartmentation, the walls, partitions, floors, doors, and other barriers provide some level of smoke protection to spaces remote from tlie fire. Tliis section discusses the use of passive compartmentation, while tlie use of compartmentation in co~ijunctionwith pressurization is discussed later. Many codes, such as the NFPA 10 1 L{/b S a j i ! ~Code (NFPA 2000c), provide specific

criteria for the construction of smoke barriers, including doors and smoke dampers in these barriers. The extent to which smoke leaks through such barriers depends on the size and shape of the leakage paths in the barriers and the pressure difference across the paths. Hazard analysis (chapter 9) can be used to evaluate the performance of con~partmentation.

Dilution Remote From a Fire Dilution of smoke is sometimes referred to as smoke purging, smoke removal, smoke exhaust, or smoke extraction. Dilution can be used to maintain acceptable gas and particulate concentrations in a room subject to smoke infiltration through leakage paths from an adjacent space. Tliis can be effective if the rate of smoke leakage is small compared to either tlie total volume of the safeguarded space or the rate of purging air supplied to and removed from the space. Also, dilution can be beneficial to the fire service for removing smoke after a fire has been estinguished. Sometimes, when doors are opened, smoke will flow into areas irltended to be protected. Ideally, such occurrences of open doors will only happen for short periods of time during evacuation. Smoke that has entered spaces remote from the fire can be purged by supplying outside air to dilute the smoke. The following is a simple analysis of smoke dilution for spaces in which there is no tire. At time zero (I = 0), a compartment is contaniinated with some concentration of smoke and no additional smoke flows into the compartment or is generated within it. Also, the contaminant is considered uni fol-mly distributed throughout tlie

Chapter 6 -Principles of Smoke Management

space. The concentration of contaminant in the space can be expressed as

This equation can be solved for the dilution rate and the time.

Example 6.2 Smoke Dilution in a Space Remote from the Elre A space is isolated from a fire by smoke barriers and selfclos-

ing doors so that no smoke enters the compartment when the doors are closed. However, when a door is opened, smoke flows through the open doonvay into the space. If the door is closed when the contaminate in the space is 20% of the bum room, what dilution rate is required so that six minutes later the concentration will be I% of the bum room? The time, r, is 6 minutes, and C& is 20. From Equation (6.2), the dilution rate is about 0.5 changes per minute or 30 ach.

Caution About Dilution Near a Fire where

CO = initial concentration o f contaminant C = concentration of contaminant at time, t a = dilution rate in number of air changes per minute = time after smoke stops entering space or time after I which smoke production has stopped, minutes e = constant, approximately 2.7 1S The concentrations COand C must be ekpressed in the same units, and they can be any units appropriate for the particular contaminant being considered. In reality, it is impossible to ensure that the concentration of the contaminant is uniform throughout the compartment. Because of buoyancy, it is likely that higher concentrations would tend to be near the ceiling. Therefore, exhausting smoke near the ceiling and supplying air near the floor will probably dilute smoke even faster than indicated by Equations (6.2) and (6.3). Caution should be exercised in the location of the supply and exhaust points to prevent the supply air from blowing into the exhaust inlet and, thus, short-circuiting the dilution operation Esnmple 6.1 Smoke Purgin!: After the Fire is Extin~uished 1. After the fire department puts out a fire, they want to clear

the smoke quickly so that they can make an inspection to determine if the fire is completely out. If the HVAC system is capable of a dilution rate of 6 ach. how long will it take to reduce the smoke concentration to I% of the initial value? The dilution rate, a, is 0.1 changes per minute, and C, /C is 100. From Equation (6.3), the time to get the concentration to I% is 46 minutes. Considering the desire of the tire department to quickly inspect the area, such a long purging time will probably be excessive. 2. If the tire department wants the space to be purged in 10 minutes. what dilution rate is needed?

The time, I, is 10 minutes, and C,/C is 100. From Equation (6.2).the dilution rate is 0.46 changes per minute. or about 28 changes per hour.

Many people have unrealistic expectations about what dilution can accomplish in the fire space. The analysis of the previous section is not applicable to spaces in which there is a fire. There is no theoretical or experimental evidence that using a building's heating, ventilating, or air-conditioning (HVAC) system for smoke dilution will result in any significant improvement in tenable conditions within the fire space. I t is well kno\vn that HVAC systems promote a considerable degree of sir mixing within the spaces they serve. Because of this and the fact that very large quantities of smoke can be produced by building fires, it is generally believed that dilution o f smoke by an HVAC system in the fire space will not result in any practical improvement in the tenable conditions in that space. Thus, it is recommended that smoke purging systems intended to improve hazard conditions within the fire space or in spaces connected to the lire space by large openings not be used.

Pressurization Systems using pressurization produced by mechanical fans are referred to as stnoke contt-01 in this book and in NFPA 92A (NFPA 2000a). A pressure difference across a barrier call control smoke movement, as illustrated in Fizure - 6.1. Within the barrier is a door. The high-pressure side of the door can be either a refuge area or an egress route. The low-pressure side is exposed to smoke from the fire. Airflow through the gaps around the door and through construction cracks prevents smoke infiltration to t!le high-pressure side. When the door in the barrier is opened, airflow through the open door results. When the air velocity is low, smoke can flow against the airflow into the refuge area or egress route. as shown in Figure 6.2. This smoke backflow can be pre\mted if the air velocity is sufficiently lar,ne, as shown in Figure 6.3. The magnitude of velocity necessary to preLrent backflow depends on the energy release rate ofthe fire. as discussed in the liext scction.

Principles of Smoke ManagemeM

High Pressure Side

'\ \\Y\';

Low Pressure Side

c u d

\\\\

\ \\\ ...

..\\\\\.\\\\

Figure 6.1 Pressure differ-ence across a barrier of a snzoke control system can prevelir smoke infiltratioii to r/7e high-press~rreside of h e barriei

..

-

\,,\'...\

,\

....' \,\,,\~.

---+ + ..

%\

..,\\.;..,

.>.,,\V:\,\\...

...%, \...~,,

. ...., .

Figure 6.2 Smoke bnc&fIowagainst low air veloci/J! tlirorrgli an open door-rvny.

.

.

,.

"-.,

. . ,:~'\ ..'..\'..'\"\.',.

Caution: Because it supplies oxygen to the fire. airflow needs to be used with great care.

-

Airflow

+ Relatively Low Air Velocity

In this case, the appiopAate physical quantity is' pressure difference. Consideration of the two mechanisms as separate has the added advantage that it emphasizes them different considerations that need to be given for opened and closed doors. To ensure that expansion pressures are not a roblem, pressurization systems should be designed so that a patin exists for smoke movement to the outside. This path could be as simple as relying on a top-vented elevator shaft, f i ed e exhaust. It is important that some be provided. The pressurization systems most com=ly used are pressurized stairwells and zoned smoke control. Elevator smoke control is less common. Detailed design analysis and general considerations about these pressurization systems are discussed later in this manual.

.' '\,\\\\\.\'\\

'.

\,\

, .-.,.................... . . . . . . . . . . . . ........................ ................ ....;:.......................................... >

, . . . ., . . . . , ...... , . . . . . . . . . . ..................................

----+ High Air

BVelocity

Figure 6.3 High uir- velocip 1171arrghan open doorway pre1~er71s suioke backj7ow.

Pressurization results in airflows of high velocity in the small gaps a,ound closed doors and in construction cracks, thereby preventing smoke backflows through these openings. Therefore, in a strict physical sense, the pressurization is equivalent to tlie mechanism ofairfiow that is discussed in the nest section. However, considering these mechanisms as separate is advantageous for discussing smoke management systems. For a barricr with one or more large openings, air velocity is the appropriate physical quantity for both design and nicasurcment. Ho\i.cver. wlien there are only small cracks, such as thosc around closcd doors, designing to and measurement of ail- velocities is impractical.

Airflow has been used extensively to manage smoke from fires in subway, railroad, and highway tunnels. Large flow rates of air are needed to control smoke floiv. and these flow rates can supply additional oxygen to the fire. Because of tlie need for complex controls, airflow is not used so extensively in buildings. The control problem consists of having very small flows when a door is closed and then having those flows increase significantly when that door opens. Further, it is a major concern that the airflow supplies oxygen to the fire. This section presents the basics of smoke control by airflow, which demonstrate why this technique is not recommended, except wlien the fire is suppressed or, in the rare cases, when fuel can be restricted with confidence. Thonias (1970) determined that airflow in a corridor in which there is a fire can almost totally prevent smoke from flowing upstream of tlie fire. As illustrated in Fizure 6.4, the smoke forms a surface sloped into the direction of tlie oncoming airflow. Molecular diffusion is believed to result in transfer of trace amounts of smoke, producing no hazard but just the smell of smoke upstream. There is a minimum velocity below in which smoke will flow upstrezm, and Thomas developed tlie follon.ing enlpirical relation for this critical velocity:

critical air velocity to prevent smoke backflow, enerzy release rate into corridor, corridor width, density of upstream air, specific heat of downstream gases, absolute temperature of downstream gases.

Chapter 6- Principles of Smoke Management

K

=

g

=

constant on the order of 1, acceleration of gravity. The units are not given for Equation (6.4), as it is valid for any homogenous system of units (Appendix A). The downstream properties are considered to be sufficiently far downstream of the fire for the properties to be uciforrn across the section. Note that_ T is for the downstream gases, and p is for upstream gases. This means that p is not calculated from T. The critical air velocity can be evaluated at p = 0.08 1 lb/ft3 (1.3 kg/m3), Cp= 0.24 Btullb OF (1.005 W k g 'C), T = 81°F (27OC), and K = I.

where

Uk = critical air velocity to prevent sn:.?ke backflow, fpm (m/?);

0

= energy release rate into cor~idor,Btu's (kW); W = corridor width, fi (m); K, = 86.3 (0.292). Equation (6.5) can be used when the fire is located in the corridor 01 when the snioke enters the corr~dor

Airflow

through an open doorway, air transfer grille, or other opening. The critical velocities calculated from Equations (6.4) and (6.5) are approximate because an approximate value of K was used. However, the critical velocities from this relation are indicative of the kind of air velocities required to prevent smoke backflow from fires of different sizes. As ca: be see;; from Figure 6.5, the critical velocity is less for wider corridors. Examples 6.3 and 6.4 illustrate the flows needed for different fires. The equation of Thoinas can be used to estimate the airflow rate necessary to prevent smoke backflow through an open door in a boundary of a smoke control system. Rilling (1980) developed another equation for calculation of the critical velocity, and Tamura (1991) conducted fire experiments to determine the critical velocity for snioke flow through an open doonvay. While the critical velocity can be calculated, the oxygen supplied is a concern. Huggett (1980) evaluated the oxygen consunied for combustion of numerous natural and synthetic solids. He found that for most materials that are involved in building fires, the energy released per unit of mass of oxygen consunied is approximately 5630 Btu/lb (13.1 MJJkg). Air is 23.3% oxygen by weight. Thus, if all the oxygen in a pound of air is con-

y;j;j!;;;;;j:;.;?;i;j:;,:

Because it supplies oxygen

to the fire, airflow needs to be used with areat care.

L

Heat Release Rale (MW) 0

-g

800

-

600

-

400

-

200

-

.-

X

0

9 m

-

.-

.-

6

0.4

0.8

1.2

1.6

2.0

2.4

Principles of Smoke Management

sumed, 1300 Btu of heat is liberated. Stated in the S1 system, if all the oxygen in a kg of air is consumed, 3.0 MJ of heat is liberated. As can be seen from Example 6.3, the air needed to prevent smoke backflow can support an extremely large fire. In most locations of commercial and residential buildings, sufficient fuel (paper, cardboard, furniture, etc.) is present to support very large fires. Even when the amount of fuel is normally very small, short-term or transient fuel loads (during building renovation, material delivery, etc.) can be significant. Because of the concern about supplying combustion air to the fire, caution is recommended when airflow is used for smoke protection. The common use of airflow to manage smoke movement in conjunction with fuel restriction in rail and highway tunnels is probably justifi-kd by the lack of appropriate smoke management alternatives. The use of fuel restriction or fire suppression t6 limit the size ofthe fire for a smoke mana,oement system relying on airflow has the potential for catastrophic failure. Therefore, the use of airflow is not recommended for smoke management in buildings except when the potential for failure of fuel restriction or fire

suppression is evaluated to be acceptable. The methods of tenability analysis discussed in Chapter 9 can be used to evaluate the consequences of such failures. Example 6.3 Airflow to Prevent Smoke Backflow from a Small Fire An energy release rate of 142 Btu/s (150 kW) can be thought of as the size of a large wastebasket fire. What flow rate of air is needed to prevent smoke backflow h m such a fire in a corridor 4 ft (1.22 m) wide and 9 ft (2.74 m) high? From Equation (6.5), the critical velocity is 286 fpm (1.45 m/ S). The cross-sectional area of the corridor is 4 x 9 = 36 ft2 (1.22 x 2.74 = 3.34 m2). The flow rate is .the cross-sectional

11

1

Example 6.4 Airflow to Prevent Smoke Backflow from a Large Fire An energy release rate of 1420 Btu/s (1.5 MW) would result in a large portion of the corridor beins completely involved in fire. What flow rate of air is needed to prevent smoke backflow from such a fire in the corridor of Example 6.3? From Equation (6.5), the critical velocity is 616 fpm (3.13 nds). The flow rate is about 22,200 c h (10.5 m3/s).

1

chapter 6-Principles of Smoke Management

Example 6.5 Airflow Through a Doorway and Fire Growth

I

1. Thomas indicated that his relation for critical velocity can be used to obtain a roughestimate for doorways. A m m fully involved ir

fire could have an energy release rate on the order of2270 Btu/s (2.4 MW). what estimate of critical v&city is obtaded 6bm the Thomas equation for a door 3 ft (0.9 m) wide? From Equation (6.5), the critical ve1ocity.k about 793 @m (4.03 mk). If the door has an of area 20 ft2 (1.9 m2), this would amount tc a fiow of 15,900 cfin (7.48 m3/s).

II/l

2. Consideration of a smaller fire, such as the wastebasket tire of Example 6.5, may be appropriate for many situations. What flow rate does the Thomas relation indicate is needed to prevent backflow for the above door?

l

IIl

Q = 142 Btu/s(lSO kW), W=3 ft(O.9m)

From Equation (6.5), the critical velocity is about 300 fpm (1.5 mls). For a door area of 20 ft? (1.9 m2), this would amount to a flow 01 6000 cfin (2.8 m3/s). 3. What size fues can this airflow support? Consider that all of the oxygen in the air is consumed, and that the air density is 0.075 lb/$ (1 -2 kg/m3). Approximately 1300 Btu of energy is released when the oxygen in a pound of air is consumed, 15,900 c& can support the following size fire: y ) ( E J ( l 3 ft

::fiy)

= 25,800 BWs (27.2 MW)

For 6290 c h , the energy release rate would be 10,200 BWs (1 0.8 MW). These fires are very large. Airflow intended to prevent smoke backflow can cause a fire to grow significantly if there is sufficient material to bum. Therefore, the use of airflow for smoke control is not recommended except when the fire is suppressed or in the rare cases when fuel can be restricted with confidence.

1

Buoyancy Buoyancy of hot combustion gases is employed in both fan-powered and non-powered venting systems. Such fan-powered venting for large spaces is commonly ~~ employed for atriums and covered s h o p p i ~malls_A concern with atrium smoke management systems is that the sprinkler flow will cool the smoke, r e d u c w y %cy and, thus, system effectiveness. There is no question that spr~fiklETlow does-cooi..mke. but i t j s unknown to what extent that cooling reduces&&.veness of fan-powered venting. Further research is needed i z t h i s area. However, the existing information can be used to develop new design information for fan-powered venting systems. NFPA 92B (NFPA 2000b) provides methods of design analysis for smoke management systems in large spaces, such as a t r i u m and shopping malls.

-

< -

_-

AIRFLOW AND PRESSURE DIFFERENCE For a crack, gap, or other opening with a pressure difference across it, a flow will result from the higher pressure to thc lower pressure. Many different equations have been used to express the relation between fluid flow rate and pressure difference with regard to air and smoke flow in buildings. This section contains a discussion of some of the more common equations, as well as a detailed discussion of flows through the gaps around

doors. The flow through a crack or other opening can be represented by the general function,

where V

=

volumetric flow rate through the path,

Ap = pressure difference across path,

f

= general functional relation.

The particular form of the functionf depends on the geometry of the opening and Reynolds number. The Reynolds number is

where

R,

=

Reynolds number, dimensionless;

D, = hydraulic diameter of flow path, in. (m);

U = average velocity in flow path, fpm (mts); v

2 = kinematic viscosity, $/S (m /s);

KR

=

1.39

X

1U3(1 .OO).

Values of kinematic viscosity are listed in Tables A.8 and A.9 of Appendix A. The hydraulic diameter is four times the cross-sectional area of the path divided by

.

Principles of Smoke Management

the "wetted perimeter" of the path. For example, the hydraulic diameter of a circle is the diameter of the circle, and the hydraulic diameter of a square is the side of the square. For the long rectangular gaps around doors, the hydraulic diameter is the gap thickness (D,, = 2a, where (z is the gap thickness). The Reynolds number is usually thought of as the ratio of-kinetic forces to viscous forces. Later sections discuss different approaches that apply for flow dominated by viscous forces, kinetic forces, or both. The pressure difference above can be expressed as

where pi = pressure at path inlet,

p, = pressure at path outlet, p = den&

gas in path,

Zi= elevaiion of the path inlet, Z,= elevation of the path outlet, g

acceleration of gravity. Equation (6.8) is for constant density in the flow path and for flows where the values of the inlet pressure, outlet pressure, inlet elevation, and outlet elevation are all constants. This representation is not appropriate for inlet and outlet pressures that vary considerably with the elevation, as is often the case for flows of hot firs gases. However, for smoke control design, analysis of flows is limited to normal building and outside temperatures. Thus, this representation is appropriate for smoke control analysis, as well as general considerations of airflow in buildings. =

density gas in path, lb/ft3 (kg/m3); KO = 776. (1.00);

p

=

KO? = 12.9 (1.00). Dynamic forces dominate flow with Reynolds numbers greater than about 2000 or 4000, depending on path geometry. At these Reynolds numbers, the flow becomes turbulent. For turbulent flow, the velocity at a given point fluctuates rapidly in an apparent random manner. Equation (6.10) is similar to Equation (6.9) except that it has been multiplied by.density (remembering that r i ~= pi'). Equation (6.9) has been applied so extensively to orifice flow meters that it is often referred to as the orifice equalion, and Equation (6.10) also is referred to by the same name. The orifice equation is also commonly used for analysis of airflow in buildings and for analysis of smoke management systems. Because the orifice equation is based on Bernoulli's equation, it strictly applies to steady, frictionless, incompressible flows. However, the flon. coefricient was introduced to account for friction losses due to viscosity and for dynamic losses. The flow coefficient depends on the Reynolds number and the geometry of the flow path. For flows through gaps around doors and through construction cracks, the coefficient is generally in the range of 0.6 to 0.7, but the presence of stationary vortices in larger openlngs such as stain\.ell doorways can reduce the flow coefficient to about O . j j . Flow areas are discussed later.

-

For standard air density of p = 0.075 1b/ft3(1.20 kg/ 111') and for C = 0.65, Equation (6.9) can be expressed as

i/ =

Orifice Equation For large Reynolds numbers- flow is directly proportional to the square root of the pressure difference across the path:

i/

=

volumetric flow rate through the path, cfni (ni3/s);

ti~

=

mass flow rate through the path, Ibis (kgls):

C

=

dimensionless flow coetlicient;

A

=

4 3

=

1

?

flow area (or leakage area). fi- (m-): pressure dillerence across path, in. H 2 0 (Pn):

( G. I I )

where

k = volumetric flow rate through the path, cfm (m3/s); Ap =

flow area (also called leakage area), ft2 (m2); pressure difference across path, in. H 2 0 (Pa);

hj

26 10 (0.839).

A

where

&

K+A

=

=

Equation (6. I l ) gives flow at standard temperature 70°F (21°C) and standard atnlospheric pressure of .7 psi (l 0 l kPa). Frequently, volunietric flows are adjusted to standard \,ol~~metric llow rates. The mass flow rate is divided by the standard density to obtain the standard volunietric tlow rate. This is convenient because it allon.s engineers to think in terms of the familiar volumetric flow rates. Further. these standard flows can be treatsd as mass flow rates because they only deviate fi-om mass Ilow ratcs by a constant.

Chapter 6-Principles of Smoke Management

Equations (6.9), (6.10), and (6.1 1) are extensively used for analysis of smoke control systems in this manual. For normally constructed buildings, these equations are recommended for all smoke control calculations. By a normally constructed building, it is meant to be one that has at least tight wall and floor leakage and that does not have gasketed or sealed interior doors. Tight leakage of walls and floors is discussed in the section on flow areas. The rest of the flow equations presented in this section are included for the unusual cases of very tight construction. Example 6.6 Flow Calculated bv the Orifice Equation 1. Calculate the volumetric flow through a path by the orifice equation for the following values: A = 1 (0.0929 m2) C = 0.65 Ap = 0.05 in. H20 (12.4 Pa)

' , 1

VHQ

:\\\\\\\\L\\\\\\\\\\\\\\\\\\\S\\\\\\\\' Figure 6.6 Parabolic velociy profile for- Poiseuille flow between two parallel plates.

p = 0.081 lblf? (1.30 kgfm3)

From Equation (6 g), the flow rate is 560 cfm (0.26 rn'ls). 2. Calculate the above flow for standard density of 0.075 lb/ft3 (1.20 kg/m3). Usins Equation (6.9),theflow is 580 cfm (0.026 m3/s).This flow is at p = 0.08 1 lb/$ (1.30 kg/m3)and not standard c h i (or rn3/s).

Plane Poiseuille Flow For low Reynolds numbers, flow is directly proportional to the pressure loss. Viscous forces dominate flow with Reynolds numbers below about 100 to 1000, depending on particular path geometry. Plane Poiseuille flow is an exact solution to the Navier-Stokes equations for the flow of a viscous fluid between nvo parallel and infinitely long plates. The velocity distribution between the plates is parabolic, as illustrated in Figure 6.6. The fluid velocity varies only in the dirxtion perpendicular to the flow, and this type o f flow is referred to as larninar flow. The average velocity, U, for plane Poiseuille flow is proportional to pressure loss (dp/d~).

Fully Developed Lammar ~ i o w

Figure 6.7 Developnzenf oflaminar-flow in a gap. there are inlet and outlet losses due to flows just outside the gap. These deviations from plane Poiseuille flow can be significant and are accounted for in methods of analysis presented later.

Exponential Flow Equation In order to accommodate the flows, which are between viscous dominated and kinetic dominated, the following exponential relation has been used extensively in analysis of airflows through buildings:

where V

C, where a = distance benveen plates (gap thickness); p = dynamic viscosity; p = pressure Real gaps in buildings are not infinitely long, and some distance is needed for the parabolic flow profile to become established, as illustrated in Figure 6.7. The pressure losses (dphh) over this inlet length are greater than those of f ~ l l ydeveloped parabolic flow. Further,

=

-

volumetric flow, cfni (rn3/s); flow coefficient for exponential flow equation, ft3 min-' (in. H20)-"(m3 S-' Pa-");

Ap = pressure difference across the path, in. H,O (Pa);

flow exponent, dimensionless. For a flow exponent of n = 0.5, Equation (6.13) is essentially the same as the orifice equation. For 11 = I , Equation (6.13) describes viscous dominated tlow. As \vould be expected from the above discussion, the flow exponent n varies from 0.5 to l . Equation (6.13) only approximates the relation bettveen flow and pressure difl'erence, and the values of 11

=

r

Principles of Smoke Management

C, and n depend on the range of Ap. This equation has

4

=

pressure difference across gap, in. H20 (Pa);

proven useful for the evaluation of flows through many small cracks in buildings at low levels of pressure difference. However, this equation is not directly related to the geometry of the flow path, and the values of C, for particular flow paths must be determined empirically. F_or analysis of buiiding airfiow, h e exponents of interior paths are often taken at 0.5, and exponents of exterior walls often are considered to be about 0.6 or 0.65.

Dh

=

hydraulic diameter, in. (m), Dh = 2a,

p v

=

density of gas in gap, lb/@ (kg/m3);

Gap Method Gross and Haberman (1988) developed a generalized approach, the gap method, for determining the leakage through gaps of different geometry such as those of door assemblies. They developed a functional relationship between the dinlensionless variables NQ and NP.

kinematic viscosity, f?/s (m2/s); KNp = 0.108(1 .OO) =

Gross and Haberman used an analytical method of Miller and Han (197 1) to account for the pressure losses in the entrance region before fully developed flow is achieved in a straight-through slot. Their relation for flow versus pressure difference is shown in Figure 6.8. Three regions of flow through the straight-through slot were identified, and equations for these regions are: Region 1 (%scous dominated region-for NPs250):

Region 2 (Transition region-for 250O(10Pa). and air temperatureis 7OSF(21 .C).

0.2

"0

0.05

0.10

0.15

0.20

0.25

0.30

Gap Thickness, a (in)

(6. 9) where voltrmetric flow rate, cfin (m3/s); dimensionless tlow; depth of gap in flow direction, in. (111): hydraulic diameter, in. (m),(D,, = 20); length of gap, fi (m); kinematic viscosity, ft2/sec (~i?/s); 60 (1 .OO). Frequently, slots around doors have one or more bends. For single- a:ld double-bend slots, the dimensionless flow, NP, can be obtaincd by multiplying values for a straiphr-thr.ough slot by flow [actors F , and 1;2 (where F , is for single-bend slots, and F2 is for a double-bend slors). These flow factors are presented in Table 6. I and Figure 6.9. Figure 6.10 shows the tlow predicted by the gap mctliod fol- a stmight gap and gaps with bends. As would bc cspcctcd, rhc Ilow incrcascs \\.it11 gap tliick-

Figure 6.1 0 Flow coefficients for stl-aigl~tgaps atld gaps with be17o's. ness, n, and the f l o is ~ less for gaps with bends than for straight gaps. I r is espected rhat the gap model predictions for a relatively \ride gap (and relatively large Reynolds number) would be closer to those of the orifice equation than predictions of the exponential tlon equation. Figure 6.1 1 compares predictions of the orifice equation, the exponential flow equation, and the gap method far a 0.5 in. (1 2.7 mm) wide gap, and it can be seen that the predictions of the orifice equation are almost identical with those of the gap method. As might be expected for a 0.1 in. (2.54 mm) gap, the predictions of the exponential flow equation with 11 = 0.65 are much closer to those of the gap method (Figure 6.12). The design book of Klote and Fothergill (1983) used Equations (6.9) and (6.1 1) for all smoke control analysis because it was bcliwcd that the orifice equation was sufficiently.accurate for design analysis. Klote and Bodart (1985) reevaluated this use of the orifice equation and the exponential flow equation. They experimentally determined flow coefficients and exponents for the leakage paths of' rhc French Firz Research Tower -

~

Principles of Smoke Management

using regression analysis. Computer flow simulations using the exponential flow equation with experimentally determined exponents were in good agreement with simulations using the orifice equation. It can be concluded that use of the orifice equation for all flow paths in normally constructed buildings yields acceptable for pressurization smoke control design purposes, No similar study was conducted for smoke management systems without pressurization.

I

Example 6.7 Gap Method for

FIGThrough Door caps

A door has the dimensions shown in Figure 6.13. What is the flow through the gaps between the door and the door frame at a pressure difference of 0.15 in. H 2 0 (37.3 Pa)? Use the following properties of air at 70°F (21 "C):

For the slot at the door bottom:

a = 0.50 h'(0.0 127 m) Dh = 2a = l .OO in. (0.0254 m) L=3ft(O.914m) x = 1.75 in. (0.0445 m) Ap = 0.15 in. H20 (37.3 Pa)

For most of the applications of this book, flows are represented and calculated by the orifice equation. Two approaches to prescribing values for C and A are:

1-

Use the cross-sectional area for A, and C is chosen to obtain the desired value of the CA product.

2- Arbitrarily choose C, and choose A to obtain the desired value of the CA product.

The first approach is used with orifice flow meters and many other flow paths for which the cross-sectional area can readily be determined and for which C values are available. For flow coefficients of many items. readers are referred to Idelcnik (1 986)The geometry of construction cracks in walls and floors is complicated and for these cracks, measurement of cross-sectional areas is impractical. The second approach above is used for these cracks with the flow areas listed in Table 6.2 for C = 0.65. It is believed that actual leakage values for walls and floors are primarily dependent on workmanship rather than construction

-

From Equation (6.1 S), NP = 28.2~106. From Equation (6.18);NQ = 2950. From Equation (6.19), V through slot at door bottom.

=

152 cfni (0.0718 m3/s) flow

Pressure Difference (Pa)

a

.Ei 6 0 0

For slots at to^ and sides:

- 0 . 6 -c E

a = 0.12 in. (0.00305 m) D,, = 2a = 0.24 in. (0.006 10 m) L= 17 ft(5.18 m) s = 2 3 7 in. (0.0602 m) Ap = 0.15 in. H 2 0 (37.3 Pa) From Equation (6.1S), NP = 51000. From Equation (6.17), NQ = 109.8. From Equation (6.19), V

=

181 cfin (0.0855 m3/s) if the slot

1

0l

0

Note: Gap thickness is 0.5 in (12.7 mm). gap depth in flow direction is 2 in. (50.8 mm).pressure difference is 0.04 in. H,O (10 Pa). and air lemwrature is 70 'F(21 . 'Cl.. l

I

0.1

0.2

3

0.3

2

o! S

Pressure Difference (in H,O)

Figure 6.11 Co~npnrisonof val-ioz/sflo\c~jln~ctio,u for a 0.5 ill. (12.7 mm) wide goy.

had been straight.

From Figure 6.9, F , = 0.93 for a single-bend slot. V = 181 ,(0.93) = 168 cfin (0.0792 m3/s) flow through slots at top and sides. Total flcw: 152 + 168 = 320 c h (0.15 l ni3/s)

Pressure Difference (Pa) Exponential with n = 0.65

m

0.015 Gap Method of Gmss and Haberman,(1988)

F L O W AREAS AND C O E F F I C I E N T S In the design of smoke control systems, airflow paths must be identified and evaluated. Some leakage paths are obvious, such as gaps around closed doors, open doors, elevator doors, windo\vs, and air transfer grilles. Construction cracks in building walls and floors arc less obvious but no less important.

.. 0.010

Y

0

-0.1

0.2

Pressure Difference (in

0 0.3

H,O)

Figure 6.12 Co~qmrisonof var-iousJ o I ~ . ~ ~ / I Ifolc ~ ~ o I ~ s n 0.I ill. (2.54 nrnl) wide gnp.

Chapter 6 -Principles of Smoke Management

0.62 in

Door (b)

F;Y~725;7k T (C)

(a)

Figure 6.13 Dimensions for Example 6.7: (a) front of door; (b) gap at top and sides, and (c) gap at bottom.

Table 6.2: Typical Leakage Areas of Walls a n d Floors of Commercial ~ u i l d i n ~ for s ' C = 0.65

'

Area ~atio~

Construction Element Exterior Building Walls (includes construction cracks, cracks around windows and doors)

Stairwell Walls lTight 0.14 X (includes construction cracks but not cracks around windows or doors ~~~~~g~ 0. I I Loose 0.35 X Elevator Shaft Walls Tight 0.18 X (includes construction cracks but Average 0.84 X not cracks around doors) loose 3.18 X

lo4

1 0-3 Io-~ IO-~

Io-~ 1o

-~

AIAj

Floors (includes construction cracks and gaps around penetrations)

I

Tight3

0.66 X 1 o - ~

Average

0.52 X 104

loose3

1 0. I 7

X

l . Flow area ratios for C = 0.65 at 0.3 in. H20(75 Pa). 2. A I S flow area. A , is wall area, and A,is floor area. Values a f area ratios based on pressurization measuremenls in buildings by Tamura and aiilson(1966). Tamura and Shaw (1976a: 1976b; 1978) and Sham et al. (1993). 3. Values exlrapolated from average floor lightness based on rangs o f tiglitness o f other constructionelements.

Io

-~

materials, and, in some cases, the flow areas in particular buildings may vary from the values listed. The second approach above also was used for the flow areas of elevator doors listed in Table 6.3. The gap method can be used to determine values of C and A for flow through gaps around doors. Tables 6.4 and 6.5 provide this flow information using approaches 1 and 2, respectively. The flows ca!culated by these tables are equivalent to each other, and users can select the approach convenient to their application. Additional data concerning building components are also provided in Chapter 25, "Ventilation and Infiltration, of the 1997 ASHRAE Handbook-Fundamentals." The leakage flow rates of door assemblies can be measured and rated at ambient temperature and elevated temperatures in accordance with UL 1784 (1990). For open stairwell doorways, Cresci (1973) found that stationary vortices form in the doorways a;~dthat the resulting flow through those doorways was about half of that which would be expected without such vortices. Using approach I , Table 6.6 lists flow areas of open stairwell doorways for C = 0.35. Alternatively, approach 2 can be used where C = 0.65 and the flow area is about half the cross-sectional area. The determination of the flow area of a vent is not always straightforward because the vent surface is usually covered by a louver and screen. Thus, the flow area is less than the vent area (vent height times width). Because the slats in louvers are frequently slanted, calculation of the flow area is further complicated.

Principles of Smoke Management

Table 6.1: Typical Flow Areas for Elevator ~ o o r s with ' C = 0.65 Flow ~ r e a '

Door Width

Closed Doors

ft

m

3.0

0.914

Tightness

ft2

m2

0.032

Tight

0.34

Average

0.48

0.045

Loose

0.60

0.056

Tight Average Loose

.

0.37

0.035

Average

0.53

0.049

Loose

0.66

0.06 1

6.0

0.56

Tight

Tight Average Loose

Tight Average Loose

I. 2.

1.07

3.5

Opened Doors

Avcrage

This table is for clc\-atordoors 7 fi (2.13 m) Ihiph. Flow areas t'or C = 0.65 at 0.1 in. H1O( 2 5 Pa). Values of flow area based on pressurizxi~n mea~~~rcn~cn~s in building by Tamura and Shaw (1976b).

Table 6.2: Flow Coefficients for Gaps Around ~ o o r s ' Gap Thickness at Top and Sides

Width

Cap Thickness at Bottom

Cross-Sectional Area

in.

m

in.

nlni

in.

nlm

ft'

m'

36

0.9 14

0.02

0.50s

0.25

6.36

0.090

0.0084

Flow Coeflicient

0.57

Chapter 6-Principles of Smoke Management

Table 6.3: Flow Areas of Gaps Around ~ o o r s Using ' a Flow Coefficient of 0.65 Cap Thickness at Top and Sides

Width

Cap Thickness at ~ o t t o m

in.

m

m.

mm

in.

mm

36

0.914

0.02

0.508

0.25

6.35

Flow ~ r e a ' fi? 0.079

m2

0.0073

l . This table is for doors 7 ft(2.13 m)l~lgh,1.75 in. (44.5 mm) thick. and with a door slop protruding 0.61 in. (15.7 111111) iron1 the liamc. 2. The flow area should not be confused tvith the cross-sectional area o f the gaps. The flow area is for uss in Ilic orilicc. cq~lstic~ii will1 C = 0.65. The tlow

the gap method.

Table 6.4: Areas and Flow Coefficients for Open Stairwell ~ o o r s ' Door Width

Flow Coefficient C 0.35 0.35

m 0.9 14 0.914

ft2

m'

Person in Doonvay2

in. 36 36

21.0 10.5

1.95 0.78

Propped Fully Open

44

1.118

25.7

2.3s

0.35

Person in Doonvay'

44

1.118

12.5

1.19

0.35

Condition of Door Propped Fully Open

1.

Flow Area

This [able i s for a door hsighr o f 7 li (2.13 m).

2. The llow arca ir !alien as halfofthc arca ofthe fully opsn door. allon.ing for the door hcing only partly opcr. 3nd a person hlocLing p m ol'ths dooncay.

Principles of Smoke Management

Example 6.8 Flow Area of Stair Pari I. What is the leakage area between an interior stairwell and the building if the stairwell walls are of average tightness? The stair well door is 7 ft (2. i3 m) by 3 ft (0.914 m), with a 0.08 in. (0.00203 m) gap on the sides and top and with a 0.25 in. (.Cl0635 m) gap a the bottom. The stairwell is 8 ft (2.44 m) by 18 ft (5.49 m) with a floor to ceiling height of 10 ft (3.05 m).

For the stairwell walls: Wall area is 2(8+18)10 = 520 ft2 (48.3 m3). From Table 6.2 for a stairwell wall of average tightness, the ratio of the leakage area thc wall area is 0.1 I X 1 03. The leakage area of the wall is 0.1 1X 1o 3 (520) = 0.057 fr2 (0.0053 m2). For the naps around the door: From Table 6.5, the flow area of this door is 0.169

(.O 157 m2).

Total flow area: Because these flow areas are in parallel (Chapter S), the total flow area is the sum of the individual areas: 0.057 + 0.169 = 0.226 (0.0210 m2) flow area between the stairwell and the building on a per floor basis. Part 2. What would the flow area be if the construction tighmess were loose and the door undercur 0.75 in. (0.0 19 1 m)?

For the stairwell walls: From Table 6.2 for a stairwell wall of loose tightness, the ratio of the leakage area to wall area is 0 . 3 5 10-'. ~ The leakage area of the wall is 0 . 3 5 10' ~ (520) = 0.182 ft2 (0.0169m*). . For the g a p around the door: From Table 6.5, the flow area of this door is 0.320 ft2 (.0297 m2). Total flow area: The flow area between the stairwell and the building on a per floor basis is 0.182 + 0.320 = 0.502 f; (0.0166 m'). This is about double the flow area of the first part, illustrating the extent to which flow areas can vary.

PRESSURE LOSS OF SHAFTS AND DUCTS

Straight Ducts and Shafts The pressure losses due to friction in ducts and shafts is represented by

where

& J=

pressure loss in shaft or duct due to friction, in. H20 (Pa);

f

= dimensionless friction factor of shaft or duct;

L

=

shaft or duct length, ft (m);

D,,

=

hydraulic diameter of shaft or duct, ft (m);

p U

=

density of gas inside shaft or duct. 1b/ft3 (kdm3); average velocity inside shaft or duct, fpm (rids);

=

Kyl, =

1 .G6 X 10-"(1.00).

The hydraulic diameter of shaft or duct is

where

A

=

area of the duct or shaft, f;(m 2 );

P

=

perimeter of duct or shaft, fi (m).

Equation (6.20) is ths Darcy-Weisbach equation for pressure loss in ducts and pipes. For ducts and pipss, the friction factor can be obtained from the traditional Moody diagram (Figure 6.14), or it can be calculated from the Colebrook equation.

where E

=

roughness of the inside surface of the duct.

R,

=

Reynolds number (sse Equation (6.7)).

fi (m);

Some categories of duct roughness, E, are listed in Table 6.7. Equation (6.77) can be solved numerically f0r.f

,

Chapter 6-Principles of Smoke Management

Reynolds Number. R& Figure 6.14 1\4oo41~ diagram fo1-jktiot7 fnciot- forflow in ducts andpipes.

Table 6.7: Duct Roughness categories1 Duct Material Uncoated carbon steel, clean

Roughness Category

ft

Roughness, e mm

Smooth

0.000 1

0.03

Medium Smooth

0.0003

0.09

Average Medium Rough

0.0005 0.003

0.15 0.90

Rough

0.0 1

3.0

PVC plastic pipe Aluminurn Galvanized steel, longitudinal seams, 50 in. (1200 mm) joints Galvanized steel, continuously rolled, spiral seams, 120 in. (3000 m m ) joints Galvanized steel, spiral scan with l, 2, and 3 ribs, 144 in. (3600 nim) joints Galvanized steel, longitudinal seams, 30 in. (760 mm)joints Fibrous glass duct, rigid Fibrous glass duct liner, air side n-it11 facing material Fibrous glass duct liner, air side spray coated Flexible duct. metallic Flexible duct. all types of Ljbric and wire -.

by the Ne\vton Raphson r i ~ e t h o dFor . ~ the,fitlll,~a!g/rflow regio17(Figure 6.14), the friction factor can be calculated from 6. As suggcstcd by Gcorze \\falton of tlic National Institute of Standards and Teclinolopy. the clliciency oTthis numerical solution is signilicnrltly i ~ n p r o ~byd suhstitutinp.~= /-I1' and solving Ibr .v.

In network computer flow tnodels (Chapter 8), it can be useful to use the equivalent orificc area for a duct or shaft. This is the area of an orifice that has the z n l c

Principles of Smoke Managemeqt

pressure loss as a section of duct. The flow through the orifice.is

The flow also can be expressed as

-

P = A,U where As = cross sectional area of the duct or shaft, ft2(m2);

where

P

=

volumetric flow rate through the duct or shaft, cfm 3

(m /s);

C

=

dimensionless flow coefficient;

A,

=

equivalent area,

U

=

average velocity in the duct or shaft, @m, (mls).

Considering Ap = Apj and combining Equations (6.20), (6.24), and (6.25) results in

ft2 (m2);

Ap = pressure difference across path, in. H20 (Pa);

p K,

=

density gas in duct or shaff lb/ft) (kg/m3);

=

776. (1.00).

Figures 6.15 to 6.19 show area ratios (A, /As) for fully rough flow for the duct roughness categories listed in Table 6.7. Hydraulic Diameter, D, (m)

I(

Example 6.9 Equivalent Area of A Shaft Calculate the equivalent area of a concrete shaft 8.6 ft (2.62 m) by 12 ft (3.66 ni) with a length equal to the floor height of 12

ft 11

From Table 6.7, the roughness category of a concrete duct is rough. This indicates that the AdAScanbe obtained from Figure 6.19. From this figure, AdAS = 12.5, and 2

2

A, = 12.5AS = 12.5(8.6 x 12) = 1290 ft (120m ) . "0

20

40

60

80

100

Hydraulic Diameter, Dh(R)

Figure 6.15 Area ratiofor-sniooth ducts.

Hydraulic Diameter, D,, (m)

.

0

20

40

_

.

60

.

~.. . ..:....

.

I

80

Hydraulic Diameter. D,, (ft)

.

.

.

100

This large equivalent area is indicative of a duct section with a small pressure lossdue to friction.

Chapter 6 -Principles of Smoke Management

Hydraulic Diameter, D,, (m)

p

= density o f gas inside stairwell, l b / P (kg/m3);

U = average velocity inside stairwell, @m ( d s ) ;

K,,

= 1.66

X

104 (1.00).

A relationship for the equivalent orifice area for the stairwell can be obtained in the same manner as was done for the duct.

Hydraulic Diameter, Dh(ft)

Values of K, are listed in Table 6.8.

Figure 6.18 Area ratio for medium rough ducts.

Hydraulic Diameter. D, (m)

Calculate the equivalent area of a stairwell 8 ft (2.44 m) by 18 ft (5.49 m) with a length equal to the floor height of 12 ft (3.66 m). There are no people in the stairs and the treads are l. FromTable6.8, the friction factor, K,, is32,andA,.JA, The equivalent area is A,

= 0.28 (8 X

= 0.28.

18) = 40 ?f (3.72 m').

2. An alternate approach is below.

From Equation (6.2 l), D =4A = -----4(S X 'g' = 11.1 ft (3.38 m). h P 2(8+ 18)

From Equation (6.28),

Hydraulic Diameter, D, (R) Figure 6.19 Area ratio for rough ducts.

SYMMETRY Stairwells Tamura and Shaw (1976b) showed that the pressure losses due to friction in stainvells is similar to that of shafts, and this pressure loss is

where pressure loss in stairwell due to friction, in. H20 (Pal; K,,, = dimensionless friction factor of stairwell; AQ=

L

= height of section of stairwell, ft (m);

D,, = hydraulic diameter of stairwell, ft (m);

The concept of symmetry can be used to simplify flon networks, thereby simplifying analysis. While advances in network modeling (Chapter 8) have reduced the need for such simplifications, symmetry can srill be useful. Figure 6.20 illustrates the floor plan of a multistory building that can be divided in half by a plane of symmetry. Flow areas on one side o f this plane are squal to corresponding areas on the other side. If the flon s and pressures are solved for one side, those on the other side are also known. To apply symmetry to a building, ei.ery floor must be such that it can be divided in the same manner by the plane of symmetry. If wind effecrs are included in the analysis, the wind direction must be parallel to the plane of symmstry. It is not necessac that the building bc geometrically synlnletric, as shown In

principles of Smoke Management

Table 6.8: Typical Friction Factors and Area Ratios for ~taiwells' Stairwell Type

Conventional Conventional Conventional Conventional Conventional Conventional Scissor

Friction

AdAs

people

Factors, K,

Per Floor

None None None High None High None

29 32 61 104 71 170 15

0.30 0.28 0.24 0.19 0.22 0.15 0.32

Floor Height 2

ft

m

Tread

12 12 8.5 8.5 8.5 8.5 14

3.6 3.6 2.6 2.6 2.6 2.6 4.3

Open Closed Open Open Closed Closed Closed .

-

I. Based on data from Tamura and Shaw (1976a) and Achakj~and Tamura (1988). 2. "High" is high density of 0.18 person/ft2(2.0 persodm2).

F

I

Knob,

1

LWPressure Side

k.4 Figure 6.2 1 Diagrari7 of f01,ces 0 1 7 n cloor- in a p/-essur--

where

Figurc 6.20 Building floor- plan illzafr~arirz,o sjx1n7efr?. concepf. Figure 6.20; it must be synimetric only with respect to flow.

F A(.

=

= total door openins force, Ib (N); moment of the door closer and other friction, Ib fi

Fff

=

PJm); door width, ft (m);

A

= door area, f? (ni2); =

DOOR-OPENING FORCES The door-opening forces due to the pressure differences produced by a smoke control system must be considered in any design. Unreasonably high door-opening forces can'result in occupants having difficulty or being unable to open doors to refuge areas or escape routes. This is addressed in the next section. The following analysis is for a door hinged at the edge with a door knob, as shown in Figure 6.2 1. Users need to adapt the analysis to fit other conditions, such as pi\ ots inset froni tlie edge. The forces on a door in a smokc control system are illustrated in Figure 6.21, and tlie sum of the nionients about the hinge is

pressure difference across the door, in. H 2 0 (Pa);

n

= distance froni the doorknob to the knob side of the

Kd

=

door. fi (m); 5.20 (1.OO).

The moment to overcome the door closer and friction consists of all moments about the hinge due to the door closer or friction forces such as friction in the hinges or rubbing of the door against the door frame. The force at the knob needed to overcome hinge friction is about 0.5 to 2 Ib (2.3 to 9 N). Some poorly fitted doors rub against the frames, resulting in extremely high dooropening forces. Ideally, such poor workmanship will be identified and corrected during building commissioning. The component fo,rce, F,, at the knob to overcome the door closer and other friction is

'

Chapter 6 - Principles of Smoke Management

This can be substituted into Equation (6.29) to obtain

d

=

distance from the doorknob to the knob side of the door, ft (m);

Kd = 5.20 (1 .OO). and this can be solved for the pressure difference as

@ =

2 ( W - d ) (F- F,) KdWA

where

F

=

total door opening force, Ib (N);

F,

=

force to overcome the door closer and other friction, Ib (N);

W = door width, ft (m); A = door area,

(m2);

Ap = pressure difference across the door, in. H20 (Pa);

This relation assumes that the door-opening force is applied at the knob. This force to overcome the door closer is usually greater than 3 Ib (13 N) and, in some cases, can be as large as 20 Ib (90 N). Caution should be exercised in evaluating the door closer force because the force produced by the closer when the door is closing is often different from the force required to overcome the closer when opening the door. Many door closers require less force in the initial portions of the opening cycle than that required to bring the door to the full open position. For this discussion, the force to overcome the door closer and other friction is that force at the very beginning of the opening process. The pressure difference component of the door-opening force can be determined from Figure 6.22 for a door 7 ft (2.13 m) high with a knob located 3 in. (0.076 m) from the edge.

Pressure Difference (in H20)

Figure 6.22 Doo,--oj>enit7gforces due lo pressure diflerence.

Principles of Smoke Management ;

Example 6.11 ~oor-openingForce. 1. What is the door-opening force for a door 7 ft by 3 ft (2.13 m by 0.9 1 m) subject to a pressure difference of 0.25 in. H 2 0 (62 Pa)? The force to overcome the door closer and other friction is 10 Ib (44 N), and the knob is 3 in from the door edge. W= 3 ft(2.13 m) Ap = 0.25 in. H 2 0 (62

Pa)

d

=

F,

=

0.25 ft (0.076 m) lOlb(44N)

ft2 (1.95 m2)

A = 3 X 7 = 21 Kd = 5.2 (1.00) From Equation (6.3 l), the door-opening force is 25 Ib ( l l 0 N). Alternately, Figure 6.22 gives 15 Ib (66 N), and adding this to the door closer force gives 25 Ib ( l l0 N).

2. What is the pressure difference across a door that has a 30 Ib (133 N) door-opening force and a frictional and door closer force of 5 Ib (22 N)? The door is the same size as in part 1 above. +

F=3O lb(l33 N) F,= 5 Ib (22 N) From Equation (6.32), Ap is 0.42 in. HzO (104 Pa).

DESIGN PRESSURE DIFFERENCES It is appropriate to consider both a maximum and a minimum allowable pressure difference across a barrier o f a smoke control system. The values discussed in this section are based on the recommendations in NFPA 92A (NFPA 2000a). The maximum allowable pressure difference should be a value that does not result in excessive door-opening forces. The force that a particular person can exert to open a door depends on that person's strength, the location of the knob, the coefficient of friction between floor and shoe, and whether the door requires a push or a pull. Read and Shipp (1979) studied door-opening forces, and they present strength data for the very young (age S to 6 years) and the elderly (age 6 0 to 75 years). From Tables 6.9 and 6.10, the five perce~tilepushing force for the very young females is only 6.5 Ib (29 N), and the five percentile pushing force for the elderly

females is only 2 0 Ib (91 N). The five percentile push force of healthy male adults is 4 5 Ib (200 N). These forces are gradually applied, and a 'jerk" method o f suddenly applying the force results in a peak force o f 175 Ib (780 N). These push forces are one handed, and the subjects are not leaning forward; the push force increases to 146 Ib (652 N) for a forward leaning twohanded push. The Life Safe@ Code (NFPA 2000c) states that the force required to open a n y door in a means o f egress shall not exceed 30 Ib (133 N). Based o n the data of Read and Shipp, it seems that this 30-lb (133 N ) limiting force is appropriate for most occupancies, but care should be exercised when building occupants are likely to have low levels of pushing and pulling strength. For a 30-lb (133 N) limitation on door-opening force with a side-hinged door with a singe knob, the maximum allowable pressure differences are listed in Table 6.1 I . The fire effect of buoyancy of "hot" smoke can be incorporated in the selection of the minimum design pressure difference. Unless otherwise stated, the minimum design pressure differences used in this manual incorporate buoyancy and are based on the idealization that the mass flo\v through the leakage paths is constant for the duration of the fire. A method for handling variable mass flon. through these paths is presented in Chapter 9. The smoke control system should be designed to maintain this minimum value under likely conditions of stack effect and wind and when there is no building fire (such as during acceptance o r routine testing). NFPA 92A (NFPA 20COa) suggests minimum design pressure differences, and these values are listed in Table 6.12. The values for nonsprinklered spaces are those that will not be overcome by the buoyancy forces of hot gases. These values for sprinklered buildings were calculated from the equation for buoyancy of combustion gases (Chapter 5) for a gas temperature of 1700°F (927OC), for a neutral plane located at a height of two-thirds of the ceiling height below the ceiling and with a safety factor of 0.03 in. H 2 0 (7.5 Pa).

Table 6.9: Functional S t r e n g t h Values f o r A g e G r o u p 5 t o 6 y e a r s '

Function Push Pull I.

.

Gender M F M F

Mean, Ib (N) 20 (90) I6 (73) 27 (120) l9 (86)

Note: :\dapkd ( i o l i ~llcad and Shipp (1979). Sul$cctr i w d only one puilics would h a w rcsultcd ill frcnwr Ibrccs.

Maximum, Ib (N) 26 (155) 2s (l 26) 41 (184) 32 (141) I l n ~ i d .Suddsnly

minimum,

Ib (N) 7.2 (32) 10 (46) 18 (82) l l (48)

Fifth Percentile, lb (NI 8. l (36)6.5 (29) 17 (77) 8.7 (39)

applied ''jerk" ~ u s h e and s pulls o r two-handed forward lesning

Chapter 6-Principles of Smoke Management

Table 6.10: Functional Strength Values for Age Group 60 to 75 years1 Mean, Function Push

Maximum,

Gender M

53 (237)

121 (540)

Minimum, Ib 0 2 1 (92)

F

45 (201)

9 1 (407)

22 (100)

111 (NI

(N)

Fifth Percentile, lb 0 23 (101)

Pull I.

21 (95)

Note: Adapted fror. Read and Shipp (1979). Subjects used only one hand. Suddenly applieda'jerk" pushes and pulls or hvo-handed forward-leaning pushes would have resulted in gearer forces.

Table 6.11: Maximum Allowable Pressure Difference Across Doors, in. H 2 0 ( ~ a ) l Door Closer Force,

S (35.6) 10 (14.5) I2 (53.4) 14 (62.3) I.

Door Width, in. (m)

0.41 (102.) 0.37 (92. l) 0.34 (84.5) 0.30 (74.6)

0.37 (92.1) 0.31 (81.5) 0.30 (74.6) 0.27 (67.2)

i\:olc: Adnpted from NFPA (2000al. Total door opening force is 30 lb (133

0.34 (84.5) 0.30 (74.6) 0.27 (67.2) 0.24 (59.7)

0.3 1 (77. l) 0.28 (69.7) 0.25 (62.2) 0.22 (45.7)

N). and the door l~eiehris 7 fi (2.13 m).

Table 6.12: Suggested Minimum Pressure Design ~ifference' Building

Ceiling

~~~e~

Height, ft (m)

AS NS NS

Any

9 (2.7) l 5 (4.6)

Design Pressure ~ifference? in. HzO (Pa) 0.05 (12.4) 0.10 (24.9) 0.1; (34.8)

I. Adnpted from NFPA (2000n). For d a i g n purposes, a sn~okscontrol systeni should maintain these minimum pressurs diflerences under likely conditions of stack elfect or wind. 2. AS for sprinklered and NS for nonsprinklsrsd. 3. TIis prsssurc dilference mcasurcd ber\\ven [hc smoke zone 2nd adjacent spnces while the afictsd areas arc in the smokc control mods.

0.28 (69.7) 0.26 (64.7) 0.23 (57.2) 0.21 (52.2)

Principles of Smoke ~ a n a ~ e & n t

Pressure differences produced by smoke control systems tend to fluctuate due to the wind, fan pulsations, doors opening, doors closing, and other factors. Shortterm deviations from the suggested minimum design pressure difference may not have a serious effect on the protection provided by a smoke control system. There is no clear cut allowable value of this deviation. It depends on tightness of doors, tightness of construction, toxicity of smoke, airflow rates, and on the volumes of spaces. Intermittent deviations up to 50% of the suggested minimum design pressure difference are considered tolerable in most cases.

WEATHER DATA The indoor to outdoor temperature difference has an impact on building airflows and pressures. For some analyses, wind data may be needed. The 1997 ASHRAE Handbook-Fundamentals, Chapter 26, "Climatic Design Information," provides weather data for locations throughout the world. NFPA 92A and NFPA 92B suggest that the 99.6% heating dry-bulb (DB) temperature and the 0.4% cooling DB temperature be used as the winter and summer design conditions. NFPA 92A and NFPA 92B also suggest that the 1% extreme wind velocity be used as the design condition.

CHAPTER 7

Air Moving Equipment and Systems he National Board of Fire Underwriters examined the NFPA fire data from January 1936 to April 1938 to determine the extent of the smoke hazards due to heating, ventilating, and air-conditioning (HVAC) systenls (NBFU 1939). Of 25 fires recorded, 19 had conlbustion of parts of the air-moving system. Ducts, duct linings, and filters bunied. In five cases of no fire in the HVAC system, smoke was distributed by the system. This report has had a nlajor impact ,on tlie materials and consiruction of modern HVAC systems, as is apparent from examination of current codes and standards. The report recommended that HVAC systems be shut d o h during fire situations to prevent them from spreading smoke and supplying combustion air to the fire. System shutdown became the standard response to fire. However, operation of the HVAC system In a s G k e controi mode has become a common alternative in recent years, as discussed in later chapters. The information in this chapter is provided as a broad and general background on air-moving systems. The material was selected to aid in tlie understanding of the smoke control systems discussed in later chapters. This information should help tire protection engineers, firefighters, and code oRicials to commur.icate with HVAC designers and to recognize and understand HVAC equipment. Because energy conservation is a major concern, energy efficiency of systems and equipment is addressed in this chapter. This chapter is not an exhaustive treatment of the firc safety requirements of HVAC systems, and the design or such systems should be done by experienced professionals. Many publications provide more detailed information about these systems and equipment (for example, ASHRAE 2000a;

T

SMACNA 1990, 1987; Handbook of HVAC Design 1990). The simplest systenls consist of a fan in a housing, such as a roof-mounted atrium exhaust fan. Most systems are more complicated, with ductwork and some of the following components: supply air outlets, return air inlets, fresh air intakes, humidifiers, filters, heating and cooling coils, preheat coils, and dampers. Ductwork is constmcted of a variety of materials, including steel, aluminum, concrete, and masonry. Duchvork of fiberglass, gypsum board, and fabrics is used with some restrictions. Discussions of fans and dampers are provided later. The air-moving systems that are discussed later are primarily intended for maintaining comfort conditions. Exhaust systems for toilets, laboratories, and kitchens are not discussed, but they are generally less complicated and use many of the same conlponents.

--

HVAC LAYOUT In large buildings, the heating and cooling loads often vary considerably from one location to another. Heat is transferred to or from the spaces near the exterior walls depending on outdoor weather conditions. Solar radiation affects each of the exterior zones differently. It is common to divide a building into four perimeter zones and a core zone as shown in Figure 7. l a. The heating and cooling capacities cd the perimeter zones agdesigned to accommodate outside temperatures and solar loads. Because of the heat produced by occupants, hghting, and equipment. the core zones often need cooling even in the winter. The perimeter zones can be conditioned by a variety of means, including fan coil units, air conditioners, and heat pumps. Generally, fan coil units are supplied

-

Chapter 7-Air Moving Equipment and Systems

with hot and cold water to allow both heating and cooling. Often, air conditioners and heat pumps are located through-the-wall. Both fan coil units and through-thewall equipment can receive ventilation air directly from the outside or from a ducted ventilation systeni. In large commerc~albuildings, ventilation air is needed to control the odors due to cooking, smoking, perspiration, and other processes.7 The perimeter zones may be served by ducted forced air systems, and the core zone is usually served by such forced air systems. Some types of forced air systems are capable of satisfying a wide range of needs simultaneously and are used to serve both perimeter and core zones. The different types of forced air systems are discussed later. ~istributionon a floor is often through ducts located above a suspended ceiling. Return air is often pulled through the plenum space above the ceiling, as shown in Figure 7.1 b. The return may be ducted above the ceiling as well. Mechanical equipment of a forced air system may be located on each floor (Figure 7. I b), on one floor (Figure 7.lc), or on several floors (Figure 7. l d). The arrangements above are but a few of those possible. There may be several forced air systems on each floor. There may be several units located in a penthouse, each serving its own vertical portion of the building. Sometimes, several air systems are used and the areas served are selected on the basis of having similar heating and cooling demands. These demands depend on occupancy, the presence of heat-releasing equipment, electrical lighting levels, and heat transferred to or from the outside. For a complicated building (such as hospitals, laboratories, and hotels), the duct systems can be intertnrined to such a level that considerable study is needed to understand which systems serve which areas.

FORCED AIR SYSTEMS Four common types of forced air systems are constant volume, single-zone systems, constant volume systems with terminal reheat, variable air volume (VAV) systems, and dual-duct systems. There are numerous variations on these systems. Generally; the heat source for heating coils is hot water. However, other sources, such as steam or electrical resistance heating, are possible. Cooling coils can be supplied with chilled water or with refrigerant. The source of heating or cooling has signiticant effects on 7. In small b u i l d i n g and residences, such odor col]trol is achie\.cd by ~iaturallyoccurring air inl?l[ration through construclion gaps and cracks.

Floor

29

25 (a) Perimeter and Core Zones

20

15 (b) Ducied Supply and Plenum Return

/

I Mechanical Penlhouse 1

-

R e q - i Duct

-

(C )

1

1

Dun 1

Central System in Penlhouse

Figure 7.1

(d) MuRipleMechanical Floors

Some HVAC a1-1-or7ge11zazts.

system economics but little effect on airflow. The forced air systems discussed in the following sections can be completely built in the field, factory-fabricated subsections can be field assembled, or completely factory fabricated systems can be installed.

Constant Volume, Single Zone Figure 7.2 is a representation of a single-fan, constant volume system. The term "constant volume" is used in the HVAC industry to indicate that the system pcoduces a constant or nearly constant volumetric flow rate of air. This system is used in residences and some small commercial applications. In this esample. return air from the living quarters is drawn i n at one location, flows through filter, fan, and coils, and is distributed back to the residence. This system does not ha\.e the capability of providing fresh outside air. These systems are intended for applications where there is sufficient natural air leakage through cracks i n walls and around windows and doors for odor control. Single-zone systems are so called because they serve only one HVAC control zone, For esample: a residential system is controlled by a thermostat to maintain the temperature in the l i v i n ~quarters. Generally, the residential system has a two-position control system, allowing only "on" and "olt" operation to maintain tempel-ature and humidity conditions. Frequently in commercial buildings. constant volume systems have two fans and are capable ol'pro\.iding

Principles of Smoke Management

ventilation air as illustrated in Figure 7.3a. The return fan permits lower supply fan speeds and quieter operation. The return air fan provides positive return and exhaust from the conditioned space. During cold weather, many large commercial buildings have so much heat generated by equipment and people that cooling is required. To save energy, cold outside air can be used for this cooling. The system of dampers and controls that maximizes the use of outdoor air for cooling is called an economizer. For systems with an economizer, the humidifier and cooling coils need to be protected from freezing. Thus, the preheat coil is used to temper the outside air to 38°F to 45°F (3°C to 7°C) when the outside air is below freezing. The preheat coil and reheat coil can be used when heating is required. The reheat coil used with the cooling coil allows precise humidity control. the supply fan and fan have the same flow rate, the system is said to be in a "balanced condition." Many designers size the exhaust fan at about 80% or- 90% o W flow of th fan provide 'light building -- pressurization (about 0-05 in. H70 [ l 2 PA1). The intent is to prevent normal infiltration of airborne dirt, odors, and pollen from the outside into the building. Figure 7.3b is a line diagram illustrating the same system as that of Figure 7.3a. In the rest of this chapter, line diagrams will be used to illustrate systems. The components of the following systems are the same as those shown in Figure 7.3a and 7.3b.

Constant Volume, Terminal Reheat The constant volume, terminal reheat system is intended to serve many HVAC control zones, as illustrated in Figure 7.4. This system can have an economizer as can all the following systems. The supply fan provides cooled air to each zone, where it is reheated to the temperature required to maintain comfort conditions within that zone. The airflow rate through the system is constant, and control is achieved by varying the heat input to each reheat coil. This system is capable of achieving a high level of temperature and humidity control for each zone. However, terminal reheat is not very energy efficient.

Variable Air Volume The variable air volume system varies the supply rate of conditioned air to the space to maintain comfort conditions. Additionally, the temperature of the supply a'' may be varied. There are many a ~ ~ r o a c h efor s achieving variable flow. In the system depicted in Figure 7.5, flow to each zone is controlled by a damper or other flow control device in the VAV unit. This unit is sometimes referred to as the VAV terminal box. Generally, the supply and return fans are capable of variable flow rates alld are controlled by the static pressure sensors. Some of the approaches that are used to achieve variable flow rates through fans are variable pitch inlet

Louver Exhaust Air +-

\

Exhaust Damper

/

Relum Fan C

C

(a) Diagram showing duct thickness Exhaust

,,n /

Return Fan

Exhaust AirC Return Air

Humidifier

/ ,Cooling

Coil

/ Outside

Outside Filter Preheat Air Damper . , Coil

\Reheat

Bu113ing Spaces

Coil

(b) Diagram with line representation of duct

Figurc 7.2 Si17gIe-jbr7sysletr,.

Figure 7.3 Corisfanfvolume, single-zone sysfem.

Chapter 7-Air Moving Equipment and Systems

1 Reheat Coil -

Exhaust Exhaust Air

Humidifier

Retum Air Damper

I

-U

Outsid Air

Supply Fan Outside Air Damper

Filter

Preheat Coil

Figure 7.4 Constant volrtnze systern with terminal reheat.

Figure 7.5

Vasiable-air-volunze(VAC.') system

vanes, discharge dampers, variable pitch motor sheaves, eddy current couplings, variable speed DC motors, and variable frequency AC motor speed controllers. As with constant voiunie systems, VAV systems can be designed to provide building pressurization.

systems have been used in multi-room buildings to accommodate highly variable heating and cooling loads. A dual-duct system can be constant volume or VAV. Operating costs of VAV dual-duct systems are less than those of the constant volume systems.

Dual Duct

FANS

The dual-duct system co~lditionsall the air at a central location and distributes it to the conditioned spaces t h r o ~ ~ gtwo h supply ducts. One duct conveys cold air, and thc other warm air (Figure 7.6). A mixing box supplying each zone combines the two airstreams in the proper proportions to achieve comfort conditions. These

ANSIIASHRAE Standard 149 (ASHRAE 2000b) establishes methods o f laboratory testing and documentation for fans used for smoke exhaust. There are two general fan classifications-xentrifugal and axial. Figure 7.7 illustrates the basic parts of a centrifi~galfan. Flow within a centrifugal fan is prima-

Principles of Smoke Management

rily in a radial directiod to the impeller. Figure 7.8 illustrates the basic parts of an axial fan. Flow within an axial fan is parallel to the shaft.

Centrifugal Fans

,

.,

Centrifugal fans used in the HVAC industry are generally classified by impeller design as forward curved, backward curved, and airfoil (Figure 7.9). Forward-curved centrifugal fans rotate at a relatively low speed and are generally used to produce high flow rates and low static pressures. Backward-curved fans rotate at about twice the speed of forward-curved fans and have a higher efficiency. The higher rotational speed requires more expensive fan construction. Both forward- and backward-curved impeller blades are single width, stamped from sheet metal. Airfoil fans are basically backward-curved fans with blades of varying thickness to improve fan efficiency. Airfoil blades are designed using the same airfoil technology that is used to design airplane wings. Required performance and economics are major factors in the selection of a fan type for a particular application. However, the following generalizations can be made concerning application. Fonvard-curved fans are used for low-pressure HVAC applications, including c

l

?

equipment. Airfoii and backward-curved fans are used for general purpose HVAC applications, and airfoil fans are usually limited to large systems where the enernv savings are significant. ~ubuGcentrifugalfans (Figure 7.10) are an exception to the classification by impeller type. Generally,

Exhaust Exhau

Air

Outsid Air

Damper

Figure 7.6

Coil

D~~nl-dz/cl sysletil.

Return

these fans have single-width impeller blades and straightening vanes to direct air parallel to the shaft. Tubular centrifugal fans are primarily used for low-pressure HVAC applications, particularly as return air fans. These fans have significant space savings over other centrifugal fans. - Backward impeller rotation is a common problem with systems with centrifugal fans. It is important to note that backward rotation of centrihgal fans results in reduced flow in the normal direction. This problem is often not recognized because of the mistaken belief that backward rotation of these fans results in backn.ard flow. The normal direction of airflow and the direction of rotation of centrifugal fans is shown on Figure 7.7.

Axial Fans The common types of axial fans used in buildings are propeller fans, tubeaxial fans, and vaneaxial fans (Figure 7.11). For propeller fans, a variety of impeller designs are employed with the intent of achieving high flow rates at low pressures. The irnpellers of propeller fans have two or more blades and are usually of inexpensive construction (for example, these blades are often stamped from sheet metal). Propeller fans are used for low-pressure, high flow rate applications, including kitchen exhaust, toilet exhaust, stairwell pressurization, and space ventilation. Tubeaxial fans have a higher efficiency and can operate at higher pressures than propeller fans. Vaneasial fans have still higher et'ficiencies and operating pressures. Blades of tubeasial and vaneaxial fans can be

Chapter 7-Air Moving Equipment and Systems

Direclionof

Bla

Rim

Impeller

Figure 7.7 Centrifugal fan components.

Guide Vane

Inlet Bell,

Head

Figure 7.8 Axial fan coniponetits.

Forward-Curved 24 to 64 Blades About 65% Efficiency

Backward-Curved 10 to 16 Blades About 75% Efficiency

Figure 7.9 Itq~ellertypes for centrifugal fans.

Airfoil -10 to 16 Blades About 80% Efficiency

-.

. .

Principles of Smoke Management

single thickness or airfoil design. Adjustable pitch blades' are used on some vaneaxial fans to obtain high efficiency. Both tubeaxial and vaneaxial fans have the advantages of straight-through flow and compact installation. Tubeaxial fans are used for low- to medium-pressure HVAC applications, and vaneaxial fans are used for low- to high-pressure HVAC applications. Unlike centrifugal fans, backward rotation of an axial fan normally results in backward flow. This backward flow is at a reduced airflow rate. More information about both centrifugal and axial fans is provided by Jorgensen (1 953), ASHRAE (2000~)and AMCA (1 990a, 1987).

DAMPERS In air-moving systems, dampers are used to balance airflow, control airflow, resist the passage of fire, or resist the passage of smoke. Balancing dampers are used in supply ducts and return ducts to adjust the airflow to the design values. These dampers can be of simple construction (Figure 7.12) or of multi-blade construction (Figure 7.13).

Centrifugal Impeller

Multi-blade dampers operated by electric motors or pneumatic pistons to vary the flow rate are called control dampers. Dampers used to resist the passage of fire are called fire dampers, and these can be multi-blade dampers (Figure 7.13) or curtain dampers (Figure 7.14). Dampers used to resist the passage of smoke are called smnke dampers, and these can also be either multi-blade or curtain. Combination dampers can be used to balance airflow, control airflow, resist the passage of fire, and resist the passage of smoke.

Fire Dampers Generally, multi-blade fire dampers are held open by a fusible link and are spring loaded. In a fire situation, hot gases cause the link to come apart, allowing a spring to slam the blades shut. In place of fusible links, some manufacturers use other heat responsive devices. In the United States, fire dampers are usually constructed and labeled in accordance with standard UL 555 (UL 1999). Prasad (1995) tested the ability of fire dampers to close under conditions of still air, airflow, ambient temperature, and elevated temperature. In response to the findings of Prasad's findings, the 1999 version of UL 555 includes closure tests for static system (with no airflow) and dynamic systems (with airflow). The dynamic tests can be at ambient temperature, 250°F (120°C) or 350°F (180°C).

<

J r . Propeller Roof Exhaust Fan About 25% Efficiency

1

-

Vaneaxial Fan About 70°h Efficiency

. Duct

Y

Arm'

Splitter Damper

c Round Damper

Figurc 7.12 Dotuper types ~tscdjorDalot~ci/~g.

Emciency

am-

Figure 7.11 Types of axial fans.

Figure 7.10 fitbular cent/-ifugalfan.

-

Wall Fan

Propeller Roof Fan About 25% Efficiency

Tubeaxial Fan About 55% Efficiency

Straightening Vanes

I

Propeller

Rectangular Damper

Chapter 7-Aii Moving Equipment and Systems

Channel Frame

\ Shafl

7

/

Shafl Extension

Blade

Angle stop \

J

l

Section

Opposed Action Damper

Note: Horizontal (floor) type curtain dampers must have spring closure, but vertical (wall) type curtain dampers can have either spring or gravity closure.

,Channel Frame

--

7=

Shafl

Extension

Parallel Action Damper

Figure 7.14 Cut-~ait~fii-e cinirpet:

Seclion

Ill, and the maximum leakaze rarts are listed in Table 7.1.

Smoke Dampers

Thc particular class of damper specified -should be --selected based on the requirements of the __-._.. application. - For example, the dampers i n the supply and return ducts can have some leakage v-ithour adversely afi'scringsmoke control system performance. Thus, a de&a-cr might select class I I or I l l smoke dampers for such an application. However, a designer might choose clzss 1 dampers for applications that require a very right damper, such as a return air damper (Figure 7.3). ~-

In the United States, smoke dampers are usually constructed and classified for leakage in accordance with standard UL 555s (LL 1999a, 1999b). The standard includes construction requil-ements and tests for cycling, temperature degradation, dust loading esposure, salt-spray exposure. air leakage, and operation under airflow. These dampers are classified as I, 11, or

Y

2__

-

Table 7.1: L e a k a g e Classifications f o r S m o k e D a m p e r s (Adapted from UL 5558 [UL 19991) At

1.0 in. H 2 0 (250 Pa)

Classification

cfmtft?

I

4 10

II II

I II II

m3s-'m-'

0.020. 0.05 1 0.203 40 At 8 in. H20 (2000 Pa) II 0.056 2s 0.147 112 0.569

At 4.0 in. H 2 0 (1000 Pa)

cim/it2

,,,Zs-l n,-3

0.04 I 0.102 0.406 A t 1.2 in. 1{20 (3000 Pa) 14 0.07 1 S

20 SO

7

-

>. 3

130

0 . L 7s 0.7 1 1

CHAPTER 8

Computer Modeling moke management applications of computer modeling have increased dramatically in the last few decades. Many computer models have been developed for fire science and fire protection engineering applications by a number of organizations. Many of these applications are very useful for smoke management design. The Smoke 1\4anagen7ent Progt-am CD that accompanies this book contains a number of computer applications that can be useful for smoke managenlent (Table 8.1). Most of these programs were developed at the National Institute of Standards and Technology (NIST). The NIST computer applications are in the public domain, \\ hich means that they are not covered by copyright protection and they can be freely copied and used by anyone. The computer applications on the CD can be classified as building airflow models, zone fire models, detector actuation models, CFD models, elevator evacuation model, 2nd collections of engineering tools. This chapter is a g e ~ e r a ldiscussion of these classes of models except for CFD models and the elevator evacuation model. The CFD models are dealt with in Chapter 17. The elevator evacuation model, ELVAC, is discussed in Appendix C. The treatment in this chapter is of a general nature. For details and equations of particular models, readers should see the documentation for the model. The equations in this chapter are only intended to describe some of the more important concepts of computer modeling, and these equations are not ~ntendedto be used for calculations. Accordingly, units are not given for variables of this chapter. However, all of these equations are valid for S1 units or any other I~omogcneousunit system (see Appendix A)

S

BUILDING AIR AND SMOKE n o w MODELS Computer programs that simulate building airflow can be useful for analysis of pressurization smoke control systems. Airflow programs that can simulate contaminates or smoke concentrations throughout a building can be useful tools for hazard analysis. The CONTAM program that is on the CD accompanying the book has air and contaminate flow capabilities. and it also is used for some of the examples of this book. A discussion of the earlier models provides a background for CONTAM. All of the airflow programs also calculate the pressures throughout the building. The National Research Council of Canada (NRCC) developed airflow programs (Sander 1974; Sander and Tamura 1973). The ASCOS program (Klote 1982) simulated airflow and was specifically developed as a research too1 for analysis of.smoke control systems. ASCOS was extensively used for smoke control design for much of the 1980s and 1990s. Yoshida et al. (1979); Butcher et al. (1969); Barrett and Locklin (1969): Evers and Waterhouse (1978); and Wakamatsu (1977) developed programs that also simulate smoke concentrat;ms.

Network Models These models represent a building by a net\vork of spaces or nodes, each at a specific pressure and temperature. The stairwells and other shafts can be niodeled by a vertical series of spaces-ne for each floor. Air flows through leakage paths from regions of high pressure to regions of low pressure. These leakage paths are doors and windows that may be opened or closed. Leakage can also occur through partitions, floors, and exterior

Chapter 8- Computer Modeling

Table 8.1: Computer Software ~ ~ ~ l i c a t i o innthe s Smoke ~anagement progmms CD' Software Classification Building Air and Smoke Flow Zone Fire

Name CONTAM ASET-C CFAST LAVENT JET AZONE

Detector Actuation DETACT-QS DETACT-T2 CFAST LAVENT JET Elevator Evacua- ELVAC tion Collection 01' Engi- ASMET neering Tools FAST I.

Comments Airflow analysis including contaminants Available Safe Egress Time - C++ Language Version is part ofthe ASMET package of engineering tools. Consolidated Fire and Smoke Transpott Model Model for the Prediction of Detector Activation and Gas Temperature in the Presence ofa Smoke Layer Model for the Prediction of Detector Activation and Gas Temperature in the Presence 3f a Smoke Layer Atrium zone fire model includes plugholir,g anddelayed smoke exhaust fan activation (Cha~ter141 Detector Actuation - Quasi Steady Detector Actuation - Time squared Detector actuation is one feature ofthis zone fire model Detector actuation is one feature of this zone fire model Detector actuation is one feature of this zone fire model Elevator Evacuation Atria Smoke Management Engineering Tools A collection of equations and fire protection engineering tools including CFAST

Note: All progmnis liskd in this table are public donlain sofiwnre developed by NIST, except for AZONE. which was devslopcd by John H. Klote. Inc.

walls and roofs. The airflow through a leakage path is a function of the pressure difference across the leakage path.

3. The net air supplied by the air-handling system or by the pressurization system is assumed to be constant and independent of building pressure.

In this model, air from outside the building can be introduced by a pressurization system into any level of a shaft or even into other building spaces. This allows simulation of stainvell pressurization, elevator shaft pressurization, stairwell vestibule pressurization, and pressurization of any other building space. In addition, any building space can be exhausted. This allows analysis of zoned smoke control systems where the fire zone is exhausted and other zones are pressurized. The pressures throughout the building and steady floii7 rates through all the flow paths are obtained by solving the airflow network, including the driving forces, such as wind, the pressurization system, and inside-to-outside teniperature difference.

4.

The outside air temperature is assumed to be constant.

S.

The barometric pressure at yound level is assumed to be standard atmospheric pressure (1 0 1325 Pa).

The assu~nptionsof the ASCOS model are similar to other network nlodels, and these assumptions are:

The results of the program are not very sensitive to changes in atmospheric pressure. For altitudes considerably different from sea level, a more accurate value of barometric pressure can be substituted by changing a statement in the subroutine INPUT and one in the subroutine CORR. The following is a simple overview of a nehvork model. This overview only considers one flow path between any two nodes, but mar,y network models allow a number of flow paths between the same two points. The mass flow in a path between two nodes can be represented as

1. Each space is considered to be at one specific pressure and one specific temperature. where 2.

Thc flows and leakagc paths are assumed to occur at midheight o f e a c l ~Icvcl.

d, - . = '1

mass tlow from node i to nod? j,

Principles of Smoke Management

functional relationships appropriate for a path between nodes i and j, pressure difference fiom node i to node j.

I

~,

A number of functional relationships for flow are discussed in Chapter 6. Possibly the orifice equation and the exponential equation are the most ccmmon such functions. A function can also be used to represent the flow of a fan, which is an exception in that fan flow is from a node of lower pressure to a node of higher pressure. The pressure difference can be expressed as Ap.. 'J = p;-p.+p;g(Z;-Zj) J

(8.2)

where pi = pressure at node i,

fi

=

pressure at node j,

pi

=

density gas at node i,

Z,

=

elevation of node i,

5

=

elevation of node j,

The solutior?to this set of equations is the pressures @,,P*,

... pN) for which all the right-hand side is zero. From these pressures, all of the pressure differences and flows throughout the building can be calculated. Because of the difficulty in solving these equations, the numerical routines of many of the above models were slow and would sometimes fail to converge to a solution. Such convergence failures seemed to happen more often with large and complicated networks. An ASHRAE-funded research project (Wray and Yuill 1993) evaluated several algorithms to find the most appropriate one for analysis of smoke control systems. They selected the AIRNET routine developed by Walton (1989) as the best algorithm based on successful convergence, computational speed, and use of computer memory. None.of the routines of this study take advantage of the repetitive nature of building flow networks, so data entry for these routines is difficult and time consuming.

CONTAM Model

(8.3)

There are two versions of this model: CONTAM96 (Walton 1997) for use with the DOS operating system and CONTAMW (Dols et al. 2000) for use with the Windows 95, 98, or NT operating systems. The technical aspects of these models are the same, and they are referred to in this section simply as CONTAM. A simple user guide for getting started with CONTAM is provided in Appendix D.

where M is the number of flow paths between node i and other spaces. The mass flows entering node i have negative values. Writing the conservation of mass equations for each node in the building results in

CONTAM uses an improved version of the AlRNET algorithm that was selected as the best algorithm in the study mentioned above. Further, CONTAM has a method of graphical data input that reduces both learning time and the likelihood of input errors.

g = acceleration of gravity.

For steady flow, conservation of mass at node i can be stated as the sum of the mass flows leaving node i are zero. In equation form, this is ,it

C/;J(A~rJ)= 0 / = I

f l ~ ( & ~+fl2(Aplr) l) + ... +fl.\i(A~lh.) = 0

1

f2,(&2l) +f22(Ap22)+ ... +J;v(@2,v) = 0 , (8.4)

Substituting Equation (8.2) into the ab0L.e set of equations yields

CONTAM was developed for indoor air quality applications, but it has been extensively used for smoke management applications. This model simulates contaminant flow, as well as airflow throughout a building. For smoke management applications, the contaminants can be the products of combustion. The CONTAM documentation considers the model to be a multi~rrnemodel where the zones would be rooms or floors of a shaft. The CONTAM model does not include an energy equation, and so the temperature of zones needs to be designated by the user. CONTAM is like the network models above except that it treats pressures and flow paths in a more general way.

where Fiis the functional relationship for flows into node i. Equation (8.5) is a set of sin~ultaneousnonlinear equations.

The pressure in room i is considered hydrostatic, and it can be represented as

Chapter 8-Computer Modeling

0

Pressure

(a) Sketch of a room fire

Figure 8.1 Bidirectional flow through an opening between two zones.

P i = pio- Pig'

(8-6)

where

pi

=

pressure in zone i at elevation z,

pi, = pressure at the floor (z= 0) of zone i,

g = acceleration of gravity, pi = density of air in zone i,

z

=

elevation above the floor of zone i.

The representation of pressure allows for simulation of bidirectional flows between two zones connected by a flow path. Such bidirectional flow can occur when two zones at different temperatures are connected by a flow path (Figure 8.1). This is not relevant for smoke control systems that rely on pressurization, but it could be significant for simulations of smoke transport that does not include pressurization. For flow paths specified at midheight of the floor, airflows, and pressures calculated by CONTAM are the same as, those of ASCOS within the limits of numerical convergence.

ZONE FIRE MODELS Zone fire models have proven utility for many fire protection applications, including hazard analysis. The concepts behind this type of fire model are the basis of most of the engineering approaches to smoke management design for atria. Early zone fire models include the Harvard Code (Mitler and Emmons l98 l), ASET (Cooper 1985), the BR1 Model (Tanaka 1983), and CCFM (Cooper and Forney. 1990). The University of Maryland has made modifications to CCFM specifically for atrium smoke management design (Milke and Mower 1994). The models ASET-C, CFAST, LAVENT, and JET are discussed below. Because zone models were originally developed for room fires, this discussion will start with room fires. In a

N

I

Fire

C

-

Airflow

C

\ \ \ \ \ \ \ \ \ \ \ L (b) Zone model idealization of a room fire

Figure 8.2 Rooni .fire(a) sketch m d (b) zone model ideafiinrion.

room fire, hot gases rise above the fire, forming a smoke plume. As the plunle rises, it entrains air from the room so that the diameter and mass flow rate of the plume increase with elevation. Accordingly, the plume temperature decreases with elevation. The fire gases from the plume flow up to the ceiling and f o m ~a hot stratified layer under the ceiling. The hot gases can flow through openings in walls to othcr spaces, and such flow is referred to as a doo~jer.The doorjet is similar to a plume in that air is entrained and the mass flow rate and crosssectional area of the jet increase with elevation, and the jet temperature decreases with elevation. Ths difference is that the doorjet is tlowing through an opening in a wall. Figure 8.21 is a sketch of a room fire. The concept of zone modeling is an idealization of the room fire conditions, as illustrated in Figure 8.2b. For this idealization, the temperature of rhs hot upper layer of the room is unifonn and the temperature of the lower layer of this room is also uniform. The height of the discontinuity bttween thcse layers is the same everywhere. This discontinuity i s called the smoke layer inre&ce. In the idealized modcl, at an infinitesimal distance above the intcrfice, the temperature and contaminant concentrations are thosc of the smoke laver. At an

Principles of Smoke Management

infinitesimal distance below the interface, the temperature and contaminant concentrations are those of the lower layer. However, in real fires, there is a gradual transition rather than an interface. The dynamic effects on pressure are considered negligible, so that the pressures are treated as hydrostatic. Other properties are considered uniform for each layer. Algebraic equations are used to calculate the mass flows due to plumes and doorjets. Many zone computer models allow exhaust from the upper layer, and this capability is essential for simulation of atrium smoke exhaust systems. Many of the computer zone models estimate heat transfer by methods ranging from a simple allowance as a fraction of the heat released by the fire to complicated sin~ulation, including the effects of conduction, convection, and radiation. Zone model application to an atrium fire is illustrated in Figures 8.3a and 8.3b. Rockett et al. (1987) compared measured data with data computed by the Harvard Code for a series of fires at the NIST Annex. The temperatures for one of those fires are shown in Figure 8.4. It can be obseryed that the temperature for the bum room is well represented by the zone fire model idealization. However, the temperatures in the corridor and lobby are only very roughly approximated by the zone fire model. This supports the opinion that zone model predictions are less realistic for spaces away from the fire room. For more general information about zone fire models, readers are referred to Karlsson and Quintiere (2000), Friedman (1992), Jones (19S3), Mitler and Rockett (1986), and Mitler (1984) and Quintiere (l989a).

m,

=mass in the upper layer,

m,,.,,

=mass flow rate into the upper layer,

r ; i , out

=mass flow rate out of the upper layer.

The mass flow rates in Equation (8.7) depend on the specific computer model. ASET-B only simulates the plume flow into the upper layer with no allowance for mass flow out of the upper layer. For this model, ril,. in is the mass flow of the plume and ril,, is zero. For more complex multi-room zone models, nz,, is the sum of all mass flows into the upper layer (plume, doorjet from another room, HVAC flow, etc.) and ril,, is :he sum of all mass flows out of the upper layer (doorjet from another room, HVAC flow, etc.).

..,

The conservation of energy equation is also known as the first law of thermodynamics. Because potential energy and kinetic energy are relatively small, they are neglected, and the energy equation for the upper layer is

Mathematical Description Many of the early zone fire models were quasisteady systems of algebraic equations, and the atrium zone fire model, AZONE, discussed in Chapter 14, is based on this approach. Other models are differential equation-based, and this section is intended to provide some idea.of the theory behind these differential equation-based.models. The upper and lower layers of a one-room zone fire model form control volumes, as illustrated in Figure 8.5. In general, the approach to zone modeling is to write the conservation equations for the upper and lower layers. ASET-B is an exception in that equations are only written for the upper layer. The equation of conservation of mass for the upper layer is

I

(a) Sketch of a n atrium fire

Plume

(b) Zone model idealization of atrium fire

Figure 8.3 All-izrm snzoke e.~hatrst (a) sketch a ~ i dfb) zone model idealizutioti.

Chapter 8-Computer Modeliig

F

Temperature Rise CC)

i

Corridor

'8 6 A

25

50

75

I

I

1

100 .

1

.

-

E Note: 8 indicates thermocouple tree. Temperature Profiles: +Measured - - Calculated from Zone Fire Model

Burn Room

I

-

0

50 100 150 Temperature Rise CF)

Temperatxe Rise)C"(

Temperature Rise ("C)

Temperature Rise ('F)

Temperature Rise CFj

Figure 8.4 ~lfecrswedtriid corrrpli~ecl/et,rpera/u~epru/iles d i e /oa 100 kW/;/-e 200 sccoi~ci.~ j a i n RocA-et/ et al. [I 98 71).

Control Volume Boundaries

..............................

I

I I

l

Upper Layer

I I

I I

I

L, hUJeu

I I

TJ h,, e,

Opening in Room

Lower Layer

Figure 8.5 C'orlrinl ~ ~ ) h i i i m , /zq)pei. u i aiitl loi\vi- 1cg~er.suj'ci

.viirplc inoirl zoilejiir iiroclcl.

200

ipition (rrdapted

Principles of Smoke Management

where

Q

=

W

=

h , i,, h,

,

ell

heat transferred to the upper layer,

work done by the smoke layer on the surroundings, = enthalpy of the mass flow into the upper layer,

For an ideal gas, Cp, C, R, and y are constants (Appendix A). The time derivative of Equation (8.10) is

enthalpy of the mass flow out of the upper layer, = internal energy of the upper layer. =

The heat transfer term, Q,, should not be confused with the heat release rate of a fire. The heat transfer term is for thermal energy that flows into the upper layer due to a temperature difference. Because the upper layer is relatively hot, the term Q,, is generally negative (for example, heat conduction and thermal radiation from hot smoke to the walls). Work is the product of a force, F, acting through a displace~ent,I (in differential form, work is dW = Fdl). The displacement for the upper layer is the moving smoke interface, which is also the surface of the control volume. The force is the product of absolute.pressure at the interface and the area of this surface ( F = pAJ. The work term is

Most zone fire models consider the gases to behave as ideal gases, and an ideal gas is one that has the following equation of state: PI.' = I I I R T

Substituting this into Equation (8.9) results in

Combining Equations ( 8 4 , (8.1 l), (8.12), (8.13): and (8.16) yields

Equation (8.17) is a form of the conservatix of energy equation for the upper layer. The following conservation of mass and energy equations for the lower layer can be developed in a similar manner:

and

(S. 10)

where p = absolute pressure, V = volumeofgas, m = mass of gas, R = gas constant, T = absolute temperature of gas. The enthalpy of an ideal gas can be expressed as

The conservation equations can be rearranged as

where C,, is the constant pressure specific heat. The internal energy of an ideal gas can be expressed as

where C,.is the constant volume spzcific heat. The gas constant of an ideal gas is

The ratio ofspecitic heats, y. is

E,,

=

net energy release rate for the upper layer,

Chapter 8-Compuier Modeling

8,

=

net energy release rate for the lower layer,

V = room volume (V = V, +

5).

Equations (8.20) through (8.23) were developed by Jones (1983), and readers should see that reference for a detailed description of the net energy release rate terms. Information about solution of such systems of differential equations can be found in many texts on numerical methods (for example, Burden et al. 198 1). Equations for plume mass flow and temperature are discussed in Chapter 13. Flow through doors and other openings in walls or partitions are calculated in much the same way as horizontal flow through an opening, which is treated in Chapter 13, except that the pressures are complicated by the possibility of both air and smoke on both sides of the opening.

ASET-C Model ASET-C (Available Safe Egress Time-C Language) is a program for calculating the temperature and position of the hot smoke layer in a single room without smoke flow to other spaces. ASET-C is one of the simplest and easy to run zone fire models. As stated above, ASET-C only simulates the upper or smoke layer. The lower layer is considered to remain smoke free and at ambient temperature. ASET-C is an adaptation of the ASET-B (Walton 1985), and it is one of the engineering tools in the ASMET package. Documentation is provided in Appendix E.

controlling vents and sprinklers in compartments bounded by walls, draft curtains, or combinations of walls and draft curtains. The JET model incorporates the conductivity factor to account for the effects of heat conduction from the sprinkler head.

DETECTOR ACTUATION MODELS Fire-driven ceiling jets can have a significant impact on the performance of ceiling-mounted detection hardware. The plume rises above the fire. As it impinges on the ceiling, the plume gases turn and form a relatively high temperature, high velocity, turbulent ceiling jet, which flows radially outward (Figure 8.6). The temperature and velocity of the ceiling jet are described by Albert's (1972) correlations. The detector actuation model, DETACT-QS, calculates the actuation time of thermal devices below unconfined ceilings (Evans and Stroup.1986). The unconfined ceiling assumption is appropriate for large spaces, such as open plan ofice spaces, but it does not account for the effects of the smoke layer on the ceiling jet in a confined space. Figure 8.7 is a sketch of a ceiling jet in a room with a smoke layer. For a fire below the smoke layer, the plume penetrates thc smoke interface, continues to rise toward the ceiling, and entrains smoke from the smoke

.....

CFAST Model CFAST is a multi-room zone model that predicts the effect of a specified fire on temperatures, various gas concentrations, and smoke layer heights in a multi-compartment structure. CFAST has many features, including forced ventilation, detector activation, and conductive heat transfer. CFAST is the primary engineering tool in the FAST package (Peacock et al. 2000). For a technical description of CFAST see Jones et al. (2000).

LAVENT Model LAVENT (Davis and Cooper 1989) is a single room zone fire model that predicts plume centerline temperature, ceiling jet temperature, and ceiling jet velocity. LAVENT can determine activation times of fusible links controlling vents and sprinklers in compartments bounded by walls, draft curtains, or combinations of walls and draft curtains.

JET Model Like LAVEKT, JET (Davis 1999) is a s~ngleroom 7one fire model that prcdicts plume centerline tempera-

ture, ceiling jet temperature, and ceiling jet velocity. SET also can determine activation times of fusible links

Detector

(a) Sketch of ceiling jet and detector

Ceiling

Note: The ceiling jet flows radially from the point wher the plume impinges on the ceiling. (b) Idealized ceiling jet flow

Figure 8.6 Ceilitig j e ~rmder a Jar ceilirrg. mid (b) idealizcd,/lo~c!.

(0)

skerch

Principles of Smoke Management,

Geiector Ceiling Jet smoke Layer

I

1

Figure 8.7 Sketch of roomfire showing ceiling jet and smoke layei:

layer. When the ceiling jet reaches the walls, the flow turns downward. The effects of the smoke layer on ;he ceiling jet'are taken into account in the zone fire models CFAST and JET. I

I

The detector models account for the thermal lag of detectors by use of the response time index (RTI), as discussed in Chapter 2. The RTI approach is appropriate for the fusible links of sprinklers and smoke and heat vents.

CHAPTER 9

Hazard Analysis ost smoke management systems provide smoke protection by minimizing people's contact with smoke or by keeping smoke completely away from people. As the name implies, tenability systems provide smoke protection by maintaining tenable conditions. Tenability svstems allow smoke contact, but the systems are designed such that the temperatures and concentrations of combustion products are limited. An analysis of these systems is called a hazard analysis, in that the level of hazard to life is evaluated. Technological advances have made hazard analyses feasible, and tenability systems based on such analyses have gained a level of acceptance in the last decade. NIST developed a group of computer programs, HAZARD I (Peacock et al. 199l), for hazard analysis in spaces consisting of a relatively few rooms, such as residences. Bukowski and Spetzler (1992) used HAZARD I to reconstruct the fire at the Happyland club in the Bronx, New York, that killed 87 persons. Klote et al. (1992) extended hazard analysis to large multi-story buildings for the study of staging areas for persons with mobility limitations. Hazard analysis is a powerful fire protection tool that has application beyond smoke management. This tool can be used to evaluate alternative building materials and furnishings. The most common smoke management applications are compartmentation and atrium protection. Compartmentation systems can be with or without pressurization. The atrium systems can have any con~binationof smoke filling, smoke exhaust, or natural smoke venting. Jt is also possible to use hazard analysis to evaluate the efect of component failure.

M

HAZARD ANALYSIS CONCEPT For a particular fire, smoke moves through the building. As people evacuate the building, they are exposed to this smoke, which has the potential to impair vision and cause incapacitation or fatality. A hazard analysis can be used to calculate such smoke flow and the consequences for building occupants. A hazard analysis can consist of one or a number of fire scenarios. Hazard analysis consists of the following components: (I) fire scenario, (2) smoke transport, (3) people movement, and (4) tenability. Fire Scenario. As stated in Chapter 2, a fire scenario can be thought of as the outline of events and conditions that are critical to determining the outcome of alternative designs. In addition to the fire location and heat release rate, 0 , the fire scenario includes the status of the doors, the HVAC systems, the smoke management system, and other systems. For details about design fires, see Chapter 2. Species ( 0 2 , N2, CO, CO2, etc.) generation can be included in the fire scenario. The scenario may also include specifics about the fuel, ignition of multiple fuel packages, and the effect of fire suppression. The selection of the fire scenario can be based on professional judgement, analysis of historical fire data, or cods requirements. Smoke Transport. Smoke can flolv far from a fire and threaten life. The major driving forces that cause smoke movement are naturally occurring stack effect, buoyancy of combustion gases, expansion of combustion gases, the wind effect, fan-powered ventilation systems, and elevator piston effect. These driving forces are discussed in Chapter 5 .

Chapter 9-Hazard Analysis

As discussed in Chapter 3, smoke consists of the airborne particulates and gases evolved when a material undergoes pyrolysis or combustion, together with the quantity of air that is entrained or otherwise mixed into the mass. The evolved gases are part of the species mentioned above. Generally, when smoke flows away from a fire, the concentrations of particulates and evolved gases decrease. Conlputer models for smoke transport analysis are discussed later. People Movement. People movement in fire situations is complicated. Some people will fight the fire. Others move against the flow of evacuating people in an attempt to find or rescue loved ones. Scme computerbased evacuation models are capable of simulating the movement of individual people. As people move through the building, they are exposed to smoke. This time-integrated exposure can be used in tenability calculations. For iilfonnatioii about calculation of building evacuation 'time and a discussion of computer-based evacuation models, see Chapter 4. In many applications, consideration is made for people who are immobilized due to an accident or physical disability. Such a person would need to wait to be rescued, and the wait could exceed the-time needed for evacuation of the rest of the building. Tenability. Tenability calculations estimate the hazard to life of a scenario. Tenability calculations address one or more of the following: exposure to toxic gases, exposure to heat, exposure to thernlal radiation, and visibility through smoke. For calculation of exposures and visibility, see Chapter 3. The exposures are time-integrated doses of toxic gases, heat, and thermal radiation. These doses can be based on the smoke concentrations at several locations as people move out of the building. Alternatively, the doses can be based on the smoke concentrations at one locatio~~ while an inlmobilized person waits for rescue.

Level of Complexity The level of complexity of a hazard analysis depends on the particular application. Analysis of sowe of these co~ilponentscan consist of straightfonvard reasoning, and others require detailed c.~lculations. A feu. ways that a hazard analysis can be simplified are discussed below. Elinii~~ate Evacuation Simulation. For esposures based on proteering immobilized people, the need for a detailed c\:acuarion simulation can be eliminated, provided thar the design wiring is sullicie~ltlylong. This is because the esposurc iimc considered Ibr a \vaitirlg person \\.ould be rnuch greater than that fbr a person e\.acuaring the buildi~lg. While a detailed eixuation sinlulation may 1101 be ~iecdcd.an csrimatc of' building evaciraricm time may srill be dcsircd.

Eliminate Heat Exposure Calculation. Detailed heat exposure calculations are not needed if the maximum temperature is relatively low. For exposure times, Figure 3.7 can be used to make such an estimate. Eliminate Radiation Calculation. If exposure to heat does not cause incapacitation, exposure to thermal radiation wiil not cause incapacitation. Exposure to heat consists of direct bodily contact with hot smoke, and exposure to thermal radiation consists of receiving the radiant flux from hot smoke. If the smoke temperature is insufficient for heat exposure to be an issue, the smoke temperature is also insufficient for thermal radiation exposure to be an issue. Eliminate Toxic Gas Exposure Calculation. For many hazard analyses, visibility is the controlling tenability condition. The method described in Chapter 3, "Tenability and Perfect Dilution," can be used to determine if exposure to toxic gases is of concern for particular tenability criteria. (This same method can also be used to help determine if heat exposure is of concern for particular tenability criteria.) Alternatively, toxic gas exposures can be estimated by a simple method, such as the FED approach, to denionstrate that exposure to toxic gases is of concern. SMOKE TRANSPORT For niost applications, smoke transport calculations are done by computer. A wide range of computer models can be used, including ( l ) zone fire models, (2) network flow models, and (3) computational fluid dynamic (CFD) models. The choice of the model depends on the specific application. Smoke transport can also be evaluated by physical modeling (Chapter 15). Use of the zone tire model FAST and the network flow model CONTAM for hazard analysis is discussed later. For general information about zone fire models and building air and network tlow model:, see Chapter S. For general information about CFD n~odeling,sze Chapter lb. Many of theses ~nodelscan simulate production and transport orspecific gases (02, N2, CO1COZ,NO2, HCI. HCN, HBr, etc.), but sinlulation of specific gases is not generally necessary for design applications. Generation of the specific gases requires detailed knowledge of rhe fuel, \\.hicl1 is usually not available in desig~iapplications. The approach presented in this chapter is one of many possible zeneral methods of calculating tcnabilir?.. The mass of fuel consumed by the fire is

Principles of Smoke Management

mass of fuel consumed, lb (g); total heat release rate Btuls (kW); chemical heat of combustion BtuAb (kJ/kg);

1 (1000). The heat release rate, Q , and the mass of fuel consumed, riz , are entered into the computer smoke transport model, which calculates the concentrations of material burned, C, at every location and each time interval in the simulation.

TENABILITY CALCULATIONS The following is one of many approaches to tenability calculations, and more extensive information can be found in Chapter 3. Tenability analysis addresses visibility, gas exposure, and heat exposure. can The mass concentration of material burned, Ci, be obtained from zone fire models. The fractional effective dose.(FED) can be used to obtain an approximation of the effects of exposure to toxic gases.

where FED = fractional effective dose at the end of interval i (dimensionless); ci = concentration of material burned at interval i, Ibl At

=

fi? (gm3); time interval, rnin (min);

LCt,, = lethal exposure dose from test data, lb ft-' min (g min). This equation is for unifornl time intervals, as calculated by computer models, and it evaluates the FED for the exposure time at the end of interval i (expos~ve time is nAt). An FED greater than or equal to one indicates fatality. The concentration, C;, is the denisty of materials that started as fuel that have accumulated at a location during the interval i. The concentration has units of mass of the material burned per unit volunle. The lethal exposure dose, LCtjO, is the product of the LCjO and the exposure time. The LCjO is the concentration of airborne con~bustionproducts that is lethal to 50% of the subjects exposed for a specified time. An FED of 0.5 can be considered a rough indication of incapacitation. When a more accurate evaluation of tosic effects is desired, the methods discussed in Chapter 3 can be used. The fractional incapacitating dose (Fl,\;) method is generally considered to be more accurate. Unlike the FED method. calculation of F,,-,! requires calculation of species concentration. The gases considcsed can be lilnited

to 02, N2,CO2, and CO. This allows simulation of the synergistic effects of CO production and O2 depletion on toxicity of CO. Considering this and that the CO is the dominant toxic gas in building fires, limiting the gases to 02, N2,CO2, and CO is appropriate for many applications. For information about CO production in fires, see Table 2.1. For any instant, the visibility can be calculated from

where

Si

=

visibility at the end of interval i, ft (m);

K

=

proportionalityconstant (8 for illuminated signs, and 2 for non-illuminated signs);

6, = mass optical density, &lb (m21g); Ci = concentration ofmaterial burned in interval i, lb/ft3

(s/m3>. Generally, contact with dry air of temperatures greater than 250°F (1 2 1°C) can be expected to result in skin barns. Also, contact with dry air at a temperatuse less than approximately 250°F (121°C) leads to hyperthern~ia.For hyperthermia, heat exposure can be estimated from

where F,,/,= total cumulative dose (dimensionless); At = time interval, minutes;

?;. C,

=

temperature of air in interval i, "F ("C);

=

5.670 (5.185);

C2

=

0.0152 (0.0273).

Incapacitation due to heat exposure would be .*.:,>.... . expect 0

0 . lL:.

Pa

.,>.,

ll..XJl

74.9

0.25:

02.7

1l.luS

74.1

5 . .

IIIL.C prcwlrc d i l k r c ~ ~ c :ire c s tt i11li11 t l ~ cd c s i :~: i ~i i i t ~ w ~;d ~ III:~~~ KIU~ CI. ~ I I I I

164

I

Principles of Smoke Management

U

L 2

0

0.1 0.2 0.3 Pressure Difference (in. H,O)

0

0.4

0.1 0.2 0.3 Pressure Difference (in. H,O)

0.4

(a) Elevator pressure differences in winter

(a) Elevator pressure differences in winter

Pressure Difference (in. H,O) (b) Elevator pressure'differences in summer

Pressure Difference (in. H,O) (b) Elevator pressure differences in summer

Note: Stairwells are not pressurized.

I

~;0'12

-0.06 0 Pressure Difference (in. H,O)

L I

0.06

(c) Pressure difference from stairwell to building

G] 0

0.05 0.10 0.15 'Pressure Difference (in. H,O)

I

0.20

(c) Pressure difference from stairwell to building

Figure 11.4 P~zssuredifference profiles calculated by CONTAM for a presszrrized elevator in bzrilding with outside exterior doors open (Esa/nple 11.4).

Figure 11.S Pressure difference profiles calculated by CONTAM for a presszrrized elevator in building with outside exterior- doors open (Examnple I 1 S).

States and the Natio~ial Research Council of Canada (NRCC) to evaluate the feasibility of using elevators for the evacuation of the handicapped during a fire (Klote and Tarnura 1987, 1986a, 1986b; Tamura and Klote 1988, 1987a, 1987b). Before this joint project, Klote (1984, 1983) conducted field tests of several elevator pressurization systems. It shoi~ld be emphasized that conventional elevators do nor ha\-e any protection

scheme for fire evacuation, and fire evacuation by these conventional elevator systems is not recommended.

Concerns about Elevator Evacuation This section provides a description of many concerns about elevator evacuation, and the nest section discusses these concerns along with one approach to

Chapter 11-Elevator Smoke Control

deal with them. The 1976 edition of the Life Safity Code (NFPA 1976) listed the following "problems" involved with the use of elevators as fire exits:* Persons seeking to escape from a fire by means of an elevator may have to wait at the elevator door for some time, during which they may be exposed to fire, smoke, or developing panic. Automatic elevators respond to the pressing of buttons in such a way that it would be quite possible for an elevator descending from floors above a fire to stop automatically at the floor involved in the fire and open automatically, exposing occupants to fire and smoke. Modern elevators cannot start until doors are fully closed. A large number of people seeking to crowd into an elevator in case of emergency might make it impossible to start. Any power failure, such as the burning out of electric supply cables during a fire, may render the elevatois~noperativeor might result in trapping persons in elevators stopped between floors. Under fire conditions, there might not be time to'pemiit rescue of trapped occupants through emergency escape hatches or doors. I t is common for elevators serving more than three floors to dsscend autoniatically to the ground floor in the e\;ent of a fire. Fire fighters have keys to control elevators rnaiiually during building evacuation and fire fighting. However, smoke infiltration into hoistways frequently threatens lives and hinders use of elevators by fire fighters. In addition, there are three other concerns. First, water from sprinklers or fire hoses could short out or cause other problenls with electrical power and control wiring for the elevator. Second, shah pressurization cocld result in elevator doors jammhg open, limiting movement of the car. Third, piston effict could pull smoke into the elevator lobby or thc hoistway, and a method of preventing this has already been presented in this chapter.

Conceptual Solution for Elevator Evacuation The feasibility of elevator evacuation for office buildings and air traffic control towers is discussed by Klote et al. ( 1992. 1994). In order to overcome the concerns discussed in the preceding section, an elevator system used as a lire exit needs to have the following

S. This c'dition ol'the L i f i So/./,r Code \\as the last cditioii to list rhcsc "problen~s."

Elevator lobbies, hoistway, a i d elevator machinery room must be protected against fire and smoke. Elevator equipment and electrical power must be protected from the water exposure of sprinklers and fire hoses. Elevator machine room must be protected from overheating. Reliable electric power must be supplied. In areas of high seismic activity, elevator equipment must be protected from earthquakes. The likelihood that elevators will be available during fires needs to be ensured by use ofmultiple cars or by quick response maintenance contracts. Elevator control must ensure safe and efficient evacuation. Communications capabilities are needed between people waiting for elevators and the fire service or appropriate building personnel. Evacuation capacity of the elevator system must be adequate for the number of people intended to use the system. As previously stated, elevator cars are controlled so that they go to the ground floor in the event of a fire alarm. In the event of fire on the ground floor, the elevator cars go to an alternate floor. The fire department or other authorized personnel can then use the elevators for evacuation. Firefighters, police, and uniformed guards have positions of authority in our society. With the elevators controlled by such authority figures, the likelihood of a large number of people crowding into the elevator and making it impossible to close the doors will probably be reduced. Of course, there may be other approaches to elevator control that could allow orderly evacuation by elevators. Reliability of electric power consists of ensuring a source of power and ensuring continued distribution of power to where it is used. Considerable experience exists in ensuring the supply of electrical power for critical functions in hospitals, communication facilities, computer facilities, and the like. For these applications, a major concern is providing backuppower when power supplied by the local utility is interrupted. These applications operate most or all of the time, and they need highly reliable power for all the time that they operate. Fire evacuation by elevators is different in that this mode of elevator operation is only needed during a building fire. At most, the fire evacuation mode of an elevator would be expected to operate for a few hours per year. Thus, the probability of simultaneously having a fire and having the utility company's power interrupted is relatively small. However, the probability of having a power distribution failure during a fire is relatively high. This is because lire frequently damages

.

Principles of Smoke Management

electrical distribution within- buildings. Therefore, the power distribution to the elevator and associated smoke control fans should be such that it is highly unlikely that a fire could interrupt electrical power to this equipment. T h x e are numerous applications of electric power and electronic systems being designed and built to function when in contact with water. Street lighting and traffic lights operate during rain, -and swimming pool lighting operates underwater. In fact, some elevators operate on building exteriors where they are subjected to rain and the other elements. It is beyond the scope o f this manual to examine specific approaches to making these systems resistant to water; however, it is obvious that the technology exists to make elevator systems function when they are subjected to water. Considerable information is available concerning the fire resistance of walls, partitions, floors, doors, etc. The ability to design and build elevator lobbies and hoistways-that can withstand severe building fire has existed for years. Smoke protection for elevator systems is the topic of the next section. Elevator doors jam open wl:x the force of the door opener is insufficient to overcome the force .of friction. The friction force increases with the pressure difference from the hoistway to the lobby. In tall buildings, elevator doors frequently jam open during extremely cold weather. This is caused by stack effect induced pressure differences. Elevator mechanics commonly adjust the door-closing forces to prevent door jamming. During elevator smoke control operation. the possibilih of door jamming may decrease or increase. If the leaka,me area of the elevator lobby doors is less than that of the elevator doors, the pressure difference across the elevator doors can be less than that normally occurring. In field

I

Machinev Room ,,Lobby

tests conducted by Klote (1 984), no door jamming was encountered at pressure differences as high as 0.3 in. H 2 0 (75 Pa). When door jamming was encountered in an elevator without smoke control, it was found that only a small additional force applied by the palms of the hands was sufficient to prevent jamming. Fire fighters can be taught to overcome door jamming this way, and elevator doors could be fitted with grips or handles to aid in this effort.

Smoke Control Considerations Smoke control systems for elevator evacuation n u t provide smoke protection for elevator lobbies, hoistways, and machinery rooms. Protection of lobbies is essential so that people will have a safe place to wait for the elevator. Protection of the machinery room is important to prevent damage to elevator machinery. Figlire 11.6 illustrates a system that pressurizes the hoistway directly and indirectly pressurizes the elevator lobby and the machinery room. As stated for other pressurization systems, the flow rate of air is highly dependant on the leaka,oe area. Because these areas can only be roughly estimated in most situations, the fan needs to be sized conservatively so that the fan flow can be adjusted to acceptable levels of pressurization during system commissioning. This fan sizing can be by choice of high values of building leakage or of safety factors. Pressurization air can also be supplied to the elevator lobbies. Examination of the relative leakage areas of the elevator system provides insight into both hoistway and lobby approaches to pressurization. Considering the leakage from the elevator lobby to the outside to be negligible,

I

Machinery /Lobby Room / P

%

$ .I

Car

Pit

(a) Shaft Pressuriiation

Building Space

3: 4-

-I-

1' 1: ,

5

I

,;, ; ' , 4.. ,., ':.:.

Fan

,,;/ ,.

\

70

'

1

0

300

Figure 14.6

600

900

Zone F~reModels

g

1200

1500

'

-ASET-C

-

CFAST

10 1800

Time ( S ) Conzpar-isoiz of clear heights siti~ulated by d@wnt rnodels.

cussed in Chapter 2. As with the steady filling equation, the unsteady filling equation can be solved for time:

where Cej3 is 0.363 (0.937).

Computer Modeling The height of the smoke layer ajove the fuel is sometimes referred to as the clear- height, and Figure 14.6 shows a comparison of clear heights predicted by different zone fire n~odelsand the steady filling equation. These predictions are for a large atrium o f H = 100 ft (30.5 m) and A = 50,000 ft2 (5780 m2) with a steady fire of 5000 Btuls (5270 kW). It can be observed that the predictions of ASET-C and AZONE are close to each other. CFAST and the steady filling equation predict lower clear heights. The differences in predicted clear height can be attributed to inherent differences in the prediciive tools. These differences include ( l ) the plume models. (2) the definition of clear height, and (3) the approach to heat transfer. For each of the zone models, the mass flow of the plume is calculated from different plume models. As previously stated, the empirical equation is conscrvativc in that it predicts the clear height as the first

3 0

Figure 14.7

,a0

- 20

,e ,I 10

0

Time (S) Coinpar-isoil of snzoke 10-vet- tettpv-rrtwes sitnirlated!C d i f f e ~ utuodels. t

indication of smoke above the fire, as illustrated in Figure 14.3. The zone models predict the clear height as the smoke interface. For these reasons, it is expected that the empirical steady filling equation would predict lower clear heights than the zone models. Heat transfer was calculated differently for each of the zone models. The CFAST simulation calculated heat transfer to gypsum board walls and ceiling based on the temperature difference between smoke layer and the gypsum board. Both ASET-C and AZONE use factors to estimate heat transfer. ASET-C estimates heat transfer by the heat loss fi-action, &which is the fraction of the heat release rate of the fire that is lost to the bounding surfaces of the room and its contents (Appendix F). The heat loss fraction is generally in the range of 0.6 to 0.9. AZONE evaluates heat transfer by the convective fraction, X,, and the wall heat transfer fraction, The convective Laction is the convective portion of the heat release rate; for more information about this fraction, see Chapters 2 and 13. The wall heat transfer fraction is the fraction of the plume enthalpy flowing into the smoke layer that is lost to the walls and ceiling. The smoke temperatures associated with the clear heights of Figure 14.6 are shown in Figure 14.7. For ASET-C, a value of 2,. = 0.6 was chosen. For AZONE, X,. = 0.7 and 11 = 0.4 wcrc used. The factors are rclatcd

v.

~ r i n c i ~ lof e sSmoke Management

as Ac = I - ( I - ?l)and, thus, AZONE was effectively simulated with Ac = I - 0.7(1 - 0.4) = 0.58. It is not surprising that the smoke temperatures are almost the same for the ASET-C and AZONE simulations (Figure 14.7).

Steady Conditions The method of analysis presented in this section is based on the simplieing assumptions below. The only mass flow into the smoke layer is the fire plume. The only mass flow from the smoke layer is the smoke exhaust. The exhaust is removing only smoke and not any air from below the smoke layer. The smoke layer height is constant (Figure 14.10). The flows into and out of the smoke layer are at equilibrium. Heat transfer between the smoke layer and the surroundings have reached equilibrium.

The smoke temperature of the CFAST simulation was higher, but the convection coefficients upon which the wall heat transfer was based are calculated from general correlations. No convection coefficients have been developed specifically for fire compartments. MECHANICAL EXHAUST j

Mechanical smoke exhaust is probably the most common form of atrium smoke management in North America. As with natural venting, mechanical smoke exhaust can be based on either a steady or an unsteady design fire. The equations of the next section deal with a steady fire, and zone fire models can be used to analyze smoke flow due to an unsteady fire.

~ i i u r 14.8 e

Before using this method, designers need to verify that these assumptions are appropriate for their application.

Figure 14.10 Mecha17icalsuioke exhalist and cotista~it clear keiglit.

Katzi~-alsmoke volti~ig.

Velocity Unaffected By Building

C

Note: Because wind can produce positive, preSsures at the top L of an atrium, natural \ smoke venting is not recommended for an atrium anached to or near a tall building in

....

Figure 11.9

.

.

.C-

>

,.

..

..

. . .:

. .,,.

.

..

.... .

Windjlo~c. pattern prodtrci~iga positive p/-esslrr-e011the top o f a n atrizr~ndue to the prcse~lcc? f a ~ u lbziilding l ~iear-by.

Chapter 14- Atrium Systems

To calculate the exhaust flow rate, the plume equations from Chapter 13 are adapted with variables redefined for the following application: 1 /3 5/3

~ z = C a I Q cz

+C,~Q,

forz>zl

(14.11)

and

where mass flow exhaust of exhaust air, Ibls (kgts);

rir

=

QC

- convective heat release rate of fire, Btuk (kW); =

Z1

c,, c,,

=

height of the smoke layer interface above the fuel, fi (m); mean flame height, ft (m);

=

0.022 (0.071);

= 0.0042 (0.00 l S);

Col0 = 0.0203 (0.032). The mean flame height is

where C,, l = 0.533 ( 0166).

0,

= convective heat release rate offire, ~d~

Cp = specific heat of plume gases,Btuflb "F (kJAcg "C); q = wall heat transfer firaction (diiensionless). As already stated, the wall heat transfer factor is the fraction of the convective heat release rate that is transf e n d to the waiis and ceiling of the atrium. This factor depends on a number of conditions, including the geometry of the space, the construction materials of the walls and ceiling, and the smoke layer temperature. An atrium with no heat transfer is referred to as an adiabatic atrium (v = 0). The adiabatic assumption is conservative in that it results in high predictions of volumetric smoke exhaust, but it is not conservative with respect to plugholing. In the absence of research about the wall heat transfer fraction, values of q are expected to be in the range of 0.3 to 0.7 for walls and ceilings of normal construction materials (brick, concrete, glass, gypsum board, etc.). The density of the exhaust gases can be calculated from the perfect gas law,

where p, = density of exhaust gases, lbrnlf? (kgh3);

91-ictlyspeaking, Equations (14. I I ) and (14.12) are for the mass flow rate ofan asisym~nelricplume into the upper layer. M'hen the axisymmctric plume equations at-e not appropriate, other plunle equations may be used. For the balcony spill p l u m equations and the window plu~neequations, see Chapter 13. l'he convective the heat I-elease rate, G,., is Q,. =

x,.Q

p = atmospheric pressure, lbflfi2 (Pa); R gas constant, ft Ibfllbni "R (Jkg K);

-

7;.

= absolute temperature of exhaust gases,

"R (K).

Alter-natively, the density of the exhaust gases can be calculated from

(14.14)

whcrc Y,,

0

=

=

and 13);

where T,. = absolute reference temperature, "R (K);

total Ilcat rcleasc rate, Btuls (kW).

p,.

convcctivc lyaction ol'heal relcasc (see Chap[cr.s2

For convei~iciicc,the tarn sr~okclayer Iieighr will be used to mean lllc heigh~of the smoke layer inlerfacc. The term ;is snioke layer licigllt above the luel. The te~npc~-nlure of the smoke layer can he cxprcsscd as T , = 7;)

density at reference temperature, lbm/ft3 (k9/m3).

There are an infinite number of pairs of T,. and p,. that can be used in Equation (14.17), and one such pair is 530°R (294 K) and 0.075 lbrn/ft3 (1.20 kg!m3). The volu~netricHow of exhaust gases in plume is

bc(l - 11 ) + --lil

c,,

i/ = volumetric tlow ofeshaust gases, cfni (m3/s):

whcr-c

I;. 7;,

=

=

s~iiokcIaycr temperature. "F ("C):

a

=

a~nbicntrcmpcraturc, "F ("C):

p,, = density ol'csllnust gases, lwft3 (kg/&);

= mass Ilow ofeshaust air, Ibls (kgs);

C,,- = 60 ( 1 ).

Principles of Smoke Management,

Example 14.2 Steady Smoke Exhaust What is the smoke exhaust needed to maintain a smoke layer height of 36 ft (11.0 m) with the design parameters listed below? 72.0°F (22OC) Ambient temperature Ceiling height 45 ft (13.7 m) Convective fraction 0.7 Oft(0m) Height of top of fuel 2000 Btuk (21 10 kW) Heat release rate Wall heat transfer fraction 0.4 Note that the smoke layer depth is 45 - 36 = 9 ft (2.7 m), which is 20% of the height of the atrium ceiling above the fuel. This depth accommodates the formation of the ceiling jet as in the section "Minimum Depth of Smoke Layer" in Chapter 13. From Equation (14.14), the convective the heat release rate is Q, = x c =~ 0.7(2000) = 1400 Btds(1480kW).

From Equation (14.13), the mean flame height is 2/5

z, = 0.533Qc

= 0 . 5 3 3 ( 1 4 0 0 ) ~=~9.7 ~ ft (3.0 m).

The smoke layer height, z, is 36 ft (l 1.0 m). Because z, is less than z, the mass flow is calculated from Equation (14.1 l):

. 1 /3_5/3

1 = 0.220, ,

+ 0.0042Qc = 0.022(1400'/~)(36~/~) + 0.0042(1400) =

102 Ib!s (46.4 kgls).

From Equation (14.15), the smoke temperature is

1) From Equation (l4.17), the smoke density is

1)

From Equation (14.18), the volumetric tlow ofexhaust gases is

'CJnsteadyConditions Unsteady analysis of an atrium exhaust system may be done to simulate a combination of smoke filling and snioke exhaust, simulate the effects of an unsteady fire, and determine the impact of activation time on smoke layer depth.

A combination of smoke filling and smoke exhaust can be used for an atrium that is not large enough to qualify for smoke protection solel!~ by smoke filling. For this combination approach, the exhaust fans need to be sized so that the smoke filling time is greater than the evacuation time, including the time it takes to become aware of the fire and to prepare for movement to an exit.

rt is the nature of fire that it is an unsteady process Probably the reason that steady fires are used extensively is that they lead to the simple steady analyses like the one above. While large steady design fires can be selected to yield conservative designs, these design fires are not realistic. See Chapter 2 for information about design fires. Zone fire models such as CFAST and AZONE can be used for analysis of atrium smoke exhaust systems \\.it11 unsteady fires. Before smoke exhaust fans can be turned on, the presence o f the fire needs to be detected. There is some delay betwzen detection and activation, and it takes some time for the fans to come up to full speed. Detection time can be estimated from the inforniation about the lag times of plumes and ceiling jets pro\.ided in Chapter 13. When appropriate, detection should takc into account the potential that there could be a stratified layer of hot air under the ceiling, as discussed later.

,

Chapter 14 -Atrium Systems

-9

500

l,=150s

5 -

1

0 60

120 180 l i m e (S)

240

0

(a) Variation of smoke layer with atrium area. A

-9 -7 .... -

----

0

180 lime (S) Variation of smoke layer fire growth. l, 120

-5

.c

. '5 .

5

-2 -1

l, = 90 S A = 1000 ft'(g2.9 m2)

60

(C)

to= 1 9 = , 300 f,=600s

-

240

0 3M)

60

-2 1 0 3M)

120 180 240 l i m e (S) (b) Variation of m o k e layer witJ~exhaust adimtion time. l ,

300

0

A=l~~)fl~(92.9rn')

Notes: 1. The Are is a 1-squared fire up to 2000 Btuk (2110 kWW). after that the HRR remains mnstanL 2. The exhaust flow rate was seleded so that lhe midness of lhe smoke layer would be 6 fl(l.83 m) at a sieady HRR of MOO Etuk (2110 k W . 3. As wilh other zone fire models, the details of lhe ceiling jet are not simulated by AZONE. Thus. onty the portions of these graphs where lhe smoke layer is Celow about 24 R(7.3 m) are realistic. 4. Other factors are: Ambient Temperature. T, = 72.0 'F (22.2 %l Ceiling Height. H= 30.0 fl(9.1 m) Height of top of fuel. H , = 0 A (0 m) Exhaust Row rate. V = 49500. h(23.4 m%) Exhaust location factor. P = 2 Exhaust location Delow ceiling, d. = 0?i (0 m) Number of exhaust inlets. , N =6 Wall Heat transfer fraction. q = 0.4

Figure 14.11 U17steadylayer- height sit~rdated.by the zonefire model AZONE. It is possible tliat the snioke layer could descend well below the design smoke layer height based on a steady analysis. To check the effect of activation, AZONE allows tlie user to specify the acti\.ation time o f the smoke exhaust fan. Figure 14.1 1a shows the effect of the atrium area on the smoke layer height as calculated by AZONE for an atrium 30 ft (9.14 m) in height with an exhaust activation tinie of 90 seconds. It can be seen tliat for an atriuni area, A, of 5000 ft2 (465 ni2) or more, the delay in activation does not have an adverse effect on smoke layer height for the conditions of the simulations. For A = 2000 ft2 (186 ni2) or less, the smoke layer drops well below the design lieight for the conditions of the simulation~. Figure 14.1 1 b shows the effect of exhaust activation time, to,,, on smoke layer height for a 30 ft (9.14 m) tall atrium with A = 1000 ft2 (92.9 ni2). As expected, the smaller the activation time, tlie less the effect on smoke layer lieiglit. At t,,, = 30 S, the smoke layer stays above design lieiglit tliroughout the simulation. Figure 14.1 1c shows the effect of tlie fire growth time, t6" on slnoke layer height for a 30 ft (9.14 m) tall atriuni with A = 1000 ft2 (92.9 ni2). As would be expected, the less the growth tinie (faster the tire), the greater the effkct on tlie smoke layer height. While a study has not been made on the effect of the activation time on smoke layer height. some gcneralizations can be made. For atria with relatively large

areas (A/H~> 5 where H is the atrium height), the effect of fan activation at 90 s would not be expected to have an adverse effect on the smoke layer heiglit. For atria with relatively small areas (A/H~< 5 ) , the smoke layer could drop below the design lieight, resulting in smoke contact with people. AZONE can be used to analyze the effects of activation tinie on the smoke layer lieight.

Makeup Air For steady flow, the mass flow of air or smoke exhausted from the top of an atrium equals the mass flow of air entering below the smoke layer. This airflow entering the atrium is referred to as niakeup ai:, and makeup air can be either supplied naturally or by fan power. Fan-powered niakeup air is often sized at 90% and 97% of the exhaust airflow rate, and the balance of the air needed to acco~nnlodatethe exhaust naturally flows through openings or leakage paths. Natural makeup air flows through openings, such as open doorways and vents, and sometimes makeup airflow paths are complex conlbinations of rooms and corridors. Computer network airflow programs, sucli as CONTAM (Chapter 8), can be used for analysis of these complex flow systems. The velocity of makeup air should not destroy the plume structure or significantly deflect the plume at an angle. It is believed tliat keeping the velocity at or below 200 fpm (l nils) will prevent sucli plume disruption.

Principles of Smoke Management

NATURAL VENTING

temperature may be less than the outdoor summer design temperature. The smoke temperature and mass flow of the plume can be calculated from the same equations that are used for mechanical exhaust as discussed later.

Natural smoke venting is common in many parts of the world, such as Europe, Australia, and New Zealand. As stated in Chapter 1, natural venting was developed in response to several fire tragedies in the 19th and early 20th centuries. Natural venting relies on the buoyancy of hot smoke to force smoke out of open vents at or near the top of the atria (Figure 14.8). Natural venting can be based either on a steady or an unsteady design fire. The equations in the next section are for a steady fire, and zone fire models can be used to analyze smoke flow due to an unsteady fire.

For an atrium attached to a tall building or very near a tall building located in open terrain, wind can produce positive pressures at the top of the atrium, as shown in Figure 14.9. Because such positive pressures can interfere with natural venting, natural venting is not recommended for atria with s ~ wind h conditions.

Steady Conditions

Makeup Air

The equation developed in Chapter 13 for the mass flow rate through the vent is

Wind

For natural smoke venting described by Equation (14.19), makeup air flows naturally through the inlet opening of area, At Makeup air is generally supplied through open vents or doorways. A sprawling atrium can be divided into a number of large spaces with smoke vents so that the smoke vents in the spaces away from the fire can be opened for makeup air.

wherc m, = mass flow rate through the vent, Ib/s (kgls);

C

=

discharge coefficient (dimensionless);

A,, = vent area, f? (m2); A.

=

inlet opening area, ft2 (mZ);

P0 - outside air density, lb/ft3 (kg/m3); g db

= =

acceleration of gravity, 32.2 ft/s2(9.80 m/ sZ); depth of smoke layer below the smoke vent, ft (m);

To = absolute temperature of outside air, "R (K);

r,

=

absolute temperature of smoke, "R (K);

Because buoyancy of hot smoke is the driving force of natural venting, the mass flow rate, );I,,, through the vent increases with increasing smoke temperature, TT. As the size of a fire increases, the mass flow rate of the plume into the upper layer increases and the temperature of the smoke layer increases. For a fire larger than the d-sign fire, the smoke temperature goes above the design value, and the mass flow rate through the vent increases above the design value. This benefit is unique to natural venting, and it helps offset the greater amount of smoke produced by fires that might exceed ths design fire. For air-conditioned atria, it is possible that the smoke temperature may be less than the outdoor summer design temperature. This can result in doivnward outside airflow through the atrium smoke vents. To avoid such downward flow through smoke vents, natural smoke venting should nor be used wlicn the smokc

TENABILITY SYSTEMS As already stated, the approaches discussed above have the goal of not exposing occupants to smoke during evacuation. Tenability systems are designed to maintain tenable conditions with occupant exposure to smoke. Hazard analysis consists of evaluation of smoke transport, people movement (evacuation time), and tenability. While smoke transport can be simulated by zone fire models, CFD modeling has the significant advantage of being able to simulate variations of temperature and concentrations of combustion products in the smoke layer. Evacuation time can be evaluated by the methods of Chapter 4. Tenability analysis should address visibility, gas exposure, and heat exposure, and extensive inforrnation about tenability can be found in Chapter 3. Ths calculation method for tenability described in Chapter 9 can be used for atria. STRATIFICATION A N D DETECTION Often, a hot layer of air forms under the ceiling of an atrium as a result of solar radiation on the arriuin roof. While studies have not been made of this stratified layer, building designers indicate that the temperatures of such layers are often in excess of 120°F (50'C). Temperatures below this layer are controlled by thc building's heating and cooling system. and the temperature profile can be considered to increase significantly over a small increase in elevation as shown i n Figure 14.12.

Chapter 14-Atrium Systems

Elevation Abjve Fwl (m) 30 60

0

90 120

Heat Release Rate:

-1w E

5.000 Btul S(5.280kW) 2.OM)Btu1 S(2.110 k W )

f

-80

p

-60

cP

D

W

-40

l I

- 20 50 0

Temperature

Figure 14.12 Temperature profile of hot layer- of air zrnder atrium ceiling.

50

100

150

200

250

P

Q

I

300

Elevation Above Fuel (R)

Figure 14.14 Average femperature of axisyn~rnetr-ic pfznne.

For redundancy when using this approach, more than one beam smoke detector is recommended. b.

The purpose of this approach is to quickly detect the development of a smoke layer at whatever temperature condition exists. One or more beam detectors are located at the roof Icvcl. Additional detectors are located at otlier levels lower in tlie volume. The exact positioning of the beams is a function of the specific design but sllould include beams a1 the bottom of identified unconditioned spaces and at or near the design smoke level \\it11 several intermediate beam positions at otlier levels.

Figure 14.13 Smoke stratificatior~under a layer of hot ail: When the average temperature of the plume is less than that o f t h e hot air layer, tlie smoke will form a stratified layer under it, as shown in Figure 14.13. Average plume temperatures are sho\vn in Figure 14.14, and it can be observed that the average plume temperature is often less tliali expected temperatures o f tlie hot air layer. Thus, when there is a hot air layer under the atrium ceiling, smoke cannot be expected to reach the ceiling of the atrium; and smoke detectors mounted on that ceiling cannot be expected to go into alami. Beam smoke detectors can be used to overcome this detection difficulty. The follo\\:ing are beam detection approaches that can provide prompt detec:ion regardless of the temperature of the air under tlie ceiling at the time of fire initiation. a.

Horizontal Beams to Detet the Smoke Layer at Various Levels

c.

I-lorizontal Beanis to Detect tlie Smoke Plume The purpose of this appl-oacli is to detect [he rising plume rather than the stnokc layer. For this approach, an arrangement ol'beams are installed at a level below tllc lowest expected stratification level. These beams need to be close enough to each other to ensure intersection of the plume, the spacing being based on the width of the beam at the least elevation above a point of fire potential.

An Upward-Angled Beam to Detect the Smoke Layer

Tile approaches described above are illustrated in Figure 14.15, and approach (a) has the advantage that i t does not require the location of a number of horizontal beams. Some bean1 smoke detectors are subject to false a ~ t i \ ~ a t i obyn sunlight, and alternative (a) min;niizes the possibility of such false activation bp orienting the rcccivcr at adownward aligle.

The purpose of this approach is to quickly detccl the development of a smoke layer at whatcver tcmperature condition exists. One or more beams arc aimed at an upward angle to intersect thc smoke layer I-cgardless of h e Imel of s~nokestratilication.

All of the coniponcnts of a beam s~iiokedetector nccd to bc located so they are accessible for nlaintenancc. For thc arrangement sliown in Figure l?. 15. a roof opciiing (not shown) could provide access for mainte~iancc.

Principles of Smoke Management

Plan View

Section

(a) Upward Angled Beams t o Detect the Smoke Layer

Suggested Spacing of Beams:

Plan View

Section

(b) Horizontal Beams t o Detect the Smoke Layer at Various Levels

Suggested Spacing of Beams: X = -B

4

Plan View

Section

(c) Horizontal Beams to Detect the Smoke Plume of beam smoke detectors. Figure 14.1 A~-ra~~,oe~nerits

Chapter 14 -Atrium Systems

M2 = mass of smoke layer at the end of the interval (kg).

Step I: Assign Values to Consfan&

The change in energy of the smoke layer can be expressed as

C,, R, P-, U. X,, a

t

Step 2: Read Data

Z.H.A.H,.,,~,.Q.~.

where

P. 4. N&". L.4".L

AE

t

Cp

Step 3: Assign lnitlal Values m,

=o; T , =C;

wall heat transfer fraction (dimensionless); Tp = absolute temperature of plume gases entering smoke layer (K);

p,=p.l(RT,,);

Q = O ; ~fr, elevation: 0.0 m

P 53.5

T 24.0

path flleakstr2 extstnvall2 stairdoor 1 intwallstr extstnvall l openstdoor

From St 1/ Amb t Ambt Rml/ Ambt Rml/

Elev

flleakshft2 inkallshft elevdoor

Elev/ Rml/ Rml/

Rml

floorleak estwalll estdoor inhvallstr openstdoor inhvallshft esnvall2 esnvall2 elevdoor openstdoor inhvallstr extwall l estdoor

Rm 1/ Ambt Ambt Stl/ Stl/ Elev/< l > Ambt Ambt Elev/< l > St2/ SW< 1> Ambt Ambt

flleakstr2 openstdoor intwallstr extstnvall I stairdoor l eststn\~all2

St2/ Rml/ Rml/ Ambt Ambt Ambt

path tlleakstr2 eststnvall2 tlleakstr2 int\\,allstr

from St 1/ Ambt Stl/ Rm 1/

zone Stl

Flow 1 7119.15 -48.70 -268.35 -101.72 -226.93 -6473.46

Flow2

Flow l 7718.22 -49.28 -7119.15 -1 38.00

Flou.2

level: ele\,ation: 4.0 m zone St l

P 7.2

T 24.7

312

Principles of Smoke Management

Ambt Rml/G> flleakshfu intwallshft flleakshfu elevdoor

f

4..

I

$

Rml

-19.6

20.0

1

I

floorleak exhvall I inhvallstr stairdoor2 intwallshft exhvall2 exhvall2 elevdoor floorleak stairdoor2 inhvallstr exhvall1

Rm1/ Ambt Stl/G> St 1/ Elev/G> Ambt Ambt Elev/G> Rml/ St2/ St2/ Ambt

flleakstr2 stairdoor2 inhvallstr extst&alll flleakstr2 extsmvall2

st2/ Rm1/ Rm 1/ Ambt St2/ Ambt

from St 1 / Ambt St 1/G> Rm 1 / Ambt Rm 1/

level: elevation: 8.0 m zone Stl

P -38.9

T 25.5

path flleakstr2 extstrwall2 flleakstr2 inhvallstr extstrwalll stairdoor2

Elev

-73.1

20.0

flleakshft2 inhvallshft flleakshft2 elevdoor floorleak exhvall1 inhvallstr stairdoor2 inhvallshft exhvall2 eshvall2 elevdoor floorleak stairdoor2 inhvallstr extwall l

Rm 1/ Ambt St l / - + St1/ Elev/:3> Ambt Ambt Elev/ Rm 1/ St2/ St2/ Ambt

Flow I 8335.10 -49.96 -77 18.22 - 145.27 -231.78 - 189.89

Flow2

Appendix D - Application of CONTAMW

St2

-39.0

25.5

flleakstr2 stairdoor2 intwallstr extstrwalll flleakstr2 extstnvall2

StU Rrn1/-=3> N1/ Ambt sue> Ambt

path flleakstr2 extstnvall2 flleakstr2 inhvallstr extstnvall 1 stairdoor2

from St 1/ G > Ambt St 1/ Rm l / Ambt Rrn 1 /

Elev

flleakshft2 intwallshft flleakshft2 elevdoor

Elev/ Rm 1/ Elev/ Rm 1/

Rm l

floorleak exhi.all1 intwallstr stairdoor2 intwallshft exhvall2 exhvall2 elevdoor floorlrak stairdoor2 intwallstr extuall I

Rrn 1 / G > Ambt St 1/ St 1/ Elev/ Arnbt Arnbt Elev/ Rm 1/ St2/ St2/ Arnbt

flleakstr2 stairdoor2 intwallstr extstn5,alll flleakstr2 extstn\.all2

St2/ Rm 1/ Rn1 1/ Arnbt St3/ Ambt

path flleakjtr2 cxtstn5-all2 flleakstr2 intwallstr extstnvall l stairdoor2

from St 1/ Ambt St 1 / Rrn 1/ Ambt Rrn 1/

Flow 1 9177.54 -51.61 -8945.69 -100.10 -238.22 -141.91

tlleakshft2 intwallshli Illeakshfi2

Elev/ Rm 1 / Elev/

-1249.5 1 34.99 891.96

level: elevation: 12.0 m zone St l

P -84.8

level: elevation: 16.0 m zone St l

Elcv

P - 1 30.5

T 26.9

Flow2

Principles of Smoke Management elevdoor

Rm1/

floorleak extwalll intwallstr stairdoor2 fan3 intwallshfi extwall2 extwall2 elevdoor floorleak stairdoor2 intwallstr extwall I

Rm l/ Ambt St 1 / 4 > st Ambt Elev/ Ambt Ambt Elev/ Rm l/elevation: 24.0 m

zone Stl

P -221.5

T 28.4

Elev

extstrwalll flleakstr2 extstrwall;?

Ambt St2/ Ambt

path flleakstr2 extstrwall2 flleakstr2 intwallstr extstrwalll stairdoor2

from St l/ Ambt St l/ Rm Ambt Rm l/

flleakshfu intwallshfl flleakshfu elevdoor

Elev/ Rm 1/ < P Elev/ Rrn1/

floorleak extwall l intwallstr stairdoor2 fan3 intwallshft extwall2 extwall2 elevdoor floorleak stairdoor2 intwallstr extwalll

Rm l/ Arnbt St1/ St1/ Ambt Elevl h b t Ambt Elev/ Rm l/ StU stU Ambt

flleakstr2 stairdoor2 intwallstr extstrwalll flleakstr2 extstrwall2

StU Rm 1/ Rm 1 / St2/< 10> St2/ Ambt

St2

flleakstr2 stairdoor2 inhvaktr extst~walll flleakstr2 extstnvall2

St2/< I I > Rtnl/ R1111/< 1 0> Ambt St2/ Ambt

zone St l

path flleakstr2 extstnvall2 fl leakstr2 intwallstr extstnvall l stairdoor2

from St1/ Ambt Stl/ Rm1/ Ambt R1111/

Elev

flleakshft2 intwallr;hli tlleakshfi2 elevdoor

Elev/< 12> R~iil/ Elev/< l O> R~nl/

R111I

floorleak extwall l intwallstr stairdool" intwallslili

Rm1/ Ambt Stl/ Stl/ Elev/< l l >

Flowl 13 179.90 -57.54 - 12356.22 -232.47 -261.49 -272.18

Flow2

Flow I 14035.98 -59.05 - 13179.90 -245.65 -267.47 -283.9 1

Flow2

level: elevation: 40.0 111

31s

Principles of Smoke Management

ex,twall2 extwall2 elevdoor floorleak stairdoor2 intwallstr _extwalll

Ambt Ambt Elev/ Rml/ St2K 1 l> St2/ Arnbt

flleakstr2 stairdoor2 intwallstr extstrwalll flleakstr2 extstrwall2

SW< 12> Rml/ Rml/ Ambt St2k1o> Ambt

path flleakstrl fan l extstrwall2 flleakstr2 intwallstr extstrwall 1 stairdoor2

f?om Ambt Ambt Ambt Stl/ Rm1/ Ambt Rm1/

flleakshft l intwallshft flleakshft2 elevdoor

Ambt Rm1/ Elev/< l l > Rm1/

floorleak extwall1 intwallstr stairdoor2 intwallshft extwall2 extwall2 elevdoor floorleak stairdoor2 intwallstr extwall l

Ambt Ambt St1/ St1/ Elev/ Ambt Ambt Elev/< l 2> Rml/ St2k 12> St2k12> Ambt

fan2 flleakstr l btairdoor2 intwallstr extstrwall l flleakstr2 eststrwall2

Ambt Ambt Rm1/ Rm1/ Arnbt St2/ Ambt

level: < l 2> elevation: 44.0 m zone St l

P -445.1

T 32.0

level: < 13> elevation: 48.0 nl zone

P

T

path

dP -76.0 -76.0 -70.4 -1.2 -72.5 -79.6 -72.0

Flow lFlow2 -77.4 1 15000.00 -60.68 -14035.98 -257.60 -273.92 -294.4 1

Appendix D - Application of CONTAMW

Note: flows in scfm pressures in Pa temperatures in "C * indicates limit exceeded

EXAMPLE OF SHAFT REPORT FOR STAIR 1 project: CONTAM project shaft report levellzone

[pal

[scfmI

< 1 2>Rm I

72.5 < 257.60

[pal

[scfm]

zone

> 257.60 ------ l 67.2 > 245.65 ------ I 61.7 > 232.47

Rml

+

+----------v----------------

Stl

I -----/Rml

< I O>/Rm I

67.2 < 245.65 1 -----61.7 < 232.47

Stl Stl

72.5

Rml Rml Rml Rml

- - p - - -

Stl

I

24.3

> 127.32

Rml

220.11

Rml

------ I

Stl I ------

16.7 < 100.10

56.3

>

--

Stl

Rml - p - - - -

Stl St l

28.0 > 140.33 ------ I 29.5 > 145.27 -p----

Stl

17.0

Rml Rml

l

27.2 -p----

St l

I

> 138.00

Rml

> 101.72

Rm l

l

Appendix E

ASMET Documentation l

1

NOMENCLATURE A

=

cross-sectional area of the atrium, m2

a

=

Cl

=

fire growth coefficient, kw/s2 0.071

C2

=

0.026

TCP

=

t,

=

absolute centerline plume temperature at elevation z, K growth time, s

Tp

=

average plume temperature at elevation z, 'C

V

=

volumetric smoke flow at elevation z, m3/s

z

=

ZJ

=

I,

=

height above top of fuel, m mean flame height, ni

CS

=

9.1

C7

0.235

j

=

=

virtual origin of the plume, m convective fraction of heat release

C8

=

0.0018

p

=

density of air or plume gases, kg/m3

C9

=

0.166

p,

=

density of ambient air, kg/m3

Clo

=

1.11

pp

=

density of plume gases at elevation z, kg/m3

Note: The variables above are given in S1 units only, because internal calculations in ASMET are in SI.

Cp

=

specific heat of plume gases, 1.005 kJ/kg-K

PART 1: ASMET DESCRIPTION

DJ

=

diameter of fire, m

g

=

Below are the equations used in each section of ASMET, except for ASET-C, which is discussed in Appendix F.

H

acceleration of gravity, 9.807 rn/s2 = ceiling height above the fire, m

n

=

mass flow in plume at height z, kg/s

P Q

=

QC

=

absolute pressure, Pa heat release rate of the fire, kW convective heat release rate of fire, kW

R

=

gas constant, 287 J kg.K

t

=

T Ta

=

time, S absolute temperature, K ambient temperature. OC

=

=

Steady Filling Equation (Solve for z)

Steady Filling Equation (Solve for t)

-Appendix E- ASMET Documentation

The density of air and plume gases:

Unsteady Filling Equation (Solve for z)

Plume Centerline Temperature

Unsteady Filling Equation (Solve for t)

Plume cecterline temperature:

Simple Plume Equations

The virtual origin of the plume and the mean flame height by the equations of the previous section, "Plume with Virtual Origin Correction."

Mass flow of plume: iil

1/3 5/3

= ClQC z

+C8Qc

Mean flame height:

Convective portion of the heat release rate: - - C Q2/5

:l-

9 c

Average plume temperature:

The convective fraction, E,, is generally taken as 0.7 for design. However, when burning a known fuel (as in acceptance testing), it may be desired to use the specific value for the fuel.

The volumetric flow of a plume:

PART 2: ASMET USERS GUIDE ASMET is a collection of tools that can be used for analysis of atria smoke management systems. This program is for a personal computer with a DOS operating system, and the program was \vritten in C. When ASMET is in the active directory, the program is activated by typing "ASMET" follo\ved by pressing the key. When the program starts, the main menu appears on the screen as shown in Table E-l.

The density of air and plume gases:

Plume with Virtual Origin Correction

Mass flow of plume: til

I /;

= C l QC (Z- z ~ ) ' / ~1 [+ c ~ Q ~ / ' ( z - z0 ,-5/3]

(E10)

This equation can be rearranged to simplify calculation: tii

I ;

= c l Q C (I-z0)

5/3

+C8Qc

(El 1)

Virtual origin of the plume: 715

- 1.02 Of

(E121

c,Q'/'- 1.020,

(E131

z0 = C;@

Mean flame height: zf =

Average plume temperature: QC TI' = T , + 111 c,

(E14)

The volumetric flow of a plume: f .

=

c4 !! p,

(E15)

The equations used for each routine are listed in Appendix C, except for ASET-C, which is described in Appendix E. Theequations of Appendix C are also addressed in the body of the text. The first time the program is run, it starts in S1 units, and the user can change units by pressing E for English units or I for S[ units. The program stores a unit indicator in file UNITS so that it M-ill start up with the unit selection from the last time the program was run. The other menu items are selected by pressing the key that is in bold type (or yellow on a color monitor). The first menu item is selected'by pressing S, and the screen for this menu is shown in Table E-2. There are two ways to enter data from this menu. The first is by pressing the key that is in bold for that menu item. The second is by moving the indicator at the right of the menu item with the up and down arrows. This indicator is next to the first menu item (ceilinz height above fire) in Table E-2. Once an item has been selected, the number for that item is entered followed by . Table E-3 shows the screen after data has been entered. The data displayed on the screen can be sent to the printer by pressing P. and pressing D returns the user to the main menu. To send results to a file, press f and enter the lile name. Use of the other items in the main menu is similar to that discussed above.

Principles of Smoke Management

-Table E-l: Main Menu Screen of ASMET. ASMET: Atria Smoke Management Engineering Tools Menu Steady Fiiiing Equation (Solve for z) Steady Filling Equation (Solve fort) Unsteady Filling Equation (Solve for z) Unsteady Filling Equation (Solve for t) Simple Plume Equation Plume with Virtual Origin Correction Plume Centerline Temperature ASET-C (C language version o f ASET-B) Input units (S1 or English): S1 Exit

Table E-2: Screen for Steady Filling Equation (Solve for z) Steady smoke filling Height of smoke layer during atrium filling from a steady fire ceilins height above fire

H (m):

cross-sectional area of atrium

A (mA2):

heat release rate of tire

Q (kW):

time

t (S):

Print results (to LPTI) Print results to file disabled

Table E-3: Screen for Steady Filling Equation After Data are Entered Steady smoke filling IHei=ohtof smoke layer during atrium filling from a steady fire

X

l

ceiling height above fire

H (m):

cross-sectional area of atrium

A (mA2): 20000.00

he31 release rate of fire

Q (kW): 10000.00

time

t (S):

80.00

1200.00 +

Prinr results (to L m l ) Print results 10 file disabled Done (rcrum to main mcnu) Hr.i:hr of smoke layer ahovc lire, z, is

17.6 m or

57.8 A

Appendix E- ASMET Documentation

EXAMPLE OUTPUT (S1 UNITS)

Steady Filling Equation (Solve for z) Height of smoke layer during atrium filling from a steady fire H (m):

ceiling height above fire cross-sectional area of atrium heat release rate of fire time

30.00 5000.00 5000.00 300.00

A (m2):

Q (kW): t (S):

Height of smoke layer above fire, z is 17.4 m or 57.2 ft

------------------------------------------------------------------------Steady Filling Equation (Solve fort) Atrium filling time for steady fire ceiling height above fire cross-sectional area of atrium heat release rate of fire height of smoke layer above fire

H (m): 40.00 A ( I ) : 10000.00 Q (kW): 5000.00 z (m): 8.00

Filling time is 1290 seconds or 2 1.5 min. ------------------------------------------------------------------------unsteady Filling Equation (Solve for z) Atrium tilling time for unsteady fire

At

800 seconds, the tire is

30.00 8000.00 0.04659 800.00

H (m): A( I ) : a (kw/sZ): t (S):

ceiling height above tire cross-sectional area of atrium fire growth constant (Menu) time

300 l0 kW or

28445 Btds.

Height ofsmoke laycr above tire, z, is 10.7 m or 35.0 ti -------------------------------------------------------------------------

Unsteady Filli~lgEquation (Solve fort) Atrium tilling time for unsteady tire ceiling height above fire cross-sectional arca ofatrium fire growth constant (Menu) height of smoke layer ab0i.e tire

H (m):

50.00 12000.00 a ( k ~ l s ' ) : 0.04659 z ( m ) 10.00 A (m Z):

Filling time is 1237 seconds or 20.4 min. At this time, the fire is 7 1754 k W or 68014 Btuts. .........................................................................

Simple plume equation Mass flow and temperature rise of an plume U illlout correction for virtual origin Elwation Heat release rate ol'lirc Ambicnt tcmpcl-atcw

r (m):

50.00

Q (k\V): Ta (C):

25000.00 7 1 .00

Principles of Smoke Management

At elevation z, the plume has: Mass flow of 1282.4 kg/s Volumetric flow of 1117.2 m3/s Average temperature of 35°C Mean flame height of 8.3 m

2827.2 Ib/s 2367016 c h 94°F 27.1 ft

............................................................. Plume with V i a l Origin Correction Mass flow rate and average plume temperature

I

z (m): Elevation Heat release rate of fire Q (kW): fire diameter Df (m): Ambient temperature Ta ("C):

-

50.00 25000.00 4.00 21.00

At elevation z, the plume has: Mass flow of 1254.7 kg/s Volumetric flow of 1094.2 mA3/s Average temperature of 35°C Virtual origin at 0.7 m Mean flame height of 9.4 m

2766.1 Ib/s 23 1 8 122 cfm 95°F 2.3 fi 30.9 fi

Plume Centerline Temperature Calculate centerline plume temperature Elevation Heat release rate of fire fire diameter Convective fraction of heat release Ambient temperature

50.00 z (m): Q (kW): 25000.00 Df (m): 4.00 (0.6 to 1): 0.70 21.00 Ta ("C):

At elevation z, the plume has: Centerline temperature 46°C Virtual origin at 0.7 m Mean flame height of 9.4 m

. .

115°F 2.3 fi 30.9 fi

EXAMPLE OUTPUT (ENGLISH UNITS)

Height of smoke layer during atrium filling From a steady fire ceiling height above fire cross-sectional area of atrium heat release rate of fire time

H (R): 98.40 53800.00 A (g): Q (Btu%): 4740.00 200.00 t (S):

Height of smoke layer above fire, z, is 17.4 m or 57.2 fi .........................................................................

Steady Filling Equation (Solve for t) Atrium filling time for steady fire ceiling height above fire cross-sectional area of atrium heat release rate of fire height of smoke layer above tire

H (R): 131.00 lO7OOO.OO A (g): Q (Btuls): 4740.00 z (fi): 26.20

Appendix E- ASMET Documentation

Unsteady Filling Equation (Solve for z) Atrium filling time for unsteady fire ceiling height above fire

H (R):

98.40

cross-sectional area of amum fire growth constant (Menu) time

86100.00 A (g): a ( ~ t u l s ~ ) : 0.04444 800.00 t (S):

At 800 seconds, the fire is 30006 kW or 28442 Btuk Height of smoke layer above fue, z, is 10.7 m or 35.0 R

------------------------------------------------------------------------Unsteady Filling Equation (Solve for t) Atrium filling time for unsteady fire ceiling height above fire cross-sectional area of atrium

H (ft): A (P):

164.00

fire growth constant (Menu) height of smoke layer above fire

a (~tuls'): z (ft)

0.0444 32.80

129000.00

Filling time is 1236 seconds or 20.6 min. At this time, the fire is 71650 kW or 67914 Btuk Simple plume equation Mass flow and temperature rise of a plume without correction for virtual origin Elevation Heat release rate of fire Ambient temperature

z (ft): Q (Btds): Ta (F):

At elevation z, the plume has: 12s1.9 kg/s Mass flow of

164.00 23700.00 70.00

2826.2 Ib/s

m3/s

Volumetric flow of I 117.2 2367054 cfm Average temperature of 35°C 94°F Mean flame height of 8.3 m 27.1 ft ------------------------------------------------------------------------Plume with Virtual Origin Correction Mass flow rate and average plume temperature Elevation Heat release rate of fire fire diameter Ambient temperature

z (ft): Q (Btds): D f ( ft): Ta (F):

At elevation z, the plume has: Mass flow of 1253.9 kg/s Volu~netricflow of Average temperature of Virtual origin at Mean flame height of

1093.9 m3/s 3j3C 0.7 m 9.4 m

164.00 23700.00 13.10 70.00

7764.4 Ib/s 2317599 cfm 95°F 2.3 ft 30.9 fi

Principles of Smoke Management

Plume Centerline Temperature Calculate centerline plume temperature Elevation Heat release rate of fire Fire diameter Convective fraction of heat release Ambient temperature At elevation z, the plume has: 46OC Centerline temperature Virtual origin at 0.7 m Mean flame height of 9.4 m

.

z (R): Q (Btuls): Df (R): (0.6 to l): Ta (F):

164.00 23700.00 13.10 0.70 70.00

Appendix F ASET-C: A Room Fire Program for Personal Computers INTRODUCTION Cooper (1981) of the Center for Fire Research, National Bureau of Standards, introduced ASET, a mathematical model for estimating available safe egress time in fires. Cooper and Stroup (1982) published a computer program to perform the calculations in the mathematical model; thus, the computer program also became known as ASET. ASET was not specifically written for the personal computer environment because at the time it was being developed, personal computers were just emerging as a tool for use in the engineering office. Since the introduction of ASET, the use of personal computers has become widespread and there has been significant interest in running ASET on personal computers. In response to this interest, Walton (1985) introduced ASET-B, a program for personal computers based on the original ASET mathematics1 model. The B was used to indicate basic, brief, BASIC, and beta. ASET is a 1500-line FORTRAN program that has many features. ASET-B is a 100-line BASIC program that was developed to be as simple and fast as possible. The most significant change in ASET-B is the use of a different mathematical procedure to solve the primary equations. ASET-B employs an equation solver that is at least five times faster than that used in ASET, while retaining mathematical agreement to within a fraction of a percent. ASET-B is an interactive program requiring a minimunl of input. These features make ASET-B easy to learn and apply. In many con\ ersations with practicing fire protection engineers, the author has found that ASET-B has become very popular. This appendix describes the ASET-C routine, which t ASMET program. ASET-C is a C language is p a ~ ofthe

version of ASET-B with improved interactive input and a few added features. The interactive input was made to be consistent with the other ASMET routines. The added features consist of allowing fire data input from a file and the use of a t-squared fire. Most of the material in this appendix is adapted from Walton's (1985) paper on ASET-B and, in many places, the adaptation consisted only of changing ASET-B to ASET-C.

DESCRIPTION OF THE MODEL The mathematical model that is the basis for ASET, ASET-B, and ASET-C has been presented in detail by Cooper (1981, 1982) and will be only summarized here. It is based on a single room or enclosure with all doors, windows, or vents closed except for a small leak at floor level. This leak prevents the pressure from increasing in the room. A fire starts at some point below the ceiling and releases cnergy and produc:~ of combustion. The rate at which energy and products of combustion are released may change with time. The hot products of combustion form a plume, which, due to buoyancy, rises toward the ceiling. As the plume rises, it draws in cool air from the room, which decreases the plume's temperature and increases its volume flow rate. When the plume reaches the ceiling, it spreads out and forms a hot gas layer, which descends with time as the plume's gases continue to flow into it. There is a relatively sharp interface between the hot upper layer and the air in the lower. part of the room, which, in this model, is considered to be at ambient, temperature. The only interchange between the air in the lower part of the room and the hot upper layer is through the plume. ASET could therefore be described as a two-layer or zone model. The basic fire phenomena are shown schernatically in Figure F 1.

Appendix F- ASET-C: A Room Fire Program for ~ e r s o n acomputers i

Air at Approximately ---c Ambient Temperature

Leak at Floor Level

l

I

"--

Figure F1 Schematic offire phenonzena.

The two unknowns in ASET-C are the height of the hot layer interface above the fire, Z, and the average temperature of the upper layer, P. It should be noted that the notation used here to describe the model is consistent with the variable names u;ed in the computer program. The unknowns, Z and P, are often referred to as the (dimensionless) height and temperature of the smoke layer since, consistent with the model formulation, smoke can only be found i n the plume and the hot upper layer. The known quantities are the.area and height of the room, A and H, the height of the base of the fire above the floor, F, and the acceleration due to gravity, G. In addition, the ambient temperature, PA, density, DA, and specific heat, CP, of air must be kno\vn. The final known quantities are the rate at which heat is released by the fire as a function of time, QT, the fraction of the total heat release, which is given off as radiation, LR, and the fraction of total heat release rate, which is lost to the contents and surrounding surfaces of the room, LC. The unknown height and temperature are determined by using conservation of mass and energy in conjunction with equations describing the plume. Since the height and temperature of the smoke layer will vary with time, T, their solutions are obtained by solving two differential equations. In developing the original equations for ASET (Cooper 198l , 1982), two dimensionless groups of problem parameters, C1 and C2, were introduced. Also introduced were dimensionless forms of the variables: time, height, and temperature of the smoke layer, initial height of the smoke layer, height of the base of the fire, and the rate of heat release. These variables are made dimensionless by dividing them bv a characteristic quantity with the same dimensions or units. Thus, the dimensionless temperature, P, is the actual temperature of the smoke layer. PF (converted to R), divided by the ambient temperature, PA (R). Similarly, the din~ensionlessrate of heat release, QT, is the actual rate of heat release, QA (kW), divided by the initial rate of heat release, Q0 (kW). Finally, the dimensionless variables, height of the smoke layer, Z,initial height of

the smoke layer, 20, and height of the base of the fire, F, are the dimensior~alvalues for these variables in feet divided by a characteristic length CL, which is also in feet. Here, as in the ASET program, CL is simply taken as one foot. Thus. the dimensionless lengths Z, ZO, and F are the same as their physical lengths in feet. The dimensionless time, T, is the actual time divided by a characteristic time, CT, of one second. The dimensionless time, T, is therefore numerically equal to the actual time in seconds. Since engineering units are used in ASET, this convention has been continued here for consistency. Conversion to S1 units is provided in the computer pro,oram. The d~fferentialequations for the dimensionless height of the layer above the fire, 2,and average temperature of the layer, P, are given below. -Cl . Q T - C 2 . Q T ' / ' 2 5 1 3

0

for 0 < Z < zo

for Z = -F

P [ C I . P T - ( P - 1 ) c 2- Q T 1 / 3 t 5 / 3 1 / ( z 0 + Z )

for o < Z < zo

2 I /3 C2 = (0.21 . C T / A ) [ ( I - L R ) . QO. G.CL / ( D A - C P - P A ) ]

In order to solve the equations for Z and P, the initial conditions must be known. One set of initial conditions, which were derived in Cooper (1981, 1982) and will be used here, assume that the fire starts with a small heat release rate, Q0, at time T = 0. Under such conditions, the initial conditions are

Although dPldT is indeterminate in the above equation at T = 0, its actual value has been found in Cooper (1981, 1981) to be

n_P - ~ 2DQO . + (Cl + C2 - ZO"') d T - C2 6.zo~/~ where DQO = dQT/dTat time T = 0. SOLUTION OF THE EQUATIONS In general, the differential equations for-Z and P cannot be solved explicitly; that is, an algebraic expression cannot be written that describes Zand P at any time 7. As a result, the equations must be solved numerically. ASET sol\-esthe difl'erential equations using a variation of the fourth-order Runge-Kutta method with variable time step. While this mcthod has a high degree of accu-

1

Principles of Smoke Management 3

j

1 2

racy, it has been determined that the improved Euler's method has sufficient accuracy for this problem. The improved Euler's method is a simple predictor-corrector type and is described in most books on numerical methods (Carhanan, Luther, and Wilkes 1969). The improved Euler's method used in ASET-C requires substantially fewer calculations than the method used in ASET, resulting in ASET-C running much faster than ASET. The improved Euler's method as applied in ASET-C is basically a technique for stepping the solution forward in time. Given the values of Zand P at a particular time, T, the method is used to determine the values of Z and P at time T + DT, where DT is a small time increment. This process is started at time T = 0 and continued until Z and P are known at all times of interest. In the case of ASET-C, an increment of one second has been found to yield results that agree well with ASET for problems of practical interest. In ASET-C, ZI, and PI are used to indicate the values of Z and P at time i7 For the first step, these are the initial values at time T = 0. 22 and P2 are used to indicate the values of Z and P to be calculated at time T + Di7 To determine 22 and P2 it is observed that the differential equations for Z and P represent the time rate of change of these quantities. The time rate of change multiplied by the time step yields the change that occurs over the time step. This would be an exact result if the equations were linear or the time steps were infinitely small. Since the equations are nonlinear, and it is impractical to make the time step infinitely small, an approximation must be used. In the improved Euler's method, 22 and P2 are first predicted using the derivatives evaluated at time I: Using 22 and P2, the derivatives are then evaluated at time T + DT. Corrected values of Z2 and P2 are then calculated using the average of the derivatives evaluated at times T and T + DT. 22 and P2 are predicted by 2 2 = 21 + DZI - DT , P2 = PI + DRI - DT

.

where DZ1 = dZldT and DP1 = dPldT are evaluated using Z = ZI and P = PI. The derivatives at time T + DT, D22 = dZlfl: and D M = dPld7; are then evaluated using Z = 22 and P = P2. Corrected values for Z2 and F2 are calculated using the average derivatives Z2C = Z l + [ ( D Z I + D Z 2 ) / 2 ] . D T , P2C = P1 + [ ( D P I + D P 2 ) / 2 ] . DT .

The predicted values of Z and P are then compared to the corrected values. In ASET-C, if the absolute value of the difference between the predicted and corrected values is less than 0.001, the solution is considered to have converged and the program proceeds to the next

time step. If the difference is greater than 0.001, the predicted values become the corrected values and the derivatives at time T + DT are recalculated. New corrected values are then calculated. In ASET-C, this procedure is repeated for a maximum of thirty times. If the differences are still greater than 0.001, a warning is printed, and the program proceeds to the next time step. The evaluation of the derivatives of Z and P requires the dimensionless heat release rate, QT, be known for all times, I: For heat release rates that are not constant with time, ASET-C requires the heat release be specified for each one-second time interval. To simplify this procedure, ASET-C uses point specified heat release rates with linear interpolation. Heat release rates can be specified at as many as 100 different times. Linear interpolation is then performed to determine the heat release rate at each time step. R U N N I N G THE P R O G R A M General Instructions ASET-C is written as an interactive program; that is, the program prompts the user with questions. As previously stated, ASET-C is part of the ASMET package of routines for atrium analysis, and a description of this package is provided in Appendix E. The mechanics of input for ASET-C, are consistent with the other routine in this package. To use ASET-C, data niust be entered for the items discussed below. Program Inputs Heat Loss Fraction. The first input is tlie heat loss fraction. This quantity is the instantaneous faction of the heat release rate of the fire that is lost to the bounding surfaces of the room and its contents. Cooper (1 98 1. 1982) has provided guidelines for selecting this parameter, which is called Lambda C (?), or ALMAC in ASET. He has detirmined that the approximate range is 0.G 0.9. The lower value corresponds to high aspect ratio spaces (ratio of ceiling span to room height) with smooth ceilings and fires positioned far away from the walls. The intermediate to high values corresponds to low aspect ratio spaces, rooms with irregular surfaces. or rooms in which the fire is within one ceiling height of the wall. The temperature of the upper layer is a function of the heat loss fraction and the heat release rate of the fire. The greater the heat loss fraction, the lower the temperature in the xpper layer. The heat loss fraction for a room mith insulated walls will be lower than the fraction for the same.room with uninsulated walls. Both ASET and ASET-C treat tlie heat loss parameter as a constant. That is, the heat lost from the room is a constant fraction of tlie heat release rate of the fire. As the heat release rate of the tire changes. tlie quantity of

-Appendix F-ASET-C: A Room F i e Program for Personal Computers

heat lost will also change, but in direct proportion to the fire. Therefore, the room will not cool down even though the heat release rate of the fire goes to zero. Height of the Base of the Fire. The second input is the height of the base of the fire above the floor in feet. For fuel items of relatively uniform surface height, such as beds, this is simply the height of the surface. For three dimensional h e 1 items, such as sofas, an average height weighted to reflect the distribution of surfaces should be used. The rate of growth of the upper layer is strongly dependent on the difference between the height of the base of the fire and the height of the smoke layer interface. Room Ceiling Height and Floor Area. The third and fourth inputs are the room ceiling height in feet and the floor area in square feet. According to Cooper (1981, 1982), the calculations may not be valid when applied to room length-to-width aspect ratios greater than 10: 1 or with a ratio of height to minimum horizontal dimension exceeding one. The equations are based on the assumption that the upper layer is well mixed and at a uniform temperature. Therefore, the results for a square room and a rectangular room of equal height and area will be the same. Output Interval. The fifth input is the output interval. This is the time step for results that are sent to the screen or printed. The output interval of ASET-B was set at five seconds, and this is the default interval for ASET-C. Maximum Time. The sixth input is the niaximuni time for the simulation in seconds. The results of the calculations will be printed at five-second intervals until the maximum time or until the end of the heat release data. Fire Growth Constant. The seventh input is the description of heat release rate of the fire. A fire gro\vth constant can be entered to define a t-squared fire, or the Menu can be activated that allows selection of a fire growth constant for typical fires (slow, medium, fast, or ultra-fast). From the menu, the user also can choose to enter data as sets of points, as was done with ASET-B. When the user selects data points, the computer waits for the run command to request the data. However, the following is a discussion of input by data points. As described earlier, the program can accommodate up to 100 pairs of times and comesponding heat release rates. The program performs a linear interpolation between the specified points to determine the heat release rates at the required times during the calculations. The data are entered by typing the time in seconds, follo\ved by a comma, followed by the heat release rate i n kilowatts. A return or enter is then typed to proceed to the nest linc.

Heat release rates entered as less than 0.1 kilowatt will be converted to that value. The program will automatically assume a starting value 0.1 kilowatt at time zero. A heat release rate at time zero does not have to be entered unless a greater initial heat release rate is required. When all of the desired times and heat release rates have been entered, a -9,-9 followed by a return is entered to terminate the data entry and begin the calculations. Actually, any negative time followed by a heat release rate will result in the same action. Optional Upper Limit on Fire. Fire growth may be approximated by the t-squared curve for some time. Because of the action of a suppression system, limitations of fuel, or limitations of combustion air, t-squared fire growth eventually must stop. The optional upper limit on fire growth allows the user to specify a heat release rate at which the fire curve reaches steady burnmg. Send Results to Printer or to File. To sent results to the printer, press P. To send results to a file, press t and enter the file name. Run Simulation. To run ASET-C, press R. If heat release rate by point entry has been selected from the Menu, the data points will be requested after the run starts. Program Outputs. The output of the ASET-B program is a summary of the input data and a table of the conditions in the room as a function of time. The first colunln in the table is the simulation time in seconds. The second and third columns are the temperature in the upper layer in degrees Celsius and Fahrenheit. The fourth and fifth columns are the height above the floor of the interface between the upper and lower layers. The sixth and seventh columns are the heat release rate of the fire in kilowatts and Btu per second. The output has the same number of significant digits as does ASET-B, which allows users to verify that this program produces the same results as ASET-B for the same input. LIMITATIONS OF ASET The use of ASET-C or any design aid requires the design engineer to make the final evaluation as to the appropriateness of the design. The ASET-C programs are based on certain engineering approximations of the fire environment and should be used to supplement rather than replace sound engineering judgment. The program results should be treated as approximate and the user is encourayed to become familiar with how changes in the input variables affect the program results. The temperature of the upper layer and the height of the interface respond differently to changes in the input data. Appropriate factors of safety should be applied to either the input data or ths program results.

1 3;j 'I

.

,.

Principles of Smoke Management

Some of the limitations of the program have been presented in conjunction with the input data requirements. There are, however, some additional limitations. The mathematical procedure used in ASET-C is very harrly; that is, the procedure will normally converge and produce results. There are combinations of input data for which the program will either fail to converge or halt due to an illegal mathematical operation. If the procedure for solving the equations fails to converge, a warning will be printed and the solution will continue. The results following this message may be in error and should be treated as such. The failure to converge is usually a result of a heat release value that changes too rapidly. In most cases, this problem can be corrected by minor smoothing of the input heat release curve.

VERIFICATION O F ASET Results of the ASET program have been compared to data from a limited number of actual fire experiments (Cooper 1981, 1982). These comparisons can be extended to the ASET-B and ASET-C programs since they produce results that are within a few percent of those produced by ASET. The fire experiments considered a mockup of a hospital room-corridor building space. Comparisons were found to be generally favorable. This does not necessarily mean that the comparison will be favorable ia all cases. Clearly, additional studies are required in this area and that work is ongoing.

Appendix F- ASET-C: A Room Fire Program for Personal Computers

-

SAMPLE RUN (ENGLISH UNITS) HEAT LOSS FRACTION = FIRE HEIGHT ROOM HEIGHT = ROOM AREA =

0.80 1.OOft 9.00ft 225.00sq ft

Fire curve input manually TIME (sec), HEAT RELEASE RATE (kW): TIME (sec), HEAT RELEASE RATE (kW): TIME (sec), HEAT RELEASE RATE (kW): TIME (sec), HEAT RELEASE RATE (kW): TIME sec 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0 95.0 100.0 105.0 110.0 1 15.0 120.0 125.0 130.0 135.0 140.0 145.0 150.0 155.0 160.0 165.0 170.0 175.0 180.0

TEMP

TEMP

C 21.3 23.4 24.9 26.3 27.7 29.2 30.8 32.6 34.4 36.4 38.6 40.9 43.3 46.0 48.8 51.8 55.0 55.3 61.9 65.8 69.8 74.2 79.0 84.3 90.0 96.2 102.9 110.1 1 17.7 125.9 134.6 143.7 153.3 163.3 173.7 184.5 195.9

LAYER

LAY ER

FIRE

FIRE

F

ft

kW

Btuls

70.3 74.2 76.7 79.3 81.8 84.6 87.5 90.6 93.9. 97.5 101.4 105.6 110.0 114.7 119.8 125.2 130.9 137.0 143.5 150.4 157.6 165.5 174.2 183.7 194.0 205.1 217.2 230.1 243.9 258.7 274.3 290.7 307.9 325.9 344.6 364.2 384.7

9.0 8.7 8.3 7.8 7.3 6.9 6.5 6.0 5.7 5.3 5.0 4.7

0.1 10.1 20.1 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 1 10.0 120.0 130.0 140.0 150.0 160.0 170.0 180.0 190.0 200.0 218.8 237.5 256.2 275.0 293.8 3 12.5 33 1.2 350.0 368.8 387.5 406.2 425.0 443.8 462.5 48 l 2 500.0

0.1 9.6 19.0 28.5 37.9 47.4 56.9 66.4 75.9 85.4 94.8 104.3 113.8 123.3 132.8 142.3 151.8 161.2 170.7 180.2 189.7 207.5 225.3 243.1 260.5 278.6 296.4 314.2 332.0 349.8 367.5 385.3 403.1 420.9 438.7 456.5 474.2

4.4

1. I 3.9 j.6 3.4 3.2 3.0 2.8 2.6 2.5 2.3 2.1 2.0 I .S 1.7 I .5 1.3 1.2 1 .o 0.8 0.6 0.4 0.2 0.0 0.0

Principles of smoke ~ a n a ~ e m e h t

SAMPLE RUN (S1 UNITS) HEAT LOSS FRACTION = 0.80 FIRE HEIGHT = 0.00 m ROOM HEIGHT = 3.00 m ROOM AREA = 20.00 sqm fire growth constant (KWlsA2):0.046890 TIME sec

TEMP C

TEMP F

LAYER m

FIRE kW

FIRE Btds

0.0

21.2

70.2

3.0

0. I

0.1

5.0

21.5

70.6

2.9

1.2

1.1

10.0

21.9

71.5

2.8

4.4

15.0

22.6

72.6

2.7

10.0

20.0

23.3

74.0

2.5

17.8

25.0

24.3

75.7

2.3

27.8

30.0

25.4

77.8

2.2

40.0

35.0

26.8

80.2

2.0

54.5

40.0

28.4

83.1

1.8

71.2

45.0

30.3

86.6

1.6

90.1

50.0

32.5

90.5

1.5

111.2

55.0

35.1

95.2

1.3

134.5

60.0

38.1

100.5

1.2

160.1

65.0

4 1.5

106.6

1.1

187.9

70.0

45.3

113.6

I .o

217.9

75.0

49.8

121.6

0.9

250.2

80.0

54.8

130.6

0.8

284.6

85.0

60.5

140.8

0.7

321.3

90.0

66.9

152.4

0.6

360.2

95.0

74.1

165.3

0.5

401.4

100.0

82.1

179.9

0.4

444.8

105.0

9 1.2

196.1

0.3

490.3

110.0

101.3

214.3

0.2

538.1

115.0

112.5

234.4

0. I

588.2

120.0

124.8

256.7

0.0

640.4

125.0

138.5

281.3

0.0

694.9

130.0

153.8

308.8

0.0

751.6

135.0

171.0

339.8

0.0

810.6

140.0

190.3

373.5

0.0

871.7

145.0

211.9

413.4

0.0

935.1

150.0

236.2

457.1

0.0

1000.7

155.0

263.5

506.3

0.0

1068.5

160.0

293.3

56 1.7

0.0

1138.6

0.0

1210.8

329.0

613.1

170.0

368.1

694.6

0.0

1285.3

175.0

412.5

774.4

0.0

1362.1

180.0

362.7

864.9

0.0

1441.0

165.0

Appendix G Data and Computer Output for Stairwell Example his appendix lists the data and CONTAM output for Example 10.4. Figure G1 is the CONTAM representation of the building. The design parameters are listed in Table G-l and the flow areas are listed in tat.!^ G-3. The CONTAM runs are summarized in Table G-3, and the CONTAM simulated pressure differences from the stair to the building are listed in Table G-4. Table G-5 is a listing of the entire CONTAM flow output for run 1. For a discussion of the results of this example, see Example 10.4 in Chapter 10.

(a) Ground F!oor

Notes. l . Values of flow areasare Iksted in Table E2. 2. This door is either opened or closed (Single-door or Open-door)

(b) Typical Floor

Symbols Single-door Leakage area of dosed single door Double-door Leakage area of closed doubles door Own-door Flow area of opened single door Elev-door Leakage area of closed elevator door Ext-wall Leakage area of canstruclion cracks and gaps in eflerior walls Elev-wall Leakage area of construction cracks and gaps in elevator shafi walls Leakage area of mstruction cracks and gaps in slairwe!l walls SW-wall 81dg-floor Leakage area of construction cracks and gaps in budding floor of the elevator shafl El vent Vent to the outside at the IOD Effectwe area to a m u n t fo; fncl~onlosses m slamell Sj[r_floor Etfecl ve area to a m u n t for fnct~onlosses in e1eva:or snaft €1-floor SWI Stairwell 1 SW2 Stawell2 FL Open plan space on the flool EL Elevafor shafl

Figure G 1 CONTAM t-e~~~-~setitatiot~~fotExatnple 10.4: (a) gro~o~d~floot. atid (1,) ~picalfloot:

337

Appendix G - Data and ComputerOutput forStairwell Example

Table G-1: Design Parameters for Example 10.4 Design number of open doors from stairwell to building Number of stories Height between stories Outside winter design temperature

4 15 12.0 ft (3.66 m)

Outside summer design temperature

93OF (34OC)

Building design temperature

73OF (23OC)

14OF(-1 O°C)

Minimum design pressure difference

0.05 in. H20 (12.4 Pa)

Maximum design pressure difference

0.30 in. H20 (87 Pa)

Table 6-2: Flow

re as' for Example 10.4

CONTAM Path Name Doors: Single - Closed Double -Closed Single - Opened Elevator - Closed Walls (per floor): Exterior Elevator Stairwell to Building Stairwell to Outside Building Floor Elevator Shaft Vent

Ext-wall Elev-wall SW-wall SW-wall Bldg-floor Elev vent

Effective Areas of shafts2 Stairwell Elevator

SW-floor Elev-floor

I. 2.

f?

Tight Building mz

Loose Building ft2 m2

Single-door Double-door Open-door Elev-door

41 1290

3.8 120

41 1290

3.8 120

A flow cocfficient, C, of 0.65 is used for all flow areas cscepr for open stairwell doors for which C = 0.35.

Effective area of a shaft is the area that results in a pressure drop equal to the friction losses of flow in the shaft. See Examples 6.9 and 6.10

Table G-3: Summary of CONTAM Runs for Example 10.4 Building Run

1 2 3 4 5 6

File

EX-10-4D EX-10-4A EX-10-4C EX-10-4B EX-10-4E EX-10-4F

Season Summer Summer Winter Winter Summer Winter

Leakage Loose Loose Loose Loose Tight Tight

Stair Supply ~ i r ' Stair Doors open2

G, 2 , 3 , 4 , 5 G G, 12, i3, 14, 15 G G, 2 , 3 , 4 , 5 G

cfm

rn3/s

20,500 20,500 20,500 20,500 13,900 13,900

9.67 9.67 9.67 9.67 6.56 6.56

The flow orsupply pressurization air was obtained by running thc computer program several times for runs I and 6 toobrain pressure differences that are 31 leas1 the mininiuni d c s i g value of 0.05 in. H+ (12.4 Pa). 2. G indicates thc exterior ground lloor stainvell door. 1.

Principles of Smoke Management

Table G-4: Pressure Differences Across interior1 Stairwell Door for Example 10.4 Run 2 in. H 2 0 Pa

N.%

.NA

Run 3 in. H 2 0 Pa NA

NA

Run 4 in. H 2 0 Pa NA

NA

Run S in. H 2 0 Pa NA

NA

Run 6 in. H 2 0 Pa NA

NA

0.171

42.5

0.204

50.8

0.110

27.4

0.162

40.3

0.214

53.2

0.1 10

27.4

0.159

39.6

0.228

56.7

0.110

27.4

0.152

37.8

0.239

59.5

0.110

27.4

0.149

37.1

0.248

61.7

0.1 10

27.4 27.4

0.147

36.6

0.253

61.9

0.110

0.145

36.1

0.256

63.7

0.109

27.1

0.144

35.8

0.257

63.9

0.109

27.1

0.143

35.6

0.259

64.4

0.109

27.1

0.141

35.1

0.262

65.2

0.109

27.1

0.139 0 . 1

34.6 34.1

0.267

66.4

0.108

26.9

0.271

67.4

0.108

26.9

0.134

33.3

0.275

68.4

0.108

26.9

33.1

0.276

68.7

0.107

26.6

0.133

I . All interior stair\rc.ll door is one br.t\;-.cn 11ic s~sinv, 2. NA indicates "no[ applicahlc" hcc2ci: therc. is 110interior stairwell door on rl~cground floor.

A p p e n d i x G - D a t a and C o m p u t e r O u t p u t for Stairwell Example

Table GS. CONTAM Flow and Pressure O u t p u t for Example 10.4 project: EX-10-4D description: E x a m p l e 1 0 . 4 Surrrmer

-

Run 1

4 SW-Doors Opened

simulation date: Janl s i m u l a t i o n t i m e : 00:00:00 ambient temperature: 93.0.F barometric pressure: 2 9 . 5 i n . Hg wind s p e e d : 0 . 0 mph wind d i r e c t i o n : 0.C d e g level: G zone

e l e v a t i o n : 0.0 f t P 0.103

EL

T . 73.4

path Elev-f l s o r Elev w i l l ~levrdoor Elev-docr

Flow 579.50 -32.15 - 273.68 -27.3. 68 926.11 32.15 273.68 273.68 -167.61 -167.61 80.68 80.68 -1038.41 - 293.32

level: 2

73.4

SW-£ l o o r Open-docr SW-wa l l SW-wall

11643.36 -11451.74 - 1 l C . 94 - 80.68

73.4

SW-f l o o r Open-doo: SW-wall SW-wa l l

11643.36 -1lrsi.74 -80.68 - 110.94

e l e v a t i o n : 12.0 f t

zone EL

P - 0.069

T 73.4

path Elev-floor Elev-wall Elev-flocr Elev-door Elev-door

Flow - 271.45 47.20 - 579.50 401.87 401.87

FL

-0.OC8

73.4

Bldg-floor Elev-wall Elev-door Eiev-door Open-docr 0per.-door Blcig-floor SW-wa l l S5i-w a l l Ext-wall

- 155.15 - 47.20 - 401.87 -401.87 1712.12 1712.12 -926.11 16.66 16.66 - 1525.34

Principles of Smoke Management

SW1

-0.005

73.4 SW-floor Open-door supply SW-wall SW-wall SW-floor

SW2

-0.005

73.4

level: 3 zone EL

~w-floo; Open-door supply SW-wall SW-wall SW-£ loor

SW2/3 FL/2 Supply FL/2 Ambt SW2/G

elevation: 24.0 ft

P -0.241

T 73.4

path Elev-floor Elev-wall Elev-floor Elev-door Elev-door

from EL/4 FL/3 EL/2 FL/3 FL/3

Flow -1104.74 46.22 271.45 393.53 393.53

FL/4 EL/3 EL/3 EL/3 SW1/3 SW2/3 FL/2 3W1/3 SW2/3 Ambt SW1

-0.181

73.4 SW-floor Open-door SW-wall SW-wa11 SW-floor

3W1/4 FL/3 Ambt FL/3 sh'1/2

SW2

-0.181

73.4 SW-floor Open-door SW-wall SW-wall SW-floor

3W2/4 FL/3 FL/3 Ambt SW2/2

level: 4 zone EL.

elevation: 36.0 ft

P -0.412

T 73.4

path Elev-floor Elev-wall Elev-floor Elev-door Elev-door

r rom EL/5 FL/4 EL/3 FL/4 FL/4

Flow -1917.62 45.09 1104.74 383.89 383.89

Appendix G-Data and Computer Output for Stairwell Example

SW1/4 SW2/4 EL/3 SW1/4 SW2 / 4 Ambt SW1

-0.355

73.4

SW-floor Open-door SW-wa l i SW-wall SW-floor

SW1/5 EL/4 Ambt FL/4 SW1/3

SW2

-0.355.

73.4

SW-floor Open-doo r SW-wall SW-wall SW-floor

SW2/5 FL/4 FL/4 Ambt SW2/3

level: 5 zone EL

elevation: 48.0 ft

P -0.584

T 73.4

path Elev-floor Elev-wall Elev-f loor .Elev-door Elev-door

Flow -2711.67 44.05 1917.62 375.00 375.00 -721.49 -44. 05 -375.00 -375.00 1361.43 1361.45 156.d.7 13.24

13.24 -1390.31 SW1

-0.529

73.4

SW-floor OpeR-do cr SW-wa 11 SW-wa1 1 SW-£ loo=

SW1/6 FL/5 Ambt FL/5 SW1/4

-3039.04 -1361.45 -102.81 -13.24 4516.54

-0.529

73.4

SW-floor Open-door SW-wall SW-wall SW-floor

SW2/6 FL/5 FL/5 Ambt SW2/4

-3039.04 -1361.45 -13.24 -102.81 4516.54

. .

w 2

level: 6 zone

L

elevation: 60.0ft

P -0.756

T

73.4

from path Elev-floor EL/7 Elev wall FL/6 ~ l e v ~ f l o c r EL/5 Elev-docr FL/6 FL/6 Elev-door

dP 0.000 -0. G01 0.000 -0.001 -0.001

Flow -2598.ii -6.21 2711.67 -53.35 -53.35

Principles of Smoke Management

FL/7 EL/6 EL/6 EL/6 SW1/6 SW2/6 FL/5 SW1/6 SW2/6 Ambt SW1

-0.701

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

SW1/7 FL/6 Ambt FL/6. SW1/5

SW2

-0.701

73.4

SW-floor Single-door SW-wall SW-wall SW-f loor

SW2/7 FL/6 FL/6 Ambt SW2/5

level: 7 zone EL

elevation: 72.0 ft

P -0.927

T 73.4

path Elev-floor Elev-wall Elev-floor Elev door ~1ev:door

Flow -2302.12 -16.45 2598.71 -140.07 -140.07 FL/8 EL/: EL/: EL/? SW1/7 SW2/7 FL/6 SW1/7 SW2/7 Ambt

SW1

-0.874

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

SWl/% FL/7 Ambt FL/7 SW1/5 SW2/8 FL/7 FL/7 Ambt SW2/6

level: 8 zone EL

elevation: 84.0 ft

P -1.099

T 73.4

path Elev-f loor Elev-wall

Flow -1994.48 -17.07

Appendix G-Data and Computer Output for Stairwell Example

Elev-f loor Elev-door Elev-door FL

-1.107

73.4

Bldg-floor Elev-wall Elev-door Elev-dqor Single-door Single-door Bldg-f loo r SW-wall SW-wall Ext-wall

SW2

-1.046

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

level: 9 zone EL

-FL/9 EL/8 EL/8 EL/8 SW1/8 SW2/8 FL/7 SW1/8 SW2/8 Ambt

elevation: 96.0 ft

P - 1.271

T

73.4

path Elev-floor Elev-wall Elev-f loor Elev-door Elev-door

from EL/10 FL/9 EL/8 FL/9 €L/9 €L/10 EL/9 EL/9 EL/9 SW1/9 SW2/9 FL/8 SW1/9 SW2/9 Ambt

SW1

SW2

-1.218

73.4

-1.213

Levei: 1 0

73.4

SW-floor Single-door SW-wall SW-wall SW-floor SW-floor Single-dozr SW-wall SW-wall SW-floor

elsvation: 108.0 f z

SW1/10 FL/9 Amb t

FL/9 SW1/8

dP 0.000 -0.008 0.000 -0.008 -0.008

Flow -1688.91 -16.95 1994.48 -144.31 -144.31

Principles of Smoke Management

zone EL

SW2

P -1.442

-1.390

T 73.4

73.4

path Elev-floor Elev-wall Elev-floor Elev-door Elev-door

SW-floor Single-door SW wall ll SW-floor

SWIW~

level: i l

P -1.614

T 73.4

patn Elev-floor Elev-wall Elev-floor Elev-door Elev-door

FL

- 1.620

73.4

Bldg-floor Elev-wall Elev-door Elev-door Singie-door Single-door 91dg-floor S%' wall ll Ext-wa 11

SWIW~

SW1

1

Flow -1399.17 -16.07 1688.91 -136.83 -136.83

"/l1 ZL/ 10 EL/10 ZL/lO SXl/lO S:i2/10 - 3/9 s;.:1/10 sx2/10 .=nbt

111.30 16.07 136.83 136.83 151.44 151.44 -87.32 69.41 69.41 -755.43

SXl/ll 'L/10 .'?mbt fL/10 %1/9

-1462.62 -151.44 -88.81 -69.41 1772.29

-C;.;2/11 3/10 3/10 .=Xbt S>;2/ 9

-1462.62 -151.44 -69.41 -88.81 1772.29

elevation: 120.0 ft

zone EL

SW2

from EL/ 11 FL/lO EL/9 FL/10 IL/lO

6 2

73.4

SW-f loor Singie-door SW-wal l

dP 0.000 -0.006 0.000 -0.006 -0.006

Flow -1137.18 -14.53 1399.17 -123.73 -123.73

!,

Appendix G - Data and Computer Output for Stairwell Example

SW-wall SW-floor level: 12 zone EL

Ambt SW2/10

elevation: 132.0 ft

P -1.786

T 73.4 -

path Elev-floor Elev-walf Elev-floor Elev-door Elev-door

from EL/13 FL/12 EL/11 FL/12 FL/12

Flow -911.05 -12.54 1137.18 -106.80 -106.80

FL/13 EL/12 EL/12 EL/12 SW1/12 SW2/12 FL/11 SW1/12 SW2/12 Ambt SW1

-1.734

73.4

SW-floor SW1/13 Si~.gle.-door FL/12 Ambt SW-wa ll FL/12 SW-wall SW-f loor SW1/11

SW2

-1.734

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

level: 13 zone EL

SW2/13 FL/12 FL/12 Ambt SW2/11

elevation: 1'44.0 ft

P -1.958

T 73.4

path Elev-floor Elev-wall Elev-f loor Elev-door Elev-door

from EL/14 FL/13 EL/12 FL/13 FL/13 FL/14 EL/13 EL/13 EL/13 SW1/13 SW2/13 FL/12 SW1/13 SW2/13 Ambt SW1/14 FL/13 Ambt FL/13 SW1/12

Flow -726.25 -10.25 911.05 -87.24 -87.24

.

SW2

-1.906

level: 14

-

73.4

SW-floor Single-door SW-wall SW.-wall SW-floor

Principles of Smoke Management

.

SW2/14 =/l3 FL/13 Ambt SW2/12

0.000 -0.055 -0.055 -0.079 0.000

-568.54 -145.53 -66.70 -79.85 860.62

elevation: 156.0 ift

T

zone EL

73.4

path Elev-f loor Elev-wall Elev-floor Elev-door Elev-door

FL

from EL/15 FW14 EL/13 FL/14 FL/14

Flow -584.77 -7.85 726.25 -66.85 -66.85

FL/lS EL/14 EL/14 EL/14 SW1/14 SW2/14 FL/13 . SW1/14 SW2/14 Ambt

78.72 7.85 66.85 66.85 143.91 143.91 -106.76 65.96 65.96 -533.25

..

SW1

SW1/15 FL/ 14 Amb t FL/14 SW1/13

-281.99 -143.91 -76.68 -65.96 568.54

SW2

SW2/15 FL/i4 FL/14 Ambt SW2/13

-281.99 -143.91 -65.96 -76.68 568.54

from EL/16 FL/lS EL/14 FL/15 FL/15

Flow -473.52 -6.17 584.77 -52.54 -52.54

EL/15 EL/l5 EL/15 SW1/15 SW2/15 FL/14 SW1/15 SW2/15 Ambt

6.17 52.54 52.54 143.04 143.04 -78.72 65.56 65. 56 -449.73

FL/15 Ambc

-143.04 -73.39

level: 15 zone EL

elevation: 168.0 ft

P -2.301

Appendix G-Data and Computer Output forStairwell Example

SW2

-2.249

level: 16 zone EL

Exhust supply

FL/15 SW1/14

Single door SW wali ~ ~ 3 a l l SW-floor

FL/15 FL/15 Ambt SW2/14

elevation: 180.0 ft

P .-2.473

systems: name

73.4

SW wall ~~Ifloor

T 73.4

path Elev-Vent Elev-floor

air flows: recirc outside 0.00 0.00 0.00 40999.97

Note: flows in scfm pressures in i ' n . ~ 2 0 temperatures in F * indicates limit exceeded

from Ambt EL/15

dP -0.008 0.000

Flow -473.52 473.52

Appendix H Data and Computer Output for Zoned Smoke Control Example his appendix lists the data and CONTAM output for Example 12.5. The example is an eight-story building with zoned smoke control and two pressurized stainvells. With the exception of the number of stories, the design parameters and flow areas o f this example are the same as Example 10.4 (Appendix G), and Figure G I is applicable. The CONTAM runs are summarized in Table H-l, and the CONTAM simulated pressure differences from the stair to the building are listed in Table H-2. Table H-3 is a listing o f the entire CONTAM flow output for run l . For a discussion of the results of example, see Example 12.5 in Chapter 12. Table H-l: Summary of CONTAM Runs for Example 12.5

Run

File

Season

Building Leakage

1 2 3 4

EX-12-5A EX-12-5C EX-12-5B EX-12-5E

Summer Summer Summer Winter

Loose Loose Loose Loose

5

EX-12-5D EX-12-SF

Winter Winter

~oose Loose

6 I.

Fire Floor Eshaust

Adjacent Floor SUPP~Y

Staircwll Supply

cfn'

m3/s

cfm

ni3/s

cfni

n19s

G 2 7 G

2800 2800 2800 2800

1.32 1.37 1.37 1.37

0.761 0.761 0.761 0.761

2SOO 2800

1.32 1.32

1.32 1.32 1.37 1.32 1.32 1.32

l600 l600 l600 l600

--I

2800 2800 2800 2800 2800 2800

1600 l600

0.764 0.764

~loorl

7

G indicates the exterior ground lloor stairwell door.

Table H-2: Pressure Differences Calculated by CONTAM for Example 12.5 Stairwell to Fire Floor

Floor Below to Fire ~ l o o r '

Floor Above to Fire Floor

Run

in. HzO

Pa

in. HzO

Pa

in. HzO

Pa

2 3 4 5 6

0.065 0.053 0.063 0.054 0.103

16.2 13.2 l 5.7 13.1 75.6

0.060 0.053 NA 0.087 0.087

11.9 13.2 NA 3 1.6 21.6

0.066 0.072 0.069 0.051 0.091

16.4 17.9 17.7 13.4 23.1

1.

N A indicates "not spplic;~hlc."

.

Appendix H- Data and Computer Output for Zoned Smoke Control Example

Table H3. CONTAM Flow and Pressure Output for Example i 2 . 5 , ~ u n1 project: EX-12-5A description: Example 12.5 Summer

-

Loose Building

-

Fire on Floor G

simulation date: Janl simulation time: 00:00:00 ambient temperature: 93.b F 29.9 in. Hg barometric pressure: wind speed: 0.0 mph wind direction: 0.0 deg Levei: G

elevation: 0.0 ft

D

T

0.044

73.4

-0.018

S?; l

Sii2

zone EL

€L

dP 0.000 -0.061 -0.061 -0.061

Flow1 855.97 -47.48 -404.24 -404.24

SW1/2 Ambt Ambt FL/G

0.000 -0.067 -0.066 -C.086

317.03 -160.52 -72.87 -83.64

SW2/2 Ambt FL/G Ambt

0.000 -0.067 -0.086 -0.066

317.03 -160.52 -83.64 -72.87

path Elev-floor Elev-wall Elev-floor Elev-door Elev-door

f rom EL/3 FL/2 EL/G FL/2 FL/2

dP 0.000 0.024 0.000 0.024 0.024

Flow1 322.91 29.57 -855.97 251.74 251.74

Bldg-floor Elev-wall Elev-door Elev-door Single-door supply

FL/3 EL/2 EL/2 EL/2 SW1/2 Supply

-0.G24 -0.024 -0.024 -0.024 0.001 n/a

-479.55 -29.57 -251.74 -251.74 19.87 2800.00

path Elev-floor Elev-wall Elev-door Elev-door

from EL/2 FL/G FL/G FL/G

73.4

Bldg-floor Elev-wall Elev-door Elev-door Single-door Single-door return SW-wa ll SW-wall Ext-wall Double-door

FL/2 EL/G EL/G EL/G Ambt Ambt Exhust SWl/G SW2/G Ambt Ambt

0.069

73.4

SW-floor Single-door SW-wall SW-wall

0.069

73.4

SW-floor Single-door SW-wall SW-wall

level: 2

elevation: 12.0 ft

T

zcne EL

P -0.128

73.4

€'L

-0.104

73.4

Principles of Smoke Management

SW2/2 FL/G SW1/2 SW2/2 Ambt SW1

-0.103

73.4

SW-floor Single-door supply SW-wall SW-wall SW-floor

SW2

-0.103

73.4

%-floor Single-door supply SW-wall SW-wall SW-floor

level: 3 zone EL

SW2/3 FL/2 Supply FL/2 Ambt SW2/G

elevation: 24.0 ft

P -0.300

T 73.4

path Elev-floor Elev-wall Elev-floor Elev-door Elev-door

from EL/4 FL/3 EL/2 FL/3 FL/3 FLi4 EL/3 EL/3 EL/3 SW1/3 SW2/3 FL/2 SW1/3 SW2/3 Ambt

SW1

-0.275

73.4 .

SW2

-0.275

level: 4 zone EL

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

SW1/4 FL/3 Ambt FL/3 SW1/2

SW-floor Single-docr SW-wall SW-wall SW-floor

SW2/4 FL/3 FL/3 Ambt SW2/2

eleva~ion:36.0 ft

P -0.47i

T path 73.4. Elev-floor Elev wail

from EL/5 FL/4

Appendix H-Data and Computer Output for Zoned Smoke Control Example

EL/3 FL/4 FL/4 FL/5 EL/4 EL/4 EL/4 SW1/4 SW2 / 4 FL/3 SW1/4 SW2 / 4 Ambt -0.447

73.4

SW-floor Single-door SW-wall SW-wall SW-floor

SW1/5 FL/4 Ambt FL/4 SW1/3 SW2/5 FL/4 FL/4 Ambt SW2/3

elevation: 48.0 ft

level: 5

P

zone EL

-0.643

T 73.4

path Elev-f loor Elev-wall Elev-f loor Elev-door Elev-door

from EL/6 FL/5 EL/4 FL/5 FL/5

FL

-0.64 4

73.4

Bldg-f loor Elev-wall Elev-door Elev door single-door Single-door Bldg-f loor S W-wa ll SW-wall Ext-wall

FL/6 EL/5 EL/5 EL/5 SW1/5 SW2/5 FL/4 SW1/5 SW2/5 Ambt

SW1

-0.618

73.4

SW-floor Single-door S W-wa ll SW-wall SW-floor

SW1/6 FL/5 Fmbt FL/5 SW1/4

SW2

SW2/6 FL/5 FL/5 Ambt

Principlesof Smoke Management

SW-floor level: 6

elevation: 60.0 ft

zone EL

P -0.8 15

T 73.4

path Elev-f loor Elev-wal l ~lev-f loor Elev-door Elev-door

from EL/7 FL/6 EL/5 FL/6 FL/6

FL

-0.8 15

73.4

Bldg-f loor Elev-wa 11 Elev-door Elev-door Single-door Single-door Bldg-floor SW-wall SW-wall Ext-wall

FL/7 EL/6 EL/6 EL/6 SW1/6 SW2/6 FL/5 SW1/6 SW2/6 Ambt

SW1

-0.790

73.4 SW-floor Single-docr SW-wall SW-wall SW-floor

SW1/7 FL/6 Ambt FL/6 SW1/5

SW2

-0.790

73.4 SW-floor Single-door SW-wall SW-wall SW-floor

SW2/7 FL/6 FL/6 Ambt SW2/5

level: 7 zone EL

Flowl 668.01 -4.68 -583.62 -39.86 -39.86

elevation: 72.0 ft

P -0.986

T 73.4

path Elev-f loor Elev-wall Elev-floor Elev-door

from EL/8 FL/7 EL/6 'FL/7 FL/7 FL/8 EL/7 EL/7 EL/7 SW1/7 SW2/7 FL/6 SW1/7 SW2i7 Ambt SW1/8 FL/7 Ambt

Flowl 609.22 3.26 -668.01 27.77 27.77

.

Appendix H- Data and Computer Output for Zoned Smoke Control Example

-0.962

S W ~

level: 8

FL/7 SW1/6

-0.024 0.000

-44.35 368.28

SW-floor Single-door SW-wall SW-wall SW-f loor

SW2 /8 FL/7 FL/7 Ambt SW2/6

0.000 -0.024 -0.024 -0.029 0.000

-178.95 -96.76 -44.35 -48.22 368.28

-

elevation: 84.0 ft

P

zone EL

73.4

SW-wall SW-£ loor

T

-1.158

73.4

path Elev-floor Elev-wall Elev-f loor Elev-door Elev-door

from EL/9 FL/8 EL/7 FL/8 FL/8

Flowl 456.28 8.48 -609.22 72-23 72.23

EL/8 EL/8 EL/8 SW1/8 SW2/8 FL/7 SW1/8 SW2/8 Ambt FL/8 Ambt FL/8 SW1/7 - 1.134

SW2

level: 9 zone EL

73.4 Single-door SW-wall SW-wall SW-f loor

elevation: 96.0 ft

P

T

-1.330

73.4

systems: name Exhust Supply

path Elev-Vent Elev-floor

air flows: recirc outside 0.00 0.00 0.00 6000.00

Note: flows in scfm pressures in in.H20 temperatures in F * indicates limit exceeded

from Ambt EL/8

Flowl 456.28 -456.28

Appendix I Inspection Procedures for Smoke Control Svstems SCOPE T h e inspection procedures described in this appendix apply to smoke control systems that are dedicated only to controlling smoke in building fires o r that make use o f air-moving equipment with another function, such as heating and air conditioning. These procedures are, o f a general nature, intended as a guide for tlie development of specific procedures for individual smoke control systems. These procedures address tlie major components of smoke control systems but, by their general nature, cannot address all possible coniponents. In this appendix, the phrase "as specified" is used to mean as specified in accordance with a contract documents, a code, or some other standard o r standards that have been agreed upon by the owner, designer, builder, code official, and other involved parties.

BARRIERS a.

b.

c.

Clieck walls, partitions, floors, and ceilings of barriers of smoke control systems for obvious and unusual openings that could adversely affect smoke control performance. Check tliat gaps around doors do not exceed the limits specified. If gasketing is required, check that it is as specitied. Check that automatic door closers in barriers of smoke control systems are as specified.

AIR-MOVING EQUIPIMENT a.

Check ducts to veriQ that materials ofduct material and construction are as specified.

Check duct installation. Duct installation, including the hangers, must not reduce the fire resistance rating of structural members and of assemblies. Frequently, structural members and asse~iiblieshave fire protective coverings, such as drywall construction or a sprayed-on layer. Check that ducts are installed in such a manner that these protective coverings are not damaged. Check that clearance from ducts to conibustible construction is as specified. In addition, check that where ducts pass through walls, floors, or partitions, the openings in construction around tlie ducts are as specified. Clieck that installation and materials of duct connectors and flexible duct connectors are as specitied. CAUTION: Become 11le cllaracteristics of duct co1it7ectors atid j1e.rible drtc~co~itiecforsare diffe~wir,orie sliorrld not be srrbs~i~rrted for 111eotliet: Check duct coverings and linings to verify that their fire safety requirements are as specified. Check that duct coverings do not conceal any service opening. Check direct access and inspection provisions. Service openings and telescoping or removable duct sections are used for direct access and inspection. Check tliat a service opening or a telescoping or removable duct section is provided in ducts as specified adjacent to fire dampers, smoke dampers. and smoke detectors. Check that these access openings are identified wit11 letters as specified. Check that service openings are

. Appendix I - Inspection Procedures for Smoke Control Systems

with normal air flow to ensure that they are not held open by the airstream. Remember to reinstall all hsible links that have been removed during inspection.

provided in horizontal ducts and plenums where specified.

f

Check air filters to verify that they have the classification specified.

g.

Check that the location, fire protection rating, and installation of fire, ceiling, and smoke dampers are as specified. Generally, fire, ceiling, and smoke dampers should be installed in accordance with the conditions of their listing and the manufacturer's installation instructions that are supplied with the damper. Further, check installation by removing hsible link (where applicable) and operate damper to verify that it fUUy closes. It is desirable to operate dampers

CONTROLS a.

b.

Check manual controls. Check that devices for manual activation and deactivation of the smoke control system are of materials and installation as specified. Check automatic controls. Check that devices for automatic activation and deactivation and control of the smoke control system are of materials and installation as specified.

,

.,

Principles of Smoke Management

Table 1-1: inspection Checklist-Barriers of Pressurized Stairwells Project: Inspection agent:

Date:

YES General: 1 All materials in plenums appropriate 2 Air filters appropriate 3 Fan inlets protected by scree~is 4 Heating equipment installation appropriate 5 Cooling equipment installation appropriate 6 Manual controls installed 7 Automatic controls installed Ductwork: I Duct material appropriate 2 Duct installation appropriate 3 Duct connectors appropriate 4 Duct coverings appropriate 5 Duct linings appropriate Duct access and inspection provisions: 1 Access at all required locations 2 Access properly identified Dampers: I Fire dampers located where required 2 Fire dampers of appropriate rating 3 Fire dampers installed appropriately 4 Ceiling dampers located where required 5 Ceiling dampers of appropriate rating G Ceiling dampers installed appropriately 7 Smoke dampers located where rcquired 8 Smoke dampers of appropriate rating 9 Smoke dampers installed appropriately 10 Combination fire and sniuke dampers located where required I I Ccmbination fire and snioke dampers of appropriate rating 12 Combination tire and smoke dampers installed appropriately Comments:

REMARKS

S

A p p e n d i x I - Inspection Procedures f o r smoke Control Systems

Table 1-2: Inspection Checklist-Barriers of Elevator Smoke Control Systems Project: Inspection agent: DESCRIPTION General: l All materials in plenums appropriate 2 Air filters appropriate 3 Fan inlets protected by screens 4 Heating equipment installation appropriate 5 Cooling equipment installation appropriate 6 Manual controls installed 7 Automatic controls installed Ductwork: 1 Duct material appropriate 2 Duct installation appropriate 3 Duct connectors appropriate 4 Duct coverings appropriate 5 Duct linings appropriate Duct access and inspection provisions: I Access at all required locations 2 Access properly identified Dampers: I Fire dampers located where required 2 Fire dampers of appropriate rating 3 Fire dampers installed appropriately 4 Ceiling dampers located where required 5 Ceiling dampers of appropriate rating 6 Ceiling dampers installed appropriately 7 Smoke dampers located where required 8 Smoke dampers of appropriate rating 9 Smoke dampers installed appropriately 10 Combination fire and smoke dampers located where required I I Combination fire and smoke dampers of appropriate rating 12 Combination fire and smoke dampers installed appropriately Comments:

Date:

YES

REMARKS

PrincipIes of Smoke Management

Table 1-3: Inspection Checklist-Barriers of Zoned Smoke Control Systems Project: Inspection agent: DESCRIPTION General: l All materials in plenums appropriate 2 Air filters appropriate 3 Fan inlets protected by screens 4 Heating equipment installation hppropriate 5 Cooling equipment installation appropriate 6 Manual controls installed 7 Automatic controls installed Ductwork: 1 Duct material appropriate 2 Duct installation appropriate 3 Duct connectors appropriate 4 Duct coverings appropriate 5 Duct linings appropriate Duct access and inspection provisions: I Access at all required locations 2 Access properly identified Dampers: I Fire dampers located where required 2 Fire dampers of appropriate rating 3 Fire dampers installed appropriately 4 Ceiling dampers located where required S Ceiling dampers of appropriate rating 6 Ceiling dampers installed appropriately 7 Smoke dampers located where required 8 Smoke dampers of appropriate rating 9 Smoke dampers installed appropriately 10 Combination fire and smoke dampers located where required I I Combination fire and smoke dampers of appropriate rating 12 Combination fire and smoke dampers installed appropriately Comments:

Date: YES

NO

REMARKS

Appendix I - Inspection Procedures for Smoke Control Systems

Table 14: Inspection Check List-Fire Safety Controls in HVAC Systems Project: Inspection agent: DESCRIPTION Manual shutdown: 1 Appropriate fans stopped 2 Appropriate smoke dampers fully and tightly closed Automatic shutdown by return detector: 1 Appropriate fans stopped 2 Appropriate smoke dampers fully and tightly closed Automatic shutdown by supply detector: 1 Appropriate fans stopped 2 Appropriate smoke dampers fully and tightly closed Automatic shutdolvn by detector system: 1 Appropriate fans stopped 2 Appropriate smoke dampers fully and tightly closed Comments:

Date:-

Appendix J Test Procedures for Stairwell Pressurization .Svstems STAIRWELL PRESSURIZATION TEST

SCOPE The test procedures described in this appendix apply to systems for stainvell pressurization. '

EMERGENCY POWER If standby power or other emergency power has been provided for the operation of the stainvell pressurization control system, acceptance testing shall be conducted with emergency power and normal power. During one test started under normal power conditions, the normal power shall be shut off to determine the ability of the stairwell pressurization systems and all associated systems to properly operate under standby power or other emergency power.

Activate the stairwell pressurization systems by a putting a detector in alarm as required by the contract documents. Test each pressurized stairwell by conducting the following steps. a.

With all stairwell doors closed (except for the exterior ground floor door if it is required to be opened upon system activation), measure and record pressure differences across each closed stainvell door.

b.

Open tlie exterior ground floor stairwell door (except if the exterior ground floor door is required to be opened upon system activation), and measure and record pressure differences across each closed stairwell door. For stainvells without a ground floor exterior door, another highly severe open door condition must be tested. This can be an exterior door not at the ground floor or a large flow path to the outside created by opening the stainvell door and other doors, including an exterior building door.

c.

Open an additional stainvell door, and measure and record pressure differences across each closed stainvell door. Repeat this step, ope!ling anotiier door each time, until the required number of d o o k is opened. The required number of doors is that nuniber that must be opened during testing as stipulated i l l tlie applicable codes or contract docu~nents.

d.

With the required number of doors opened, clicck flow direction tliroi~gh open door-

NORMAL OPERATION TEST With all building HVAC systems in normal operation, any zoned smoke control systems shut off, and the stairwell doors closed, measure and record the pressure differences across each stainvell door. The sign convention for all pressure difference readings in the stairwell tests is: a pressure dityerence resulting from a flow from the stairwell is positive, and a pressure difference resulting from a flow to the stainvell is negative. Evaluate these pressure differences to detennine that they are appropriate for the balanced HVAC system. Generally, this would be about 0.01 inches of water gage, but pressure differences as large as 0.03 inches water gage are not a causc for concern. However, higher pressure differences may occur for special systems such as those intended to control airbornc pollutants. Additionally, greater pressure dillkrcnccs can be caused by stack effect (as explained in Chapter 5).

Appendix 1-Test Procedures for stairwell Pressurizatiori Systems

e.

ways using a 6 ft strip of tissue paper secured at the top of the door h m e . Check that the measured pressure difference is within the acceptable range, as defined in the contract documents. If the pressure difference is not in the acceptable range, double check that the states of fans, dampers, and doors is as required. if any of these were not as required, they should be fixed and the zone retested. After this, if the pressure difference is not acceptable, the flow rate of air to the stairwell in question should be measured and adjusted as appropriate. If the

pressure differences are too low after these actions, excessive air leakage paths in the construction should be filled, caulked, or sealed as appropriate. (Often it is very difficult to locate leakage paths in buildings. Chemical smoke from smoke bombs can be used to find these leakage paths. The stairwell is filled with chemical smoke and pressurized, while the low-pressure side of the stairwell barriers is examined for smoke leakage that indicates the location of a leakage path.) Then the zone should be retested.

Principles of Smoke Management

Table J-1: Test Work Sheet-Pressurized Stairwell Project Stairwell No. Test Agent: Doors in Pressurized Stairwell

-

Comments:

Pressure Difference (inches of water gage)

- Flow Direction From Stair To Stair

Appendix K Test Procedures for Zoned Smoke Control Systems SCOPE The test procedures described in this appendix apply to zoned smoke control systems that are either dedicated systems or part of systems for heating, ventilating, and air conditioning (HVAC).

EMERGENCY POWER If standby power or other emergency power has been provided for the operation of the zoned smoke control system, acceptance testing shall be conducted with emergency power and normal power. During one test stated under normal power conditions, the normal power shall be shut off to determine the ability of the zoned smoke control systems and all associated systems to properly operate under standby power or other emergency power.

SMOKE CONTROL DIAGRAM Identify the exact location of each smoke control zone. If it is not part of the building plans, make a smoke control zone diagram of the building. This diagram should include the locations of all zone boundaries and of all doors in those boundaries.

NORMAL OPERATION TEST With all building HVAC systems in normal operation, the zoned smoke control system shut off, and the smoke barrier doors closed, measure and record the pressure differences across each smoke barrier door. Evaluate these pressure differences to determine that they are appropriate for the balanced HVAC system. Generally, this would be about 0.01 inches water gage, but pressure differences as large as 0.03 inches \vater

gage are not a cause for concern. However, higher pressure differences may occur for special systems, such as those intended to control airborne pollutants. Additionally, greater pressure differences can be caused by stack effect (as explained in Chapter 5).

SMOKE MODE TEST Each smoke zone is to be individually tested by performing the following sequence. Activate smoke control system operation in the zone. This should be accomplished by putting one of the detectors into alarm that are intended to activate the snioke control system in that zone. Check that the operation of fans is as required by the contract documents. Check that the position of smoke dampers is as required by the contract documents. Also, check that any smoke dampers required to be closed are fully and tightly closed. Check to verify that all doors required by the contract documents -:o be closed during smoke control system operation are fully closed and that they operate freely, allowing use during evacuation without becoming jammed in their door frames. This should include doors in the boundary of the smoke zone being tested. Measure and record pressure difTerences across all the closed doors in the boundary of the smoke zone being tested. Pressure differences resulting from air flowing to the snioke zone being tested are to be recorded

Appendix K-Test Procedures for Zoned Smoke Control Systems

age path. Exterior walls, interior partitions, floors, and ceilings, including areas above suspended ceilings, must not be overlooked when hunting for excessive leakage areas.) Then the zone should be retested.

as positive values, and pressure differences resulting fiom air flowing fiom the -smoke zone being tested are to be recorded as negative values.

f.

Check that the measured pressure difference is within the acceptable range, as defined in the contract documents. If the pressure difference is not in the acceptable range, double check that the state of fans, dampers, and doors is as required. If any of these are not as required, they should be fixed and the zone retested. After this, if the pressure difference is not acceptable, the flow rates of air to and from the smoke zones in question should be measured and adjusted as appropriate. If the pressure differences are too low after these actions, excessive air leakage paths in the construction should be filled, caulked, or sealed as appropriate. (It is often very difficult to locate leakage paths in buildings. Chemical smoke from smoke bombs can be used to find these leakage paths. The high-pressure sides of smoke barriers are exposed to heavy concentrations of chemical smoke, while the low-pressure side of the barrier is examined for smoke leakage that indicates the location of a leak-

g.

Test for smoke feedback into supply air. Place six smoke bombs (three-minute duntion size) in a metal container, simultaneously ignite all bombs, and locate container near exhaust inlet in smoke zone being tested so that all of the chemical smoke produced by the bombs is drawn directly into the exhaust airstream. Check that air supplied to other zones of the building has no trace of chemical smoke. If chemical smoke is detected in this supply air, its path should be determined, the path should be blocked, and then the smoke feedback test should be conducted again. (The two most likely causes of smoke feedback are a leaky or party opened return air damper and an outside air inlet located in the vicinity of the exhaust air outlet.)

h.

Make sure that this zone has been returned to its normal setting before continuing to test other zones.

Principles of Smoke Management

Tz51e K-l: Test Work Sheet-Zoned Smoke Control System in Normal Operation Project: Test Agent: Doors of Smoke Control Zone

Date: Pressure Difference (inches of water gage)

Flow Direction From Zone

To Zone

1

Comments:

Appendix K-Test Procdures for Zoned Smoke Control Systems

Table K-2: ~. Test Work Sheet-Zoned Smoke Coritrol System in Smoke Control Mode -

Project: Test Agent: -

Date: Yes

No

Fans operating appropriately Smoke dampers in required position Pass feedback test

-

-

Doors of Smoke Control Zone

Comments:

Pressure Difference (inches of water gage)

Flow Direction From Zone To Zone

Appendix L Inspection Procedures for Atria Smoke Exhaust Systems SCOPE The inspection procedures described in this appendix apply to atrium smoke exhaust systems. These procedures are of a general nature, intended as a guide for the development of specific procedures for individual smoke control systems. These procedures address the major components of smoke control systems but, by their general nature, cannot address all possible components. In this appendix, the phrase "as specified" is used to mean as specified in accordance with a contract of documents, a code, or some other standard or standards that have been agreed upon by the owner, designer, builder, code offkial, and other involved parties.

as specified. CAUTION: Because the characteristics oJ duct connectors and flexible duct connectors are d~fferent,one should not be substitutedJor the otheu. d.

e.

AIR-MOVING EQUIPMENT a. b.

c.

Check ducts to verify that materials of duct material and construction are as specified. Check duct installation. Duct installation, including the hangers, must not reduce the fire resistance rating of structural members and of assemblies. Frequently, structural members and assemblies have fire protective coverings. such as drywall construction or a sprayed-on layer. Check that ducts are installed in such a manner that these protective coverings are not damaged. Check that clearance from ducts to combustible construction is as specified. In addition, check that where ducts pass through walls. floors, or partitions, the openings in construction around the ducts are as specified. Check that installation and materials of duct connectors and tkxible duct connectors are

f. g.

Check duct coverings and linings to verify that their fire safety requirements are as specified. Check that duct coverings do not conceal any service opening. Check direct access and inspection provisions. Service openings and telescoping or removable duct sections are used for direct access and inspection. Check that a service opening or a telescoping or removable duct section is provided in ducts, as specified adjacent to fire dampers, smoke dampers, and smoke detectors. Check that these access openings are identified with letters as specified. Check that service openings are provided in horizontal ducts and plenums where specified. Check air filters to verify that they have the classification specified. Check that the location, fire protection rating, and installation of fire, ceiling, and smoke dampers are as specified. Generally, fire, ceiling, and smoke dampers should be installed in accordznce with the conditions of their listing and the manufacturer's installation instructions that are supplied with the damper. Further check installation by removing the fusible link (where applicable) and operate damper to verify that it fully closes. It is desirable to operate dampers with normal airflow to ensure that they are not held open by the airstream. Remember

Appendix L-Inspection Procedures for Atria Smoke Exhaust Systems

to reinstall all hsible links that have bken removed during inspection. b.

CONTROLS a.

Check manual controls. Check that devices for manual activation and deactivation of

the smoke control system are of materials and installation as specified. Check automatic controls. Check that devices for automatic activation and deactivation and control of the smoke control system are of materials and installation as specified.

Test Procedures for Atria Smoke Exhaust Svstems SCOPE The test procedures described in this appendix apply to systems for atrium smoke exhaust systems.

EMERGENCY POMrER If standby power or other emergency power has been provided for the operation of the atrium smoke exhaust system, acceptance testing shall be conducted with emergency power and normal power. During one test started under normal power conditions, the normal power shall be shut off to determine the ability of the atrium smoke exhaust system and all associated systems

to properly operate under standby power or other emergency power.

EXHAUST OPERATION TEST With all building HVAC systems in normal operation and any pressurized stainvells, zoned smoke control systems, and other smoke management systems shut off, activate the atrium smoke exhaust system by a signal from a smoke detector or initiating device. After activation, determine that the smoke exhaust fans are operating as intended. The volun~etricflow of the smoke exhaust fans should be measured before the eshaust operation test.

Principles of Smoke Management

Index A Acceleration of gravity 66, 90, 93, 121, 122, 183, 184, 191, 196,197,207,218,219,222,243,261,268,321 Activation 8, 148, 154, 168, 205, 206, 208, 236, 249, 277,278,356,36 1,370,371 Air density 67,74,78,79,81,82,92,93, 143, 153, 158, 191, 195-196,207,241 gas constant 67, 190,261,268 properties 97,220,268,269 specific heat 269- 270 Airborne matter 2,63 Airflow 2-4, 6, 70, 71, 74, 78, 79. 87-95, 97, 109, 112, 113, 115, 117-119, 120-122, 142, 148, 150, 154, 158, 169, 172, 173, 175, 179, 181, 197, 206, 207, 210, 213, 226, 235, 236, 238-240, 247, 257, 289-293, 295-301, 3 12,369 Anemometer 78,240,241,245 ASCOS 119, 120, 122 ASET 120, 122, 123, 126, 199,202,203,249,257,321, 323,329-333 ASMET 120, l26,32 l-323,329,33 1 Atria 4, 8, 120, 131, 181-185, 189, 192, 195, 196, 199, 201, 206, 207, 2 10, 215, 2 17, 221, 223, 225, 253, 254, 274,275,322,323 Atrium mechanical exhaust 199 natural venting 4, 190, 199, 203,207 smoke filling 129, 199,201,205,221,248,272,323 Attenuation coefficient (see extinction coefficient) AZONE 120, 123, 195, 199? 200, 202, 203, 205, 206, 211-215

B Barriers 5,87.88,2 10,235,236,254,355,357-359,362, 366 Base fuel package 23- 26 Benioulli's equation 93, 240 Boundary conditions 229, 232, 233 Boundary layer 56, 75, 78. 226.230, 245, 255 Buoyancy 2-4, 66, 71, 73, 74. 79. SO. 87, SS, 92, 107. 129, 150, 175, 176, 179, 181, 189-191, 195, 207, 217, 220,221,251,329

C Calorimeter 13, 14, 25, 252 cone 14,248 open air 14, 15 oxygen consumption 13. I ? room 14

Carbon dioxide (CO2) 27,36,37, 252 Carbon monoxide (CO) 8, 27, 34, 36, 38, 252, 254, 256, 271 Carboxyhemoglobin (COHb) 38 Chimney effect (see stack effect) Church Street fire tests 4 Clear height 202, 203 Colebrook equation 10 1 Commissioning 3, 7, 9, 105, 146, 152, 161, 167, 175, 235,236,247 Communicating spaces 197,210,224 Compartmentation 2, 3, 5, 6, 32, 87, 129, 172, 180, 199, 291 Computational fluid dynamics (CFD) 3, 197, 247, 250 Confined Flow 190 Conservation of energy 123, 125,219 Conservation of mass 84, 121, 123, 125, 219, 229, 291, 330 Conservation of momentum 219,228,230 CONTAM 119-122, 130, 132, 137, 139, 154, 155, 161, 165, 180, 206, 257, 289, 290, 292, 293, 295-298, 312, 320,337,338,349 Contaminant 3,87, 88, 120-123,243,290,291, 298 Control volun~e123, 125, 158, 188, 189, 225, 244 Convective fraction 24, 182, 184, 202, 204, 205, 223, 245,321,322,325,327 Critical air velocity 89, 90, 244

D Dampers6,9, 111, 113, 114, 117, 139, 169, 175, 178, 236, 357-359, 362,366, 369 balancing 1 17 barometric 148, 149, 168 bypass 149 chatter 149, 169 control 1 17 curtain 1 17 fire 3, 117. 149,254,257, 355, 357-359 leakage classification 1 18, 178 multi-blade 117, 1 18 return 178, 179, 366 smoke 3, 79, 87, 1 17, 1 18, 178, 179,257, 355-360, 365,368,369 Darcy-Weisbach equation 101 Decision tree 5, 6 DETACT-QS 2 l , 120, 126 DETACT-T2 2 1, 120 Detectors 19, 127, 169, 247, 250, 365 Diameter fire 182, 184,325-327 hydraulic 92, 93, 95, 96, 101, 104, 243, 299 plume 183

Index

Differential pressure (see Pressure difference) Differential pressure instruments 237 Dilution 2,3,45-47,87,88, 130, 172, 177,243 Dimensional Analysis 2 17 Dimensionless groups 2 19,330 Door-opening force 105-107, 145 Duct 3, 8, 79, 101-104, 111, 112, 114, 117, 118, 140, 149, 169, 173, 178, 179, 236, 239, 243-245, 253, 255, 272,290,355- 359,369 Duct, access 357- 359

E Economizer 1 13 Egress 7, 27, 5 1-53, 56, 57, 59, 60, 88, 107, 120, 126, 161,244,249,253,254,277,329 Elevator 1- 4, 49, 63, 80-82, 89, 97-99, 133, 139, 142, 143, 155, 157-159, 161, 165-169, 171, 172, 236, 247, 248, 250-252, 256, 272-274, 277-279, 281- 287, 291293,295,301,338,358 car motion 68,69, 158, 277 evacuation 119, 120. 157, 158, 161, 165, 166, 167, 277,278,285,287 piston effect 66,79, 129, 160,252 ELVAC 119,120,277,284,285,287 Energy conservation 7, 11l , 149, 157 English units (I-P units) 3, 259, 265, 268, 282, 322, 325, 334 Evacuation 1, 3, 6, 7, 27, 29, 37, 48-52, 56-63, 87, 119, 120, 130, 133, 140, 141, 146, 148, 157-159, 161, 165168, 175, 199- 202,205, 207, 244, 250- 252, 254, 274, 277-279,284,285,287,365 component-by-component 57,59,60 constrained flow 57 density 6,52,53, 55, 56, 58-61 empir~calcorrelations 5 I hydraulic a~alogy5 1. 56 velocity 5 1,52,53, 55,58-62 Evacuation 53 Exhaust fan 176 Exhaust inlets, number 193, 194,2 10,213, 244 Exhaust inlets, separation 175, 194 Expansion 66,74,89, 129. 172, 175 Exponential flow equation 94, 96, 97, 243 Extinction (attenuation) coefficient 28, 29,3 1, 32, 245

F Fan 2-4, 6, 9, 10, 66, 79, 87-89, 92, 109, 111, 112, 114, 121, 129, 139, 140, 146, 138, 149, 152, 158, 161, 167169, 171, 175, 177, 236, 737, 239, 247, 251, 272, 274, 289-295, 297, 301, 315, 316, 319, 357-360, 362, 365, 366,368

airfoil blade 115 axial 115 backward flow 115, 1 17 backward rotation 115, 117 centrifugal 114, 115, 117, 141, 146, 148, 154 exhaust 111,113,120,169,172,175-177,205,206, 244,245,371 forward curved 115 propeller 115, 141, 142 return 113, 179 roof-mounted 11 1, 140, 141 supply 7, 1 13, 154, 179,225 temperature 176, 177 tubeaxial 115, 1 17 vaneaxial 115, 117 variable flow 6, 169 FAST21, 120, 126, 130, 1)2, 137,254,271 Fire building 3,4,5,7, l l , 13,29,36,49,63,7 1, 79, 88, 90, 107, 131, 139, 157, 166, 167, 177,237, 251,252,257,271-273,275- 277.355 design 11,21, 129, 180, 188, 199,203, 205. 207 fighters 8,81, 139, 149, 166, 167 flaming 8, 13,29, 32,33,34,237 fully developed 13, 18, 37, 133, 188 growth coefficient 22.245, 221 growth time 206 research tower 7 1, 96 'scenario 2 , 21,4 1 , 50, 129, 249 size 7, 11,21, 192, 250 smoldering 8, 29, 237 spread 87, 172, 185,257 sprinklered 2, 7, 19, 107, 180, 188, 232, 237, 252 steady 1 1, 21, 192, 200-203, 205, 207, 2 11, 215, 323-325 suppression 5, 6, 7, l 1. 19, 25, 9 1, 129, 199, 249, 252,253, 257.332 test 2,4,23,28,44, 73.21 7,248,251,252,255,256, 271,273, 274 t-squared 18, 21-23, 192, 201, 202, 214, 215, 329, 332 unsteady 21, 192,201,203,205,207,21 l , 324,326 ventilation controlled 13, 18, 188 Fire Dynamics Simulator (FDS) 23 1, 253 Flame height 19, 182-186, 204, 205, 244,321,322,325327 Flashover 1 1, 13, 254 Flexibility 6, 7 Flow area effective 63-66, 70, 79-51, 143-145, 150, 152. 161, 172-174,243 parallel paths 63-65 serles paths 63-65

l

I

l

Principles of Smoke Management,

Flow coefficient 4, 63-66, 70,78,79, 81, 82, 93, 94, 96, 97, 103, 133, 145, 152, 159, 163, 164, 174, 191, 196, 243,338 Fractional effective dose (FED) 36,46, 131,243 Fractional incapacitating dose (Fm) 40,41, 44, 131 Friction losses 66, 93, 143, 150, 161, 163, 164,338 Fuel package 14, 19,23-26, 129,253

G Gas law (see Ideal gas law) Governing equations 2 19,220,225,230,231

H Haber's Law 36 Hazard analysis 3, 5, 7, 61,87, 119, 122, 129, 130, 131, 133, 168,207,248 Heat exposure 3,27,44,45,47, 130, 131, 133,207 Heat release density 22, 184,244 Heat release rate (HRR) automobile 17 Christmas tree 14, 15 cribs 17 furniture 13-15, 21 kiosk 14 pallets 17, 22 peak 14, 15, 17,25 sprinklered fires 19 Heat Transfer Scaling 223 Height limit 145-147,243 HVAC 6-10, 79, 88, 1 1 1-113, 115, 117, 123, 129, 139, 172, 175, 176, 178, 179, 226, 236, 250, 25 1, 255, 360, 361,365 Hydrogen bromide (HBr) 34,36 Hydrogen chloride (HCl) 34,36,250 Hydrogen cyanide (HCN) 34,36,252

I Ideal gas law 67, 143 Ignition 2, 5, 11, 19, 22-25, 34,45, 124, 129, 223, 237, 247 Inspection 88, 235, 236,355-360, 369, 370 lnternational system (SI) units 3, 259, 261

J JET 2 1, 120, 122, 126, 127,249 Johnson City Retirement Center fire I ;

,

L LAVENT 2 l , 120, 122, 126 Leakage area (see flow area)

M Manometer 238,24 1

Manual stations 8 Mass optical density 28,30,32,34,46,47, 131, 133,245 Metric units (see International system units) MGM Grand fire 1,71, 157,248,257 Modeling detector activation 120, 126, 192,226, 227 Froude 21 7,221,222,224 network 104, 180 pressure 221,222 salt water 256 saltwater 221 turbulence 229- 232 zonefire4,5, 180, 181,211,274

K Navier-Stokes (NS) equation 94 Neutral plane 63,67, 70,71, 73,74, 82- 85,243,273 Newton Raphson method 102 Newton's second law 2 18 N-Gas model 39,40,42,243,244,252 Nomenclature 277,321

0 Objectives, smoke management 5 Open doors 74,87,97, 105, 140, 141, 154,338 Optical density 28,29,3 1,32,34,46,47, 13 1, 133, 245 Orifice equation 70,93, 94, 96,97, 100 Oxygen (02)8, 13,37,38,39,41,42, 74, 79, 89,90-92, 175,250,252,254

P Panic 49,50,25 1,254,255 Percentage obscuration 28-30,245 Perfect gas law (see Ideal gas law) Physical (scale) modeling 130, 197, 217,219, 22 1 Pirot tube 240,241 P!ugholing 120, 181, 193-195, 210,211,213,244, 245 Plume average temperature 188, 189,208,325,326 axisymmetric 181-186, 188, 189, 199, 204, 21 1, 244,245 balcony 186,187, 197,204,257 centerline temperature 126, 182-184,322,323,325, 327 corner 185, 186, 188 maximum height 189,245 wall 185, 186, 188 window 188,204 Poiseuille Flow 94 Post-flashover fire 13,27 1 Power law 75 Prandtl number 2 17, 2 18, 220

Index

Pressure difference average 142, 145, 162 critical 158, 159 design 107, 109, 162, 168, 172, 175,338 Pressure sandwich 8, 17 1 Pressurization 2-5,7,8,87&9,97-99, 105, 113-115, 119, 120, 122, 129, 139, 140-146, 148-150, 152-155, 157159, 161, 165-169, 173-176, 180, 210, 226, 237, 248, 249,251,256,272,273,275,292,293,338,361 Pull box (see Manual station) Purging 87, 88, 149, 168, 172

R Radiant fraction 24 Reliability 8, 9, 62, 166 Remote control center 8 Resiliency 6, 7 Response time index (RTI) 20,21, 127,244 Reynolds averaging 229 Reynolds number 78, 92-96, 101, 217, 220-224, 240, 244,299 Roosevelt Hotel fire 1 Roughness 101-103,245,300

S Safety factors 7, 146, 152, 161, 167 Scaling relations 217, 221-223 Shopping malls 92, l81,252,272-275 Similitude 217,219,22 1 Smoke backflow 88-92,181,244,256 bombs (see Smoke, chemical) chemical 236,237,362,366 dampers (see Damper, smoke) definition 27 detectors 8,208,209, 224, 249, 355, 369 exhaust 4, 5, 7, 87, 114, 123, 129, 149, 169, 175, 194, 195, 203-206, 210. 214, 250, 252, 369,371 filling 129, 18 1, 199, 200, 201, 205, 248, 272,323 horizontal flow 126, 195, 196,295, 301 layer interface 122, 190, 195,204, 332 shaft 3,87, 142, 149,150, 169, 172, 175,256 venting 3,4, 129, 149, 169, 172, 190,207,210 Specific heat, constant pressure 125,2!8,228,265 Specific heat, constant volume 125, 2 18, 21 9 Specific heat, ratio 20, 46, 89, 125, 177, 189, 204, 2 12, 219,243,261,269,270,321,330 Sprinkler activation 2 time constant 19,20 Stack action (see Stack effect)

Stack effect 66, 70, 71, 73, 79-84, 107, 108, 129, 142, 167,179,251,273,361,365 Stack effect, normal 66,67,175 Stairwell pressurization analysis 147 compartmentation 141 multipleinjection 140, 141, 146, 148, 150 pressure profile 142, 145, 146 single injection 140 vestibules 141 with open doors 146, 148, 150 Stairwell, pressure losses 104 Standard atmospheric pressure 67, 73, 93, 120, 190, 261, 268 Stratification 207,208,236,249 Symmetry 104,105, 146, 152,229,283

T Temperature, conversion 261 Thermal inertia 223, 224, 244 Thermal radiation (radiant heat flux) l l, 23, 24, 27, 45, 47,48,125, 130, l31,255 Thornas's equation 89,90,92 Time lag ceiling jet 191, 192, 205 plume 192, 205 Toxicity 3, 27, 34,36-39, 42,43,45, 47, 109, 13 1. 133, 135,250,252,255,256,271 Tracer gas 237 Transient fuel 21,9 1 Transmittance 27-29,244

U Units of measurement 259

v Vector 227,228,247,248,250 Vestibules 141 Virtual origin 182-185, 245,250, 321-327 Viscosity, dynamic (absolute) 93,94,217-2 19,227,228, 23 1,245,268 Viscosity, kinematic 92,95,96, 218,245 Visibility 3,27,29,3 1,32,34,45-48, 130, 13 l, 133. 134, 136,244,251,272 Volumetric flow 64, 74, 92- 94, 96, 103, 1 12, 144, 150, 152, 174, 176, 177, 190, 194, 204, 205, 213, 222: 223, 239,240,244,322,325,326,37 1

W Weather data 109, 290, 296, 297 Wind 6, 66-69, 74, 75, 78-80, 104, 107-109, 120. 129, 141-143, 148, 172, 207, 226, 243-245, 248, 249, 251,

Principles of Smoke Management

252,255,256,274,290,292,295,296,299-301,3

Wind data 78, 109,274,296

z Zero floor leakage idealization 70, 7 1, 142

12

Zoned smoke control 2, 3,4, 8, 74, 89, 120, 139, 142, 149, 171, 172, 175, 178-180, 236, 237,273, 349, 359, 361,365,367,368,371