BRE 368

Design meth smoke and h

ventilation

H P Morgan B K Ghosh G Garrad R Pamlitschka J-C De Smedt

L R Schoonbaert

OF

ST. J8

Photo acknowledgomsnts

— conq it

Wontcoe

Brussels International Airport Company (MAC)

Rae con.' at Colt Plates 1,

35

and 6 Cooper Qoip: Plate 4 F$ET: Plates2, Ji, .12, .13 and .14

BRE

Garston.Watford WD2 7JR

Design methodologies for smoke and heat

exhaust ventilation

H P Morgan BSc, PhD, C Phys, M InstP, F I FireE

B K Ghosh

MSc, BA, C Phys, M InstP, Dip Math

G Garrad BSc, MSc Dipi Ing R Pamlitschka(Colonel)

J-CDeSmedt AlFireE Ing L R Schoonbaert

DipI CFPA, Al FireE

Prices forall available BRE publicationscan beobtainedfrom: CRC Ltd

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BR368 ISBN 1 860812899

©CopyrightBRE 1999 Firstpublished1999

Publishedby ConstructionResearch CommunicationsLtd bypermissionof BuildingResearch EstablishmentLtd Applicationsto copy anypart of this publication shouldbemadeto: CRC Ltd

P0 Box202 Wattord

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Front coverphoto:

Hot-smoketest atBrussels Airport,Belgium

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1

______________

Foreword

Useby fire engineers ofsmoke and heat exhaust ventilationsystems (SHEVSasthey havebecome

known) has grown in recentyears.It istherefore welcomethatthis guide has beenproduced whichprovidesthe fireengineer with assessmentdesignmethodologiesfor theuse ofthese systems. SHEVSrequire the most carefuldesign prior to introduction. It is importanthowever to ensure, aswith all fire-engineeringdesigns,that due regard is taken overissuessuchasescape time andfire growth since thesefeatures provide thebase uponwhich the designparameters canbe made. It is also important that dueregard be ultimatelymade regardingthe maintenance ofany systemsinstalledand current guidance,primarilywithin the BritishStandardsInstitution's DI)240 Firesafetyengineeringzi buildings.DD240 hasintroduced the overalldesign processwhichthefire engineer should consider.DD240 also makes it clear that caution is necessaryandthatall options haveto be consideredbefore entering intoa particulardesign process.SHEVSis oneofthose options and thisbooktherefore provides comprehensiveidentificationofthe issueswhichneed consideration.Itis particularlyimportant to payattention,as the document outlines,to the restrictionsofcomputer softwaremodelling programs, as it is alsofor the fire engineer to recognizethereare limitationsastowhat any systems (and that includes SHEYS) can achieve. Withthesethoughts in mind, thisbookprovides amost usefuland comprehensivereview of current thinkingregarding SHEVSdesignmethodologiesforutilization bythe fire engineer.

D T DavisOBEQFSM CEug FiFireECIMgt

HM ChiefInspector ofFire Servicesfor Scotland iJune 1999

iv

Preface

Thisguidesummarizes the adviceavailablefrom theFireResearch Station,to designers ofSmoke and HeatExhaust VentilationSystems (SHEVS)for atria andotherbuildings.Itbuilds upon currently availablepublishedadvice (especiallyBRE Report Design approachesforsmokecontrolin atriumbuildings[13],butalsoBRE Report Desinprinciblesforsmokeventilation thenclosedshopping cenfres24l), byincluding moreguidance ontheuseofthe methods given, and by includingthe results ofresearch carried out since the publicationofref. [13] in 1994. Inparticular,the use ofa design firesizeis considered inmore detail, including: adiscussionofgrowingfires, formulaeand calculation methods todetermine the deflection ofsmoke curtainsinfire situationsso thatthespecificationofsmoke curtainscan become part ofthe SHEVS design, the effectsdue to airflowon theefficiencyofnatural smoke exhaust ventilators and on the stabilityofsmokelayers.

•• •

This guide does not consider the scenario whereafire in a room connecting to an atriumcausesa flame plume to rise intotheatrium. Inthis context, anylarge space adjoiningthe fireroommay be considered to be an atrium, egmalls in shopping complexes. A discussionis included ofthe factorswhichneedto beconsidered whenspecifyingthe hardware (ventilators,smoke curtains,etc.)required to implementthe design in abuilding. Some adviceis alsoincluded on: factorstobeconsidered ininstallingthe system inbuildings, howtotest thefinctioning ofthe equipment separately and as a complete system onceit has beeninstalled, and 'goodpractice' measuresinvolvingthemanagement andmaintenance ofthe system whenthe buildingis in everyday use.

•• •

Thepurpose ofthisbooktherefore isto provide practical guidanceon the design ofsmoke-control systems.It reflectscurrentknowledge andis basedonthe resultsofresearchwhereavailable, including asyet unpublished resultsofexperiments. In addition,itdraws on the authors' cumulativeexperience ofdesignfeaturesrequired forregulatory purposes inmanyindividual smoke-control applications.Manyofthese designfeatures have evolvedover several years by consensusbetweenregulatory authorities,developers andfire scientists,ratherthan byspecific research. Themethodology underpinning the bookis explicitlyempirical in approachand caneasilybe extended to most buildings.Whereguidanceis necessaryto address practicaldesign issuesbut there aregaps inthe establishedknowledge-base,theauthors haveexercised theirprofessional judgement in offeringconservative,pragmaticadvice.When guidanceis offeredinthese circumstancesanypotential weaknessesare madeexplicit.Related to this is the continuance ofthe philosophy usedin the book's predecessor BRE Reports'3'241that evenwherea document is difficult to obtain, or even verbal private communicationis the source ofadvice,it is listed as a reference. HPM, BKG,GG, RP,J-CDe S, LRS

June 1999

V

About the authors

Howard P Morgan Principal Consultant, Fire ProtectionSystemsCentre, Fire Research Station (FRS), BRE Head, FRS(Asia)Centre Technical Director, FRSAFSET(Asia) Ltd, Hong Kong Fire Research Station, BRE, Bucknalls Lane, Garston, Watford, WD27JR, UK Email: [email protected]

BijoyGhosh Senior Fire Consultant, Fire Research Station (FRS), BRE

Fire Research Station, BRE, Bucknalls Lane, Garston, Watford, WD27JR, UK Email: [email protected]

Gordon Garrad FireScientist,Fire Research Station (FRS),

BRE

Fire Research Station,BRE, Bucknalls Lane, Garston, Watford, WD27JR, UK Email: [email protected]

vi

Aboutthe authors ColonelR Pamlitschka Head ofFirePrevention Department, Professional Fire Service, Vienna, Austria Head of Smoke-Control Department, Prüfstelle für Brandschutztechnik des Osterreichischen Bundesfeuerwehrverbandes, Austria CO Ma. 68, Hauptfeuerwache Mariahilf, Gumpendorfer Gurtel 2, A-1060Wien, Austria

Jean-Claude De Smedt Managing Director/PrincipalConsultant,International Fire Safety Engineering Technology (IFSET),Belgium Managing Director, FRS/IFSET(Asia) Ltd, HongKong

NVIFSET SA, Stationsstraat35, B-i730ASSE, Belgium Email: jcds@ifsetcom

Lieven R Schoonbaert SeniorConsultant, International Fire SafetyEngineering Technology OFSET), Belgium Director, FRSAFSET(Asia) Ltd, Hong Kong NV IFSET SA, Stationsstraat35, B-1730ASSE, Belgium Email: [email protected]

VII

Contents

Chapter 1

Foreword

iii

Preface

iv

Abouttheauthors

v

Contents

vii

Abbreviations

xii

Nomenclature

Xiii

Introduction 1.1

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1 .9

Chapter 2

General principles of smoke production,

Chapter 4 Chapter 5

1 1

2 2

4 5 6 7

8 10

movementand control 2.1 2.2 2.3 2.4

Chapter 3

Thehazardsofsmoke The regulatorybackground The role of smoke and heat exhaustventilation Smoke and heat exhaustventilation as a part offire safety engineering A brief history of smoke ventilation The atrium:descriptionand behaviour in fire Active control of the fire Implementation of a smoke and heat exhaustsystem in a building The purposeof this book and its relationship to earlierguidance

1

Fire growth and smokeproduction Pressurization and depressurization Throughtiow ventilation (or smoke exhaustventilation) Smoke and heat exhaustdesign philosophies

10 12 12 13

Design-firesize

14

3.1 3.2 3.3 3.4

General

14

Growingdesignfires Steady-state designfires Acceptablefailure rates

15 16

Escape times

Smoke control on the storey of fire origin 5.1

Within the fire room 5.1.1 Plumes above large fires 5.1.2 Plume above smallfires

19

20 22 22

22 24

viii

Contents

Effects of adjacent walls on entrainment into the plume 5.1.4 Effects of sprinkler 5.2 The flow of hot gases out ofthe room of origin into a taller adjacent space(eg an atrium or mall) 5.3 Ventilation of single-storey smoke reservoirs (including the balconyspacewheresmoke is contained 5.1.3

25 25 25 27

and exhausted from beneath a balcony)

5.4 5.5 5.6 5.7 5.8 5.9

Smoke layertemperature Effects of sprinkler systems in smoke reservoirs Flowing layerdepth Localdeepening Automatic smoke curtains Inletair 5.10 Minimum numberof exhaustpoints 5.11 Throughflowventilation:area of naturalventilation required 5.12 Naturalventilatorsand wind effects 5.13 Required ventilationrate (powered exhaust) 5.14 Slit extract

Chapter 6

Chapter 7

Chapter 8 Chapter 9 Chapter 10

28 30 30 31 31

5.15 False ceilings 5.16 The use ofa plenum chamberabove a false ceiling 5.17 Maximum dimensionsfor smoke reservoirs

32 34 35 35 37 37 37 38 38

Smokeventilation within multistorey spaces (egthe atrium)

39

6.1 Smokemovementintheatrium 6.2 Channelling screens 6.3 Entrainment into 'spill plumes'risingthroughthe atrium 6.3.1 The effective height of rise fromthe spill edge to the smoke layer base 6.3.2 Entrainment calculationmethods 6.3.3 Recommendations for selecting a spill plume formula 6.4 High temperatureplume 6.5 Firesontheatriumfloor 6.6 Throughflowventilation: remaining design procedures 6.7 Limitationsto the use of throughflowventilation

39

40 42 42 44 49 49 50 50 50

Alternative forms of smoke control for atria (including multistorey malls but excluding throughflow ventilation)

53

7.1 Voidfihling 7.2 Compartmentseparation 7.3 Depressurization ventilation 7.3.1 Principles 7.3.2 Naturaldepressurization 7.3.3 Naturaldepressurizationand wind effects 7.3.4 Powereddepressurization

53 53

Depressurization/smoke ventilation hybrid designs Atrium smoke layer temperature Additional design factors

59

10.1 Atrium roof-mounted sprinklersystems 10.2 Controlled fire load on the atrium base

53 53 54 57 58

61

64 64 64

________

Chapter 11

ix

Contents

10.3 Air-conditioned atria 10.4 Channelling screensand hybrid systems

64

10.5 Wind-sensing devices

65

10.6 Crossdraughtwithin the atrium 10.7 Crossflowwithinthe gas layer 10.8 Wind effects on horizontalventilators

65 65

Interactions with othersystemsin the building

67

11.1 Sprinklers

67 67 67 67 69

11.1.1 Automaticsprinklers 11.1.2 Automaticsmoke exhaustventilation 11.1.3 Sprinklerscombinedwith smokeventilation 11.2 Fire-detection systems 11.3 Heating, Ventilation and Air Conditioning (HVAC)/ Air Conditioning and Mechanical Ventilation (ACMV) 11 .4 Pressurization of stairwellsand lobbies 11.5 Lightingand signage 11.6 Public addressand voice alarm systems 11.7 Security 11.8 Computerizedbuilding control systems

Chapter 12

SHEVS andthe fire services 12.1 General 12.2 Design objectivesfor SHEVS and implications for the design-fire as a basisfor design 12.2.1 Fundamental fire-fighting objectives 12.2.2 Design objectivesfor SHEVS in connection with fire-fighting objectives 12.3 Circumstances which reduceor impede the ability of a SHEVS to assist fire-fighting operations 12.3.1 Factors adverselyaffecting successfulintervention

by the fire services 12.3.2 Additional provisions for optimizingthe effectiveuse of a smoke-free layer created by a SHEVS

65

66

69 70 70 70 70 71

72 72 72 72 73 76 77 77

for fire-fighting operations 12.4 Circumstanceswhere a SHEVS is of minor benefit for fire-fightingoperations 12.5 Circumstanceswhere SHEVS are not applicable 12.5.1 Premises with risk of fast-growing fires 12.5.2 Premiseswhich must not be enteredin case of fire because of other prevailing hazards

13

Selection of equipment

13.1 General 13.2 Natural smoke and heat exhaustventilators 13.2.1 Time taken to come into full operation 13.2.2 Coefficientof performance 13.2.3 Resistancetoheat 13.2.4 Opening under load: snow 13.2.5 Opening under load: side-wind

77 78 78

78

79 79

80 80 80 81 81 81

x__________

Contents

13.2.6 13.2.7 13.2.8 13.2.9

_________________________

______________________________

Lowambienttemperature

82

Reliability

82

Abilityto resist windsuction Abilityto resist rain penetration 13.3 Powered smoke and heat exhaustventilators 13.3.1 Timeto come into full operation 13.3.2 Resistancetoheat 13.3.3 Opening under load: snow 13.3.4 Opening under load: wind 13.3.5 Lowambienttemperature 13.3.6 Reliability 13.4 Automatic smoke curtains 13.4.1 Timeto deployto the fire-operational position

13.4.2 Speedoffallofbottombar 13.4.3 Resistance to hightemperature 13.4.4 Reliability 13.4.5 Fail-safe 13.5 Air inletsand doors 13.6 Smoke dampers 13.7 Smoke ducts

Chapter 14 Chapter 15

Chapter 16 Chapter 17

Installation

—

82 82 82

82 83 83 83 83 83

83 83 83 83 84 84 84 84 84

86

Acceptance testing (commissioning)

89

15.1 General 15.2 Testing and commissioning 15.3 Hot-smoketests

89 89

Maintenance,management and re-testing Some common mistakes in the design of smoke ventilation systems 17.1 Mis-location ofthe point source of a 'point-source' smoke plume 17.2 Inadequate specificationof smoke curtains 17.3 Installation does not follow design 17.4 Mis-use of computer models 1 7.5 Mistaken perceptionsof conflict between

92

91

94 94 94 94 94 95

active and passive fire precautions

Chapter 18

Smoke ventilation design and enforcement of regulations

Chapter 19

Acknowledgements References

Chapter 20 Annex A:

96 97 98

Annex B:

Design procedure with a growing design fire Design procedure with a steady-state design fire

Annex C:

Deflection of smoke curtains

Annex D: Annex E:

109

AnnexF:

A comparison of differentspill-plume calculation methods User's guide to BREspill-plume calculations 1977fire at IMF building, WashingtonDC (basedon reference [18])

AnnexG:

Design procedure for hybrid systems

119

101

103 106 112 117

xi

________________

Contents

Annex H:

Effect of a buoyant layer on the minimum pressure recommendedfor a pressure differentialsystem

120

Annex I:

Aspects of hot-smoketests to confirmthe performance of SHEVS Casehistory — smoke-control design in 'D3 Espace Leopold Bui!ding', European Parliament, Brussels

121

Annex J:

______________________________

________

123

XII

Abbreviations

ACMV

Airconditioning and mechanicalventilation

Building ResearchEstablishmentLimited British Standard BSI British Standards Institution CEA Comité Européen des Assurances CEN Comité Européende Normalisation CFD Computational fluid dynamics Eqn Equation FRG Fire-resistingglazing FRS FireResearchStation HST Hot-smoketest HVAC Heating,ventilationand airconditioning IFSET InternationalFire Safety EngineeringTechnology NIST National Institutefor Standardsand Technology(USA) NPP Neutralpressure plane RTI Responsetimeindex SHEVS Smokeand heat exhaust ventilationsystem BRE BS

XIII

Nomenclature

Note:

An additionalNomenclaturelistcan befound in Annex E

A

Functiondefined by Eqn(7.3) Area ofthe fire(m2) Area ofthe gaps between smoke curtains, orbetween curtain and structure (m2) Area of inlet (measured)(m2) Plan areaofsmoke reservoir (m2) Area of exhaustventilator (measured)(m2) Areaof opening (window),eg betweenaside-room and an atrium (m2) Specific heat ofair(kJkg1K1) Aconstant (kgms1kW') Coefficientof discharge foravertical opening the opening Cdfor flows out of anopening where abalcony or canopyprojects beyond ata for flows spill edge. Cd Entrainmentcoefficient in Large-fireplume model' Coefficientofdischarge lie theperformance coefficient) foran inlet Dimensionlessentrainment coefficient, found experimentallytobe0.44 for a free plume, and 021 for an adhered plume Aconstant inZukoski's small-fireplume modef43 Wind pressurecoefficient Wind pressurecoefficient acting on aninlet Wind pressurecoefficient acting onthe leewardsideof building Wind pressurecoefficient acting on anexhaustventilator Coefficient ofdischarge (ietheperformance coefficient) for anexhaustventilator Horizontaldeflection ofasmoke curtain, measured atits bottom bar(m) Visible depth of smoke layer inthe smoke reservoir (m) Depthofan opening between anatrium and a side-room, measuredfromtop to bottom ofthatopening (m) Effective depth ofsmoke layer — only used as part ofspillplume entrainmentcalculation(m) Depth ofsmoke beneathan exhaustpoint(m) Depth ofa smoke layer under a balcony (m) Depth ofa downstandfascia (m) Diameter offire (m) Designdepth ofa smoke layer in a reservoir (m) Depth ofaflowing smoke layer ina vertical opening (m) Maximumdepth ofsmoke inan atrium (m) (Note:Thiscan either be tothefloor,orthe maximumallowable in a

Af Ag

A Ares

A5

A c C Cd CdO CdS Ce

C

C C5 C5

CPL

C5

d d1

d0 d2

D DB Dd

Df D1

D Dmax

Dmn

g h hb h5 H H5

H L

hybrid SHEVS/depressurizationdesign) Minimumallowable smoke layer depth in a hybrid SHEVS/depressurizationdesign (m) Accelerationdue togravity (ms2) Height ofthetop ofa vertical opening/window abovethe base ofthefire insidethe room (m) Height ofrise ofa thermal line plumefroman opening or balcony edgetothe smoke layer (m) Height ofrise ofleakage gases fromthe base ofthehot gaslayer in the smoke reservoir to theceiling inthe adjacent protected area (m) Height ofavertical opening (m) Height ofthe atrium (m) Height tothe ceiling (m) Channellingscreen separation; also length ofaspilledge(m) (Note: L = W foraspill plume rising directly abovean opening)

xiv

Nomenclature L M M1)

Mr M0RIL

M M1 M1,

MB M1

M

M n N P q

q Q

Q,

Q I T T3

T T T0

v, V V1

W

W W X

y Y1

Ypi Y

Y

i y fiM ADB

Ap o

°3

0

o p p0

Length of the smoke curtainfromtop to bottom bar, measured along the fabric (ml Massflow rate (kgs') Massper metre length ofthe curtain's bottombar (kgm1) Massperm2 ofthe curtainfabric(kgm2) Critical exhaustrate atan exhaustpoint priorto the onset of plugholing )kgs Massflow rate of smoky gases exhaustedfromthesmoke reservoir (kg 1) (Note: UsuallyMe = M) Massflow rate rithe plumeabovethe fire (kgs 1 Massof gas flowingthrough the gap between smoke curtains, or betweencurtain and structure Ikgs) Massflow rate under a balcony (kgs I) Mass flow rate entering a smoke layer in a reservoir (kgs1) Mass ofgasflowing into gaslayer in protected area, having leaked through gaps in smoke curtains (kgs 1) Mass flow rate flowing through averticalopening (kgs1) An integer used to identify one stage in an iterative process Number of exhaustpoints Perimeter offire(m) Heat release rate 1kW) Heat release rate per unit fire area (kWm2) Heat flux 1kW) Convective heat flux in the gases after the initial flame plume )kW) Convectiveheatflux passing through avertical opening (or under a balcony)(kW) Afunction defined by Eqn(H.11 time after ignition Is) Absolutetemperature of gases (K) Massweighted average absolutetemperature ofgaslayer under a balcony (K) Maximumvalue ofabsolutetemperature in a layer beneatha ceiling or soffit(K) Mass-weightedaverage absolutetemperature of gas layer in areservoir (K) Absoluteambient temperature (K) Wind velocity at the same heightas thetop ofthe building (m s1) Volumetricflow rateof gases (m ) Volumetricflow rateof gases exhaustedfroma reservoir (m3si) Width ofverticalopening (ml Width of balcony(distance fromvertical openingto front edge ofbalcony)(ml Characteristicwidth oftheventilator/exhaust point (m) Heightfromthe base ofthe smoke layer to the NPP(m) Effective heightof rise ofaspill plume (m) Height abovethe top ofthefuelto thesmoke layer immediately above (ml Height ofthevirtual origin ofthe plumemeasured abovethetop ofthe burning fuel Im) (Note Thisusuallytakes a negativevalue) Height abovethe NPP in a smoke layer (m) Height fromthe base ofthe fireto the smoke layer immediately above (m) Height abovethe base ofthefire tothe virtual originofthe smoke plume(ml (Note:This usuallytakes a negative value) Coefficientin critica exhaustrate eqn (kgm3) A constant definingthe steepness of atime-squaredfire growth curve (kWs21 Entrainmentrate into both free ends of a spill plume(kgs') Empiricalheight ofvirtual source below a spill edge (m( Additional smoke depth due tolocal deepening(m) Buoyantpressure rise aboveambient at a heightYNpP abovethe NPPlPa) Temperaturerise aboveambient of smoky gases (°C( Thmperaturerise aboveambient of smoky gases under a balcony(DC) Temperaturerise aboveambient of smoky gases in areservoir 1°C) Temperaturerise aboveambient of smoky gases in a vertical opening (°C) Densityof gases lkgmi) Densityi:f ambient air (kgm1l

s

1

1

Introduction

1.1 The hazards of smoke Inthe context offire theterm smokeisusedto describe liquidand/or solid particulatesproduced by combustion offuel materials,suspended in a mixtureofair and gaseousproducts ofcombustion, including steam. It is thus convenientto use the word smoke' to includeboth theparticulate and thegaseousproducts, including any air which is entrained intothe fireplume and into subsequent smokeflows, Thegaseouscombustion Products usually include toxic gases, the most common in buildingfires being carbon monoxide,although hydrogen cyanide and other toxic gasesmight he presentto some extent; irritants such as Acrolein;and relatively harmlessproducts such as water and carbon dioxide,Smoke pai-ticles themselves can.be irritants,and can be particularlydangerous to people Who are subjectto asthma or other respiratory problems.'['he reduction in oxygendue to combustion can itselfbe dangerous in sonic situations,and can result inthe suffocationofvictmstrapped in smoke. Theheat inthe gasesdue to combustionis alsopotentially hazardous, eitherto people who might be immersed in the hot gases orby heatradiation from the hot smoky gasesifthegas temperature ishigh enough. The reduction invisibilityin smoke alsorepresents a severe hazard, It hampers evacuation andthe rescuing of disabled orinjured occupants ofbuildingsaswell as affectingfire4Ightingoperations which can result in large fires involvingseriousthreat to livesand the environment. In general,ifthe visibility through thesmoke is sufficient or the emergency exits are visibleto the escapees,the toxic products will not stoj:) those people from escapingto safety. In practice this means that either the smoky gasmust be diluted with sufficient clean airto achieve a safevisibility(typicallyof10 iii which has come into)widespread use internationally,although it has avery weak scientificbasis, and should only be regarded as approximate),orthereshould he aphysical separation between the smokygases and the people at risk. Note that thedirectproducts of combustion may needto be diluted by more than one thousand times byvolume to achieve a safevisibility.

Smoke ispotentially lethal, Itis a wellestablishedfact that in the UK most deaths from tires aredue to smoke inhalation ratherthan tothe victimhaving been burned. However, the majorityofthese deaths occur in dwellings. Deaths from fires in other premises are relatively infrequent.This impliesthat the Iifesafety measures required by legislationformost public and commercial buildingshavebeen effectiveon the whole,

1.2 The regulatory background Eachcountry in the world has its OWfl approach to the

creation and enforcement of regulationscovering the topicofsafety in fire. Eachhas its own history bywhich it developed thatapproach. In this section we focuson the UK, inview of'its earlyand continuing development of fire regulations. FiresaiCty in buildingsmust, inthe UK, conform to the relevant regulations (eg guidancefor England and Wales is given in Approved 1)ocument B1l). The principal objectiveofthese regulationsis to safeguardlife l:y: reducing the potential for fire initiation, controlling firepropagation and spread, the provisionof adequate means ofescape :ibr the building'soccupants.

•• •

Means ofescape in case offire was first introduced to the BuildingRegulationsfor England and Walesin 1973. Prior to that datethepowersofcontrol in Englandand Wales over means ofescape had been contained in other legislation•2•-4•, Historically, the prevention of fire growth within (or between) buildingshasbeen achieved by the containment ofthe fireand its products, by means of coinpartmentation and/or separation. The designof structural compartmentation and separation has been largelyempirical and the concepts gradually refinedand enhanced in such a waythat the BuildingRegulations now cC)ver primarilylifesafetyandthe protectio of means of escape. It is necessarytoconsider four major aspects ofbuildings'— purpose,size,separation and resistance tofire to promote safedesign. Smoke and beat exhaust ventilation doesnot appear directly in the UK's regulations,except in some Local

i

2

Design methodologies for SHEVS

Acts.It has formed part oftherecognized package of measuresneededto merit aRelaxation from the Building Regulationsforshopping mallssince 1972; and atthe time ofwriting has become an indirect requirement of whichrequires that newmalls Approved Document inEngland andWales comply with BritishStandard BS 5588:Part io61 whichin turnrequires thatmalls should have smokeventilation as anessentialpart oftheir safety provisions.Itis expected that a similarlinkwillbe establishedbetweenfuture editions ofApproved Document B and BritishStandard BS 5588:Part7for

distances for escape,and measures for detecting the fire in an early stage andalertingthe occupants ofthe building. Itshould be noted, however, that compartmentation maynotbe sufficientby itselfto assist firefighting. Facilities toremove smokeand heatmay be ofbenefit forfirefightingoperations, and in some cases a reduction ofcompartmentation may be inevitableas a result offirefightingpractice (eg smokemayspreadout ofa smallroomintoa number ofotherrooms through dooropeningsheldopen byfire hoses). Theassessment ofsuitablefacilitiesto remove smoke andheat from such smallrooms and theirneighbouring spaces duringand after extinguishingprocedures will be a case-by-case decision in accordance with the experience andtraining offire fighters,and not as a result ofcalculation.These precautionsforremoving smoke andheatare notwithin the scope ofthis book. A SHEVSis more likelyto be advantageousin a larger room, suchas an exhibitionhall, shopping mall, or a factory,wherethereis no internal compartmentation and wherethetravel distances areappreciable. A SHEVSis no differentin principlewhetherdesigned for alargesingle-storeyspace whichis essentially alarge box (egmanyfactories, or exhibition halls),orfor a complicated (but undivided) space containing many storeys ofbalconies ormezzanine levels with potential firelocations in rooms to the sideofbut open to the main space.As can be seen below, theformer can beregarded. as aspecial case ofthe latter.

atria7. Severalother countries havelegislationconcerningthe protection ofpropertyin case offire —especiallythat propertyneighbouringan object on fire—and the protection oftheenvironment (egair pollutionand/or contamination ofwaterand soil) whichwill be endangered ifafire islikelytoreachan unmanageably large size.

1.3 The role of smoke and heat exhaust ventilation Thisbookfocuses on the use ofsmokeand heat exhaust ventilation,ratherthan other forms ofsmoke control suchas smoke control usingpressuredifferentials (although it does also discussthe need to allow for the interactions betweensuchsystemswhendesigning). As mentioned insection 1.1, thecombustion products from buildingcontentfiresmay require averylarge dilution to achieve a safevisibility. Withtypically smoky fuelssuchasmanypolymers thisdilution can reachone thousand timesthe initialvolume ofcombustion gases. This isdifficultto achieve forthesizeoffire wetypically have to consider in designingfire safetymeasures,and is rarely afeasibleoption —butitmaybepossiblewherethe designfireis small, and the buildingvolume is large. Physical separation ofsmoke and people is conventionallyachieved usingwalls anddoors, andis specifiedintheregulationsofmost countries,differing only in details.This approach cannot, by definition,be usedwherethe people (orproperty, or escape routes) being protected from smoke are in the same undivided space as the fire; and in many modernbuildings,large undividedspaces are usedto improve the appearance and environmental ventilation.Itis this scenario where smoke andheat exhaust ventilation is ofvalue. The principles areverysimple.Hot,buoyantgases from afire riseto form a stable layer in areservoirbelowthe ceiling suchthatacoolerclear layerofsufficientheightmay be presentforlong enough toachieve safeevacuationof occupants. Often it isnecessary tovent the smokefrom the reservoirusinga natural or mechanicalexhaust. In thisbooksuchaSmoke andHeatExhaust Ventilation System willbe referred tousingthe acronym SHEVS. It is raretofind circumstanceswherea SHEVSis requiredwithin a smallroom. It isusuallysufficient in such circumstancesto ensuresafety byacombination of fire-resistingcompartmentation, sufficiently shorttravel

1.4 Smoke and heat exhaust ventilation as a part offire safety engineering Every fireis a chemicaland physicalprocess producing

energy (mainly heat) and smoky gasesas well as other less hazardous products. Therefore, every fire prevention concept must have the same mainobjectives: to avoid ignition and thusthe outbreak ofa fire at all, to protecthuman beings,goods, the buildingandthe environment from the hazardous effectsofthe products ofthe fire (egheat and smoke) aslongas they arestill beingproduced bythe fire, to hamperand finally stop the production ofheat and smoke (ie to extinguishthe fire).

•• •

Anyfire prevention concepttherefore should be a composite ofwell-selected measures beingin tunewith eachother, and which hamperorstopthe production of heatand smoke, and/orwhichprotectthe objectswhicl areintended tobeprotected(people,property, etc.) by separatingthem from smoke andheat.Wherethis last cannotbefully uchieved, the purpose must be todiminish the effectsontheprotected people and/or objects. Theserelationships areillustrated inFigure 1.The thickarrows represent those influenceswhichdiminish the production ofsmoke andheat; orwhich reduce then effects;orwhichkeep the hazardous products of combustion awayfrom the endangered people orobjects to be protected. The thinarrows show the interactions

1 Introduction

3

INFLUENCES STRUCTURAL(PASSIVE) FIRE PRECAUTIONS

TECHNICALFIRE PRECAUTIONS tiredeteciton systems, extinguishing and firesuppression

Fftresistant stmcturea for

compartments. means ofescape, accessrotitas, cc bustbiIityofstructure

systems,

fixinstalledfirefighting equipment

Irisers,

Limitation of fuel, preventing thespread ofproducts of combustion

C/, LU

C)

z LU

D

-J PRODUCTS OF COMBUSTION

l

SMOE ha .raslr

HEAT fru ther res

spa

struGturc

7 7

t

('OrOSOfl

Reductionoffire duration

Reduction of effect of smoke andheatby removing them

ORGANISA1IONALRRE PRECAUTIONS

noperatiorts

andto eaceaflon teterveningplans, pnwisfonofeidingulsh1ngaents

SMOKE ANDHEAT EXHAUST VENTILATK)NSYSTEM (SHEYS)

_________________________

INFLUENCES Figure1 The roleofSHEVSin Fire Safety Engineering

betweenthe differentactivitieswhichproduce those influences. Figure 1 demonstrates thatany SHEVSexistswithin a much more comprehensivefireprevention concept. Structural(passive)fireprecautionsseparate whatis protected (egpeople, goods) from the products of combustion (egsmoke and heat) bystructural means, In most cases this means thatthe relevant structure will be fire resisting.This form ofprotection impliesthat everythinginside a fire compartment maybelostifno further active measuresto extinguishthefire takeplace or cannot beperformed;these activemeasures can include anattack by thefireservices. Peoplehaveto be ableto leave the compartment which isonfire and reacheithera structurallyprotected safeplace, orthe exterior ofthe building,in asufficientlyshorttime ifthey are to be safe. A SHEVScanremove thehazardous products of

combustion,smokeand heat, from the compartment and canseparatetheobjects and/orpeople tobe protected from smoke and heat already insidethecompartment, at leastuntilthe firehas reached acertain size (design-fire size) wherever the SHEVShas been designed tocreate a smoke-freelayer beneathabuoyant smokylayer. Because ofthis smoke-free layer,firefightthgoperations canbeperformed moreeasilybythe fire services, which will control and stop production ofsmokeand heatmore quicklyand lessentheireffect on any people and goods remaining inthebuilding.Itfollowsfrom this, thatthere is a close correlation betweentheeffect ofa SHEVSand possiblefire-fightingmeasures,including the effectofthe latteron thelikelydesign-firesize (see Note 1,nextpage), whichin turn influencesthe designofaSHEVS. Technicalfireprecautionsmainly affectthe reduction of thetime betweenignitionand thefire being attacked

Design methodologies forSHEVS

4 successfully,thus preventing further growth.

• Automatic fireattack suppressionor extinguishing the fire

systems,

•eg

sprinklers, directly. Automatic fire detectionsystems (especiallysmoke detection systems) shortenthe time untilsuccessful fire fightingoperations canbe performed. This is especiallytruewherethe fire servicesare called automaticallyon the operation ofthedetection system. Notethat wherethe automatic smoke detectionsystem triggers theSHEVS, the fire-fighting approach and attack are supportedby the smoke-free layer createdbythe SHEVSby callingthe fire services at a very earlystage offire development. Such detection systems alsoalertoccupants ofabuilding whoin turn maybeable(supported by asmoke-free layer due to an effectiveSHEVS) to attack an automaticallydetected, and usuallytherefore still small, firethemselveswith technicalfire precautions suchas the portable extinguishersorhosereels provided in the building,even before the firebrigade is

on site.

In thisway, SHEVSinteract with technical fire precautions and fire-fightingoperations, whichtogether havethe potential to influencethedesign-firesize. It has to be admitted, however,that the effectivenessoffirst-aid fire fightingbythe occupants ofa buildingis questionable in many cases,and should notbeconsidered when assessingthe design fire. Nevertheless,the effectiveness ofafire-fightingapproach canbe improved iftrained staff familiarwithfire-fightingtechniques and the technical fire precautionsare presentand are supported by an effectiveSHEVS. This leads to organizationalfireprecautions, whichare a partofthe Fire SafetyManagement arrangements for a building.These include: trained staffto: — start fire fighting(eg 'WorksFire Brigades'),and/or — manageevacuation,and/or — assist fire-fightingactivitiesperformed by the fire brigade (egby deliveringall informationneeded about usage andpopulation ofthe building,critical items insidethebuilding,technicalbuilding equipment includingtechnicalfireprecautions and theirintended function); intervention plans, includingsuchprovisionsfor emergency management as: — fire preventionplansofthe building,or — fixedinstalledcommunication devices,or — extinguishing agents in store readyfor use bythe fire services (especiallyifdistinctiveagents are to be usedfor certain fuelspresent, whichmustnotbe attacked byplain water);

•

•

Note: The concept ofthe design fire isdiscussed in more detail rnChapter 3,Forthe present purpose, whereaSHEVSisdesignedtoassrstoperationalfire-fighting,the design-firesize isthe most pessimisticbut still realistic assumptionofan area, ormorepreciselyofavolume, involvedin the fire andproducing acertainamountofheat, whenthe estinguishingmeasuresthe attack on the fire bythe fire services)become successfulsothatthefire doesnot5mwany larger.

• the organizationalprecautions for assistingevacuation of which include: building

may

— acoustic guidancesystemsor — trainedevacuation staff.

Allthese organizationalfireprecautions willassistfirefightingoperationsbecause they allow more ofthe fire brigaderesources toconcentrate on extinguishing operations with fewer ornocrews having to be employed insearching orrescuing people. All the precautionslisted above,technical and organizational,enhance an early successfulattack on the fire. Thus, the hazard caused by the products of combustion (smokeand heat)to people, the buildingand its environment is diminished. Ithas to bebornin mind, however,thatthe effectivenessofall the precautionslisted above benefit considerablyfrom the creation ofa smoke-free layer produced by a well-designedSHEVS. In other words, a SHEVSshould he an integral componentofan overall fire prevention conceptand ofthe fire-fightingstrategy, whichbecomes considerablyless effectivein the absence ofa SHEVSto create a smoke-freelayerat an earlystage

in the fire.

1.5 A brief history of smoke ventilation Smokeventilation is notnew. Our distant ancestors knew

that iftheywantedto lightafire inside a hut theyneeded to make aholein the roof,otherwise the occupants ofthe hutwould be choked by smoke. Modern smoke ventilationmerely appliesthe same principleto large fires in modernbuildings. Smokeventilation as adedicated fire precaution became popular for industrialbuildingsfollowingsome large fires (egGeneral MotorsplantinMichigan,USA,in 1953, see Plate 1; theJaguarplantin Coventry, UK, in 1957,

and Vauxhall Motors at Luton, UK, in 1963). Only

the last ofthesethreeplants hadautomatic ventilators81. During the 1960sthe Fire Research Station (FRS)inthe UK developed design algorithmssuitable for circumstanceswherethefire would be directly belowthe thermally buoyant smokelayerformed beneaththe ceiling9'10. The technique wasmostly usedas awayof reducing propertydamageby allowingfire fightingto become much more effective. Afire in the linked Wulfrunand Mander Shopping Centres inWolverhampton,UKin 1968[11], alerted people to thetremendous potential forthe spread ofsmoky gases in covered malls. Itwas realizedthatsucha fire could cause a largeloss oflife ifit occurred whenthemall was beingusedby the public. Researchersrealizedthatthe smoke ventilation approach already developed forlarge spaces could be adaptedto keep smokeentering amall safelyabove peoples' heads; thus protecting the means ofescapein the mall. Research intothe wayin which smoke moves within mallscontinued throughthe 1970s, leading to the development ofdesignformulaefor calculatingthe

1

Introduction

5

measureswillserve to improve the property-protection aspectsofthefire-protection package,although where thesmokeventilation system is solelyintended to ssist in fire-fightingoperations (ie to assistthe fire servicein protecting the propertyand/or contents) the design criteria required for safety canbe differentfrom these required to protectthe general public inview ofthe specialequipment and clothingusedbyfire-fighters.

1.6 The atrium:description and behaviour

;

Plate1 Fire at General Motorsplant,Livonia, Michigan, USA, 1953

movement ofthe smoke, the mixing ofair into the smoke, and hence the sizes ofthevents orfans needed to exhaust the smoky gasesin orderto maintain the smokelayerin the mallsat asafeheight. Asummary ofthe designadvice availablefrom FRS was publishedin 1979u•This advice has been expanded and updated in the lightoffurther research and experience,and has been incorporated in the most recentdesignguidanceavailablefrom FRS'3. Inthe late 1970s, researchbegan on the related problems ofatrium buildings.The mainfeature ofan atrium buildingis that a centralvoid rises throughtwo or morestoreys, allowinganysmoke entering the void to affectmorestoreys than the originalfirestorey. Unless,of course, these floors are separated from the atriumby fireresistingconstruction, in whichcase the atrium is merely aroom withanunusuallyhigh ceiling! It follows that design calculationmethods whichapply toatriain general, includingthe case wherethe fire is on the baseof the atrium directly beneaththeceiling,also cover virtuallyallother buildinggeometries ofinterest. Note however thatthe design-firesizes dependvery strongly onthe use and contents ofthe building. It should bereadily obviousthat a shopping mall of two or morestoreys represents a special case ofan atrium. Itis an atrium with a singleclass ofoccupancy. The smokemovement willbesimilar,the smokehazards will besimilar,andthe smoke control solutionscan be expected to be similar. The pivotal problem forboth mallsand atria is that smokeentering thevoid must not beallowedto endanger thesafeescape forpeopleinthe mall ortheatrium itself; or for people inany adjacent space open tothe mall oratriumonanystorey. In atria ormultistoreymalls, every storeyopento the void is potentiallyrapidly affectedby smokefrom afire on anyotherstorey. Twofires that illustratethiswerethe fire in the RegencyHyatt hotelat O'Hare in Chicago in 1972[14] and the firein the StJohn's Centre in Liverpool in 1977[15]. It follows that to protectthe safe escape ofthe building'soccupants,specialmeasures are needed for

atriaasfor malls. Anymeasuresto protectegressfrom abuildingwill alsoassisteasier entry for fire fighters.Hence, the same

in fire Socialandtechnical changes haveled to changes in buildingenvironmentswhich incorporate new(or revived) buildingforms andthe useofinnovative construction techniques and newsynthetic materials. Thebuildingsadoptingthese changes oftenhave includedwithin theirdesignlarge spacesorvoids, often integrated with many ofthe storeys.These largespaces have been describedas malls, atria, arcades and light wells.The generic termfor the buildingtype tends lobe 'atrium' andby theirvery nature, they can often run contrary to the traditional BuildingRegulations' approach in terms ofhorizontal compartmentation and verticalseparation. The originalatriumwasanentrance hall in aRoman houseand was one ofthe most important rooms ini:he building.The conceptofthis space hasevolved architecturallyover the past few hundred years and now applies to structuresmuch larger than the typicalRoman house. Modern atriaare designed such that the visualand spacial 'outdoor' environmentsare createdindoors6. In Romantimesthe control ofany smoke andhot: gases thatmayhave issuedfrom afire in a room adjacent to the atriumwaslikelyto have beenasimple matter, provided therewereno adverse windconditions (due to local topography ofadjacent structures) then the smoke and heatwould undoubtedlyvent itselfviathe open portionofthe atrium roofknown as the'compluviurn' (generallyusedforlighting purposes). Modern atriumbuildingstend to contain large quantitiesofcombustiblematerialand often have openplanlayoutsincreasingthe risk ofthe spread offire. The populationswithin such buildingshavealso increased, hencetherehasbeena substantialincreasein thenumber ofpeople tobeprotectedand evacuated in an emergency. Modern atriumbuildingsare usuallydesigned withthe atrium as a feature which canbe appreciated from within theadjacent rooms. Theroom/atriumboundary is usuallyeitherglazedor completelyopen. Thuswhen compared with 'conventional'buildings,this architectural/aesthetic requirement imposes additional problems oflife safetyduringafire, as smoke, hot gases and evenflames may travel from one (or more) rooms intotheatrium andthenceaffect areas which, but for the presence ofthe atrium, would not be affected. In conventionalmultistoreystructures thereis always thepossibilityoffire spread up theoutside ofthe building withflames issuingfrom one room and affectingthe

6

Design methodologies for SHEVS

floors above. Examplesofthis modeoffirespreadare an office block in Sao Paulo'71 andthe Villiers Buildingfire in Londonon l9January, 1979. Ifthe escape facilitiesfrom the variousroomsare ofa suitablestandard and are segregated from other compartments (as required inthe UK), thereshould not (in theory) be anyserious hazard to lifesafetyinthis fire condition. Itis only whenthe means ofescape are inadequate or the parameters dictating their designare violated,that the loss oflife may occur. Ifabuildinghas an atrium thenthis fireand smoke spreadcanalso occur internallysince thereisgenerally a maximizationofthe window areaand/or openboundary betweentheroomsandthe atrium. Hence,thereisan increased risk toother levels oftheentry ofsmoke and toxicgases andevenflamesfrom afire. Anumberofmethods canbe usedto ensure safetyin an atriumbuilding. BS 5588:Part givesthe relevant Code ofPractice describingwhichcombinationsof measures are currently recommended and in which circumstances.Oneofthosemethodsis smoke andheat exhaust ventilation. Experience offires inatriumbuildingsin the USA'4'181 has shownthe problemofflametravel internally through the atrium tobe minor in comparison with the problem ofhotand toxic gasesaccumulatingand fillingthe atrium; spreading throughout the building;and affectingescape routes. Thus, thereappears to be a needfor aproperly designed smoke and heatexhaust ventilationsystem in atrium buildings. The ideal optionwould be to prevent any smokefrom a room fire entering the atrium at all. Aneasily understood wayofachievingthis is to ensure that the boundary betweenthe roomand the atrium is both imperforate and fire resisting,and that the atriumbase hasonlya very restricted use. This option hasfrequently beenused,but is architecturallyrestrictive.Consequently it is not favouredby designers.Theconcepthas been labelledthe 'steriletube'E'S]. Wherethe boundary betweenthe roomand the atrium is open, itis sometimes feasibleto provide a smoke ventilation system within the room, to maintain smoky fire gasesabove the openingto the atrium. Unfortunately, itis often verydifficult, impractical,orextremely expensiveto fit aseparate smokeexhaust system to each and every room, however small. Occasionally, circumstances dictate thatsmoke control dedicated to eachroomin this wayis themostviableoptionfor protecting the atrium (this can occur, for example,when the roomlayout isofalarge area, ispredominantly openplanand open-fronted). Therehavebeen several examples ofthis.Nevertheless, it remainsgenerallytrue that this option is rarely foundto be appropriate for most

away in wholeorin largepart). Thisis becausethe airspeed neededfrom the atrium intothe roomin order to prevent the movement ofsmoky gases theotherway through the same opening, can vary betweenabout 0.5 ms1 and approximately4 ms1 depending on gas temperature, etc. All ofthis air must be continuously removed from within the fire room in orderto maintain theflow.Thequantitiesofair-handlingplantrequired will often exceed the size ofsmokeventilation systemsfor many typical atrium room openings. Note, however, that pressurizingthe atrium may be a viableoption wherethe atrium facadehas only relatively smallleakage paths. Wheresmoke from a firein aroom canspreadintothe atrium, withthe possibilityofrapid further spread affectingother partsofthebuilding,therewill be an extreme threat to safeevacuation ofoccupants from the affected parts ofthe building.Similarthreatswill occur if thereis a serious fire in the atrium space itself. In either case,the threat to means ofescape whichare either within the atrium, or are in spacesopento the atrium, can develop rapidlyunless some form ofsmoke control is usedintheatrium, in order to protectthose means of escape. In otherwords, a smokecontrol system inthe atrium is essential to ensurethat escape is unhindered, ensuringthatanylargequantities ofthermally buoyant smoky gasescan be keptseparate from people who may still be usingescape routes, or awaitingtheirturnfor evacuation.Therefore, the role ofa smokecontrol systersi isprincipallyoneoflifesafety. In orderfor a design tobe achieved,itis necessaryto identifythe various 'types' ofatrium thatare built. These canbe simplydefined asfollows. The'steriletube'atrium: the atriumis separated from theremainder ofthe buildingby fire-resistingglazing (FRG). The atriumspace generallyhas no functional use other than as a circulationarea(Figure2). The closed atrium:the atrium isseparated from the remainder ofthe buildingby ordinary (nonfireresisting)glass.The atrium space may well be functional (cafeterias,restaurants, recreation,etc) (Figure3). Thepartiallyopen atrium:here some lowerlevelsare open to the atriumand the remaining levels closed off byglazing (Figure4). Thefrillyopen atrium:some ofthe upperlevelsor all of thebuildinglevelsareopen to the atrium (Figure 5).

7

atriumbuildings.

Another possibilityisthatthe atrium should be pressurizedto prevent smokemoving from a room into theatrium. This is notusuallyaviableoptionwherethe opening betweenthe room andtheatriumis large (egan open-fronted room or room whose glazing has fallen

b

• • • •

1.7 Active control of the fire A more detailed discussionofactivefire fightingis

presented in Chapter12. Itshould be remembered thatfire fightingbecomes both difficultand dangerous in a smoke-loggedbuilding. Itfollowsthat to assistthefireservices,the smokecontrol system should becapable ofperformingits design function for aperiod oftimelonger than that required fir the public to escape (seealso 12.2.2.1),thus allowinga speedierattack on thefiretobe made afterthe arrivalof the fire service. Anymeasuresto protectegress from a

1 ntroductkn

Figure2 Sterile tube: fire-resisting glazingbetween atriumand

Figure3 Closed atrium:standard (non fire-resisting) glazing

compartments

between atriumand compartments

7

Figure4 Partially openatrium Figure5 Fully openatrium

buildingwill also assisteasier entryforfire fighters. Hence, the same measureswill servetoimprove the propertyprotection aspects ofthe fire-protection package (seealso 12.2.2.2).Wherethe smoke ventilation system is solelyintended to assistin fire-fighting operations,the design criteriarequired for safety might be differentfrom thoserequiredto protectthegeneral public inview ofthe special equipment andclothing used by firefighters (seealso 12.2.2.4). Anysmoke control measures needto specifya maximumfire size for its designandsprinklers are often needed tolimit the sizeto thismaximum.It is also likely that some kind ofsmokeventilationwill be required to maintain a clear escape route. Thus both sprinklersand smokeventilators are needed to achieve aproperlife safety design. Atpresentthereis considerabledebate overthe effectsofinteraction betweenthetwo.One

argument is that opening the smokeventilators on smoke detection, iebefore sprinkler operation, may delay the activation ofsprinklersand thus have detrimental effect on sprinklerperformance. Onthe otherhand, ifthe opening ofsmokeventilators is delayeduntilsprinkler operation, theremaybe considerablesmoke loggingand the effectivenessoftheSHEVS may be seriously compromised. This debateis discussedin more detail elsewhere in thisbook.

1.8 Implementationof a smoke and heat exhaust system in a building Whenthe 'concept design' ofthe SHEVShas been completed satisfactorily(egby followingthemethods describedinthisbook), therestill remains a great dealto bedonebefore thesystem is successfullyinstalledin a

8

Design methodologies for SHEVS

fullyfunctioningstatein the finishedbuilding.The ideas mustbeturnedintophysicalreality,inawaythatensures thatthe resulting arrangement will functionas desired whenthefireactually occurs:regardless ofthe conditions applying at the time. Itfollowsthat therearemany necessaryconsiderations whenselectingthe equipment neededto make the design areality.Theequipment (hardware) must be ableto function inthefire condition expected underthe design conditions,and oughtto havebeen testedbythe manufacturers and/or thesuppliersto confirmthis. The equipment should alsobe appropriate to the circumstancesofthe buildinginwhichit is to be fitted. Thesecircumstances includethe geographicaland meteorologicalconditions expected,both atthetime of the fire andin normal use. It isnotthepurpose ofthe presentdocumentto try toprovide detailed guidanceon the selection ofsystemsin all circumstances. Nevertheless,some pointers towards the parameters which should be considered are described in Chapter 13. Even the best equipment can beinstalled wrongly. There havebeenmanyinstances wherewhatwas installed did not exactlycorrespond to whatwas intended, or wheretheinstallationprocedures have not beenworked out in sufficientdetail. It isnot the purpose ofthis bookto provide detailedguidance similarto the equipment specification.Nevertheless, some guidance concerning procedures is included in Chapter 14. Humannature being as fallible asit is, it is desirable thatwhen asystem is fullyinstalled,it should be tested forftinctionality.This caneitherinvolvetests to confirm thatthe equipment still performsto specification (perhaps most important whereducts are usedto move the gases) withoutactuallysimulating thebuoyancy of fire gases, orit can involvespecial tests (hot smoketests) to confirmthat both theequipment and the design conceptitselfareperformingto expectation. Once again, the discussionandadvicein this bookis limited to outline guidance, and can be found in Chapter 15. Asthe fire may notoccuruntilmany years after the system isinstalled,it is alsonecessaryto ensurethatthe hardware is capable ofsurvivingmanyyears of installationand is still ready to serve its purpose ifa fire occurs. This impliesthat thereoughtto be regular maintenance and re-testing procedures as part ofa larger fire safety management strategyforthe buildingin question. Somediscussioncanbefoundin Chapter 16.

Protection Associationofthe USAhasdeveloped a Code22 whichsets out afire engineering approach to the design ofsmoke control foratria (termed 'Smoke Management' in the USA). While this code is inmany ways very comprehensive andbroaderin purpose than thisbook, some ofthe approaches useddifferfrom alternativeswith which UKdesigners are more familiar, and canbe more approximate thanmethods currently recommended byFRS. This particularlyapplies tosmoke entering the atrium from adjacent rooms. Some other countries have recognized existing publicationswithin theirownguidelines.Forexample, Singapore has referred in its 1997 Codeofpracticeforfire precautionsii'z bui7dings231to BRE guidanceonthedesign

1.9 The purpose of this book and its

relationship to earlierguidance Previousguidanceto designers ofatrium smoke control systems within the UK has been provided bythe British Standard BS 5588:Part 7 Codeofpracticeforthe incorporationofatriain bui/dings, andthe BRE Report Design approachesfor smokecontrol inatriumbuildings['31. Therehave beena number ofqualitativepapers, and otherpapersusingrelativelysimple models ofsmoke movement within atria'921. The National Fire

ofSHEVS24'131.

It canbe notedthatthere is amajor differencebetween any application ofthis booktosmoke and heat exhaust ventilationofshopping mallsofmore than one storey, andtheearlier guidanceforsuchmallspublishedby BRE241.The diflèrenceis not so muchinthe formulae andtheresulting design solutions,as inthe underlying philosophyofdesign.The earlier guidanceadopted the view that itwas possibleto specify agenericallytypical smokeflow rateleavingfrom the front openingofa retail unit,whenspecifyingthe flowparameters in the smoky gasesapproaching the spilledge. Itfurther assumedthat thesetypicalflowratescould be takento bethose measured experimentallyin ascale model ofa shop unit51.The result wastogive a relativelysimple calculation,whichallowed for differentwidths ofthe unit's front opening, without the designer or the regulator having to worry about changes ofcontentsin the units, or ofdetail differencesbetweenneighbouringunits. The disadvantageofthis earlier approach isthatitbecomes unreliableforreal mallswhichdeparttoo far from the dimensionsmodelled in the experiment251. Inpractice, this means that the earlier guidancestrictly only applies forstoreyheights close to 5 m, andfora 5 MW, 3 mx 3 m design fire. Theadvantage ofthis current bookis that it allowsthe circumstancesofthefire in the unittobe included explicitlyin calculation,includingthe actual dimensions ofthebuilding.This impliesthat separate calculations must be doneforfires located ineachand every unit suspected ofbeingapotentially 'worst case' forthe mall inquestion. In practice, the current bookis themore powerfultechnique for design,butthis advantage is gained atthe expense ofsome loss ofrelative simplicity compared with earlier guidance. Note, however, that wherethereal mall's shape and dimensionsareclose to those on whichthe earlier guidancewasbased, that earlier guidancecan still be usedwith confidence. It is hopedthat the current bookwill support the Regulatoryand Standard Codes being developed byBSI and CEN.This bookcannotcover all the infinite variations ofatrium design. Instead, it givesgeneral principles forthedesign ofefficientsystems,with simplifieddesignprocedures for an ideal model ofan atrium and then further guidanceonfrequently

1 Introduction encountered practicalproblems.Asthedesign procedures are ofnecessity simplified, the bookalso gives their limitationsso that,whennecessary,amoredetailed designby specialistscanbe carried out. The above-mentioned designprocedures and guidance documents arebasedon the useofzone models: in which the problem is divided into separate zones (which may or may notinteract); andrelatively simple formulae (often empiricalin origin)are usedtodescribe the smokeand heatmovement in eachone. While thisis avery powerfultechnique which canbe applied with confidenceto amajority ofsmokeventilationdesign circumstances,it must be recognized that abuilding geometry whichdeviatestoo far from the idealized geometry usedin deriving the designformulaecannot be designed usingthoseformulae. Sincethe mid-1970s, field modelling has been developed whichexploitsthenewtechniques of computational fluiddynamics (CFD) todeduce how, and atwhatrate,smokewould fill an enclosure.Itdoesthis by avoiding resortto experimental correlation,as faras is currently possible,and byreturning tofirstprinciples to solve the basic lawsoffluidflowand thermodynamics.As a consequence,withadequate validation,this typeof modelling should have wide application. Theuse ofa

9

computer is necessarysince the techniqueinvolvesthe solution oftensofthousands ofmathematical equations forevery step forwardthe simulationmakes,and consequentlyinvolvesrelativelylongcomputational timescompared withthe use ofzonemodels. This makes CFD simulationsrelativelyexpensive,particularlywhen usedfor buildingswith complicatedgeometry.Asthe computersbecome faster and more powerfial andthe algorithmsevolveand improve, CFD islikelyto become cheaper andto gain more widespread use in Fire Safety Engineeringincludingthe smokecontrol designprocess. Users ofCFD models should be aware ofthe importance of: correctlyidentifyingthe boundary conditions appropriate tothe precise circumstancesofthe design, correctly identifyingthe appropriatenessofthe submodelsused, forexample the heat transfer and radiation model, turbulence model, etc. usinga smallenough grid size so that the converged solution isindependent ofthe grid size.

• • •

TheCFD methodology isbeyond the scope ofthisbook, but a full descriptiontogetherwith adiscussionofcurrent limitationsis given,for exampleinreference [26J.

10

________________

2 General principles of smoke production, movement and control

2.1 Fire growth and smoke production In most instances,a room (compartment) fire maybe

assumed toburn in eitheroftwoways. Fue/BedContra/is whenthe rate ofcombustion,heat output and fire growth depends onthe fuel being burned and thereis more than sufficientoxygen presentto support the combustion.This isthe 'normal' fire condition found in mostsingle-storeybuildings whilstthe fire is still small enough for successfulsmoke control. T/entz/atthn Controliswherethe rate ofcombustion etc. is dependentuponthe quantity ofair availableto the firecompartment, assuming that anymechanical ventilation systemshavebeen madeinactive.

• •

The quantity ofsmoky gases produced, ie the massflow rate offire gasesin andfrom the compartment, andthe energy (heatflux) contained therein, may be very differentforboth regimes.It istherefore important to identifythe regime whichappliesand to determine the mass flow and the heat fluxwithin the smoky gases. It is important to understand the basic mechanisms whichcontrol thefire condition. A step-by-step history ofa growingfire may be as follows. 1 The fire starts for whatever reason, itsrate ofgrowth depending uponthe materialsinvolved,their orientation and positionsrelativeto eachother. In most practical compartments there is sufficient oxygen to support combustion in thefirstfew minutes, andthe firegrowth and smoke production are controlled by thefuel,ie fuel bed control. 2 Smoke from the fire rises in a plume to the ceiling.As theplumerises,airis entrained intoit, increasingthe volumeofsmoke and reducing its temperature. The entrainment increases with increasingheightofrise of theplume. The smokespreads outradially underneath theceilingand forms a layerwhichdeepens as the compartment begins to fill. Ifthe compartment is open totheatrium (or a mall),thenthe gasesflow out immediatelythey reachthe opening. Ifthe compartment isglazed or the opening is below a deepdownstand then the smokesteadily deepens. As the layergets deeper thereis less height

for the plume ofsmoke to risebefore it reachesthe smokelayer,henceless air is being entrained, with the result that the temperature ofthe smoke layer increaseswith layerdepth, even for a steady fire. Most fireswill continue to grow larger as the layerdeepens, reinforcingthis effect. 3 6 mmplateglassmayshatter whenexposed to gasesas littleas 100 K warmer thanambient. Oneofthemain reasons forglassbreakage is the differentthermal expansion values ofthe glassand itsmountings; breakage at relativelylow temperature may result whenthereis noprovision for differentialexpansion. Thus, oncethis temperature is passed,thereis an increasinglikelihood that the glasswill fracture.Ifthe compartment is sprinklered and the water spray hits the glass, the localizedheating oftheglassby radiation from the fire andbythe gas layer, combined with sudden coolingdue to the water spraymayincrease the likelihoodoftheglassbreaking (note:there are 'deluge' sprinklersystemsdesigned to keep the glass cooland prevent it from breaking).Plate or 'float' glass breaksin an unpredictableway.A crackmay not result in glassfallingout;but theassumption that glasswill fall away once broken is asafeassumption for design in the circumstancescovered in this book. Thesmoke and hot gases will thenflow externallyto the atmosphere, orentertheatrium (where one is present), or both, depending uponthe natureofthe compartment and its relativeposition in the building, thesize and position ofthefire inthe compartment, andthe strength ofdifferingglazing systems. In atriumbuildings,ifthefire canbe accidentallyor deliberatelyventedto the atmosphere then the threat to otherlevelsviathe atrium is greatly reduced. There will,however, be instanceswhen afire willvent all its effluent gas into the atrium, and thisis generallythe worstdesign scenario (Figure6). Thereis so muchmixing ofambient air intothe plume that,exceptclose to the fire itself, the hotsmoky gasescan be regarded asconsisting ofwarmed air, whencalculatingthe quantity (massflow rate)being produced in the compartment. 4 Initially,this mass flow rate ofsmokewillbe controlled by the fuel bed, as mentioned above. However,the

2 Smoke production, movement and control

11

Air Inflow

Figure6 Smoke enteringan atriumfromafuel bed controlledfire

Figure7The onsetofflashover

in an adjacentroom

geometry ofthe openingontotheatrium has a crucial effect. Asthe fire grows largein comparisonto the area ofthe opening,the air supply to thefire is'throttled', causingthe fire toburninefficiently. 5 This leads to thesituation wherethe inabilityofthe compartment tovent the gases effectively duetothe restricted areaavailablecausesthe layerto deepen further,whichcombined withthe increasingfirearea, causesthe layertemperature to rise. Once thelayer temperature reaches approximately 600 °C, then in mostcompartments thedownward radiation from the gas layer is sufficientto cause ignition ofthe remaining combustiblematerialsinthe compartment (Figure 7). Wherethere is sufficientfuel within the compartment forthe entirecompartment to become involved,the layertemperature will rapidlyriseto flame temperature, very approximately 1200 K (930 °C). The rate ofburning,heat output and massflow leavingthe compartment are now strongly dependent uponthe geometry oftheopening, ieventilation control (Figure 8). 6 The transition from thefuel bed controlled fire with a layerat 600 °C totheventilation-controlledcondition is very rapid, and may takeonly seconds. This condition is often known as 'flash-over'. 7 Theremaybe an intermediate situationwherethe compartment has flashedover or the firehas simply grown to encompass the entire widthofthe compartment, butwherethe quantity ofair now required to maintain combustion is adequate, even thoughtheonly surfaceavailable forairentrainment is the widthofthe opening (as opposed to the fire perimeter for afuel-bed controlled fire).This condition isknown as the 'fully-involved,largeopening fire' (Morgan& Hansel![271). 8 Thereare many factorswhichdeterminetheprevailing condition includingthe type and disposition ofthe fuel, the dimensionsoftheenclosure andthe dimensionsof the ventilationopening. Theycan, however, be

Figure8 Afully involved ventilation-controlled fire reducedto two principalparameters for most

compartments:

AH°5, (where A is the areaofthe opening intothe atrium andHis the heightofthe opening); and Af (theareaofthe fire). Fora further discussion,see eg references [27—29]. Note: Both the fully-involvedlarge-openingfire and

9

ventilation-controlledfireconditionswillalmost certainly produce flamesfrom the opening intothe atrium. Thepresence ofsprinklerswill usuallyserve to prevent fire growth proceeding to fullinvolvement;ifthe burning material isnotshielded from the water spray thenthe fire is likelytobe extinguished (or almost extinguished);with shielding,the firewill continueto burn, although it islikelytobe maintainedin afuelbed-controlled stateand the fire size willbelimited.

12

________________

2.2 Pressurization and depressurization Inpressurization, air is introduced intoan escape route (usuallya stairway)at arate sufficient to hold back any smoketrying to pass onto that route. The pressure differenceacross any smallopening ontothe routemust be large enough to offsetadverse pressurescaused by wind,buildingstack effect and firebuoyancy.It must also be low enough to allow the escape doors tobe opened with relativeease.The air supply must alsobelarge enough to produce avelocity sufficientto holdback smoke at any large opening onto the pressurizedspace. Therequirements aresomewhat contradictory. Pressurizationsystemsare designed to have adequate air flow across anylarge openings (egdoors). Excessive pressure differenceacross asmall opening (when the doors are closed) canbe prevented by the use ofdampers (egbarometric dampers).Experience ofpressurization designssuggestthatitis well-suitedtothe protection of stairwaysused as escape routesin tall buildings,although the technique canbe usefulin othercircumstances. Codesforpressurizationcanbe found in BS 5588: Part4[301• Depressurizationis a specialcaseofpressurization, wheregasesare removed from the smoke-affectedspace ina waythatmaintains thedesired pressure differences and/orair speeds across leakage openings betweenthat space and adjacent spaces30. Note that depressurization doesnot protectthe smoke-affectedspace in any way. Instead it protects theadjacent spaces. In the circumstances ofan atrium, itis sometimespossibleto use the buoyancyofthesmoky gases themselvesto create the desired depressurizationeffects.This is explainedin moredetail in section 6.3.

Design methodologies for SHEVS generalapproach needed forsuccessfuldesign.

Air mixes intothe fire plume as it rises givingalarger volume ofsmoky gases. Thesegasesflowoutwards below the ceilinguntil theyreachabarrier (eg thewalls,or a downstand, see Plates 2 and 3). The gasesthen form a deepening layer,whose buoyancy can drive smoky gases throughnatural ventilators (or alternativelysmoky gases can be removed using fans). For anygiven size offire, an equilibriumcan be reached wherethe quantity ofgases beingremoved equalsthe quantity entering thelayerin the fire plume —no significantmixingofair occurs upwards intothe base ofthe buoyant smokelayer.Itis essentialthatsufficientair enters the space below the layerto replace thegases being removed from thelayer, otherwisethe smokeventilation system will not work. Thedesignprocedures aredescribed indetail in the remainder ofthis book, andthe calculationprocedures aresummarized inAnnex A (for time-based calculations involvingagrowing design fire)and in Annex B (for steady-state calculations).

I

2.3 Throughflowventilation (or smoke exhaust ventilation) Smokeexhaust ventilation (throughflowventilation)is

usedwhenthe fire is inthe same space as the people, contents, or escape routes being protected, withoutit filling that space.The intention is to keep the smoke in the upperregions ofthe buildingleaving clean airnear the floor to allow people tomove freely.This stratificationorlayeringofthe smoke is made possibleby the buoyancyofthe hotsmoky gases produced bythe fire, and it follows thatto be mostsuccessfulthe high-

level smoke layer must remain warm. Smoke ventilation is therefore onlysuitable for atria wherefires can cause smoke to enterthe atrium space and forlargesinglestoreyspaces which arehigh enoughfor an appropriate layering.Suchfires can eitherbefuel-bed-controlledfires at thebase ofthe atrium, orfires in adjacentspaces (rooms)whichallow smoky gasesto enterthe atrium. Much ofthe current bookis concerned withthe calculationofdesignparameters for smokeventilation systemstailored to the circumstancesfound in various types ofatria. First, though, it is worthreviewingthe underlying principles ofsmokeventilation and the

Plate2 Example of a fixedglazed smoke curtainin a shopping mal

Plate3 Example of afixed smoke curtainbeingused as a reservoir boundary

2 Smoke production, movement and control

2.4 Smoke and heat exhaust design philosophies Thesmokeventilationsystemcan bedesigned tofulfil one or more separate requirements within a building. Protection of means of escape The objectiveisto achieve a desiredsmoke-free clear layerbeneatha smokelayer.This is a commonlyused approach wherethepurpose ofthe smoke exhaust ventilation system isto allow the continued useofescape routeswhich arein the same space as the fire (examples include enclosed shopping mallsand many atriaorlarge single-storeyspaces,egforpublic assembly).The thermally buoyant smokeforms alayerbeneaththe ceiling.The smokeexhaust (using eithernatural smoke exhaust ventilatorsorpowered smoke exhaust ventilators)is calculatedto belarge enoughto keep the smoke at asafeheightabove the headsofpeople using the escape routes for a given designfire size,evenwhile thefire is stillburning. Itis essentialthat thesystem comes intooperation as early as possibleduringthe fire, and itis usualtoinitiate the operation automaticallyon receipt ofa signalfrom asmoke detection system. Temperature control Wherethe heightofclear air beneaththe thermally buoyant smoke layer is nota critical designparameter, it is possibleto use thesame calculationprocedures as for protection ofmeans ofescape,but in a differentway.The smokeexhaust canbe designedto achieve a particular temperature ofthe gasesinthebuoyant layer.This allows theuse ofmaterialswhichwouldotherwisebedamaged by hottergases. A typical exampleiswherean atrium facadehasglazingwhichisnotfireresisting,butwhichis known to beableto survivegas temperatures uptosome specifiedvalue. The use ofa'temperature control' smoke exhaust ventilation system insucha casecould, for example,allow the adoption ofa phased evacuation strategy from higher storeys separated from the atrium only by suchglazing. Assistingfire-fightingoperations In order for firefighters to dealsuccessfullywitha fire in a building, itis firstnecessaryfor themto drive theirfire appliancesto entrances givingthemaccessto the interior ofthe building. Theythenneedto transport themselves andtheir equipment from this pointto the scene ofthe fire.

13

In extensive and multi-storeycomplexbuildingsthis may involvetravelto upperandlowerlevels, and may takesome time. This travel,as well asthe fire-fighters' effortsto effectrescues and to carry outfire-fighting operations, may be seriouslyhampered ifthe buildingis full ofhot smoky gases. The provision ofheat andsmoke ventilation systemsrequired to assistmeans ofescape or fortheprotection ofproperty, may alsoaidfire fighting. Thereis often the desire to designa smokeexhaust ventilationsystem specifically for fire-fightingoperations, wherethedesign philosophies aresimilartothatusedfor a SHEVSdesignforlifesafetybutthe functional requirements maybeless stringent (ie moresevere conditionsmay be acceptable)because ofthe specialist equipment and clothing available. IftheSHEVSis designed solelyto assistfire fightingand has no other life safety implications,and certain other appropriate circumstancesapply (egwhenthe primary design objectiveispropertyprotection and automatic extinguishingsystemsare present), it canbe appropriate toleave the ventilatorsclosed (this mayreduce fire growth) untilthe firebrigade arrivesand then to open themmanually.Functionalrequirements should be agreed bythefire serviceresponsiblefor the buildingin question. The applicabilityofSHEVS to operational fire fighting, andthe close relationshipbetweenthetwo,isdiscussed in much greater detail in Chapter 12. Property protection Smokeexhaust ventilationby itselfcannot prevent a fire from growinglarge. It will guaranteethat afire inthe ventilated space has a continuingsupply ofoxygen to

keepgrowing. Itfollowsthat smokeexhaust ventilation canonly protectproperty byallowingactive intervention ofthe fire servicesto be quickerand moreeffective.Depending onthe materialspresent, apropertyprotection philosophy may be basedonthe needto maintain the hot buoyant smokelayerabove sensitivematerials,or maybe basedonthe needtomaintain the smoke layerbelowa criticaltemperature. In eithercase,the functional requirement for keyparameters onwhichthedesign must be based,need notbethe same as wherethe primarypurpose is life safety. Theywill dependonthe circumstancesapplyingineachcase.These key functional requirements must be agreed with allrelevant interested parties.

14

____ _____ ____ _____ _____

3 Design-fire size

3.1 General Manyareasoffire safety engineeringrequire the identificationofan appropriate fire size uponwhichthe design canbe based. Designfires can takemany forms, forexample,when consideringfire resistanceofdoors and wallsa fullydeveloped post-flashoverfire on oneside ofthedoor or wall is assumed:the designfire in this case will be a frilly-involved fire compartment. Smoke exhaust ventilation is only ofvalue whenthe people, contents orstructure being protectedare in the same space as the fire, and it is therefore conventionalto consider only pre-flashover fires. Thatscenario is also commonly found wherethe 'timeto danger' for the building'soccupants isbeingcalculated, eitheras part ofa smoke and heat exhaust ventilation system design or asa separate calculation.The calculationofthe quantity of smoke and heatproduced byafire requires a knowledge ofthe sizeofthefire,in terms ofarea, perimeterand heat fluxdeveloped perunitareaorfrom the fireas awhole. Whendesigningsmokeventilation ordepressurization systems,the massflowrate and heat fluxdeveloped in the room aremajorparameters in the calculationofthe system requirements, changes in whichcan substantially affectall ofthe subsequentsmoke flow conditions. Ideally,the designfire would be based on the materials within an occupancy,suggestingthat the choiceofa design fire should be straightforward.Unfortunately,this is notthe case.Whilethe heat release rates formany materialsare known, it is rarely possibleto say thata fire will consist ofaknown quantity ofmaterial.Within an occupancya fire will involvea combination ofdifferent materials,so that the heat release rateforthat occupancy will be a function ofallthe materials present. Hence the development ofa fire is dependenton a number of factors,including: theprecise location ofthe ignitionwithrespect to the

• •• the typeofmaterials present, the quantity ofmaterialspresent, •• theposition ofthe materialsrelative to eachother, chemical reactionsbetweenmaterials present possible iftheir containment is fuel,

•the

destroyed by fire, position ofmaterialsrelativeto walls,ceilingsand

similar,

• the availabilityofoxygen (in sealed rooms afire can become oxygen-starved), • thepresence andeffectivenessoffiresuppression • changing ofburningbehaviour dueto ageing of materials. devices,

Consequently,there is no methodavailable to calculate the development ofa fire in any but thesimplest fuel arrays. The likelysize ofafire can only be deduced from the analysisofthe statisticsoffires in thetypeof occupancy ofinterest, orfrom experiments on appropriately similar fuelarrays. The values for fire growth and fire sizecontained in this bookare based on both statistical analysesand experimentalwork. Itis worthnoting herethatdesign firesbasedon statistical analysisare always based on animplied acceptable risk whichcandiffer forvarious applications,andwhichis always ultimatelyrelated to public opinion. Adesign fire caneitherbe asteady-state fire with constantheatoutputor atime-dependent growingfire to whichthe means ofescape and evacuationtime for the particular buildingoccupancy could be related (see also section 12.2.2.1).Steady-statefires for designcalculation invarious occupanciesaregiven in the relevant standards and thesehaveusuallybeenused historically.Although it is acknowledgedthata real fireis notusually'steady state', itis relativelysimple to assessthemaximum size a fire can reasonably be expected to reachduring the escape period in aparticular scenario, and to design a smokecontrol system ableto copewith that. Theassumption ofa steady-statefireallows the smoke control system to cater for allfires up to designfiresize, andby not consideringthegrowth phaseofthe fire, often introduces asignificantmargin ofsafetyto the system design.A firewill produce smaller quantitiesofcooler smokein its early 'small'stage, depending on the nature andarrangement offuels.The reduction ineffectiveness ofa natural SHEVS dueto the lower temperature will be compensated by the reduction in the quantity ofsmoky gas needing to be exhausted. Onthe otherhand, useofagrowingfire could result in a less onerous design criterion which mayresult in

15

3 Design-fire size considerablesavingsin the implementationofa SHEVS design in alarge orcomplexbuilding.Historically,one reason for not usinggrowing firesfor designhasbeen the lackofavailabledataaboutfire growth rate invarious occupanciesand scenarios.Research has been carried out in thelastfew years, atFRS and elsewhere,to determine thelikelyfire growth rate insome occupancies.Dataare still not availablefor many scenarios.Itis hopedthat a database offire growths willbebuiltupwhichwill enable widespreaduse ofgrowing fires for SHEVSdesigns.Any fire safety strategymust inevitablycomparethe timeto the onset ofdangerous conditions, which in turn depends strongly on the assumed fire growth rate,totheestimated evacuation timefor occupants aswell as tothe attendance time offire-fightingservices. Such strategies arevery sensitiveto influencesontheseparameters, whichcaninclude the inappropriatebehaviour of escapingpeople, minorchanges inthe building's geometry, trafficjams orroadworks onthe accessroutes ofthefire-fightingservices, temporary absenceoffire crews at the nearest fire stations forwhatever reasons, etc. Eithermethod ofassessmentofthe designfire sizecan sometimesbe baseduponavailablestatisticson firedamaged areas butmayhaveto dependupon experiencedjudgement, basedon the anticipated fire loadwhere amorerigorous approach is notfeasible. It followsfrom theforegoingthat thereis astrongly subjectiveelement in assessingwhatfire size is acceptablyinfrequent for safedesignpurposes. Clearly, an 'average'fireforsafety design is unacceptable,since by definition,nearly halfofallfires would grow larger.Also, it is unreasonableto expecta SHEVSto be designed for the largestpossiblefire.

3.2 Growing design fires Thetime-dependentgrowingdesignfire hasthe attraction oftrying to model thereality ofgrowing timevarying fires. For horizontal fire spread atime squared (or 't2') curve maybeconsidered:

q=yt2

(3.1)

where:

q= heat release rate (kW), y= aconstantdefiningthe steepness ofthe curve (kWs2),

t=timeafterignition (s).

This approach isfollowedin severaldesign guidance documents for smokecontroI22'28'29includingNF'PA 92B221, whichclassifies thefires asslow, medium,fast and ultra-fast.Values foryforthose fire growth rates are given in Table3.1. Wherethis approach is useditis desirableto carry out other calculations(egthe firesizeat the onset of flashover)to setan upperlimitto whatwould otherwise beaninfinitefire growth. Inreality,ofcourse, any actual sample offires occurring in the same nominal occupancywill never be describableby asingle growth curve.Therewill bea

Table 31 Various t2fire growth rates Timeto reach Fire 1000kW growth

(s)

(kWs2)

Ultra-fast Fast

73 146 292

0.18760 0.04689

584

0.00293

Medium Slow

0.01172

distributionofgrowth curvesdepending on suchfactors as variationsin fuellayout andvariations inthelocation ofthe initialignition.This distributionmeans in principle thatthe designer should choose an appropriately pessimisticcurve: putperhaps too simply,any design basedon an averagecurve impliesafailurerate ofone in two.This is usuallyunacceptablewherelifesafety is involved.Itis nevertheless unreasonablefor the designer to base thedesign on theworstcurve possible— this would be anexplosion.The designer (ormoreusuallyin practicethe enforcer ofregulations)must decidewhere the limitsofreasonableness lie. Ideallythiscould be specifiable in terms ofthe constant yinEqn3.1 beinga specifiednumberofstandard deviationsaway from the meanvalueappropriate to the classofoccupancy.Also, for some scenarios,the growth rate mayvary with time, eg afire maygrowat a 'medium' rate for thefirst five minutes andthen change intoa 'fast'fire. Ramachandran31 has pioneered the analysis ofthe UKFire Statisticsdatabaseto deduce not only fire growth curves (expressedin exponentialform) butalso toderive the probabilitydistributionsforthosecurves. Unfortunatelytheavailabledatado not cover many occupancytypes ofmajor interest tothe smoke control designer. Exponentiallygrowing fires have alsobeenusedin some other documents[22] Thefire growthis given as:

q=c(exp(f3t)—l)

(3.2)

whereuand 3 areconstants (note:theseconstantsarenot thesame parameters represented by uand 1 elsewherein the presentwork). Exponential growth can bevery rapid andprincipallyapplies to fire spreadinvertical surfaces. Theyarenotnormallyusedfor SHEVSdesigns. Thereisaremaining sub-group ofgrowingfires for designuse. These are wherethefuel loadcorresponding toaspecificoccupancyhasbeenrecreatedundera calorimeter (egthe 'sprinkleredcalorimeter' at FRS[3233]) and hasbeen burnedso thatthe heatrelease rate and otherimportant parameters areknown as afunction of time. These datacanthen be usedby designersto predict the consequencesofwhatwould have happened ifthat same fire had been burned in the buildinggeometry of interest tothe design.Thistechnique isusefulinthatit canallow aconfident departure from themoreusual designfires for aspecificapplicationwherethe fuelload

16

Design methodologies for SHEVS

is not likelyto vary much from the arrangement studied in the experiment.

A designprocedure with a growingdesignfireis summarizedin Annex A.

Some designers offire safety systemsassumethat a growing design fire in the presence ofsprinklerswill grow until ithasbecomelarge enough to trigger the first sprinklerhead,afterwhich it willprobably decline or be extinguished.It is often cited as a pessimisticassumption that it issufficientfor designerstotakeasthelargest size fire that which triggers the firstsprinkler and thereafter remains constant22'28291 —butnotethatBS DD 240 (the lastofthe threereferences)also allowsthe designer to selectotheroptions includingthat thefire should continue to grow. Thereis a considerablebodyofknowledge concerning the effectofsprinklerson specificfuelarrays usedin experiments.It is clear from these experimentsthat the effectivenessofsprinklersdepends stronglyonthe degree to whichthe fuel is shielded from the water spray (egreference [32]). It is also clear from theseand many other experimentsthat thereis a wide range ofpossible fire growth behaviour,and thatwhile sprinklerswill usuallycontrol afire and will often extinguishit, therecan becircumstanceswherethe fire canindeed grow after the first sprinkleroperates. Unfortunatelythere appear tobe no experimentallyderived statisticsavailableto quanti the probabilitiesofthese possibilities. Thus, the commonly held assumption that the upper limit to agrowing designfire can be takento be the size at whichthe firstsprinkler operates, remains unconfirmed. As mentioned earlier, resultsfrom experimentalwork inwhichfireswith thefuel loadtypical ofa specific scenario have beenstudiedunderacalorimeter can provide informationfor use in SHEVSdesign. The experiments provide heat release rates and other relevant parameters in the rigas afunction oftime. The resultscan thenbe extrapolated to build up a realisticfire growth scenario for the buildingofinterest. Resultsfrom some recentexperimental workaregiven inTable3.2.

3.3 Steady-statedesign fires Thereis acommonmisconceptionthat a steady-statefire is meanttobe onewhichgrowstoaparticular size,and thencontinues at a constant burning rate limitedby some factor suchas limited availabilityoffuel or limited ventilation.In practice, this definitionhas not featured in the 'steady-state'approachto specif,ring designfires. The actual approach followedin the UK andmany othercountries over the past 30 to 35 years has beento assessthe largest sizethe fire is likelyto reachduringits development (includingthe effectofthe fire servicesin controllingthe size offire aswellas the effectiveness of sprinklersorother extinguishingmedia), and to design the system as ifthefire wasalways ofthis size.This approach requires the assumptionthat anysystem able to achieve safedesign conditionsforthis largefirewill also achieve safetyfor all smallerstages ofthe same fire (see section 3.1 above).It alsofollowsfrom this concept that the steady-statedesign fireis inherently astatistical concept. As for thegrowingfiredescribed above, assumingan 'average' maximumfire size will implyan unacceptable failurerate of50%, whereas the largest possiblefire is alwaysunreasonable.The designer and regulator has to adopt the concept ofasubjectivelyacceptable largest designsize (seealso section 3.1). Unfortunately,steadystatedesignfires contain no informationabout the actual times involved inthefire. TheUK FireStatisticsaremuch easierto analysein terms ofthe largest fire-damaged arearecorded afteran incident than in terms ofthe actual growth rate (egMorgan &HanseIl34 and Ghosh351).Another approach to the maximumareahas been discussedby Ramachandran61 usingmainly informationfor fires in

Table 3.2 Results ofexperiments simulating differenttypesofoccupancy HRR at operation of Fire Heat release rate (HRR) 1st quick-response Type of growth rate occupancy per m2 fuel sprinkler Retailpremises

Fast to ultra-fast

280—650 kWm2

Between 100 kW (videos) and 700 kW (packets of crisps)

HRR at operation of

1st normal-response sprinkler

Notes

Between 500 kW and 1000kW

This occupancy type can contain a wide range of fire hazards, leading to a wide rangeof growth ratesand heat release rates. The arrangement of materials can alsohave a significant effectonfire growth, eg fire growth may bemore rapidingoods displayed on

Cellularoffices

Medium

270 kWm2

Libraries

Slowtomedium

150—650kWrn2

shelving. __________ The fireload mainlycomprised furniture, papers and computers. Thefuel comprised hardback and paperback books.

Note: Heat release rate valuesare priortosprinkler operation.

3 Design-fire size

____

______

17

(b) 100 50

(a) 200

20 100 10 50 40 30 E

5

20

10

5 4 3 2

0

5 10152025

50

I

% ofsamp'e >

0

20

40 % offires>A1

60

80

Figure9Percentage offires exceeding a specifiedfire-damaged area: (a)offices, (b)retail areas

the textile industry.References[34,35] followedthe earlierMorgan & Chandler°1 paper defininga 'relative frequency',such thatit represents the percentage offire

incidentsoutofadefined population ofincidentswhich exceed aspecifiedfire-damaged area. For example,in Figure9a (fromreference [34]), 10% ofincidentsfrom a population definedas fires startinginofficeswhere sprinklersare present, exceed a fire-damagedareaof 16m2. In thiscase,whichhas become thecommonly adopted designfire for sprinkler-equippedoffices,we can say thatthe designfirehas arelativefrequencyof10%. Another exampleis the more recentstudyby Ghosh3 of fires startingin retail areas ofretail premises (Figure9b), although the decision as tothe designfiresizefor sprinkler-equippedpublic areas ofretail premises was taken on the basisofmuch weakerevidence5'24. Figures 9a and 9bshow that sprinklershavethe effect ofreducing the frequencywithwhichfires exceed any given area, for all except the smaller fires. It is alsowell establishedthat sprinklers,whenin operation, makeit muchless likelythat a fireinaroom will achieve flashover.It is common inthe UK to speciIr that sprinklersbefitted,as part ofthesmokeventilation concept, in order tokeepthefire within limitswhich allow morepractical smokeventilation.Indeed, inthe UKthe fittingofsprinklersin shops opento enclosed shopping malls, combined withsmoke exhaust ventilation in those malls, is mandatory. It canalso be seen from Figures9aand 9b that different occupancies (in this case offices and retail areas) donot followthe same curve. Itimmediatelyfollowsthatthereis no suchthingas a universaldesignfire. Eachdifferent

class ofoccupancy must be expected to have itsown characteristicdesignfire.

It is also impossiblein most casesto arriveat a heat release rate from the UK FireStatisticsdatabase, and so it has alwaysbeen necessaryto assumeor derivefrom some othersourcea valueofheat release rate per squaremetre appropriatetothe occupancyin question.Ithasbeen usual to assume apessimisticvaluefrom afrequency distributionofheatrelease ratesper squaremetre, where this can be deduced27. This approach necessarilymeans that apessimisticview hasbeenintroduced in two separate stagesoftheargument in arrivingatadesig:nfire. It canalsobenotedthat wherethereis alackofreliable evidenceto support the choice ofeithera growing cr a steady-statefire, itis usuallymorepracticabletoassess thelargest sizethat a fire might reasonablyachieve rather thanthetime itmighttaketo reach suchasize.This means,forexample,thatwhenthereisnoclear evidence availableto support a choice ofeitheraparticular constantinthe 't2' growth formula, or astatistically reliablesteady-statemaximum fire, it isusuallysafer to ask an experiencedfireofficerto assessthesize offire his first-attendingcrew would begin to extinguishthan to ask himto assesshowlong the fire would taketo grow to that size.

Workondesign guidancefor smokeventilation systemsinshopping centres5'24usedthe principleof selectinga fixed sizeoffirethatwould cater for almost all ofthe fire sizeslikelyto befound in that class of occupancy and then deducing apessimisticheat output from thatfire37'241. This procedure hasbeen adopted for occupanciesother than retail, which are alsocommonly

Design methodologies for SHEVS

18 Table 3.3 Steady-state design-fire sizes Fire Occupancy type

area, A

perimeter, P

Heatrelease rate density,q

Totalconvective heat flux

(m2)

(m)

(kWm2)

(kW)

10

12

9

625 625

5000

5

Fire

Retail areas Standard response sprinklers Quick response sprinklers No sprinklers

2500

Entire room

Width ofopening

Standard response sprinklers

16

14

255

2700 (closetothe fireflume) 1000 (atthewindow)

Nosprinklers:fuel-bed controlled No sprinklers: full involvement

47

24

255

8000(closetothefireplume) 6000(atthe window)

Entire room

Width of opening

255

?

1200

?

.-

Open-planoffices

ofcompartment

..

Hotelbedroom Standard responsesprinklers No sprinklers

2 Entire room

6

250

Width of opening

100

400 (close tothe plume) 300 (at thewindow) 1000(atthe window)

(typically c. 20m2)

.-

Carpark (a burning car)

10

-

400

12

3000(closetothe plume)

-

Notes: Experimentsin a opriakieredcaisrimeter indicate thatthe fire sizes issomeoccepancies msybe smallerthee gineeisthe table, batasyetthere is not enoaghintormatisn togixe reliableasIans. Desige fire sizes for offices asd hotelrooms are sotofficially 'epproxed'choices,althoeghtheyore widely soed. Recentintormation osbaraisg cars ooggestothatmodern cars ese materialswhich may sometimesgixehigher borniegrates than isthe Table.The positionis not yetcleartorcarsoshre incar parks, arid thisrecommesdotionmay changemhenbetter data become available.

associated with atrium buildings,ie officesand hotel bedrooms34'351. Table3.3 summarizesseveral ofthe more commonly adoptedsteady-state design fire sizes incurrentuse. The heat release rate (qfAf) isthetotal heatgenerated by combustion per second, and is the parameter measured in

most calorimetryexperiments. Some ofthisheat is radiatedfrom the flames, and warms the surrounding walls,floor, etc. The heat remaining in the gases is the convectiveheat flux, and is the heatflow parameter

required for calculationsofsubsequent smoke movement. Whenconsidering an unsprinldered office occupancy thereexiststhepotential for flashoverto occur, and for theentirefloor becoming involvedin fire. Even ifthe buildinggeometry can accommodate this fire condition, thedestructive powerofafullyinvolvedofficeroom fire is suchthat smokecontrol systemscannotusuallybe designed to protectsatisfactorilymeans ofeseapein this situation, except for fires in smallrooms. An assessment ofthe mass flowrate andheat fluxfrom aroom fire will allow the potentialforflashoverto be estimated,and thencewhetheradditionalprecautionary measures are required, egsprinklers.This bookwill only provide gnidaneeforthe designofsmoke control systemsfor a fuel-bed-controlledfire in anoffice,and afullyinvolved fire in a hotelbedroom. Gases flowingintothe atrium from a fire deep within a large-area officewith operating sprinklersmaybe cooler than is assumed in the 'sprinkleredoffice' designfire

above. The mass flowrate ofgasesentering the final reservoir will be less than would becalculated usingthe valuegiven above. Even forthis scenario, therefore, the above value should erronthe side ofsafety.Designers wishingto takesprinklercooling in the firecompartment morerigorously'intoaccount should adopt a fullyfireengineered approach appropriate to theirspecific circumstances,forexample byusingthe methods described insection 5.5 to assessthe effectofsprinkler cooling on the outfiowinggases. Theuse ofthe bedroom floor areafor the hotel bedroomdesign firereflects the situationwheretherearc nosprinklers present. Unpublished research on sprinklered bed fires1391, wherethe lowheat output per unitareawas comparable tovalues for hotelbedrooms, suggest that the much lowerfuel load (compared withan office) expected in ahotelbedroomutilizing conventionalsprinklersshould makeitpossibleforthe smokygases to be cooled sufficiently tobe retained within the room oforigin (assumingthe windowis not open). The operation ofsprinklers islikelyto coolany smokefrom afire and suppressthatfire to suchan extent thatthe glazingto the bedroom willprobably remain intact. This is particularlytruefor double-glazed windows. The same research391 indicatesthatthe use of conventionalsprinklersin a residentialenvironment may not, however, allow conditionswithin the roomto remain tenable, and it may be inferredthatthe presence ofan open window to the room could produce hazardous

3 Design-fire size conditionsinthe atrium, at least above the floor offire origin.Thereare no statisticaldataavailableonfires in sprinkleredhotelbedrooms in the UK; consequently,any choice ofdesignfire size willbesubjective.Should a designer wishto examinethe effectofa plume emanating from an open window in a sprinkleredhotelbedroom, it would not seem unreasonabletouse a valueof6 m perimeter(equivalentto asinglebed) with a convective heatoutputofaround 500 kW asthe designfire. Research intothe use offast-responsesprinklersin a residentialenvironment°'41 has clearlyshown that at the time ofoperation ofthesesprinklersthe conditionsinside theroomswerestill tenable, ie therewas no life-safety risk from thesmoke, evenwith excessiveceilinglevel temperatures. This clearlyindicatesthat for anygases flowingintotheatrium (egthroughan openwindow) the further entrainment induced by the risingsmokeplume willensurethatconditionswithin the atriummust be tenable, regardless ofthe smoketemperature or smoke production rateinthe room. Whileitis possiblethatthis may also be true for cellularoffices employingfastresponse sprinklers,thereis no evidence (experimentalor empirical)to validatethis, andso toerr ontheside of safety,thisbookwillregard sprinklered offices employing fast-responsesprinklersinthe same wayas offices using conventionalsprinklers.Further research andstatistical dataaredesirablein thisarea. Thedesignprocedure for a steady-statedesignfireis summarizedin Annex B.

3.4 Acceptablefailure rates It has already beennotedthatit is never feasibleto design

afire safetyengineered systemto copewiththe largest

19

possiblefire, orthefastest possiblefiregrowth rate, In practice, itis alwaysnecessaryto designfor the largest reasonablesize offire; orin otherwordsfor afire which will be exceeded in anacceptablysmallproportion offire incidentslikelytooccurinthe occupancytype ofinterest tothe designer.Wherethe dataexistsin thecorrectform, this essentiallymeans choosingan appropriatevalue of relativefrequency andfindingthe correspondingareafor thedesign fire. Similarlyforgrowingfires, it is always necessaryto choose a designfire whose growthratewill be exceeded inanacceptably smallproportion of incidentsin the typeofoccupancyofinterest.As has already been notedabove, the paucity ofavailable probabilitydistributionsofgrowth curvesmakesthe choice ofdesignfire difficult. For both steady-stateand growing designfires, these decisionsare necessarily subjective(more so wheredecisionshaveto be basedon an experiencedjudgement inthe absenceofaknown probabilitydistribution). Oneexpects differencesofperception. It is common to findthatindividualsresponsiblefor a singlebuildingwill seeas low those values ofprobabilitywhichthe regulator will see asunacceptablylargewhenapplied to alarge numberofsimilarbuildingsforwhichhe has responsibility.

Whatconstitutes an acceptable point in a probability distributionalso depends onthe likelypublicreactionin potentially multi-fatalityfires.Anecdotal evidence,egthe strengthofthepublic reaction followingamajor multiple-death fire suchas the Kings CrossUnderground Station fire in Londonin 1987 after many decades withoutany firedeathsin similarcircumstances,suggests that forsome types ofpublic buildingtheacceptable failurerate can be very low indeed.

20

____ ____

_________

4 Escape times

SHEVS are often designed such that a clear layerwill remain for an indefiniteperiod, provided thedesignfire size is not exceeded.Ifthe purpose ofthe smoke control system is purely forlife safety then a clear layeroniyneed be maintainedforsuchaperiodthat safeevacuationofall the occupants cantakeplace. In thesecases, itis important todetermine both the availableescape time and the required escape time to ensurethatthe available escape timeis at leastas long as the required escape time. Availableescape time is defined as the timefrom the detectionofafireto the 'time to danger' whereescape becomes impossibleorvery difficult. The time to danger isthe timeuntil: the clear layerheightis less than3 m (may be lowerin some cases), or thehot gas layertemperature is 200 °C or more.

• •

Ifthe clear layer (ievisibilityofatleast10 m) wastoo

shallow then escape would bethroughsmokeand will be difficult. Radiationfrom alayerwhose temperature is morethan200 °C maycause severe painand discomfort. It is relativelystraightforwardto calculatethe available escape timefrom procedures given in this book. Itis much moredifficult to assesswhat therequired escape timeswill be. In general,they will havetwo components: alerting time and evacuation time.

• •

Alerting time Alerting time is the time needed for the people to realize that thereis a lifethreatand to startto move. Evacuation time is the time needed to reacha place ofsafety. Alerting time will dependon many factors,some ofthe most important being the type ofalarmgiven and the availabilityoftrainedstaff. Proulx & Sime421 have shown thatwhenusing only afire bell, as an alarmthealerting time canbe nearly 10 minutes, whereas withvoice-alarm and staffintervention thiscan be reduced to 60—90s. Note that alerting times canchange due to too many false alarms or to failureofthe alarmsystem. Experience has shown thatpeopletend to ignore alerts ifthey occur frequently.

Evacuation time Evacuationtimewill dependon the traveldistance,the

numberandwidth ofexits,and the population.It also depends on the presence ofstragglers, disabled or injured people andthe unpredictablebehaviour ofhuman beings in an emergency: people whohavealready reached a safe environment will often gobackintoan endangered zone for subjectivereasons (ega motherlooking for her child from whomshe became separated during evacuation). Also,the population ofabuildingcannot be estimated accuratelyfor allcircumstances,eg in the timebefore Christmas there canbe far more people than normal inside ashopping mall. In this case,the required escape time can be longer than assumed in the design.This could leadto deaths ifthe safetymargin included in the design is insufficient. It isbeyondthescopeofthisbookto discuss escape times in detail. In general, specialisthelp should be sought for egress calculations.In some scenarios,itis not possibleto consider smoke control withoutan estimate of escape times. Thesensitivityofthe 'time to danger' totheassumed fire growth rate has been discussedin Chapter 3. This introduces a probabilisticaspect tothe conceptofthe availableescape time. Similarly, the timeneededfor safe evacuation ofoccupants should ideallybe described in terms ofprobabilities,although the dependence on human behaviour makesthis difficult. Ideally,it should be possibleto calculatethe combined probability ofa design being successfhl taking intoaccount allthe separate probabilitiesofthe differentassumptions,both inthe availabletime for escape and in the time required for escape. Unfortunatelythis willbeimpossibleto do with accuracy in most cases because ofthe inadequacyof availablesupporting data, and it willbe necessaryto approximate to a greaterorlesserextent. This inturn suggeststhe need for adequate safety margins to be applied to the results and conclusionsofsuch calculations.

It should notbeforgotten that the time required for safeescape ofthe occupants from abuildingmay notbe the only timelimit which has to be consideredwhen

carrying out atime-based SHEVSdesign. It isusefulto regard fire-fightersasbuildingoccupants while they are

________________________________

____

inside fightinga fire; the design ofthe SHEVSshould not

allow themto be putat risk simplybecausetheoriginal occupants have escaped. Anychoice ofdesign

4 Escapetimes

____

21

parameters whichleads, for example,tothe prediction thatfirecrewsmay be caught in aflashovercannotbe regarded as goodpracticeinSHEVS design (seealso section 12.2.2.1).

22

_________________________________ ______________

5 Smoke control on the storey of fire origin

ofthe opening (Figure 11).Whereno downstand exists,

5.1 Within the fire room In anysituation involvingthe potential movement of smoke intoescape routesitis alwayspreferable, although notalways practicable (as in most shopping malls),to control the smokein the fire room and henceprevent its passageto otherwiseunaffected areas. Ventilationofthe fire roommaybe achieved eitherby a dedicated SHEVS orby adapting and boostingan air-conditioningor ventilatingsystem. The latter systemsare usually designed to distribute air uniformlythrougha space and notto establishthermalstratificationas in a SHEVS.It followsthat control dampers will usuallybeneededbe neededto modifythe mode ofoperation, egto keep exhaust points nearthe ceilingopen and to shut down air supply from the ceilingdownwards, as well as other related changes in operation. Ifthe compartment isopen to anadjacent atrium, then thecompartment musthave eithera downstand barrier tocreateareservoir within the compartment, or a high-powered exhaust slotat the boundary edgeto achieve asimilar effect (Figures lOa and lob). Theminimum height ofthesmoke layer base in the room must be compatiblewiththe openings ontothe atrium, with the layer depthbeingno lowerthan the soffit

and an exhaust slot is usedinstead,the exhaust capacity provided willneed to be compatiblewiththe layerdepth (Figure 12). See section 5.12 on exhaust slots(slitextract). More generally,the minimumheightto the base ofthe smoke layer formedin the smoke reservoirshould be chosen on the grounds ofsafety. Some minimumvalues arelisted in Annex Bfordifferenttypes ofoccupancy of thebuilding. This typeofplumeis definedas an axi-symmetric plume as the smokeflow should be approximately symmetricalabout an axis; intheabsence ofwindtheaxis willbe vertical.Having establishedthe clear layer height inthe room, the mass flowrate ofsmoke canthen be calculated.

5.1.1 Plumes above large fires Plumesabove large fires can be considered tobe those where:

Y

1O(Af)°5 (m)

(5.1)

whereY istheheightofrise oftheplumeand A(m2) is the areaofthe fire. WorkbyHansell43 drawing onworkby Zukoskiet (b)

(a) Exhaust from compartment

Exhaust from compartment

Downstand

Boundary edge exhaust slot

downstand

Figure10 Smoke ventilation withina compartment:(a) use of a downstand to createa smoke reservoir, (b) use of a 'slot exhaust' to preventsmokefrom enteringthe reservoir

5 Smoke control on storey offire origin Exhaust from * compartment

Ce

iJDownstand

The earliestform ofEqn (5.2) wasby Thomas et a1191,and was developed from theoretical considerations forthe flameregion above extensive areas offire: wherethe fire isnot close to any wall,the ceilingismuchhigherthan theflame region ofthe plume, and air is free to app:roach the firefrom all sides. The basic equation was simplifiedby merging constants,and bygivingcertain parameters values

* Volumetric flowrate sufficiently great to prevent smoke spillage beneath downstand for height of rise V.

Figure11 Plume height and layerdepthwith a downstand

Boundary edge exhaust slot *

* Volumetric flow rate sufficiently great

to prevent smoke spillage beyond the exhaust slot for height of rise Y.

Figure12 Plume height and layerdepthwith a slotexhaust

al441 andQuintiere et al45 to modifyearlier studies by

Thomas etal9 and Hinkley4 has shown that the rate of air entrainment intoa plume ofsmokerisingabove afire, Mf, maybe obtainedusingthe equation:

Mf= Ce Py3"2 (kgs1)

(5.2)

where: Ce

= 0.19 (kgs'm52) forlarge-area rooms suchas

= 0.34 (kgs'm512)for smallrooms suchas unitshops,

cellularoffices, hotelbedrooms (prior to flashover or fullinvolvement),etc. with ventilationopenings predominantlyto one side ofthe fire (eg from an office window in one wall only).Thusmost small rooms will takethis value. P = perimeter ofthe fire (m).

/

Exhaust from * compartment

23

auditoria,stadia,largeopen-plan offices, atrium floors,etc. wherethe ceilingis wellabove the fire. = Ce 0.21 (kgs1m5"2) forlarge-area rooms, suchas openplan offices,wherethe ceilingis close to the fire. (Note:it isnot known how andunderwhat conditionsoneshould regard a ceilingas being close to the fire. Until betterevidence appears, it is hereby suggestedthat Ceshould takethe value 0.21 whenever Y is> (it is here suggestedwithout evidence that one can assume Dd>2D),we can assume that Cd0 = 0.65. Forall intermediate cases,assume that Cd0 = 0.8.

• D •

Note: the number'2'in Eqn (5.8) istheresult of

combiningvarious parameters, andhas dimension.

It is clear thatthis represents an unsatisfactoryposition, and this approachcanbe expected tobesuperseded as

soonas a more comprehensive experimental study can leadtoabetter,morewidelyvalidated,correlation. Earlyexperiments in smokeflow in shopping malls50 and unpublishedfurther analysisofthe dataatFRS have shown that the smokeflowingfrom aroomwith adeep downstand andthen underabalcony beyond the opening becomes moreturbulent with increasingmixing ofair. This analysiswasbasedon the differencesin temperature measured beneaththe downstand at the opening, andbeneaththe balcony.In the continuing absence ofbetterevidence,we suggestthatforthe purpose ofengineeringdesignthemass flow rate of smoke entering the balcony reservoirMB canbetakento be approximatelydouble theamountgiven byEqn (5.7) ie:

=2M (kgs1)

MB

(5.9)

This assumptionistakeninthespirit ofthephilosophy of this bookdeclared in thePreface,andis known tobe crude. Furtherresearch is highly desirable.

Notethatfor the specificcaseofsingle-storey shopping mallswhose ceilingsare nottoo much taller thanthe shop units opening intothose malls, therehas beenan alternativeempirical correlation2451. In this approach, allthe calculationsofolltflow from the firecompartment detailed insection 5.2, aswell asEqn (5.9), aresimplyreplaced byEqn (5.1) withY being the hLeight measured from the base ofthe fire tothebase ofthe buoyantsmoke layer in the mall andwith Cetakingthe value 0.38. It is believedthatthis correlation willbreak down for mallswherethe smokereservoirlayer's base is toohigh above thetopofthe fire-compartment'sopening (ie the window betweenshop unitand mall),and it is suggested that this simple correlation should notbeused wherethe layerbase is morethan2 m above thetop of the opening241.Instead, the designer should employ the calculationmethodsdetailed inChapter 6.

5.3 Ventilationof single-storeysmoke reservoirs (including the balcony space where smoke is contained and exhausted from beneath a balcony)

Thissectionappliesboth whereanaxisymmetricplume rises directly intoa smokereservoir,andwherea smoke reservoiris formed onthe same storey asthefirebut outside the roomoffireorigin. This latter case occurs whenthesmoke cannot be contained within the room of origin becausethe rooms have demountablepartitions; and/or insufficient replacement air canbe provided; and/or theengineeringimplicationsaretoocostly or difficult to apply, then the smokeand hotgaseswill be able totravelfrom the room oforigin intothespace beyond. This space can be a single-storeymall, or part of the same storey asthe fire-room.Thissection therefore applies to anysmokereservoir formed on the samestorey asthefire-room,butadjacentto thatfire-room. Some atria aredesigned with balconies around the

28

Design methodologies forSHEVS

Atrium

Figure17 Schematicsectionof anatriumwith balconies Figure 19 Under-balcony smoke reservoirventing into an atrium smoke reservoir

4

ofthe reservoir to ensurethatthe smoke retains its

(Exhaust from

balcony reservoir Atrium Balcony edge screen

Figure 18 An underbalconysmoke reservoir

perimeterofthevoid, serving all the rooms at that level. Figure 17 illustratesinschematic form an atrium with floors (two levels only are shown inthe Figures) which have balconies which leave a considerableareafor pedestrians. On eachlevel thereis a large areasituated beloweachbalcony.Ifscreens (activated by smoke detectors or as permanent features) are hungdown from thebalcony edges, theregion below eachbalconycanbe turned intoa ceilingreservoir (Figure 18). In this case,the clear air height beneaththe smoke reservoirmustalso be selected on the grounds ofsafety;seeAnnex B for a listing oftypical minimumvalues.This is similartothe procedure usedin multistoreyshopping complexes241. This reservoir,however it has been formed, can then beprovided with its ownexhaust system. Smoke curtains canbe positioned (egacross thebalcony) to limitthesize

buoyancy.Eachreservoir should be limited to an areanot exceeding 1300 m2 in area, with anupperlimit to the area ofthe fire—room of1300 m2 wherepowered smoke exhaust is used; or 1000 m2for eachparameter where natural smokeventilation is used (by analogywith shopping malls241).Note that it is logicallyequivalentto specifythatthe total areaoffire-room plus adjacent smoke reservoir should not exceed 2000 m2 fornatural smokeventilation,or2600 m2 ifpowered smoke ventilationis used. Alsoby analogywith shopping malls1241, the smoke reservoir should havea maximum length of6O m. See section 5.17 belowfora fuller discussionofthe limits tosmokereservoir size. Wherethe smoke reservoiris formedbeneatha balconyin amultistorey space (egan atrium ormall),the screens around thebalconies will,in general,befairly close to potential fire compartments (egoffices). Being close, smokeissuingfrom such a compartment will deepen locallyon meeting atransverse barrier. The depth ofthesescreens should takeintoaccount local deepening (seesection 5.7). Smoke removedfrom theselower-level reservoirsshould usuallybe ducted to outside the buildingbutcan be ducted intothe ceiling reservoirofthe atrium (Figure19). The mass flow rate ofsmoketo be exhausted from the atrium roofwill then be that calculated for the under-balcony condition[50]

5.4 Smoke layertemperature Themeantemperature rise ofthe smoke layer above ambient, 0, canbe calculatedfrom:

Mc

(K)

(5.1(a)

5 Smoke control on storey offireorigin where: convective heatfluxin the gases (kW), Q= =

M mass flowofsmoke (eg orMB) (kgs'), c = specificheat capacity ofthe gases (kJ (kg)1K1). Tables 5.la to 5.ld givethe temperature rise 0 for 1 MW,2.5 MW, 5 MWand 6 MWconvectiveheat fluxes respectively.Note that an ambient temperature of 15 °Celsiushas been assumedwhenpreparing these

M

29

maycause difficulties for people escapingalong abalcony beneaththesmoke layer,especiallyifthe balconiesform a major escape route. The maximumsmoke layer temperature whichwill allow safeevacuationwithout unduestress is oftheorderof200 °C. Ifthis gas temperature (or lower) cannot be achieved underthe balconythen consideration should be given to:

Inunsprinklered fire situationsa high smokelayer temperature will result in intense heat radiationwhich

•• alternative escape shorter escape paths along the balcony, • the installationofsprinklers,abovethebalconyto cool the further.

Table 5.la Volume flowrateand temperature ofgases fora 1 MWconvective heatflux Mass Volumerate Temperature flowrate of gases of exhaust above (mass rate (at maximum ofexhaust) ambient temperature) (kgs') (°C) (m3s')

Table 5.lb Volumeflowrateand temperature ofgase fora 2.5MWconvective heat flux Mass Volumerate Temperature flowrate ofgases ofexhausi rate above (mass (at maximum ofexhaust) ambient temperature) (kgs') (°C) (m3s')

Tables.

4 6 8 10 12 15 20

25 30

35

40 50

10

12 15 20 25 30 35

40 50 60 75

90 110 130 150 200

gases

258 165 124 99

6.2 7.7 9.4

10 12 15

11.0

83 66

12.6 15.1

20 25 30

165 124 99 83

50 40 33 28 25 20

19.2 23.3 27.4 31.4 35.6 43.8

35

71

40 50 60

62 50 41 33

______

Table 5.lc Volume flowrateandtemperatureofgases fora 5MWconvective heatflux Mass Volumerate Temperature flowrate of gases of exhaust above (mass rate (at maximum ofexhaust) ambient temperature)

(kgs')

routes,

(°C)

(m3s')

495 413 330 248 198 165 141 124

22.2 23.9 26.3 30.5

34.5 38.6 42.7 46.8

99

55.0

83 66 55 45 38 33

63.2 75.4

25

87.7 104 120 137 178

75 90 110

248

206

28 23

15.2 16.8 19.3

23.4 27.5 31.6 35.7 40.0 48.0 56.1 68.4 80.8 97,2

Table 5.ld Volume flowrateandtemperatureofgase fora 6 MW convective heatflux Mass Volumerale Temperature flowrate of gases ofexhaust above (mass rate (at maximum of exhaust) ambient temperature) (kgs1) (°C) (m3s') 12

495

15

396

29.1

20

297 238 198 170 149 119 99 79 66 54

33.2 37.4

25 30 35 40 50 60 75 90 110 130 150

200

46 40 30

26.7

41.1

45.5 50 58 66 78 91

107 123 140 181

30

Design methodologies for SHEVS

5.5 Effects of sprinklersystemsin smoke

Nevertheless,an approximateestimate canbe obtained as follows. Ifthe smoke passinga sprinklerishotter thanthe sprinkleroperating temperature that sprinklerwill eventuallybe set off. The sprinklerspraywill then cool the smoke. Ifthesmoke isstill hot enough, the next sprinklerwill operate coolingthe smoke further.Astage will bereached whenthe smoketemperature is insufficientto set offfurther sprinklers.The smokelayer temperature can thereafter be assumedto be approximatelyequal to the sprinkleroperating temperature beyond the radius ofoperation ofthe sprinklers.Thisradius isgenerally not known. In the absence ofbetterinformation,itmaybe acceptable to assumethatnomore sprinklerswill operate thanareassumed when calculatingthe designofsprinkler systemsand theirwater supply (eg 18 headsfor Ordinary Hazard Group 3). Forpowered exhaust systemsthe cooling effectof sprinklerscan be ignored in determining the volume exhaust rate required. This will errontheside ofsafety. Alternatively,this further cooling and the consequent contraction ofsmoky gases canbeapproximately estimated on the basisofan averagevaluebetweenthe sprinkleroperating temperature and the calculatedinitial smoketemperature. Wherethefan exhaust openings are sufficiently wellseparated it can be assumed that one opening maybe close to the fire, and will extract gases at thefull initialtemperature given byEqn (5.10).The other openingsinthese circumstancescan be assumedto be outsidethe zone ofoperating sprinklers,andwill extract gasesat the sprinklers'effectiveoperating temperature. Thenumberofpotential 'hot' and 'cool' intakes must be assessedwhencalculatingtheaverage temperature of extracted gases. Ifthe sprinkleroperating temperature is above about 140 °C, or ifit isabove the calculatedsmoke layer temperature, then sprinklercooling canbe ignored for natural ventilators. Notethat the effectofsprinklercooling is to reduce the heatflux withoutsignificantlychangingthe mass flux. It followsthat once a newvalue of0has beenestimated, thenewheat fluxcanbefound using Eqn (5.10).

reservoirs Offices,shops, assembly,industrialand storage or other

non-residential purpose groups in England and Wales are nowexpected to havesprinklers iftheyhave a floor more than30 m above ground level.Multistoreybuildingsin the assembly,shop, industrialorstorage purpose groups will alsobefitted with sprinklersifindividual uncompartmented floors exceed a given size.Sprinklers mayalsobe requiredinothercircumstancesfor insurance purposes. The actionofasprinkler system inan office on the cooling ofgasesflowingfrom the office totheatrium is accounted forinthe derivation ofthe 1 MWheat fluxat the window271.It is,however, theusual practice in the UK to assume that the heat fluxleavinga shop unit throughits window has the same value as forthe initial convective heatfluxclose to the fire plume.This differencein approach can only be explainedhistorically, and rationalizationofthedifferentapproaches awaits further research. Wherethe smoke layer is contained wholly within the room oforigin by a smokecontrol system and has alarge area, the sprinklerswill cool the smokelayer further. Similarly, wheresmoke is collectedwithin abalcony reservoir adjacent to sprinklered rooms, operation of sprinklersunderbalconies will leadto increased heat loss reducing the buoyancyofsmoke,whichin turn can contribute to aprogressiveloss ofvisibilityunderthe smoky layer. Whenthe fire occursin an adjacent room, the operation ofsprinklers in an adjacent smokereservoir outside that room will not assistin controllingthe fire. If too many sprinklersoperateoutsidethefire room, sprinklersin the room could becomeless effectiveas the availablewater supply approaches its limits. It followstherefore that sprinklersneedonly be installedinasmoke reservoir: ifthe smokelayertemperature is likelyto exceed 200 °C, and thus produce sufficientradiationto bea danger tolightly cladpeople belowthe smoke, and thustoimpedeescape, or ifthereis thelikelihoodofsufficient combustibles beingpresentto pose a significantthreatofexcessive firespread.

• •

Apowered exhaustsystem, to a reasonable approximation,removes afixed volume ofsmoke

irrespective oftemperature. Therefore, iftheextentof sprinklercooling is overestimatedthe system could be under-designed. A system usingnatural ventilators depends onthe buoyancy ofthehot gasesto expel smokethroughthe ventilators. In thiscase, the system would beunderdesigned ifthesprinkler coolingwereunderestimated. The heatlossfrom fire gasesdueto the water spray from sprinklersis currentlythe subject ofresearch and datasuitablefor designapplication arenot yetavailable.

Q

5.6 Flowinglayer depth Smokeentering a ceilingreservoirwill flow from the

point ofentry towards the exhaust points. This flow is driven bythe buoyancyofthesmoke. Even ifthere is a very large ventilationareadownstream (egiftheceiling downstreamwereto be removed) thisflowinglayer would still haveadepth related to the widthavailable undertheremaining ceiling(which cannowbe considered aba]cony),the temperature ofthe smokeand themassflow rateofsmoke.Workby Morgan[52] has shown thatthis depth canbe calculatedforunidirectional flow as follows:

5 Smoke control on storey offire origin r

DB

0.361 Cd

M87

[o 05 W T°5

(5.11)

where: DB

= flowingsmokelayerdepthunderthe ceilingor

balcony (m), MB = mass flow rate underthe ceilingorbalcony (kgs1), WB ceiling or balconychannel width (m), Cd = 1 ifno downstand ispresentat right angles to the flow; 0.6 ifa deep dOwnstandis presentatright angles totheflow. Note: the subscript'B' can simplybereplaced with '1' in Eqn (5.11) foritto apply to the minimumdepthofflow in

=

31

The extentoflocal deepening canbefoundfrom Figure20. The depth ofthe establishedlayer (DB in Figure20) underthe balcony immediatelydownstream of thelocal deepeningmust firstbe foundusingthe design procedure given in the preceding sections.Usuallythis means in the channel formed between the void edge screen andthe room facade.The additionaldepth DB can thenbe foundby inspection ofFigure20, allowingthe necessary minimumoverall depth (DB +LDB) ofthevoid edgescreen tobe found53. Thefollowingscale-independent formulacanbe used to approximateto Figure2O{54u]:

anysmokereservoir or flowingbuoyant smoke layer,. instead ofsimplyto an under-balconyflow.

(5.12)

Values ofCd foran intermediatedepth downstand cannot

be statedwith confidencefor the wide range ofgeometry tobe foundinpractice. Itis suggestedthat eitherofthe

extreme values should beadopted inseeking a conservativedesignapproach. The resultingvalues oflayer depthfor different balcony reservoir widths and mass flowrates ofsmoke aretheminimum possibleassumingan excessofsmoke exhaust employed downstream:consequentlyit represents the minimumdepth forthatreservoir.The depthmust bemeasured below thelowest transverse downstand obstacleto the flow (eg structuralbeams or ductwork) ratherthan the true ceiling.Representative valuesare shown in Tables5.2a—d for 1 MW, 2.5 MW, 5 MWand6MWconvective heatfluxesrespectively, and for flowsbeneatha smooth ceiling. In order to useTables 5.2 to findthe minimumdepthof flow beneath a deep downstand (ega structural beam) across the direction offlow, find the value inTables 5.2 corresponding tothesame massflowrate and channel width, andthen multiplythatvalueby 1.67.

5.7 Local deepening Wherea buoyant layer ofhotsmoke flowsalongbeneath a ceilingand meetsatransversebarrier, itdeepenslocally againstthatbarrier because the energy ofthe approaching layeris converted tobuoyantpotential energy againstthe barrier asthe gases'downward velocityis brought to a ha1t531. Whendesigningasmoke ventilationsystem foratriaor for shopping malls, in whichthe balconies are acting as reservoirs,it is often necessaryto control the path of smokeflowusingdownstand smoke curtains.These are typically installedaround the edge ofthe voids to prevent smoke flowingupthroughthe voids. Ifthe void edgeis close to the fire room this local deepening could cause smoke to spillbeneaththe smokecurtain and flow up throughthe void, possiblyaffectingescape from other storeys. Clearly,thevoid edge screens must be deep enough to contain not only theestablishedlayer,but also theadditionallocal deepening outside theroom onfire.

where:

at the transverse ADB = the additionaldeepening barrier

(m), H == the floor to ceilingheight(m), the established DB flowinglayerdepth (m), WB = thedistancebetweenthe opening and the

transversebarrier (ie balcony breadth) (m).

5.8 Automatic smoke curtains Itis commonplaceto use automatic smokecurtainsto form part ofthe reservoirboundary.Smoke curtains can also be usedtoachieve separation betweenthe main smokereservoir andadjacent spaceshigher than the designsmokelayer base in the smoke reservoir,by deployingfrom ceilingtofloor intheopeningbetween suchadjacentspaces and the smokereservoir.These devices areusuallymade ofanappropriate fabric,ableto withstand the temperature predicted for the smokygases theyarein contactwith. Thecurtains areusually contained ina box fastened to the ceiling,and deploy to the designposition on receivinga signalfrom the SHEVS control system. When deployed the fabricis keptunder tension by aweighted bottombar, which also servesto keep the curtain straight. Automatic smoke curtains areusuallydesignedsuch thatwhentheyarein theirdeployed position theyhang freely,beingfastened to the buildingstructure only at theirtop edge, and depending on theweight ofthe integral bottom barto holdthem vertical.The buoyancy ofthehot smokelayer exerts apressureon the surfaces containing the layer. The pressure ofthe smokelayer acts onthe curtain as ifitwere a sail, pushingit sideways.If the pressureis too greatthenthe sidewaysdeflection becomes significant, the bottomedge ofthe curtain lifts, and thecurtain might not contain thesmoke layer,thus causingtheSHEVSto fail to achieveits designpurpose. See Plate 4 for an example ofalightweight curtain being deflected byan airstreamfrom afan intended to simulate smokebuoyancy. It is cruciallyimportant that all smoke curtainsforming

32

Design methodologies for SHEVS

Table 5.2a Minimum reservoir depths or minimum channelling screen depths for 1 MW convective heatflux. Unimpeded flow: smoothsoffit Massflowrate entering the smoke layer Channelwidths (m) 4 6 8 10 12 15 (kgs')

Table 5.2b Minimum reservoirdepths or minimum channelling screen depths for 2.5 MWconvective heatflux. Unimpededflow: smooth soffit Mass flowrate entering the smoke layer Channelwidths (m) 10 12 15 4 6 8 (kgs')

4 6

8

10 12 15

20 25

30 35 40

50

0.57 ______0.51 ______ 0.36 0.49 0.77 0.59

0.31

0.42 0.61 0.52 0.96 0.74 1.157 0.88 0.73 0.63 1.347 1.03 0.85 0.73 ____________________ 1.635 1.25 1.03 0.89 2.107 1.61 1.33 2.581 1.97 1.63 3.044 2.32 1.92 3.549 3.55 2.24 _______________ 2.52 4.00 3.05 4.95 3.78 3.12

1.14 1.40 1.65 1.93 2.17

2.69

0.27 0.37 0.46 0.56 0.65 0.79

0.24

1.01 1.24 1.46 1.71 1.92 2.38

0.87

10 12 15 20 25 30 35

1.07

40

1.26 1.66

50 60 75

2.05

90

0.32 0.40

0.48 0.56 0.68

1.47

Note 1:The minimamdepthsforbi-directionalsmoke flowcanbe foundbylookingatthe column correspondingtotwicethe actualwidthofthe channelorreservoir.

110

1.058 1.204

0.81

1.420

1.08 1.36 1.63 1.89

1.776

2.13 2.481

2.833 3.186 3.88 4.60 5.64 6.66 8.04

0.92

0.67 0.76 0.89 1.12 1.90 1.56 1.78

2.16 2.43 2.96

2.0 2.44

3.51 4.31

2.90 3.55

5.08 6.14

4.20 5.1

0.57

0.51

0.65 0.77 0.96 1.16 1.35 1.54 1.73 2.11 2.50 3.06 3.62 4.37

0.48 0.68 0.85 1.02 1.19 1.36 1.53 1.87 2.21 2.71

3.20 3.87

0.44 0.50 0.59 0.74 0.88 1.03 1.17 1.32 1.61 1.91 2.34

2.76 3.33

See NotestoTable5,2a.

Note 2:Tofindthe minimumdepth offlowbeneathadeep dswristandlega structural beam) across the direction offlow, find the value in Tables5.2 correspondingtothe same massflowrate andchannelwidth, andthen multiplythatvalue by1.67.

Table 5.2c Minimum reservoirdepths or minimum channelling screen depths for5MW convective heatflux. Unimpeded flow: smooth soffit _______ Mass flowrate entering the smoke layer Channelwidths (m) 4 6 8 10 12 15 (kgs') 10 12 15 20 25 30 35

40 50 60 75 90 110 130 150 200

1.082 1.206 1.386 1.68 1.97 2.25 2.54 2.82 3.38 3.94 4.78 5.62

0.83 0.92 1.06 1.28 1.50 1.72 1.94 2.15 2.58 3.01 3.65 4.29

5.14

0.68 0.76

Table 5.2d Minimum reservoirdepths orminimum channelling screen depths for 6 MWconvective heatflux. Unimpeded flow: smooth soffit Mass flowrate entering the smoke layer Channelwidths (m) 4 6 8 10 12 15 (kgs')

0.59 0.65 0.75

0.52 0.58 0.67 0.81

3.01

0.91 1.07 1.22 1.38 1.53 1.84 2.14 2.59

3.54

3.05

4.243.653.24

1.98 2.33 2.79

4.94 5.64

4.26 4.86 6.35

3.25 3.71

110 130 150 200

4.85

SeeNotesto Table52a.

0.87 1.06

1.24 1.42 1.60 1.78

2.13 2.48

0.95

1.36 1.63 1.89 2.30 2.70 3.77

4.31 5.62

12

0.57 0.70

20 25 30 35 40 50 60 75 90

0.82 0.93

1.08

1.22

0.45 0.50

.

1.05

1.17

1.40 1.63

15

1.22 1.40 1.68 1.95

2.22 2.49 2.76 3.29 3.82 4.61 5.40

0.93 1.07

1.28 1.49 1.69 1.90

2.10 2.51

2.92 3.52 4.12 4.92 5.71

0.77 0.88

0.66 0.76

1.06 1.23 1.40 1.57 1.74 2.07 2.41

0.91

2.90 3.4 4.06 4.71 5.37 7.0

1.06 1.21 1.35 1.50 1.79 2.07 2.50 2.93 3.50 4.06 4.63

6.04

0.59 0.67 0.81

0.51

0.94

0.81

1.07 1.20 1.33

0.92

1.58 1.84 2.22 2.60 3.10 3.60 4.10 5.35

0.58 0.69

1.03 1.14 1.36 1.58 1.91 2.24 2.67 3.1 3.53 4.61

See Natesto Table5.2a.

partofaSHEVS are'fitforpurpose'. This means that whatever the intended purpose ofeachcurtain in the SHEVSdesign, it must be ableto fulfilthat purpose in its dejlectedposition.Itis therefore necessaryto calculatethe expected deflectionofeachcurtain inthe design, andto usethesecalculationsto speciflythe properties required ofthecurtains. Somecalculationprocedures areset out in Annex C.

5.9 Inlet air Theremustbeadequate replacement air for the efficient operation ofa smokeventilation system. When ventilatingcompartments directly,ifthe facadeis normallysealed then facilities should be provided for the necessaryquantity ofreplacementair to be supplied to the fire room automatically.This requirement often

5 Smoke control on storey offire origin WB=6m

0.65 0.6

33

WB4m

WB=8m

0.5

——

8m widechannel

—

6 rnwide channel

— .—

4 mwide channel

NB: Flowawayfrom barrier is bi-directional ri all cases

0.4

NB: Errorbars are one standard deviation

E

0 0,3

0.2

0.1

0

0

1.0

1.5

2.0

2.5

D8(m)

Figure20 Local deepening at a transverse barrier

Plate4 Experimental smoke curtaindeflectingundertest makesthe provisionofsmokeventilationto the room of

origin prohibitiveorundesirable.The provision of replacement air to asystem employingbalcony reservoirs is far easier,provided the balconies are opento the atrium, as is also the provision ofreplacement air to systemsemployinga smokereservoir in an atrium or mall.

In naturallyventilated SHEVSdesignshaving natural inlets, the effectofthe flowresistance ofthe inlet openings is explicitlyincludedinthe designequations usedto calculatetheventareaneeded. See for example Eqns (5.15a andb).

Naturallyventilated systemshaving more than one smokereservoir,andwheretheremaynotbe sufficient inlet areaavailable at low level, maybe able touse open ventilators in reservoirswhich are notaffectedby smoke as inlets for replacement air. This is becausethe ambient temperature air entering the buildinghas no intrinsic buoyancy, and so can move up ordown as easilyas moving sideways.Itis important that whatever the height oftheinletopenings, thereplacement air must bebelow the smokelayerinthe affectedreservoir whenitfirst comes intocontact with that smokelayer.Itis also important thatventilators functioningasinlets should not betoo close toventilators emittingsmoke, orthereis a danger thatsome smokewillbe drawn back intothe building.Therehas been no research intothe minimum separation betweenventilators actingas inlets andthose emittingsmoke, butit is suggestedhere thatthis minimumseparation should be 6 m. Areplacement airflow beneath a buoyant smoke layer can disturb the interface and cause the smoke to mix downwardsifthe relativevelocityis too large.Itis good practice to ensurethatthe airspeed ofthe replacement air,whereit firstcomes intocontactwitha buoyant smoke layer,is less than 1 ms'. Iftheareaavailablefor inlet becomes too restricted, incoming airflowthroughescape doors may be attolD highavelocity foreasy escape.Such air inflows through doors in public buildingscould hinder escapees.

34 _______________

_______________

Design methodologies for SHEVS

Research551 on the abilityofpeople to move throughan

exitagainst an opposing airflowhas shownthat movement is not impeded forairspeeds below 5 ms, although people actingas test subjectsreportedthatthey believedthatthey were being slowed by the air moving againstthem atthis airspeed. Measurements ofthe subjects' actual walkingspeeds showed that itwas not seriouslyimpeded below10 ms1 (although some discomfortwas reportedatthese higher airspeeds).This suggeststhat inflowairspeedsshould not usuallyexceed 5 ms for psychologicalreasons.Consequently a5 ms1 maximum limitis currentlyadoptedintheUKand is recommended in thiscurrentbook. Othervaluesmaybe appropriate for other circumstances.For example,inbuildingswherethe population is largely familiarwiththe escape routes; wheretheincoming airis entering the fire room directly, or wherein the instanceoftheinletairbeing supplied via the atrium and the major escape routesareaway from the atrium, then aless onerous parameter canbe applied, A fan-driveninlet air supply may beused, but cangive problems whenmechanicalexhaust is used (the building willusuallybefairlywell sealed in such circumstances). This isbecause the air warmedby the firebefore being takenoutwill have a greater volumethan the cooler inlet air. As the firegrows and declines,themismatch in volumebetweenthe inlet air andthe exhausted firewarmed air willalso change. This can result in significant pressure differencesappearing across any doors on the escape routes, making themdifficultto open and potentially impeding the easy use ofescape routes. For this reason simple 'push—pull'systems, ie powered inlet and powered exhaust systems,should be avoided,

5.10Minimum number of exhaustpoints Thenumberofexhaust points within the reservoir is important since, for any specifiedlayerdepth,there is a maximum rate (MCRJT) atwhichsmoky gasescan enter anyindividualexhaustpoint.Anyfurther attempt to increase the rate ofexhaust throughthatexhaust point merely serves to drawair into the orificefrom below the

smokelayer.This is sometimes known as 'plug-holing'. Where'plug-holing' is presentpartofthe installed exhaust capacity is being 'wasted' by drawing clean air intotheorificesofthe ventilators instead ofsmokygases. This is notnecessarilyaproblemifthefireis smallerthan themaximum assumed for design;but represents awaste ofcapacityforthe designfiresize itself.Iftheeffect has beenignored whencalculatingthe necessaryfan capacity (orthenecessarytotal areaofnatural ventilators),then it followsthat 'plug-holing' at the designfire condition will represent a failure ofthe system as the ventilators will not be exhaustingthe full amount ofsmoky gases required. It followsthat, for efficientexhaust, thenumberof exhaust points must be chosen to ensure that no air is

drawnupinthis way. Thecritical exhaust rate MCRITfora ventilator away from awall is givenby561:

_2.05 p0 (g GlUT

1 0)°' D2w°'5 T

(5.13)

1

where: MCRIT

= criticalexhaustrate at an exhaustpointprior to

p0

(kgs1), = density ofof'plugholing' air at ambient temperature (kgm3),

the onset

acceleration dueto

g

D

(ms2), = depth ofsmoke layergravity below the exhaust point

T0

= absoluteambient temperature (K), = excess temperature ofsmoke layer (°C),

(m),

01

T1 W\T

= T0 + O (K)

= characteristicwidthofthe ventilator (m) (egthe

diameter, orthediameter ofthe circle ofthe same area). The equationimplies that the availableexhaust rate increasesrapidly with increasinglayerdepth. It also impliesthat a number ofsmallventilators maybeused instead ofa sing]elarge ventilator to optimize the exhaust efficiency.

Proximityto awall will reduce the availablesmoke dischargecapacity, although only limited dataare availableforthis particular scenario.Ifthe ventilators are smallcompared with the layer depth then the critical exhaust ratecan befound from reference [57],with the constant subsequentlyre-analysedby Heselden58. Heselden's methodofanalysisis strictly onlyapplicable where the characteristic widthoftheventilator orificeis much smaller thanthe depthofsmokelayerbeneaththe ventilator.It is muchmore common for the characteristic widthofthe orifice tobe comparable to thedepth beneathatthe onset of'plug-holing'.Nevertheless, Heselden's analysisgivesmore pessimisticresults (ie a larger minimum numberofexhaust points required) than the alternativesforventilators notclose to side-walls,and consequently canberegardedas aworst-case methodfor ventilatorswhichare close to walls.

/

MGRIT = 13 1 gD

7

2

1/2 1

)

(kgs1)

(514)

Therequired number ofextract vents (N) is thengiven by:

N

M MCRJT

whereMe= mass flowrateenteringthe layer (ie MforMB) (kgs). Wheresprinklersareinstalledand additional cooling ofthesmoke layer needstobe accounted for, the number ofexhaust pointsrequiredcanbe determined by calculatingthe critical exhaust rate for an opening using

Eqns (5.13)or (5.14), whichever is appropriate, taking into considerationthe lowergas temperature due to sprinkler cooling. Wherevery largeorphysicallyextensiveventilators areused(ega long intakegrille in theside ofahorizontal duct) an alternativemethodis possible.For this case,

5 Smoke control on storey of fireorigin Eqn 5.11 canbe usedwith WBre-defined to be the total

horizontal accessibleperimeter ofalltheventilators within thereservoir (egthe total length ofintakegrilles in the example above) and the 'minimumreservoirdepth' corresponds to the depthofthesmoke layerbeneaththe topedgeoftheintake orifice. Intermediate size intakes (ie wherethe ventilator width is comparable to the layer depth) cannotbetreated so simplyand it is recommended that Eqn (5.13)beused.

5.11 Throughflowventilation: area of natural ventilation required A natural ventilationsystem uses thebuoyancy ofthe smoke toprovide the drivingforce for exhaust.The rate

ofexhaustislargely dependentuponthe depthand temperature ofthe smoke. The advantage ofa natural

ventilationsystem is that it is very simpleand reliable, and cancope with a wide range offire conditions. Should the fire growlarger thanthedesign fire sizefor any reason, a greater depthand temperature ofsmokeleads toanincreased exhaust rate, soto anextenta natural ventilation system hasaself-compensatingmechanism. Theprecise relationshipbetweenthe massflow rate extracted, the ventilator area, the inlet areaandthe smoke layer is given byThomaset aJJ9]:

M

—

poA,Cj2gDOiTJ2 2

T+IkT1 (AC)

3/2

(5 15a)

and canbe re-arranged algebraicallyintothemore convenient form:

kC=

M1T (5.15b)

ACJ2 [2PD OT[Mi]J

35

ignorescoolingofthe smoky gases after they leavethe fire plume).

5.12 Natural ventilators and wind effects Whennaturalventilatorsareusedfor smokeexhaust, it is important that they are positionedwheretheywill not be adverselyaffectedby external wind conditions. A positive windpressurecanbe much greater thanthepressure head developed by a smokelayer. Shouldthis occur the ventilator mayact as an inlet ratherthan as an exhaust. However,ifsitedin an areaofnegativewindpressure,the resultant suction force on a natural ventilatorwouLd assist smoke exhaust (Figure21). Tallbuildingsor taller areas ofthesame building(such as rooftop plantrooms, etc.) can create a positivewind pressure onlowernearby roofs.Steeply pitched roofs ie, roofs over300 pitch,mayalsohaveapositivewind pressure onthe windwardslope. A suggestionsometimes advanced foroffsettingwind over-pressure,is to increasethe total areaofnatural ventilation per reservoir.Since the over-pressureis, by definition,force per unitarea,this will usuallynot'work andindeed could exacerbatethe problemby allowing evengreaterquantitiesofair tobe driventhroughthe ventilator to mix intothesmoke. In some cases it may be possibletoretainnatural ventilation openingsin avertical plane byarrangingthem to face inwardsto eitheraregion shelteredfrom wind action, orwherethe wind will always produce asuction. In othercases theerection ofsuitablydesigned screens or wind baffles (outsidethe verticalwall or window holding theventilators) canovercome wind interference andmay even be able to convert anover-pressureintoasuction. Thereis alsothe possibilityofselectivelyopening ventilatorsinresponse tosignalsfrom awinddirection sensor. Expertadviceshould be sought forsuchdesigns. Duetothecomplexity ofwind-induced air flow over some atriumbuildingsand the surroundingbuildings,it

where:

= measuredthroat areaofventilators (m2), = total areaofall inlets (m2),

= coefficient ofdischarge (usuallybetween0.5

and 0.7), = entry coefficientfor inlets (typicallyabout0.6), = M1 mass flow rate ofsmoke tobe extracted (kgs'), p0 = ambient air density (kgm3), g = accelerationdueto gravity (ms2), D = depth ofsmoke beneath ventilator (m), = temperaturerise ofsmoke layer above ambient (°C), = T1 absolutetemperature ofsmoke layer (K), = T0 absolutetemperature ofambient air (K). Tables5.3 a—dgivethe minimumfreeareaofventilation required basedonEqns(5.15), ignoringthe effectofany inlet restriction (ie assuming an infiniteareaofinlet ventilation),and for a convectiveheatfluxthroughthe ventilators (note that this heatfluxis the same as Qf ifone

Winddirection

pressure

Figure21 Positioning naturalventilatorsto be shelteredfrom wind action

36

Design methodologies for SHEVS

A

Table 5.3a Minimum total ventilation area (m2) needed for asmokereservoir(fromEqn 5.15 withC = 0.6); Q = 1 MW

A (m2) needed for = a smokereservoir(fromEqn 5.15 withC 0.6); Q =2.5 MW Table 5.3b Minimum total ventilation area

Mass

Mass

flowrate

flow rate

(exhaust rate)

(kgs') 4 6 8 10 12 15 20

25 30 35 40 50 60

(exhaust rate)

Smokedepth beneath ventilators (m) 2 3 4 5 7 1.5 2.1 3.2

4.5 5.9 7.4 9.9

1.8 2.8 3.9

1.5 2.3

1.3

3.2

2.7

5.1

4.1 5.2

3.6

7.0

6.0 8.9 12.0

6.4 8.5

14.5

12.5

10.2

19.6

17.0

25.3 31.4 37.9

21.9 27.2 32.9 45.2 58.8

13.9 17.9

52.2

67.9

22.2

2.0

4.5

15.5

10

(kgs')

Smokedepth beneathventilators (m) 1.5 2 3 4 5 7 5.13 6.23

4.4 5.4

3.6 4.4

15

8.0

6.9

5.6

20 25

11.2 13.5

9.7 11.7

7.9

9.6

3.8 4.9 6.8 8.3

3.8 5.6

30 35

18.4 22.5

16.0 19.5

13.0 15.9

11.3 13.8

7.6 9.8

40 50

26.8 36.0

23.2 31.2

19.0 25.5

16.4 22.1

1.1 1.7

1.0 1.5

0.8 1.2

10 12

2.4 3.2 4.0

2.1

1.7

2.7

3.4

2.3 2.9

5.4 7.9

4.6 6.7

10.8 13.9

9.1 11.7

26.8

19.2 23.2

17.2 20.8

14.5 17.6

12.2 14.7

60 75

46.5 63.2

36.9

32.0

24.2

41.5

20.2 26.3

90 110

81

48.0

28.6 37.2

31.4

Notesto Table5.3:Toallow forthe effectof limitedfresh air inletsthe fo]lowingguide canbe used asan alternativetsEqs 5.1 5):

108

40.3

3.1

54.7

32.9 44.7

28.5 38.7

70 93

57.3 76

50.0

66

2.8 3.4 4.4 6.1

7.4 10.1 12.3 14.7

10

2.4 2.9 3.7 5.2 6.3 8.5

2.C

2.4 3.1

4.3 5.2 7.1

8.7

10.4 12.4

10.4

19.7

16.7

14.C

25.5 34.6 44.4 59

21.5 29.3 37.5 50.0

18.C

24. 31.4 41.7

Note: See Notes toTable5.3a.

Ifthe inletareatotheatrium istwice the exhaustventilationarea givesbyTable5.3the indicated ventilationareaandthe inletareashould both be increasedbyapproximately10%.

Ifthe inletareaisequal tothe exhaastventilationarea,the indicatedventilationareaandtheinlet area shouldboth be increasedbyapproximately35%.

Ifthe inletareaixhalfthe exhauxtventilationarea, the indicatedvestilatios areaandtheinletarea should both be increasedbyapproximately125%.

A

Table 5.3c Minimum totalventilation area (m2) neededfor a smoke reservoir(fromEqn 5.15 withC= 0.6);Q= 5MW

A

Table 5.3d Minimum totalventilation area (m2)needed for a smoke reservoir(fromEqn 5.15 withC =0.6); Q = 6MW

Mass

Mass

flowrate

flowrate

(exhaust rate)

(kgs') 10 12 15

20 25 30 35 40 50 60 75 90 110 130 150 200

Smoke depth beneathventilators (m) 1.5 2 3 4 5 7 5.3 6.24 7.7 10.3 13.0 16.0 19.1

22.3 29.3 36.9 49.3 63 82 104 126 189

Note: See Notesto Table5.3a.

4.6 5.4 6.7 8.9 11.3 13.8

16.5 19.3 25.4 31.9 42.7 54 71

90 109 164

3.8 4.4 5.4 7.3 9.2 11.3 13.5 15.8 20.7

3.3

2.9

3.8 4.7

3.4 4.2

6.3 8.0

5.6 7.1

9.8

8.7

11.7

10.4

2.5 2.9 3.6 4.8 6.0 7.4 8.8

13.7

12.2 16.1 20.2

10.3 13.6 17.1

27.0 34.4

22.8 29.1

45.1

38.1

57 69

48.0

18.0

26.1

22.6

34.9 44.4 58 73 89

30.2

134

38.4 50 63 77 116

103

59 87

(exhaust rate) 10

(kgs')

15

5.5 6.4 7.8

20 25

10.2 12.9

30 35

15.6 18.6 21.6

2.1

10

2.4 3.0 4.0 5.0

12

6.2

7.4 8.6

Smoke depth beneath ventilators (m) 7 1.5 2 3 4 5

11.4 14.3

40 50 60

19.1

75

46.7

24.3 31.9 40.2 49.0

90 110 130

59.2 77.2

73

150

200

28.2 35.2

4.7 5.5

6.7 8.9 11.1 13.5 16.1

18.7 24.4 30.5 40.4 51.2 66.9 83.8

3.9 4.5 5.5 7.2 9.2

3.3 3.9 4.8 6.3

11.1 13.1 15.3

9.6 11.4

19.9

17.2

24.9 33.0 41.8 54.6 68.5 83.3

21.6 28.6

96.8 117.8

102.0

175.9

152.3 124.4

Note: See Notes toTable5.3a.

7.9

13.2

36.2 47.3

10

3.0 3.5 4.3 5.6 7.0 8.6

2.5 2.9 3.6 4.7 6.0

10.2 11.8

8.6 10.0 13.0 16.3 21.6 27.4 35.8 44.8 54.5 81.4

15.4 19.3

25.6 32.4 42.3

59.3

53.0

72.1 107.7

64.5 96.3

7.2

2.1

2.5 3.0 4.0 5.0 6.1 7.2

8.4 10.9 13.6 18.1 22.9 29.9 37.5

45.6 68.1

5 Smoke control on storey offireorigin

37

maysometimes be desirableto carry out boundary layer wind tunnel studies to establish the windpressure over thebuilding'senvelope. Once areas ofover-pressureand suctionhavebeen identifiedforall possiblewind directions,designofventilators orfans can proceed as before. Theinteraction betweenthe windand horizontal natural ventilators is discussedfurther in section 10.8. Apowered exhaust system should beusedwhere positivewindpressures are likelytobeaproblem, or whereit is necessaryto extract smokeviaan extensive ductwork system.

DroD screen Balcony Reservoir screen

5.13 Requiredventilation rate (powered exhaust)

Apowered smoke exhaustsystem consists offans and

associated ductwork designed to remove the mass flow rate ofsmokeentering the smoke reservoir,and tobe capable ofwithstandingthe anticipated smoke temperatures. The controls andwiring should ofcoursebe protected, to maintain the electricalsupply tothefans during afire. The massflow rate ofsmokedetermined from the previoussections can be converted tothe corresponding volumetric flow rateand temperature, usingTables5.1a to 5.ldor thefollowingequation forselection ofthe appropriatefans: M1T1

po7J

(5.16)

where: = volumetricexhaustraterequiredin the reservoir V1 (m3s1),

M1

= Mfor MB determined from theprevious section (kgs 1),

= ambient air temperature (K), T1

p0

=T0+01(K),

= densityofambient air (kgm3).

Figure 22 Slit exhaust

smokepassingthe slit(egentering the atriumvoid), itwill not necessarilymaintain aclear layerwithin the room itself, andthe space belowthe smokelayermaybecome 'fogged'.The exhaust should beprovided very closa to the opening from acontinuous slitwhichmaybe situated in theplaneofthefalseceiling. Wraight59 showed thatpowered exhaust from a slitat right anglesto a layer flowcould completelyprevent smokepassingthat slit, provided thatthe exhaust rate at theslitwasatleast5/3times theflow inthe horizotital layerflowingtowards the slit. This allowsausefulgeneral methodfor sizingsuch an extract: firstcalculatethe flow rate ofgasesapproaching the opening(orgap in thebalcony edge screens)using sections 5.2—5.4 above as appropriate, multiplythis massflow rate by 5/3. usingthe known layer convectiveheatflux (and allowingfor sprinklercooling usingsection 5.5 above if appropriate) calculatethe volumetric exhaust rate required from the slit, usingEqn (5.10) to calculatethe meangas temperature drawn through thefan, and Eqn (5.16)to calculatethe requiredfancapacity.

• ••

5.14 Slit extract

5.15 False ceilings

Whenremovingthe smokefrom acommonbalcony reservoirand thereis no possibilityofusingdownstand screens to prevent the passage ofsmoke orwherever a physicalbarrier maynotbeused, a slitextract system maybeemployed over the length ofthe flowpath to supplementthemainreservoir exhaust system and replacethe screens (Figure22). Aslitextract system can be usedacross aroom'sopeningstoprevent any outflow ofsmoke, or atabalcony edgeto protectan atrium. Such a system islikelyto work bestwith further exhaust distributed within the fireroom,whichfor a sprinkleredroommaypossiblybe provided bythe normal ventilationexhaust system,the normal ventilation input and recirculation ofair being stopped, orfor an unsprinklered room, beprovided by apartial smoke exhaust system.Whilst this system is designedto prevent

Where thereis an unbroken falseceilinginthe fire room

or balcony,itmust be treated as thetop ofthesmoke layer.Ifthefalseceilingis porous to smoke, ieifithas an appreciablefree area, any smokecurtainsforming the smokereservoir must be continued above the ceiling.If theproportion offree areais large enough, thereservoir andits screens mayevenbetotally abovethe falseceiling. The permeableceilingoughtnotto interfere appreciably withtheflow ofsmokefrom thefireto the smoke ventilationopenings above the falseceiling. Ithasbeenshownexperimentally601 that a minimum freeareaof25% canbeusedas a 'rule ofthumb'valu.e whichwill allow smoketo flowthroughalmost unhindered. For single-storeyand balconyreservoirs cool smoke canbe expected to affectsome nearby rooms undersome circumstances,but would not significantly

38

Design methodologies for SHEVS

hindersafe escape.Free areas ofless than25% are possibleinsomecircumstanceswhile still allowing safe

5.17 Maximum dimensionsfor smoke

conditions; it is possibleto calculateapproximately smoke flow through the ceilingfrom firstprinciples— expert adviceshould besoughtwherethis possibilityis

thoughtto be desirable.

516The use of a plenumchamber above a false ceiling Somedesignshave been seen in which the space above

the mainly solid falseceilingin arooforabove abalcony isusedforthe exhaust ofair for normal ventilation purposes. Afan extracting air from this space (effectively aplenum chamber) reduces its pressureand sodraws air from the space belowthrough a number ofopeningsin the falseceiling.In theeventofa fire afan ofsuitably larger capacity starts up and draws smoky gasesintothe chamber in a similarway.

Apotentially valuablebonus ofsuch a system in a sprinklered buildingis that the sprinklerswhich are normallyrequired inthe space abovethefalseceilingwill coolthesmoky gasesbefore theyreach the fan. Furthermore, it canbe desirableto leave the false ceiling belowthe exhaust points'solid' (ie notableto pass smoke) to prevent air beingdrawnup throughthe smoke layer.A sufficiently extensive areaof'solid' falseceiling willensure thatthe smokepasses throughatleastone sprinklersprayen route to the extract. Theplenum chamber should notbelargerin areathan itsassociated smoke reservoir.Larger chambers should be subdividedby smokescreens extending thefull height ofthe chamber, and belowthe falseceilingtoform a complete smoke reservoir below.The minimumnumber ofopenings through the falseceilingrequiredwithin a singlesubdivisioncan be found from section 5,10.The total areaofsuch openingsper reservoirshould be decided byconsideration ofthe designpressure differencesbetweenchamber and smokelayer, andofthe flowimpedance ofthe openings concerned. A system of reasonablywide (perhaps 1 m or2 m) slots surroundinga region offalseceilingcould perhaps be usedinstead of screens belowthe falseceiling.

reservoirs Mostthroughflowsmokecontrolsystemsare designed with an arbitrary limitationto the ceilingreservoir of between 1000—3000 m224'9'25, one reason being to prevent excessiveenergy loss from the buoyantsmoke layer.Manyatriacannotphysicallyor architecturally adoptsuchreservoirformations,and iflarger thanthe areas mentioned above willcause additionalenergy to be lost from the layer.Ithasbecomethe common practice to specifythat the maximum areaacceptable for asmoke reservoirshould be 2000m2 wherethereare natural ventilators and the objectiveis toprotectescape routes; risingto 2600m2 for powered ventilatorsand the same objective;risingto 3000m2 wherethe objective is to protectproperty with no significantlife-safetyobjective. Note, however, that in the UK, these same principles areexpressed differentlywhenthebuildingis a shopping mall:with natural ventilators, smokefrom shop units of upto 1000 m2 plan areacanentera mall smoke reservoir which can itselfbe up to 1000 m2 inplan area; with powered ventilators eachvalueincreases to 1300 m2. There is no scientificreasonforthis differentwayof expressingthe principles.Instead, the differenceis based on decisionsmade byUKRegulatoryAuthorities as to theeaseofenforcement in thecircumstances applyingto shopping malls. It is likelythat this maximumareawillbe revisedwhen mathematical modellingofheat transfer processes from smokelayers becomes sufficiently reliablefor confidence in theresults. Currently,however, thebest available argument forthe presentlimitis that thereis no clear evidencethat it has proved excessivelylarge anareain real fires. Another commonly adopted limit, applied simultaneouslywith the arealimit, is to apply a maximum lengthto eachsmoke reservoir of60 m, measured along the mid-line ofthe reservoir.The origin ofthislimit has never been formallypublished, but anecdotallyfirst appeared in 1972[5] basedon aUK committee beliefthat peopleescaping belowabuoyant smokelayershould be ableto move out from belowthatlayerin less than 30 m from anypoint. This was expressed as a maximumlength ofreservoirinthe interests ofsimplicityofenforcement. The committee's opinion wasbasedon an assessment of the probable psychologicalreactions ofmembers ofthe general public in suchcircumstances.

39

6 Smoke ventilation within multistorey spaces (eg an atrium)

6.1 Smoke movement in the atrium Whenthe smokeand heat cannot, for variousreasons,be confined andremoved from theroomoforigin or associatedbalconyspace, the use of'throughflow' or steady-stateventilationfrom the atrium itselfis usually considered. Thisform ofsmoke control is commonly called 'smoke ventilation'or SHEVSandis based upona defined buoyant smoke layer being establishedat some point within the structure,with a 'clean' layer ofair beneath. Themass flowofgasesentering this layer being equivalenttothatflowingoutthroughthe exhaust system (Figure23). Thebase ofsuch a layer is usuallyata height chosen for safetyreasons (See Annex B,whereit is noted that the clear heightabove the highestexposed escape route should be 0.5 mmorethan for the single-storeycase described in Chapter 5), orto avoid breaching the practical'cutoff' limitsoutlined in section 6.7 below. Once the heightofthislayerbase is chosenfora lowest-

level fire, the heightabove the topofthe opening (or above the edge ofthe projecting canopyorbalcony above theopening where relevant) must be establishedwhere thefire is in an adjacentroom. Notethatwhenthefire is onthe floor ofthe atriu.m and is directly belowthe smokelayerthat forms underthe atrium ceiling,entrainment intotherisingaxi-symmetric plume is similarto thatgiven in section 5.2 above. This special case is discussedin section 6.4below. In general, however, theworstcondition tobe catered for is a fire in an adjacentroomonthe lowestlevel,as resultsinthe most entrainment in the rising smokeplume andhencethelargest quantity ofsmokygas entering the buoyant layer. Thefirecondition in the compartment (thedesign fire) should bespecified,andthe mass fluxleavingthroughthe compartment opening and anyentrainment under1:he projecting balconyorcanopycan be calculated as described in sections 5.1—5.3. Asthesmoke flows throughthe room opening intothe atrium space it will either:

I

/1

Inlet

Figure23 Throughfiow ventilation ofan atrium

1L1

E

40

_____ ____

______

• rotateupwardintoaround thetop edge oftheopeningand theatrium space as aplume, or directly • pass flowundera horizontal projection suchas abalcony ofthe the to the

beyond opening, pass edge projection and riseupwards intothe atrium space as a plume.

Suchplumes areoften referred to as 'spill' plumes, or as 'thermal'line plumes. Theterm 'line' denotesthat the base ofthe plume immediatelyfollowingrotation is long

Design_methodologies for SHEVS

______

Reductionsin the mass flow rate ofsmoke entering the

smokelayercan usuallybe effectedby changes to parameters 3 and 4. In practice, the heightofrise ofthe plume is usuallychosento permitsafeevacuation,leaving only adependency on the length oftheline plume.

6.2 Channellingscreens Whentheatriumhas aplanefacadewith no horizontal

and relativelynarrow. Lineplumes maytakeone oftwo forms:adhered plumes or free plumes. Adheredplumes arewherethe smoky gasesproject directly from acompartment opening, and the plume attachesto the verticalsurfaceabove the opening whilst rising upwards.Thiswill also occur whenthereis a vertical surfaceimmediatelyabove anyrotation point intothevoid. Thesurfaceoftheplume in contactwith the ambient atmosphere inthe atrium will cause additionalair to be entrained intoit (Figure24a). This typeofplume is alsoknown variouslyas asingle-sided, attached orwall plume. Freeplumesarewherethe smoky gasesprojectintoa space beyond ahorizontal projection (ega balcony),thus allowingthe formingplume to rise upwards unhindered. This creates alarge surfaceareafor entrainment on both sidesofthe plume along itsspillwidth (Figure24b),for whichreasontheyarealso known as double-sided plumes. The degree ofentrainment intothe risingplume, and hencethe totalquantity ofgasesenteringthe smokelayer forming underthe ceiling ofthe atrium space,is governed basicallyby four initialparameters251: 1 the mass flow rate ortemperature ofthe gasesat the edge ofthe rotation pointintothe atrium, 2 theheat fluxofthe gases, 3 thelengthofthe line plume entering the atrium, measured along theedge past which the smoke spills, 4 the height through whichthe plume must rise.

projections, the lengthofthe plume is determined bythe widthofthe opening throughwhich the smokeis passing. When, however, smoke is abletoflow unrestricted under a horizontal projection,eg a balcony, itwill flow forwards towards the balconyedge, and laterallysideways.It will continue to flow sidewaysuntil it meetsan obstruction or loses sufficientenergy to become stagnant and will then rise intothe atrium space as avery long line plume (Figure25a and Plate 5).This resultsin large quantitiesof airbeing entrained and henceavery large massflow rate ofsmokeentering thelayerin theatrium roof. This excessiveentrainment canbe reduced by restrictingthesidewaystravelofthe smoke underthe balcony and hencereducing the lengthofthe line plume. The devicesusedtoachieve this arecommonly known as channellingscreens, andliterally'channel' the smoke from the exit from the room to the balconyedge (Figure25b and Plate 6). This conceptis used in smoke control systems in multistoreyshopping centres24. The minimumdepthrequired for apairofthese screens to channel all the smoke is dependentontheir separation at the void edge (L).Somevaluesfor 1MW, 2.5 MW, 5 MW, and 6MW convectiveheat fluxesare given in Tables 5.2. Alternatively,the minimumchannellingscreen depth maybecalculated using Eqn (5.11), modifiedto:

(a)

(b)

DB=---- MBT 05 Cd

L05]

(m)

-Ji H Figure 24(a) adhered plume, (b)free plume

6 Smoke ventilationwithin multistorey spaces (a)

(b)

r

—

TT :*

Figure25(a)Smoke spreading sidewaysbeneath a projectingcanopyor balcony; (b)smokeconfined to a compactspill'plume by channeling screens

Plate 5 Smoke spreading beneath a balcony

41

Plate6Use of channeling screens

42

Design methodologies forSHEVS

where:

6.3 Entrainment into spill plumes rising through the atrium

0— B

fixed midway across a compartment opening will serve nopurpose since smokewill flow on both sides simultaneously. Ifchannelling screens arecreatedusingfreehanging smoke curtains then their deflectionsand consequent rise oftheirbottombarsmust be takenintoconsideration. Deflection ofsmokecurtains is giveninAnnex C. Research suggeststhat channellingscreens are unnecessaryifthe balconyprojects no morethan 1.5m beyondthefire room61. Thisresearchhas alsoshown thatbalconies whichareshallow (90% offires have notbeenlarger thana specified areawhenthe fire brigade started asuccessfulattack on them) orfrom experiments whichprovide evidencefor the effectiveness ofextinguishingsystems,the

12.2.2.3 SHEVS designobjective 'propertyprotection

only'supportingfire-fighting objectives II and IV, and, ifalso designedtodo so,III Forsome occupancies,thereis no, orjustavery low, risk tolives due to threatfrom smoke.Thiswill be truefor all circumstanceswherethere are very few or usuallyno persons inside alire-affectedcompartment (egas in most warehouses,especiallyifthey are automaticallyloaded andunloadedby robots (seealso section 12.3 below). Another example concerns premises wherethe means of escape are provided by compartmentation: iewhere corridors andstaircasesare enclosed byafire-resistant structure and protectedfrom ingressofsmoke (egby vented lobbieswith fire doors orby pressurization systems).Under these circumstances,SHEVSneed not provide asmoke-free layer from the very beginning ofthe outbreak ofa fireto ensurethat people are ableto escape. Wherethe concern is limited to property protection therearetwo main approaches possible,although the distinction between them can be blurred: property protection mainly relying on fire-fighting

• • operations, property protection mainly relying on effectivenessof extinguishingsystems.

12.2.2.3aPropertj'protectürnrelyingonfire-JIghtingoperations In this case a SHEVSis supposed to support fire-fighting operationsby removing smokeand heat in sufficient

amounts for fire-fighterstobe able to: enterthe compartment on fire,

•

12 SHEVS and thefire services

•• theitlocation ofsothe stillrelatively small that therest ofthe extinguish quickly remains identifl,i

compartment

fire, and

undamaged.

75

But the temperature rise duetothe fact that heatis not exhausted from a closed space also enhances fire spread and, intheabsence ofsprinklers,can leadto early flashover.

This means that a SHEVShas tobe designedtocreate a smoke-freelayerin the fire compartment.This smokefreelayer neednotbeprovided from thevery beginning ofsmokeproduction (as mentioned above)butmust be availableforfire-fightingoperations. This consideration onlyhasan influenceon the time for actuating the SHEVS, but not on the designfire size and the resultsof consequent calculationsfor designingthe SHEVS (see also section 11.1.3). Therefore, aSHEVS intended to protectpropertyonly by supportingfire-fightingoperationsbycreating a smoke-free layer,willnot needless technical effort put intothe designthanwill systemsfor lifesafety plus propertyprotection. A delay in actuating the SHEVSis only tolerable ifthe temperature rise dueto smokelogging ofthe compartment is notso severethatitmayignite other goods away from the fire's origin,or mayseriously endanger the building'sstructure. This is unlikelyto happenifthe SHEVSisactuatedby a flowswitch in the sprinklersupply,particularlywherequick-response sprinklersare usedto ensure that the sprinklersystem starts operating as earlyas possible,and wherethat operation has the minimum delay dueto heat extraction by theSHEVS. Despite this temperature criterion, caution has to be applied whenconsideringthe adverse effectswheresmoke is notremovedfrom thevery early stagesofthe fire. Ifgoods, contents, liningsorstructure maybe destroyed orbecomeunusablebecause ofthe corrosive and contaminating effectsofsmoke, any designconcept involvingdelayed response ofaSHEVSis ofminor benefit to protectsuchgoods orproperty. Wherethis isa significantconsideration,actuating the SHEVSon a signal from smoke detection canbe recommended. Itis also awell-experiencedfact thatit takes a significanttime to create asmoke-free layer in an already smoke-logged space, especiallyifnatural throughflow ventilation is used. Forthis reason, the actuation ofa SHEVS on detection ofsmoke is also preferable for assistingfirefightingoperations in these circumstances.SHEVS designedto open on a signalfrom smoke detection support fire-fightingobjectiveIII,which isto separate valuableitems (egworks ofart, documents, data, etc.) before being affectedbythe fire and/or itsproducts (smokeand heat). The reasonswhythe actuation ofa SHEVSshould be delayed until the actuation ofsprinklers,or should be deferred until the arrival offire-fightersoften can be considered to be asfollows. A SHEVSencourages thedevelopment ofafire by ensuringthat the firehas asupply ofair. Therefore, it should only be actuated ifextinguishingorcontrolling operations eitherby fire-fightersorby extinguishing systemsare already inprogress. This is true in principle.

Therefore, ifthe interveningtime ofwell-equipped fire servicescan be expected to be reasonably short(eg 10 minutes afterbeingalerted by asmoke-detection system),the maximum benefit ofaSHEVS creating a smoke-free layercan be obtained ifitis actuated on smoke detection before the fire-fightersarrive (aslongas the design firesize remains manageableforthe firefighters).

This is likelyto apply forproperties below'High Hazard'risks ('Extra-HighHazard'in older terminology) whichareprotectedby sprinklersorfor very low risks (due to the nature ofthe contents) even ifnot protected bysprinklers. Nevertheless,it has tobebornein mind that inthe

absence ofsprinklerprotection thedesign firesizes can be larger, often getting beyondmanageable sizesforthe fire brigade.Wherethis happens,a SHEVSis not auseftil component ofthe fire-preventionconcept and limitation ofpropertylosses canonly beachieved by compartmentation. Ifthe interveningtimeforfire servicesis assessedto be longer than 10 minutes (for risksbelow HighHazard, for which 10 minutes maybe toolong), firesizes will bemore likelyto growbeyond manageable sizesifno extinguishingsystem is used. In thiscase installationofan extinguishingsystem to control the fireuntilfire-fighting operationsbecome successful, has to be ensured. Thereis awidespreadbeliefamongst people in the sprinkler world, that this can only be achievedby activatingaSHEVS after sprinklershave come into operation. Ithas tobekept in mind, however, that contentssusceptibleto smoke might notbe protected by this approach as the compartment could be totally smoke logged bythe time fire-fightersarrive.Acompronhise solution (as explainedin section 11.1) could beto activate the SHEVSon a flow-switchinthesprinkler supply provided that quick-responsesprinklersare usedas mentioned above. This makes itmuch more likely that sprinklerswill be ableto control thefire until extinguishingiscompleted by fire-fighters.Thiswill only apply for risksbelowthe (Extra-)HighHazardcategory. Another frequently heard argument for actuating a SHEVSmanuallyisthe beliefthatfalseactuatingby the smoke-detection system causesopening ofnatural vents and leads to property damage dueto rain, snow or freezing.This problemmust not be solvedby rely[ngon manual actuation ofthe SHEVS,butinstead by making thedetectionsystem more sophisticated andreliable. 12.2.2.3bPropertyprotectionrelyingon effectivenessof extinguiththgsystems

Wherethereareadverse effectsfor fire-fightingas outlinedin sections 12.3 and 12.4 below, orlong interventiontimesforfire servicesso thatsuccessfulfirefightingis onlypossiblewith the support ofextinguishing

76

Design methodologies for SHEVS

systems, theremust besufficientconfidencethatthese systems will achieve their designed purpose and will not be influencedadverselyby othersystemsincluding SHEVS. This istrue for storagerisksbelongingtothe HighHazardcategory andfor otherstoragerisksifthe intervention time ofthe fire servicescan become considerablylong (egmorethan 15 minutes, or even less for fast orultra-fastfire-growth rates). In thesecircumstances,andtogivethebest chance for complete extinguishingby the extinguishingsystem,it would be wiseto activate a SHEVSonly manuallyfrom a safeplace outside a fire compartment atthe discretion of thefireservices.This is discussedfurther in sections 12.3

complete the task ofextinguishingthe fire. Although any devices (egwindows, simplelight domes, etc.) allowing smokeand heat release out ofa compartment on fire can in principle assistfire-fighting operations, these cannotberegarded as a SHEVS,which has tobe designed and calculated followingthe methodologies outlined in this book.

and 12.4. Thiskind ofSHEVS cannot provide asmoke-free layer whenfire-fightingservices arriveattheplace ofthefire because itis activatedonly whenthe fire-fightersoperate it. Such a SHEVScan only clear a compartment from smokeand heat after arrivaloffire-fighters.Nevertheless, it canstillprovide access for themto extinguishany remaining burning fuelwhichhad not been extinguished bythe extinguishingsystem. Prior to activationin these circumstances,it is quitelikelythatthe compartment will havebecomefilledwith smoke, even down to the floor. This allowsthesmoke to become hotter,faster,thanwith theSHEVS in operation, and givesthe sprinklers (or otherextinguishingmedium) thebest conditionsfor earlyoperation andtherefore thebest chance of successfulsuppression ofthe fire. WhentheSHEVS is activated, the buoyant smoky layer should lift, allowing fire-fightersto see andmove around beneaththe hot smoky gases. The designofsucha system requires that a designfire sizeshould beassessed,and thatthe system should be calculated as it is desired to beafterithas been activated. Additional informationis given in section 12.2.2.4. 12.2.2.4 SHEVS designobjective 'assisting fire-fighting

operationsonly', mainly supportingfire-fighting objectiveII Thereis no special design dedicated only to assistingfirefighting operations. Eachfire-fightingoperation pursues atleastone ofthe four fire-fightingprinciplesdiscussed above.Using extinguishingmeasureswithout simultaneouslyaiming at protection oflife or property, or ofprotecting the environmentis asenseless exercise. Therefore, eachSHEVSdesigned for one ofthe design objectives 'life safety' and/or 'propertyprotection' automaticallyassistsfire-fightingbycreating asmokefreelayer(except underadverse designassumptions for design objective 'life safety only' as outlined in section 12.2.2.1.

No smoke-freelayeris initiallyprovided for firefighters at theirarrivalbySHEVSfollowingthe design objective'propertyprotection' relying on effectiveness of extinguishingsystems as discussedin section 12.2.2.3b) above, although a reasonably clear layer willbecome established quicklyoncetheSHEVShas been manually initiated whichwill enable the fire-fightingservicesto

12.2.2.5 SHEVS designobjective supportingfire-

fightingobjective IV The fire-fightingobjectiveIV canusually be achieved withoutsupport ofaSHEVS especiallyiffire-resistant structuresand compartmentation are applied toprevent spreading offire and smoke. Inthis case,any opening in thestructure will havean adverse effecton preventing smokefrom affectingthe surroundiflgsofthe building.It

is usuallysufficientto have alarge enough water supply and extinguishingcapacity forthe fire serviceson site to prevent fire spread. It is worthmentioning,however, that large amounts ofsmoke and toxicgaseous or dusty materialsspreading from theircontainers whichhave beendestroyed by thefirewill endanger the environmeni evenwherefire spread isprevented. Therefore, SHEVScan contribute to achieve firefightingobjectiveIV by creating asmoke-free layer and thus supportingthe fire-fightingobjectivesII andIII so thatthe fire is less likelyto become largeenoughto threatenthe environment byits consequences.Itfollows thatany SHEVSservingpropertyprotection will also contribute to protection ofenvironment.

12.3 Circumstanceswhich reduce or impedethe abilityof a SHEVS to assistfirefightingoperations A SHEVSonits owncannot prevent or slowfire growth. Even whereit serves toprotectthe means ofescape there is often a needforthe fire serviceto search the buildingto confirmthat no-one remains, orto rescue people who havefailedto evacuate the building.Itfollowsthat even with aSHEVS, thereisoftenstill aroleforthe

intervention offire servicesto save lives. It is also the case thatthe fire serviceswill have amajorrolein

extinguishingthe fire and thus protecting property. ASHEVS, ifwell designed,cancreate a smoke-free layerwhichassistsfire-fighting.Forcertain risks and/or underadverse circumstancesa successfulintervention of thefire servicescanbecome impossiblewithoutthe presence oftechnical precautions suchas fire detection or automatic fire-extinguishingsystemsin spite ofthe presence ofasmoke-free layer whenthe fire is first attacked. It is fundamentalthat successfulfire-fightingactivities canonly beperformed ifthefirebrigade is called and can arrive on site before the fire compartment is fullyinvolved in fire, andwhen thefire isstill smallenoughto be controlled andfinallyextinguishedby the available means forfire-fighting.The latter requires that thereis a large enough water supply (or supplyofother

12 SHEVS and thefireservices extinguishingagents ifneeded) and sufficient fire-fighting equipment on site. Notethatthe referencehere to afire compartment appliesprimarilywherethefire compartment is large (which will almost alwaysbethe casewherea SHEVSis employed).

12.3.1 Factorsadversely affecting successful intervention by thefire services Noautomatic fire-detection system to alertthe fire

• servicesautomatically • Inadequate water supply (or supply ofother

•

extinguishingagents ifneeded) on site for asuccessful suppressionofthe firebyfire-fightingactivities Inadequate fire-fightingequipment on siteavailablein time: this can be dueto the location ofthe building relativeto the numberandlocationsofthefire stations, andto the number and typeofapplianceswhichare allocatedto intervene in a buildingin case offire.The presenceofobstaclesaffectingthe access for firefighters andtheir applianceshave tobetakeninto account aswell.

12.3.2Additionalprovisions for optimizingthe effective use ofa smoke-free layercreatedby a SHEVS for firefightingoperations In order to gainfullbenefitfor fire-fightingoperations from the smoke-free layer created by aSHEVS, andto avoid adverse effects outlined in section 12.3.1above,the followingprecautionshave to be observed. 1 Thebuildingdesigner should provide automatic fire detection and automatic alarmtransmission tothefire services.

2 Thereshould be an adequate watersupply,or a sufficientreserveofextinguishingwaterifthe normally

availablewater supply from afixed pipe network is insufficient.Whereappropriate, ensure that sufficient stocks ofspecialextinguishingagents (ifneeded for certain fuels,egfoaming agents) are present. 3 Thereshould be direct unhindered access to the buildingfor the numberofappliancecrews dedicated to intervene in case offire in thebuildingconcerned. Thefire serviceshould ensure that after receipt ofthe alarm,they can deliver within 10 minutes the extinguishingcapacity needed(manpower and equipment) to extinguishthe design fire. Inview ofthe many practicaluncertainties (eghaving to drive throughheavy traffic, orthepossibilityofappliances from thenearest fire stations being ata differentfire whenthe call arrives) it is wise to allow asafety margin of100%.Ifthis is not possible,oris difficult to achieve, fire-fightingprecautions have tobe made inside the buildingcomprising trained fire-fightingstaffwith correspondingfire-fightingequipment to deliver the extinguishingcapacity. 4 Alternatively,a fixedautomatic extinguishingsystem (egsprinklers)can be provided in the building.Whileit cannot be guaranteed thatsprinklerswill extinguisha fire, they are known tobe very goodat controllingfire growth and thus reducing the size offire which the fire

77

servicefinds on arrivalatthe scene, andwhichhas to beconsidered in 2 and3 above.Thepresence ofa properly designed automatic extinguishingsystem will usuallyremovethe need for an on-site,specially trained group ofemployeesacting as a 'worksfire brigade'.Note, however, that theremay still be a need for suchgroups wherethereare special circumstances. Having takenthese precautions,the fire servicescan take full advantage ofa smoke-freelayercreatedearlyby an automaticallyactivatedSHEVS (preferablyon smoke detection),with agoodchance ofbeing ableto extinguish astill relativelysmallfire immediatelyafter arrivalon site. Thus, the objectivesfor life safety, propertyprotection and also environment protection canbeachieved..

12.4Circumstanceswhere a SHEVSis of minorbenefit forfire-fightingoperations Forsomebuildingsand fuelsit isnot possibleforthe fire brigadeto apply water byusinghoses directly and. immediatelyon all the burning fuel,because ofthe arrangement ofthatfuel.In suchcircumstances,the fire willstill become larger eventhoughit is being attacked. This ismainly true for high riskssuchas high-rackstorage with narrow aisles between the racks,or storage inracks withoutclear aisles allowingfree movement (eg whereracksareloaded and unloaded automaticallyby robots). In caseoffireinside suchracks,thereis no safe accessleading near enough totheburning fuel to apply thewaterproperly, whetherthere is a smoke-freelayeror not. Ontheirwaythroughsuch burning racks firefighters would be endangeredby burning goods falling down on themorby collapseofthe racks.A SHEVSwill be ofvery limitedvalue in such cases,since it is incapable ofaffectingthe primary problemofrapid fire growth and spread. In thesecircumstances,only fixed automatic extinguishingsystemscanbe applied successfullyto control the fire. Thebenefit ofa smoke-freelayer in this caseis not important in the firststage offire-fighting,because firemenwill not enterthe fire compartment immediately for safetyreasons,as outlined above,butwillinstead rely on theautomatic extinguishingsystemsto contro [the fire.These extinguishingsystemswillbe more effictive in relativelysmallandsealed spacesifthe fire is not ventilated. In very large poorly sealed spacestherewill be enough oxygenforcombustion.A SHEVScan beusedto remove heat from the fire-affectedspace, andto reduce the temperature ofthe smoke layerunderthe ceiling compared withanunventilated space, and thus reduce the number ofsprinklers opening faraway from thefire. Thus, unnecessarywater and pressure losses on the extinguishingsystem are reduced and the effectiveness of the extinguishingsystem is enhanced. Itshould be noted, however, thatthisbenefit only occursifthe SHEVS comes intooperation eitherbefore the sprinklersoperate orimmediatelyafter thefirst sprinkleroperates.

78

Design methodologies for SHEVS

WheretheSHEVS has not operated very early,and thebuildingispossiblyfullofsmokewhenthe fire service arrives,fire-fightersshould release the SHEVSmanually from outsidethe fire compartment andthusavoid backdraftwhenthe access doors are opened. When the fire is controlled oralmost extinguished by the sprinklers the SHEVSwill gradually establisha smoke-free zone. Thenfire-fighterscanevenclimbinside the racks or remove goods to get accessto still glowingfuel and fire pockets for final extinguishing. The removal ofheatwill also havereduced the thermal stress onthe buildingstructure and racks,whichmakes these follow-up extinguishingactivitiessafer for the fire-

fire completely and notjustto control it. This is different to the usual designbasisforsprinklers,which aims at control although inmost cases sprinklersalsoextinguish

afire.

Therefore, forsuchrisksitwill be sufficientto take precautions to remove the smokefrom the affected space afterthefire has beenextinguished.In most cases the existingopenings for natural lightand accessto the space will be sufficient,especiallyifportable fans are applied by the fire brigade.Sometimesit will be necessaryto provide additional openings ofa few squaremetresforthis purpose whichare normallyclosed and can be opened manually.

fighters.

12.5 Circumstanceswhere SHEVS are not applicable 12.5.1 Premiseswith riskof fast-growing fires Wherethereis ahigh probabilityoffast development ofa firewhichmakes firesuppression or extinguishing systems necessary,installationofaSHEVSwould serve nousefulpurpose. Examplesforsuchfire risksarewhere flammableliquidscan cause large liquidpool orjet fires, orwherethe spread ofcombustiblegases or dusts can cause explosions. These riskscan only be overcome by installedfoam or gas-extinguishingsystems, or suppressionsystemswhich prevent the outbreak ofafire.Inmost casesthese systems will only be effectivein a relativelysealed space. Therefore, SHEVS designed to create a smoke-free layer basedonbalancingairinflowagainst smoke exhaust are notapplicable.Theextinguishingorsuppression systems inthesecases have to be designed to extinguisha possible

12.5.2 Premises which mustnot be entered in caseof firebecause ofother prevailing hazards Examplesfor suchrisks arepremises inuniversities, hospitals,research orindustrial plants wherehazardous

infectious,viral orbacterial, substancesorradioactive liquidsordusts are handled whichmust not be released intothe open atmosphere, egwith the smokeofa fire. Therefore, suchpremiseshave to betotally separated from other spacesby completelyleaktight and fireresisting construction.Smoke spreadin this case is not a matterfordiscussion.Theenclosing structure must be fire resistant and all openings forventilation must be shut by fire-resistantand gastightdampers. Theproblem willbeto remove the cold, contaminated smoke from the compartment after the firehas been extinguishedby automatic extinguishingsystems. For thispurpose, special equipment with appropriate cleaning deviceshas to be provided —this isbeyondthe scopeofthis book.

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13 Selection of equipment

13.1 General No designisofany valueunless it resultsinthe installationofa system whichis fitfor its intended purpose. This concept of'fitnessfor purpose' is ofcritical importance for allfireprotection measures,and notjust for a SHEVS.All fire protection measuresshare the common feature thatthey mustworkas intended when a fireoccursevenifthat fireis a rareeventin thelifetimeof thebuilding.This carriesimplicationsforhowthe equipment to implement adesign must bespecified,as wellas for howthatequipment must be installed, serviced,and maintainedduringitstimein the building. This carriesthefurther implicationthatthe equipment oughtto becapable ofbeingservicedand maintainedin as easy amanner as possible. Aknown bad example concerns smokeventilators whichhavetobemanuallyclosed by someone climbing onto the building'sroof, especiallywhena testofthe fhnctioningofthe system resultsinmanyventilators beingopened. It is unlikelythatmany managers will carry out suchatestmorethanonce, in view ofthetime, trouble, and possiblewindand rain damage which might occur while the ventilators arebeingreset. And yet without regular functionalteststhere canbe no confidencethatthe system will operate whena fire does occur.The answerto this paradox is, ofcourse, to specifv equipment whichcanbe closed easilyby operation ofa simple switchin the central control panel, but to make thatswitch inaccessibleto everyone except an authorized person so that arealoperation ofthesystem is not terminated prematurely.Regularandfrequent fbnetional testing is especiallyimportant wherethe SHEVSis designedto reduce the threat tolife. These simple principlesapply to all the specialist equipment neededfora SHEVS.'Fitness forpurpose' can be met in many cases byensuringthatthe equipment has beentestedin an appropriate way. Note the word 'appropriate'.Thishides aconsiderable degree ofnecessarycomplexity.In general,anitem of equipment will have to function whenexposedto a variety ofdifferentenvironmental conditions. These will themselvesvary from place to place: egequipment in

Scandinaviaorthe Alpswillhaveto operate even when thebuilding'sroofis coveredwith deepsnow; whereas in

tropical countries thereis no such need. The test methodswill have to reflectthesedifferingrequirements, and will often pass an item ofequipment as being in a particular 'Class',ie performingbetterthan one valueof the testedparameter, but notachievingthe valuedefining the next Class. Similarly, the designmethodology described elsewherein this reportwill describe the conditionsto which the item ofequipment will be exposed.For example,the designcalculationswill predict the highest smokelayertemperature towhichsmoke curtains,fans, or natural ventilators willbe exposed;another example is that thedeflection calculationsfora hanging smoke curtain will leadto the specificationofthe minimum weight ofbottombar and fabricfora particular application. The test methods carried out on the product (theitem ofequipment) by its manufactureror supplier should allow the specifierto selecttheappropriate Class or Classes forthe conditionspredicted by thedesign. It is regrettablytruethat atthe time ofwriting, many of thesetestseitherdo notexist asStandards,orare still in Draft. The developingEuropean Standards in the PrEN12101 seriesoncepublished should fill theneed within Europe, but ithasto berecognized that the specifierofequipment fora SHEVSin many parts ofthe worldwill continue tohaveto relyonthe resultsofadhoctests carried out bythe manufacturer(orby the supplier). It must alsobe recognized that theenforcer offire regulationsfaces the same difficulties. This reinforcesthe desirabilityofearlyand continuing consultationbetween the regulator andthe equipment specifier (who maynot alwaysbe the same as the system designer)inorderto ensurethat theequipment being installed intothe buildingis appropriate to the needs both ofthe building and ofthe environment to which the system willbe exposed.The authors suggest,for example,thatwherean item ofequipment can be obtained satisingany one ofa range ofclasses, then itshould be the ultimate responsibilityofthe regulatorto specifr which Classis appropriate to the circumstancesofthe building. Economies can sometimesbe obtained ifan item of

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Design methodologies for SHEVS

equipment serves adualrole. That is, whereit fulfils a non-fire role in everydayuse, and changes to afire-role as an integral part ofthe SHEVSfollowingdetection ofthe fire. Examples would include doorswhichalsoserve as inlets for replacement air; and ducts which serve the HVAC/ACMVrole untilthey are needed as part ofthe SHEVS. These dual-role itemsfacethe challenge of having to meet all the requirements ofnormal use, as well asallthe appropriate requirements for thefire protection application.In otherwords,the specifier(and the regulator) must be satisfiedthat those items are 'fit for purpose' in both roles. It is notthe purpose ofthis chapterto be a comprehensivelydetailed guide to allofthe requirements ofevery last nut, bolt, and wire usedin a SHEVS.Neither is it an attemptto describe eachtest method. What followsis instead intended tobe an indication,for some ofthemajorcomponents ofa SHEVS, ofsome ofthe factors whichneed to be considered ifthe installed system isto be 'fitforpurpose'.

ofthe SHEVSisto protectlifesafety (egby protecting escape routes), and that it should be the responsibilityof an enlightened buildingmanagement to carry outsuch tests. It has already been noted in section 13.1 that such tests are unlikelyto bedone ifeachtime thereis a

13.2 Natural smoke and heat exhaust ventilators 13.2.1 Time takento comeintofull operation WhenaSHEVSisrequiredto come intooperation, itwill usuallybeanurgentneed.Part ofthe designand specificationprocess should be to decidewhichsequence ofoperation ofthe differentitems ofequipment will be needed so as to avoid one interferingwith another. At the same time, wecan recognizethatveryfew real fires are likelyto grow explosively, and iftheydo then a SHEVSis not appropriate to cope with anexplosion!It seems a reasonable compromiseto suggest that the entireSHEVS should come intoitsfullyoperating statein atime ofnot more than one minute from the initiatingsignalbeing generated (whether byhuman orautomatic means). Natural smokeand heat ventilators only operate to pass smoky gaseswhenthose gasesbuild up beneath them.Therewill be no clear adverse effectson the rest of the system iftheytakeas long to open fullyas the restof the system takes to deploy intoits fire-operationalstate. It follows thatit is reasonableto allow a maximumtime of one minute for the ventilator to open fullyto itsfire-open position. This maximum time should apply,however, regardless oftheforces or temperatures towhichtheventilator mightbe exposed,and so this maximum time must be satisfiedas a 'pass' criterion in allthosetest methods for otherparameters wheretheventilator is required to open as part ofthe test. Most ventilators availableon the market open in much shorter times than oneminute, so this isnot an onerous criterion. It is notadirectlife-safetyissue ifthe ventilator cannot close as quickly.One should,however, consider whether the ventilator will befaced with a requirement for repeatedfunctionaltesting duringits installedlifetime.It is theopinion oftheauthors that suchregular and frequent testing is highly desirablewherever the purpose

significantcost (intime, effort,or inconvenience). Consequently it is felt thatall ventilators specifiedfor use in a SHEVShaving alife-safetyrole should be capable ofbeingclosed automatically,on receipt ofa signalfrom the control panel. Thetimetakento close is less critical,and could wellbelonger than one minute. An additionalfeature essentialto allventilators except those intended for use in manuallyinitiated systems,is that theventilator should open (ie should 'fail-safe') whenever there is a loss ofpowerto the usual opening mechanisms.

13.2.2 Coefficient of performance

Thepurposeofa natural ventilator istoallow smoky gases toflowthroughitfrom insidethe buildingto the outside.Its abilityto do this obviouslydepends on the sizeofthe opening(known asthe geometric free area) and on the resistanceto flow ofthat opening including any turbulence-generatingfeatures within it (egsprings, rods,louver blades,etc.). The geometric free areais easily determined by simple measurement ofthe sizeofthe opening inthe plane wherethe ventilator is fastened onto thebuilding.Anolderbut less usefuldefinitiontookthe narrowest part ofthe flow-path through the ventilator. This canbe difficult tomeasure, and whencombined with the measured coefficientofperformance (see below) leads to the same practicalresult. The only significance ofthe olderdefinitionshould be that everyone concerned should be aware ofthe possibilityof confusion!The resistancetoflow isless easy, and requires atest ofthe entireventilator (except wherethere is a sufficientcollection ofexistingmeasurement dataon similarventilators for an assessmentto be made— possibleon only afew ventilator shapes). Suchtests canbe done bydrivingair at ambient temperature through the ventilator bya measured pressure difference,orbyusinga thermally buoyant hot gas layer to simulatethe firecondition. Current tests use the former method, while the latterhasbeen demonstrated experimentallyas being feasible.We then havethe followingrelationship:

Ap=

''V2 2(CA)

2

(13.1)

where:

= pressuredifferencebetweenthefront ofthe

ventilator (ie insidethe building) and the back (ie outsidethe building) (Pa), = p density ofthe gasespassing through theventilator (kg m3), V = volume flow ratethroughthe ventilator (m3 sd), = geometric free areaofthe ventilator (m2), = coefficient ofperformance.

C

13 Selection ofequipment Note: The product

Area.

is know as theAerodynamicFree

Thecoefficientofperformance is also known asthe dischargecoefficient. It isa measure ofthe efficiencyof the ventilator's design,highervaluesindicatinga higher efficiency. Ausefulbenchmark is the well-known value for a simplehole in an infiniteplanebaffle, for which C,=0.6.Carefulshaping oftheflowpath throughthe ventilatorwill leadtohighervalues,while turbulencegenerating devicesinthe gas-stream will reduce the value.

It is known (see egsection 10.8) that a side-wind

blowing across the outletfrom the ventilator can increase the flow resistanceand leadto a reduction in the value. Thebetter testmethods include a wayofmeasuringthis effectbyrotating theventilator in a selectableairstream (simulatingthe side-wind) while the aerodynamicfree areais being measured. Such tests usuallyrequire that the worst (ie the lowest) valueof correspondingto the worst combination ofside-wind speedand direction must be cited bythe manufacturerand/orsupplier as beingthe appropriate valueforuse indesign calculationssuch asin section 5.11. It is commonly foundthatventilators having kerbs (see section 10.8)and no parts projecting above the plane of the outletopening (ie above thetop ofthe kerb) do not suffer adverse problems from side-winds.Ventilators having a singleflap which rises above the opening in the fire-operational position can cause catastrophic problems to the coefficientofperformance,with or withouta kerb present.

C

13.2.3 Resistance to heat

Anatural smoke andheat exhaustventilator canbe expected to experience exposuretothehotgases passing through it. In general,however, one doesnot expect the operating mechanismsto be ableto surviveexposureto heat— theventilatorwill be expected to openwhile the firehas onlyjustbeen detectedand is still small. The exceptionto this concerns ventilatorsdesigned to beused in applicationswherethe SHEVSwillbetriggered manuallyrelativelylate in the fire. These latter ventilators must beableto withstand considerable exposureto heat while remaining closed,andyet stillbe able to open satisfactorilywhencalled uponto do so. Relativelyfew existingdesignsare suited tothis combinationof circumstances. Withthis exception noted, we canstatethat the important heat-resistingproperties ofaventilator should all apply whenthe ventilator is already open. Theventilator must not reduce its aerodynamicfree areawhensubjectedto a throughflow ofhotgases. This must be demonstrated by the test method. The ventilator must not allowhot or burning parts or flamingdroplets to fall ontopeople orobjects belowthe smokelayer since this could result in injury or in secondary fires. This requirement also concerns the safety offire-fighters,who should notbe endangered by, forexample,hotplasticpartsfallingon them.

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Theventilatormustnot cause the hot gasesemitted from it toplayonthe roofsurfaceoutsidethe building since this could cause secondary fires. Similarly, the outsideofthe ventilatorbodyshould notbecome

sufficiently hotto threatenthe rooftowhichitis fixed.

13.2.4 Openingunderload:snow Snow comes inmany differentforms,depending on the

proportions ofice, air, andliquidwaterinthe mixture.In general,older, more compacted snow willbe denser, although partiallythawedsnow can alsobeverydenseas waterdisplacestheoriginallytrapped air. Withthepossibleexception ofventilators designed for manual triggering,weexpectthata SHEVS will come into operation very early in the fire. It followsthatit isnot reasonableto dependonthe heatofthe fire gasesinside the buildingmelting enough snow above the ventilator forittoopen despite a relativelyweak opening mechanism. Therequirement fora natural ventilator is thatit should be able to open successfully, evenwhenit is covered on the outsideby alayer ofsnow.The depth and density ofthat snow will vary with the location andthe season,as wellas being subject to the usual random chance ofweather. in practice this is not such a problem as it might seem becausethose countries andlocalities wheresnow loads might be aproblemwill already have theirown Codes forstructural loading with designlimits for theexpected snow loads.Theselimits cansimplybe adopted forspecifyingthe appropriate load Classfor ventilator operation, as proved byan appropriate test. Note that ifa ventilator is designed tobe mounted on sloping surfacessteep enough that snow cannot build up, thereis no needto testforthis parameter.Aminimum slope of45° should ensure thatnosnow will build up on

the slope. Onthe otherhand, theremaybeobstacles on a roof (egstructures for lift machinery,chimneys)whichcan cause considerablyhigh and dense packagesofsnow due tosnowtransport bywind.In theselocations ventflators must not be installed. 13.2.5 Opening underload: side-wind

It has beenstated in section 13.2.2thatparts ofa ventilator whichproject intoa side-windblowingacross

the ventilator canaffectthe measured coefficientof performance.Ifsuch apart (eg aflap,or the dome ofa domelight) hasto open againstthe wind direction,it may bepossiblefor the force ofthat wind to prevent it from opening fully (even ifthereis alockingmechanism to holdthe partin place onceithasbeenfullyopened). It follows that the ventilatorshould have been testedwith a real or simulatedside-windto ensure thatits opening mechanismis strong enough to function properly.One canexpectthatthis is nota problem for any ventilator withoutany moving parts projecting intothe external wind.

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Design methodologies for SHEVS

13.2.6 Low ambienttemperature Whenanypieceofmachinery is cooled,parts made of differentmaterials contract at differentrates, and lubricating oils and greases tend tobecomemoreviscous. This is obviouslyalsotrue for natural ventilators.Thereis a chance that abadly designedventilator, ifcooled sufficiently, may require a much larger force than usual to open to the fullyfire-operationalposition. Thereis evena chance thatmoving parts ofthe openingmechanism mightfail to clear other parts ofthe ventilator,which mightthen jam.Ofmore specificconcern to those ventilators powered byhigh-pressuregas cartridges is the fact that the pressure in the cartridgewill fall at lower temperatures. Itwill usuallyneedaconsiderable dropin temperature before these factorsbecomeimportant. Lowvaluesof ambient temperature occur in many northerncountries, and evenin northern Scandinaviathere are some unheated buildingsusedfor storage. Consequently,depending on the climaticconditions expected forthe localityofthe building,the specifierand regulator should satisfythemselves that the selected ventilators are capable ofopening satisfactorilyat the lowest temperature likelyto be experienced.

13.2.8Abilityto resistwind suction Natural ventilators should neverbeexpected to operate

13.2.7 Reliability Anyventilator must be made ofmaterials expected to keep theirproperties for the expected lifetimeofthe SHEVS.This is primarilya matter for designby the manufacturer.

Perhaps more important istheneed to be surethatthe SHEVSwillworkwhenneeded, however many years might have passed since installation.This implies aneed for regular maintenance by appropriately skilled personnel, perhaps most often satisfiedby some form of regular servicecontract. Wherethere is a high dependence on successfuloperation, suchas wherethe purpose ofthe SHEVSis to protectlife safety,it will usuallybedesirableto havea regular programme of functionaltestingaspart ofthe responsibilityofthe building'smanagement,in order to identifyfailures as theyoccur and to replace faultycomponents. Whereversuchaprogramme isenvisaged,itwill be necessaryto specifyventilators (and other equipment) whicharedesignedto survivethe number ofopen/close cycles expected over the lifetimeofthe installation.This reliabilityshould have been confirmedby arepeatedoperation test, wherethe ventilator's own opening and closingdevices havebeen used(perhaps with aseparate external sourceofpower) for that number ofcycles.For example,ifthe expected programme isforweekly operation over a20-year lifespan,the minimumnumber ofcyclesbecomesmorethan 1000. Ifthe ventilator is intended to be usedfor day-to-day comfort ventilation, closingwhenever itrains (as is one applicationin practice) the minimum number ofcycles can be much greater still.

in positionswheretheymay be exposed to wind-induced overpressures.It followsthat theywill only normally experience wind-induced suctions.Ifa ventilator can be forced openby thesewindforces whenit is supposed to remain closed (ie whenthere is no fire),itwill become an embarrassment to the building'smanagement and there is astronglikelihood that it will be fastened shut permanently. Natural ventilators should be ableto withstand the largest suction force expected for the location on the building,and forthatbuilding'sown location. Wind forceshavebeen well researched over the years in view oftheir importance forstructural windloadinginthe designofbuildings91'921, and appropriate values ofwind force canbe adopted from these sourcesto identifythe appropriate Classofventilator.Itis important that any ventilator specifiedhas been tested for its abilityto remain closed underthe applicationofthe appropriate simulatedwindibrce.

13.2.9 Abilityto resistrain penetration ManyapplicationsofSHEVSwill be in circumstances wherethe ventilatorsmust not allow any rainpenetration in normal everydayuse. This doesnot matterduringthe emergency circumstancesofa real fire, but one does not want theventilators to be covered over bysome sortof fabricto stop rain penetration (as has happened). It follows that the abilityofaventilator toresist rain penetration can have safetyimplications,as well asbeing practicaland cost-related. Anadditional feature whichcanbeconsidered for ventilators intended to be usedfor day-to-day comfort ventilation is arain sensor,whichautomaticallyclosesth ventilatorswhena sensitivesurfacedetects water. It is, of course, necessaryfor the rain sensor to beexcluded from thecontrol algorithm whenafire isdetected.

13.3 Poweredsmoke and heat exhaust ventilators 13.3.1Time takento comeintofull operation As fornatural ventilators,powered smokeand heat exhaust ventilators (almostalways this means fans, although other devicesare possible)must fit intoa SHEVSdesignwhichallowsthe entiresystem to come intofulloperation quicklyoncethesystem has been initiated. The only complicatingfeature withfans is that they usuallyhave amuchlarger starting current than when running atfull speed, and this often requires that the fans bestartedin sequence,ratherthanall at the same time. In orderforthe entiresystem to be operating within one minute,this means thatindividualfans haveto bequicker in running upto Eill speed. Amaximum timeof3O secondshasbeen suggested as being appropriate,and should represent the 'pass' criterion in all testsof individualfanswhichinvolvesfurtingthe fan.

13 Selection ofequipment 13.3.2 Resistance to heat Inthesame wayasthe natural ventilator,the fan must be able to continueworking for long enough forthe SHEVS to achieve its designpurposes,whenexposed to the expected gas temperatures passingthroughit. The design conditionsforthe exhausted gasescan vary from below 100 °C toflame temperatures, depending on the purpose ofthe design. Consequentlymosttest methods will identifyclasses,eachofwhich isacombination ofgas temperature and exposuretime. Examples include '200 °C for 2 hours', '300 °C for 1 hour','600 °C for 1 hour', and many more. In practice, different combinations have beenrequiredby differentregulatory authorities in differentcountries.Thereis noapriori universally correctcombination,but the choice should be dictated by the designcalculationswith ofcourse a good safety margin for the time inview ofthe usual uncertainties in time-dependent aspects ofthe design calculations.

Othersecondary aspectscanbeimportant, eg the external casing ofthe fan should notbecome hot enough to igniteanythingin contact, andwherea separate coolingair supply isusedfor the motor it should notbe hotenoughto ignite (or dischargedin aplace where ignitionofany)nearby materialsmightbepossible. 13.3.3 Opening underload: snow Manysmokeexhaustfansare mountedwith their exhaustspointingupwards. Sometimestherecan be otherdevicesto close theexit from the fan.Someofthese maysimplybe flaps whichareheldopenbythe force of the exhausted gases. Others maybe similar to the

automaticallyopening natural ventilator mechanisms. Forallofthese thereis thepossibilitythat snow may accumulateonthe exhaust ofthe fan, or even fillthe throatofanunprotectedfan. As stated in section 13.2.4, one cannot dependonthe heat ofthefiregasesto melt thesnow —theSHEVSmust operate earlyinthe fire whenthe gasesbeingexhausted willbebarely above ambient temperature. Thesnow load whichthe fan must overcome canbe selected in the same wayas fornatural ventilators (see 13.2.4 above), andmustbeappropriate forthe location of the building.Theselected fanfor any applicationshould havebeentestedandpassed in aClasssuitable forthat location.

13.3.4 Opening under load:wind Fansarecommonly specifiedwherewind overpressures

areexpected onthe roofofbuildings.Sometimesthese pressures canbelarge.Fans fitted withdevicesto close the exhaust opening whenthe fan is not in usewill need to be able to overcome thedynamic pressuresofthe wind.Wherethis isrelevant to aSHEVS design,the fans must be specifiedasbeing able to open to the filly operating position inless than 30 seconds againsta load simulatingthe wind pressure.

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13.3.5 Low ambienttemperature Theproblemfacing afan in low ambient temperatures is essentiallythe same as for natural ventilators.The solution is alsosimilar,in thatthe ventilator should be shownby asuitabletestto beableto operate fullyin less than30 seconds in ambient temperature conditions appropriate to the location ofthe building.

13.3.6 Reliability Thesame argumentsinfavourofregular functional testingapply to fans asto natural ventilators when usedin aSHEVS.Itfollowsthatthe fan should havebeentested for an equivalentnumberofstart/stopcycles compared withthenatural ventilator,for asimilaruse.

13.4Automatic smoke curtains 13.4.1 Time to deployto the fire-operational position Automaticsmokecurtainsservetwo mainroles.They canprovide partofthesmoke reservoir's containing boundary, or they can channel the smokeflow while the smoke is en route tothe reservoir.Ifthe SHEVSis to reachits full operating condition in one minute, thenthe curtainscan takeupto that one minute to deploy.

13.4.2 Speed offall of bottombar Ifa curtaindeploys too quickly,itsbottombarcanreacha relatively high velocity and represent adanger eitherto someone whose head is inthe way, or to the fixings holding the curtain tothebuilding'sstructure ifthe curtain reaches its full extension and stops withajerk. Thecurtain needstobedesigned in sucha waythatitwill notdamageitself even ifthe designcalculationsof section 5.8 leadto the specificationofaveryheavy bottom bar. Inmany designsthis is achievedwith a frictionbrake, and with the curtain fallingunderitsown weight.It is important that the test on the curtain allowed for the heaviest weights which might occur in the design ofthebuilding'sSHEVS. Onecannot simplyexpect a curtain mechanism that worked with alightbottom bar to be equallysuccessfulwith aheavy bar. Themaximum allowablespeedto avoid injury to people is more difficult to assess. Many curtainswill beso designedthat they never reach head height, and so this criterion is notrelevant to them.Othercurtains, suchas thoseintended to close offa higher storeyfrom an atrium, carry agreaterrisk. Thereis no clear guidanceon howtotackle this problem. Beingstruckbyaheavy bar travellingateven 1 m could be dangerous.Perhaps the bestcompromise isto allow the curtain to fallatupto 1 m s1, but to designthe positions ofthesecurtains in order to minimizethe exposureofpeopleto this risk. 13.4.3 Resistance to high temperature It is generallytruethat smoke curtainsshould be ableto survivethe temperatures towhichtheywill be exposed, as predicted bythedesign oftheSHEVS. Thatis, the curtain should beabletocontinue to fulfil itsfijnci:ion as a barrier to the movement ofsmoke.It doesnot matter

84 from asafety pointofview ifthe mechanisms which deploy the curtain are destroyed, as long asthe curtain remains functional andinplace. Typical temperatures ofgases in contactwith the curtainswill rarely exceed 200 °C in most reservoir applications.Typical temperatures experienced by channellingscreens could be higher, perhaps approaching flametemperatures, whichcanbe pessimisticallytaken(ie ahigh value) tobe about 600 °C

and above.

A differentargument canbe put forward,thatifthe gasesin a smoke layer in areservoir reachtemperatures whichwill cause radiativeignition ofmaterialsaway from the originalseatofthe fire, the entire compartment is about to flash over. Once this has happened the firewill be much larger thancanbe controlled bythe SHEVS, andso the subsequentfailureofthe SHEVSiseffectively irrelevant:it will already have failedto meet its design purpose. This pessimisticargument suggests thatthe highest temperature gases that asmoke curtain can usefullybe expected to contain in most cases willbe about 600 °C. Consequently thisis a common upper temperature limit in tests on smoke curtains. Therewill alwaysbe some applicationswherecurtains may be exposed to higher temperatures (egifacurtain is usedto close offan otherwise open shop front) andthe fire could belocatedvery close tothat curtain. Fortunatelysome newcurtain materials appearing on the market are ableto withstand the full fire-resistance heating curve usedin furnacetests (although notmeeting the insulationrequirement for fire resistance),and canbe regarded asblurring the distinction betweensmoke curtains andlightweight fire shutters. 13.4.4 Reliability Thesameargumentsapplyto the advantagesofa programme ofregular functional testing, as applied to the natural ventilators.Forthesame reasons,wherever such a programme is envisaged,the curtainsmustbetestedfor their abilityto remain functional after the appropriate numberofdeploy/closure cycles,which should in principle be the same number asforthe ventilators, althoughthe additional number oftest cyclesfor ventilators intended to provide everyday ventilationneed notbe taken intoaccount for the numbers oftestcycles for smokecurtains. As withtheventilators,it is ofgreatimportance that curtains intended to meet the needsofsuchaprogramme canbemotoredbackintotheir'concealed' positions easilyon receipt ofa'reset'signalfrom the control panel. Hencethecurtains usedin the reliabilitytest should use their ownon-boardmechanisms,to close as well as to open. It isalso important fortheheavier curtainsthatthe reliabilitytest should have been done on equivalently heavy curtains.

Designmethodologies for SHEVS 13.4.5 Fail-safe

It is important thatall smoke curtains specifiedfor the

SHEVSshould be designed to deploy intotheirfireoperational position whenthesource ofpoweris cut off forany reason. This isperhapsthe main reasonwhy manydesignsusegravityto deploy, slowed and controlled by afriction device.

13.5 Air inlets and doors Inlets for replacement air havetheadvantage that they oughtnever to be exposed to high-temperature gases.

Thereis alsothe disadvantagethatat thetime ofwriting there is no specifictestforairinlets required for SHEVS. Thefunctional requirements fordoors and inlets can be identifiedas being thefollowing. Thereisa needto open fullywithin thesame1 minute as the entire SHEVS. WheretheSHEVSusesapowered exhaust, the doors/inlets need to be ableto openbefore any ofthe fans havedeveloped an appreciableexhaust flow, otherwise the fans could developa significantdrop in pressure insidethe buildingwhich might prevent the inlets from opening. In practice, this maymeanthat the doors and/orinletdevices must be able to open within 2 or 3 seconds ofreceipt ofthe signalto open.

• •

13.6 Smoke dampers Asmoke damper is a deviceusuallyfitted intoaduct, but possiblymountedontothe duct opening intoaroom,or

servingto redirect air flows from one duct path (egfor HVAC/ACMVpurposes) intoanother(egfor smoke exhaust). At thetime ofwriting,there areno clearlydeveloped publishedStandards forsmoke dampers, although there isanUnderwriters' Laboratory Standard931. Some performance requirements can, however, be identified. Thedamper must be able to move intoits fireoperational position fastenoughto allowthe SHEVSto meet its 1-minutetarget. Note that some dampers will have to move from opento closed positions, whereas otherswillhaveto move from closed to open. Thedamper must be able to withstand theanticipated gas temperature towhichit is exposed, and simultaneouslythe pressure differencesto whichitwillbe exposed,without moving from thefire-operational position. When openinthe fire-operationalposition, the damper must not fail byincreasingthe flow resistance. Whenclosed,itmust not allow increased leakage;the leakagepast aclosed smoke damper must be minimal. In many designs,the fire-operationalposition ofan individual damper will depend on the detectedlocation ofthefire.Insuchdesignsthere canbe nofail-safe position forthe damper.Consequently,thedampers for such designswill need an unusuallyhighlevel of reliability. This places even greater stress on the importance oftestingthe damper throughalarge number ofoperating cycles.

13 Selection of equipment 13.7 Smoke ducts

A smokeductis a ductintended to carry smokeaspart of a SHEVS.Thereareno specifictestStandardsforsuch ducts atthe time ofwriting, although aduct which meets

therequirements offire resistance canbeexpected to be satisfactoryforsmoke ventilation.Thislevel of specificationis necessaryforthose ducts which pass throughfire-compartmentboundaries since the duct mustnowserve effectivelyas an extension ofthat

85

boundary andshould bebuilttothe same requirements as thatboundary. Notethat theductmust be able to survive hottemperatures inside the ductand cold outside, and alsocold inside and hotoutside (where the duct is exposedto afire in the next compartment). AlesserStandard isreasonable for ducts whichare designedto be wholly immersed in a smokereservoir since theirfailureifthe gas temperature passes600 °Cwill be nomoresignificantthanfor thecaseofthesmoke curtain mentioned above.

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14 Installation

Whenthe SHEVShas beendesigned,the equipment needed to implement that design has beenspecified,and that designhasbeendeemedacceptable in principleby the RegulatoryAuthorities, thereremains thetaskof installingthe equipment intothe buildingfor which it is intended. This stephas provided many examples oferror in practice. It is notthe roleofthe current bookto provide a detailed descriptionofallthe procedures necessaryfor successfulinstallation.Nevertheless,a discussionis presented in outline form to alert the readerto some of the more important aspects. Whilea system may be installed bya singlecontractor, it is morecommonlythe casethatmany ofthe individual pieces ofequipment will be fitted byspecialist contractors. For example,the smoke curtainsmaybe installedby a differentcontractor to the ventilators;or whereuse is madeoftheHVAC/ACMVsystem as partof the SHEVStherewill alsobe adivision ofresponsibility for differentequipment. The possibilitiesfor confusion aremany. Itis important that there should be a single contractor responsible for co-ordinating the activitiesof every participant in the installationofthe SHEVS. Itis important that this co-ordinating contractor should be experienced inthe fieldofSHEVS design and installation,and that its personnel involvedshould fully understand the concept design in all its aspects.This can be expected to be the case where the co-ordinating contractor is also the designer ofthe system; but where this is not thecaseit is important that the co-ordinating contractor should liaisecloselyand frequentlywiththe designers ofthe SHEVSconcepts. Therehave been many exampleswherelatearchitectural changes have adverselyaffectedtheeffectivenessofthe SHEVS without the installershaving realizedthatthiswas the case.

It is, as has beennoted, often the case that thepeople who developed the 'concept design' donot continue with theresponsibilityto turntheirconceptintophysical reality. It istheresponsibilityoftheco-ordinator ofthe installationprocess to ensurethat: all the separate components are compatible, all the connections are correctly specified,and the specificationsofthe equipment areappropriate to the designconceptand to the circumstancesboth of

•• •

the buildingand ofthe location ofthebuilding. Theparameters identifiedin Chapter 13, and the results oftesting onthe differentproducts, areespecially important. It is particularlyimportant here that the proposedmaintenance and re-testing regime should be establishedprior to specificationofthe equipment. This will allow the correct specificationofequipment interms ofthe 'reliability'test (seeChapter 13) and in terms ofthe abilityto deploy/returnequipment easily usinga remote manual signal in order to ensurethat routine functional testing is easy, and willnot cause excessivewearinthe system. Easeofreplacement and/or maintenance of faulty components mustalso be bornein mind; eg it would beunwise to locate a smoke detector inthe middle ofa large areaoffragile glazed ceilingat thetopofa multistoreyatrium. It is the co-ordinating contractor's responsibilityto ensure that the control sequence allowsthe different parts ofthe system to comeintooperation without impeding or overloadingother parts. It is his/her responsibilityto ensurethat allinterconnections with the non-fire buildingsystems (eg with the HVAC/ACMV system),and with the other essentialfire safety systems (eg the smoke detectionsystem) have been considered and properly specified.In short, it ishis/her responsibilityto ensure that the design concept is implemented correctly. Ifthe installersofthe SHEVS areto be sure ofsuccess, theyneedftll and sufficientinformationon all the equipment usedin the system.Therefore, all suppliers mustgivethe necessary informationon recommended methodsfor fixingcomponents, forelectrical wiring,for operating instructions,andfor recommended commissioningprocedures fortheir particularproduct. The suppliersshould also givefull informationon the important parameters forlinkingtheir productto others, egby givingrecommended maximum and minimum pressuresin pneumatic lines needed to provide operating energy for aventilator.Not only the technical detailsof theproductand therecommended methods of installation,but alsothe limitsthereofneed to be defined. Itcanbeseen from the above that thereneeds to be a continuing liaisonbetweenthe installer and the creatorol

14 Installation the concept. It is usuallyamistaketo assume that a design canbe boughtfrom one consultantand installedby another withoutany continuinginvolvementofthe first. Itis even worse to assume thathaving bought the concept, the developer only needs to employ specialist contractors with no co-ordination atall for installation. Many examples existofallthese faults, whichusually derive from abeliefon the part ofthedeveloper or his/her agents thatfire is a simplethingwhichdoesnot require the continued applicationofspecialist engineeringexpertise. Someaspects ofinstallationhave a directbearing on safety,as well asonthe successfuloperation ofthe complete system. The positioning ofventilators and ducts presentspecialproblems, and special attention needstobe given to thefollowingdetails. Ventilatorexhausts (natural or powered) needtobe positioned so that the hot gasesemitted from them will notbedeflected onto the rooforwall surfacesclose to theventilator.Allgases emitted should bedirected away from the building'sstructure. Combustibleparts ofthe roofstructure adjacent to smoke ventilators needto beprotectedas flamescan ignitethe vulnerablezonearoundtheventilator.Itis suggested that protection should extend atleast0.5 m aroundtheventilator. Combustiblematerials,whetherstructure, linings, or surfacefinishes,should similarlybe protected where theyareadjacent to ducts which areintended to carry hotsmoky gasesthrough a compartment or outside

•

• •

wall.

• The free areaofa natural ventilator needsto be free of obstruction above and below the

ventilatorfor atleast 2 m in orderto avoid increasingthe flow resistanceof thatventilator, exceptwheresuchan obstruction has beenexplicitlyincluded inthedesign calculations. Thiscanrepresentasignificantconstraint on structural features nearventilators. Theoutletofapowered ventilatorand/oritsductwork must be free ofany obstructionsover a distanceof1.5 times the diameter ofthat exhaust outlet.Thisis also intended toavoid thecreation offlowresistances which mightincrease the back-pressureonthe fan and hencereduce thevolume flow rate ofthe exhaust. Wherewinddeflectorsarefitted to avoid wind overpressureproblems on natural smokeexhaust ventilators,butthosedeflectors do notform part ofthe ventilator itself,careshould be taken to ensure that

• •

snow (where climaticallyrelevant) cannot collect and create a greater snow load for the ventilator to overcomewhenopening. Care should alsobe taken to ensure that anysuchdeflectorswill not experience wind-drivenresonantvibrationwhich can accelerate fatigue and early failureofthe deflectors.

Whereemergency power suppliesmust be installedto back-up the powersupply for the SHEVSin case of failureofthe Mains powersupply,specialattentionmust begiven to correctlabelling ofequipment and switches,

87

andto the provisionofprotection from damage (mechanicalor byfire)both forthe power supply andfor all ofits connections totheSHEVS.The objectivemust beto ensurethat theback-up supply cannot be prevented from operating whenneeded. Switchingbetween main powersupply and emergency powermust beautorriatic, and sufficiently fastto ensure that theSHEVS continues to fulfil itsfunctionwith no risk tothebuilding's occupants orto the SHEVSdesignobjectives. The worst caseforback-up power supply is whenthe Mains supply failsatthe start ofthe fire. Consequently, the emergency supplypowermust be designedto fulfil its duty duringtherequired operation time ofthe SHEVS. The same level ofprotection andlabellingmust be giventothe electrical cablingaswell as to the control panels.The manual controls must be located outsidethe smokereservoir andmustbereached easily,in sight ofa safe accessdoororroute. Wherethe SHEVS is designed to be triggeredby a manual fireman's switchratherthan by an automatic method, themanual controls must be locatedoutside thefirecompartment servedby the SHEVS,and must be on the primaryaccess route planned foruse byfire-fightersentering the building.This istoallow the SHEVSto remove any threatofbackdraft before any fire-fightershaveto enterthe affectedfirecompartment. Ductwork forming part ofthe SHEVS must belabelled clearlyas suchandthe hangers mustbeconstructed in such a waythat the duct system will stay in place forthe required operation time. It should notbe forgotten thatin some circumstancesthe hangers aswell asthe duct may be exposedto hotgases, and so theyshould becapable of surviving the expected smoketemperatures. Another occasionalmistake involvingducts is tofail to make allowanceforthe thermalexpansionofthe ductwhenit is exposed to hotgases. The expansion ofa duct constrained atboth endswillusuallyleadto a splitinthe duct. Whensmokedampers areinstalled,aremovablepanel or grid should provide easy accesstothe activator and damper blade. No element attached to the smokedamper should obstruct the properfunctioningofthe damper blade. It isgoodpracticeto selectdampers which make it easy to see the position ofthe damper, directly,byan electrical indication,orby amechanical pointer external to the casing. It has beenacommonmistake to fit dampers in inaccessiblelocations, often obscuredby otherequipment or structure, in such a waythat it is impossibleto assesswhetherthe damper has operated satisfactorilyor not. This canmakeboth testing and maintenance checks extremelydifficultto do, and therefore less likelyto bedone. Air inlets areneededforagoodsmokecontrol installation.These are normallylocated at low levelin ordernottodisturb the smokelayer in the reservoir. Thereis a realisticchance thatblockingthe airinlet will occur ifpositioning (eg inthe sidewall) isnot designed carefully. Controllableinlets, includingautomatically opening doors wherethese form part ofthe air inlet

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Design methodologies for SHEVS

provision,mustbe connected to the emergency back-up power supply. Wheninstallingsmokecurtains and particularly automatic retractable curtains, special attention needsto be givento the maximumgap betweenfabricand structure, and betweenadjacent curtains whereseparate curtains are combined to form alongrun ofcurtain, when inthe deployed position. Ideally thereshould be no gaps at all.This is notpracticable,although whereadjacent curtainsform a straight run it is possibleto overlapthe curtains,and to clip togetherthe bottombars, in a way whichminimizesthe leakage gap betweenthesheetsof fabric. It is more difficult to reduce the size ofthe gaps betweenthe edge ofa curtain and the adjacent structure. It is moredifficult still toreducethe gap size wherethere is ajunctionbetweentwocurtains whicharenot aligned, although inthis case the effectsofbuoyant deflectionof the curtains in opening upthe gap can be reduced by using aheavier bottombar. Thelarger the gap the more smoke willleakthrough, and the worse the effectwill be on the nominallysmoke— freeside. It is possible,thoughdifficult and beyond the scope ofthe current book,toestimate the movement and rate ofbuild-up ofsmoke onthe side supposedly clear of smoke.The problem iscomplex, and depends on the air movements and on the volume ofthe space the leakage of smokeis entering, as both factorsinfluencethe dilution of thesmoke. What is safein onecircumstancecanbe dangerous in another. Atthetime ofwritingthereis no consensus on the safe limitsto suchgaps, although it

is suggested hereinthat the pragmatic approach canbe adopted ofassumingthatthe total areaofall suchgaps may not exceed 1% ofthe total curtain surface. These gap sizesare sufficiently smallthatthey arevery sensitiveto the detail and quality ofthe work ofthe installers,indicatingthe essentialtaskofthe co-ordinator in checkingthat installationhas beendone satisfactorily. Other important decisionsrequiredoftheinstaller concerns the specification,design, location, and ergonomic layout ofcontrol panels, bearingin mind the requirements ofthe Fire Serviceas well as ofthe building'smanagement.Somefurther detailsare included

in Chapter15. Lastly,and very importantly,theremust be a set of detailed engineeringdrawings (the Detailed Engineering Plan) showing the complete SHEVSinstallationas well as ofthe related systems. These latter canbe.expected to include the sprinklerand smoke-detection systemsin mostcases, and should also indicateall the control dampers in the HVAC/ACMVsystem whichhave arole to play during afire. ThisPlan should be prepared in advance ofany actual installationofequipment, and should be revisedduringinstallationso that it is at the end an accuraterepresentation ofwhathas beenfitted intothe building.These drawingsoughtto be made availableto the FireServiceaswell as tothebuilding's management, togetherwiththe SHEVSDesign documentation. It is cruciallyimportant that these drawingsshould be updated whenever any changes are made to the system duringthe building'slifetime.

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15 Acceptance testing (commissioning)

15.1 General Before handing overthe installationto the final user, afile

should be preparedby the installercontaining all relevant technicaldocuments, test reportsofthe individual components,as-built plans,set pointsand anacceptance report. The system cannot be commissionedwithout thesedocuments. Theas-builtplanshould represent thewholesystem, indicatingquantity, size and location ofthe ventilators,air inlets and other SHEVSelements,fixingofthe main elements (egductwork), location ofthe control panels, smoke dampers and theiraccess,labellingofthe whole and eventuallyindicatingtheprotective measures to mechanical damage.An electricalwire plan should be provided ifan emergency powersupply unitis installed. Thewholeconstitutesthe Detailed EngineeringPlan referred to in Chapter 14. It is an everydayexperiencethatwhat is builtis not always exactlywhatwas intended, anditwillbe necessaryto carry out commissioningtests on the system once it has been installed.These tests should include the followingitems (not an exhaustivelist). Reaction time ofthe SHEVSto open Airflowmeasurementsforpowered ventilators Simultaneousopening ofventilators and air inlet devices Eventualpneumatic leakageswheresuch power suppliesare used Reaction ofautomatic andmanual controls Start-up time ofthe emergency power supply Behaviourofthe automatic smoke curtains

•• • • •• •

15.2 Testingand commissioning

It isrecognized that requirements mayvary from country to country, and that occasionallycircumstancesmight

require ad-hocdepartures from the procedures. Hence the procedures inthis section areintended to bea guide ratherthana set ofrigidrequirements. Ingeneral, the checks and tests given inthe box opposite are recommended.

Testingand commissioningchecks

• • • • •

Designcheck Mechanicalcheck Control and actuation check Electrical check Runningcheck — Initial start — Functionaltest incontrol — Balancingand regulatingofairflow

Thefollowinginstrumentsand tools will very ofrcn be required: clamp-on ammeter, voltmeter, anemometer, smoketracer.

•• ••

Except for simple devicessuchas pitot-static tubes, inclined manometers, U-gauges and similar, all instruments,meters, etc. usedfor testing purposes should: be provided in duplicate, haveamanufacturer-claimedaccuracyofnot more thanplus or minus2%ofrange, be manufacturedto an appropriate standard or recognized equal international or national standards whereappropriate and available. havebeencalibrated by a recognizedtestingor calibrationlaboratory not more than threemonths priorto the dateoftest. The calibrationcertificate provided bythelaboratory should beavailableduring

•• • •

the test.

Design check

The as-builtlayoutshouldbe checked againstthe system designer's approved plans. Mechanical check Check the resultsofthe pressure test on the smokeexhaust-systemductwork whichshould havebeen carried out duringconstruction. Perform the mechanical check as per test procedure for fans and motorized dampers. Check smokezoneboundary and automatic smoke

• • •

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• •

curtain location accordingto approved smokecontrol designlayout. Check motorized fire smoke dampers are correctly connected, and that the smokeand fire damper blade andbearing rotate smoothly. Check that smoke curtainsdropdown smoothly and thebottombars stopatthe correctposition.

Design methodologies for SHEVS

•

indicate afault detectedon: — the signallingwire connectingthe control panel to the smoke extraction system control panel, or — the wiringothedetectors. All equipment servingthe smokeexhaust and complementary replacementair systemsshallbe provided with an appropriate emergency power

• Perform the electricalcheckasper testprocedures for fan and motorized supply.

•

Control and actuation check Check thatall systems automaticallyactuate and remain in operation until reset bythe testers, either manuallyorby activation ofacentral resetcontrol. Check thatwhenin 'fire' mode, all other building systemsconnected with the SHEVS are put intothe appropriate fire-operational state. Check thatmultiplexerorsimilar devicesdo not affect transmissionofactuating signalsfrom the automatic fire-alarmpanel forthe operation ofthe smoke exhaust systemsunless suchdeviceshave the approval or certificationofone ofthe testing authorities. Check that eachsystem is provided with amanual on/offcontrolswitch and indicator light at the master fire control panel. — Check thatswitches for all smoke exhaust/removal systemsare grouped in one areaofthe panel togetherwiththose for staircasepressurization systemsor similar. — Check that all switcheshave the same method/directionofoperation. — Check that adevice that senses effective operation oftherelevant smoke/airhandling system (ega centrifugalswitch oran air pressure switch) actuates the indicator lights. — Check that all switchesand indicators are clearly labelledto show operating positionsand systems served and stating thatthe controls shallbe operated only by authorized personnel.

•

• •

Electrical check Prior to the initialrunning ofanyelectricallydriven fan, the followingprocedures willbe adopted. Ina normal situation,all smoke and firedampers must be installedas per the designlayout. Foreachsimulatedposition ofthe firerecognized in the design scenario, thesmoke andfiredampers in the extract and supply systemsmust eithermove into, or remainin (as appropriate), theirdesignfireoperational positions. Should therebe a failure ofthe supply make-up fans (where includedinthe design) then only the supply system must shutdownandallsmoke andfire dampers on the supplyductmust returnto the design position. Theexhaust system shall continue to operate. Should therebea failureofthe powersupplyto the smoke andfire dampers, thesemust move intotheir fire-operationalpositions wherethese have been identified in the design scenario.Note that in some designstherecan be nofail-safe position. Both audio and visualwarnings must be provided to

• • • •

•

damper.

Runningcheck All systemsmust be completed and tested to ensure that theyarefunctioningcorrectly before the final full testand demonstration takes place.A full setoftest andfunctional operation checkrecords should be prepared, and may be required tobe submitted to the authorities.It is also recommended hereinthat the system designer should observethefull test and attach to the Report a signed comment confirmingor otherwisethat he is satisfiedthat the installation(s)areoperating in accordance with his design. Fulland complete records must be kept ofall tests and the resultsthereof typicallyincluding the items listedin the Boxbelow). Initial start Performthe test run as pertest procedure for fan and motorized damper.

•

Functional test incontrolcheck Check thatinterlock offans and dampers function properly. Check the properfunction ofremoteON/OFF operation.

• •

Balancing andregulatingofairflowshouldbe checked. Anyadjustments needed to achievethedesign airfiows should be made, andtheir effectivenessconfirmedby appropriate re-testing. This, however, doesnot guarantee that the control mechanisms,or the computer software,will correctly operate everythingin the correctsequences,orfollowing theappropriate logicwheredevicesmayhavemore than onefire-operational statedepending, eg on thelocation ofthe fire. It is desirableas partoftheacceptance test Itemstoinclude in a running checkrecord

• • •• • •• •

Recordsofpressure testing during construction Make,serial no.typeand owner ofall instruments used, together with acopyofthe calibration certificates Actual measurementstaken Resultingairfiows, current, belt tensions, shaft speeds, etc. Make,serial no. type and useofevery device checked, including rotational speeds, pressure drops/generation, etc. Date andtime oftests Signatureof operator/tester orsupervisor and anywitness for each test Signatureofdesigner confirming his/her acceptance

15 Acceptance testing (commissioning) procedure totrigger operation ofthe SHEVSbyinitiating a realisticsignal (for examplebyblowing asmallquantity ofsmoke intoa smokedetector) and thenconfirmingthat all ofthe desired actions have in fact occurred. Where differentpatterns ofactions are required forfires in differentlocations,all ofthese oughtto be checkedby simulatingdetection ofa fire in differentlocations or in differentways (the lattermightinclude break-glassfire alarm points, or simulatedoperation ofsprinklers,instead ofa smokedetector).

15.3Hot-smoketests There is amore complicatedoption: the Hot-Smoke

Test.Thisuses real fires in controlled conditions, inthe buildingasclose to completion aspossible,in order to provide aflow ofbuoyant smoky gaseswhichcantest not only the operation ofseparate components, but alsoto testin aquantitativemanner theproperftinctioningof the designconceptitself.In otherwords, to testthatthe properfunctioningofthetotalsystem hasbeenachieved. Variations on this techniquehavebeen developed in Australia94'951 and in the UK and BelgiumLS9961. Both

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methods use alcohol fires in view oftheirclean and predictableburning.The Australianmethod is restricted to firesdirectly beneaththefinal smokereservoir, whereas the BRE technique has alsobeen usedfor fires in sideroomswheresmokecan spillintoa larger mal].or atrium. Both use artificial smokesto markthe firegases andto make themvisible:the Australianmethoduses pyrotechnic smokegenerators;the BRE method uses oilmist generators ofthe type widelyusedin theatres and forfire-servicetraining. Hot-smoke tests arenot needed wherethereis confidencein the designscenario, and inthe design calculations.Theyare desirablewherever it is not possibleto feel suchlevelsofconfidence.A summaryof pointstobeconsidered by anyonecontemplating theuse ofhot-smoke testsis presented in Annex I. Wherethe commissioningoftheinstallationis checkedbyan independent body, detailsofthe testing body, the names ofits representatives,the test methods employed andthe results ofthose tests, as well asthe engineeringplan availableto thatbody, should all be mentioned inthe acceptance report.

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16 Maintenance, management and re-testing

Whatever the basic objectiveofthe SHEYS, itwillbe intended to thnction properly whenthe fire happens. Fires are essentiallyinfrequent events,whichcan occur in a randomway. It isvery unlikelythat thefirewill happen immediatelyafterthe system has been installedand successfullydemonstrated towork. Years might pass before the system is called upontowork, andthen it is criticallyimportant that the system doesindeed work as designed. Buildings will not remain static inthe intervening years, andthe usual forcesofcorrosion and decay can be expected to operate. Itfollowsthen, that aswith any otheractive system involvingmachinery,thereis a need forthe system to be maintained and servicedduringthese years.This places a major responsibilityonthe building's management. A regular checkon the system is essentialto ensure that itwill operateas designed,ifneeded. Also, intervention oftrained staffis sometimesbeneficialor even necessaryto achieve satisfactoryevacuation ofthe occupants inthe eventofafire. For example,calculations done at FRS L1001 haveindicated thatthe presence of trained staffto help withevacuation is ofgreatbenefit in large single-storeybuildings.It is difficult to ensurethat thereis acontinual training programme, particularly whenthe 'ownership' ofabuildingchanges. The bestwayto confirmthatthe SHEVS is workingas intended is to generate afire-detection signal (egby blowinga smallamount ofsmoke intoa smokedetector) and confirmingthat all the devicessupposed to operate actuallyhave operated satisfactorily. Ifthis is done regularlyitis more likelythat anymechanical or electricalfailureswillbeidentified in time for the fault to be corrected. It is also more likelythat anypoor maintenance will be identifiedintimeto becorrected. The optimum extentand frequency ofregular retesting ofthesystem will inevitablydependon circumstances.Systemshaving a crucialroleinprotecting life safetyoughtto be testedmuch morefrequentlythan those whichhave no suchrole. Even wherelife safetyis concerned, the frequencyoffunctional re-testing may vary. For example,itwould bedesirableto check the operation ofaSHEVS in a largeshopping complexat least once aweek, whereas in an office buildingit may be

moreappropriate totest it once a month. It maybemore appropriate for systemsintended forpropertyprotection to be testedonceayearin some cases.It can be expected that the RegulatoryAuthorities havingresponsibilityfor a buildingwill have a strong interest inthefrequency of functionalre-testing, especiallyifthe SHEVSis intended to protectthelivesofthe public. The building'smanagement will find theirtask much easier ifthey have been provided with fulldocumentatioi' summarizingthe designconcepts, in all the different scenariosconsidered, aswell as the 'Detailed engineering plans' and documentation recommended tobe provided bythe installer in Chapter 15. It isalso important that the key individualin the building'smanagement should be familiarwith this documentation,and should understand theideas involved.These documents, takentogether, form the basis ofa'log book' forthe SHEVS, and could usefhllybewidened to include all other aspects offire safety,although that goes beyond the scope ofthe

current report. The manager's taskwill alsobe eased ifthe installerha provided a 'maintenance file' as part ofthe logbookin which the management can record all maintenance, modifications,tests andtheir results,etc.,duringthe building'slifetime. The maintenance programme canbe subdividedin differentsections,in directrelation to the frequencyof checking.Notethatthe frequenciessuggestedhere are intended to beillustrative, and are certainlynot intended to beuniversalfor all applications!

Basic functional check (once a month) The component parts oftheSHEVS areoperated and people can see,hear or smellmalfunctioningparts: pressured air leakagesare quitecommon, a rusty spring canprevent natural ventilators from closingagain. All defectiveparts must be repaired or replaced immediately.

• •

Maintenance programme (oneper 6 months) On thebasis ofa maintenance checklist,all moving partsoftheinstallationwillbelooked at andreplaced

• • where Special attention is givento corrosion,mechanical necessary.

16 Maintenance,management, re-testing

•

damage,penetrations, blocked activators,overheated electricalparts. All parts are cleaned andrelabelled wherenecessary.

Full functionaltest(once per year)

After the maintenance tour, afunctional check must be worked out, possiblyattendedby a representativeofthe RegulatoryAuthorities,to seewhetherthe installation still complieswiththe acceptance report. This test starts with the triggering ofone or more detectors inthe testedzone and all subsequent automatisms (ie the actions whichfollow automaticallywithouthuman intervention) are checked out (reactiontime, emergency powersupply unit comingup, openingorclosingofdampers, lowering ofsmokecurtains, ...).

•

This test shall be activatedand the equipment resetfor every smoke control zone. Results should berecordedin the logbook.

Apartfrom themaintenance programme, a SHEVS management program needsto beset up. This means

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thatthe usermust verifythroughthe years whetherthe installedsystem is stillcapable ofdealingwith areal-fire situation. It is usuallyeasy to recognizewhenamajor structural modificationto abuildingwill influencethe functioning ofa SHEVS.Forexample,changing a workshop intoa high-rack warehouse willhavebig implicationsforthe design parameters ofthe SHEVS. It isless often realized thata successionofsmallmodifications,eachone seeminglytootrivial to matter, can cumulativelyaffect the functioningofaSHEVS. Itshould alsoberecognized that many buildingsspecialistswith noknowledge offire caneasilyfailto distinguishbetweenwhat is major and whatis minor.Whereas-builtplans,test reports and maintenance programs have beenkept fullyup-to--date,it is more likelythat changeswillbecorrectly identified, and that mistakeswill be more readily noticed and corrected. Notein this context thatthe building's managers share withthe RegulatoryAuthorities (inmost countries) the responsibilityforcommissioninga new SHEVSanalysisand re-designifthe building's modificationschange the assumptions and conditions whichwere appropriate to the originaldesign.

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17 Some common mistakes in the design of smoke ventilation systems

17.1 Mis-location of the point source of a point-source smoke plume Someofthe formulaeavailablefor the calculation ofthe mass ofair entrained intoa smokeplume risingdirectly

above a fire are derived for smallfires. When applied to fires which are not small(such asthose in real fire scenarios),they require a correction whichtreats the smoke as thoughit was risingfrom apoint (zero width) source at a distancebelowthe real fire which depends on the actual physicalsize ofthe fire. Severalguidance documents statethat it is acceptable to ignore this correction and to takethe plume height asbeingthe heightofthelayerabove thefloor (orthe base ofthe real fireifdifferent).However, suchan assumptioncan leadto an underestimate ofthe mass ofsmoky gases entering the smokelayer.For example,whenthe fire diameter approaches theheightofrise ofthe smokeplumethe mass ofair entrained into the smoke can be underestimated by more than a factor oftwo.

17.2 Inadequatespecification of smoke curtains Research by FRS has shownthat the existingdeflection

tests for smoke curtainsare virtuallymeaninglessin terms ofactual behaviour,and that it is necessary to bring smoke curtainsintothe designprocess97,usingthe procedures given inAnnex C. It is necessary tospecify thecorrectcombination ofcurtain materialweight and bottom bar weight to ensure that the curtain deflection remainswithin acceptable designlimits for the particular application.In general, the hotter and deeper the smoke layerbecomes, then the heavier the curtain and/or bottombar must be. This inturn canrequire major differencesin the components, egthecurtainmightneed stronger motors, stronger brakes and stronger attachments tothebuilding. Specificationofa smokecurtain which istoo lightfor theapplication canresult inexcessivedeflection,with accompanyingrise ofthe bottombar and leakage of smoke past the curtain. Another common mistake is to position smoke curtains which are lightenoughto deflect appreciably,on

the line betweencolumns.This position hasthe apparent advantage ofeconomizing on the necessarylengthof curtain, and hence on cost. Unfortunately,wherethe columns are rounded orotherwise lackingin parallel

surfaces,any smalldeflection leads to a rapidly increasing gap betweenthe curtain's edgeand the column's surface, with consequent smokeleakage pastthe curtain.

17.3 Installation does not follow design Itis common for detail designchanges to occur during

the construction ofbuildings.Apossible consequenceis that an initiallycorrectdesignbecomes unsuitable.An exampleknown to the authors is ofsmoke curtainsbeing 1.5 m too shortwhenfitted. Itis desirablethatthe fire safety system designers be retained bythe buildingdesign team to comment onall designchanges and to confirm that thefinal installedsystem fulfils the designconcept.

17.4 Mis-use of computer models Every computer model ofany aspect ofsmoke movement is based on mathematical representations of theunderlyingphysics.In zonemodels theseareoften empiricallyderived formulae.In CFD models these are more fundamentallybased,solving conservation equationstypically for mass,momentum, enthalpy, etc. It is often forgotten thatthe equations expressing turbulence in current commercialCFD models are also

partlyempirical.

Empirical relationshipsofwhatever sortall share the common feature that they have been developed to fit a specificrange ofexperimental circumstances.They may not be as accuratefor othercircumstances outsidethat range. This affectsthe reliabilityofvalidation ofthe model: within the appropriate rangesa model can be correctly shown to match reality — but outsidethe appropriate ranges ofparameter values the same model cangive grosslyincorrect answers. It is never simply enough to note thata model 'hasbeen validated'. One exampleofthis typeofproblem concerns the expressionfor the fire size at the onset offlashover ina compartment. Oneofthemostcommoncorrelationsfor this relationship is based onworkby McCaffreyet al981,

17 Common design mistakes and variationson this areusedin designguidance, eg refs28'291.McCaffreyet al's correlation was derived for a testroom ofless than 30 m3 in volume,withwindow openingswhichwere predominantly tall compared with theirwidth. Itcanbeshownthatvery different relationshipscanbe expected for the firesize at the onset offlashoverinverylarge rooms havinglarge openingsrc9i. Anothercommon exampleconcerns the common practice in ZoneModels basedon small-fireplume formulaeto defaultthe location ofthe virtualpointsource to thebase ofthe fire regardless ofthesize ofthe fire (see section 17.1for amore detaileddiscussionofthis error). CFD models dependfor accurate modelling ofreality on the correctness ofthe initialand oftheboundary conditionsusedto definetheproblem mathematically. These 'input conditions' are essentialto statecorrectly thephysicaland chemicalnature ofthe problem being studied, andifthey are inappropriate,theCFDmodel will givean inappropriate result.Anotheressentially mathematical constraint isthatthe computationalmesh size (ie the selected dimensionsofeachelementary 'calculationvolume') mustbeappropriate tothe problem being studied. In practice, this means thatthe'solution' to the calculationmust be independent ofthemesh size, whichcannotbe automaticallyassumedfor all circumstances. Thevalidityofa CFD model for a given application would depend onthe fact thatit incorporates proper descriptions,throughsubmodels,ofthedominant physical andchemicalprocesses (suchas combustion, radiation,turbulence, etc.) forthat application.Because ofthe often partially empiricalnature ofthe built-in submodels,validationofthe CFD model is crucialto ensurethe validityofits submodelsfor aparticular application.It follows that a successfulvalidationforone applicationwill apply to other scenariosinthe same category ofapplication,but not necessarilyto other categories. Forexample,caremust be takenwhena CFD modelvalidated for smokemovement is applied to problems involvingflame spread. In general,one can say that in view ofthe complex nature ofCFD models, knowledge offire science and ofCFD isessentialfor 'correct' use fora practicalfire application. The foregoingparagraphs should notbeseen as an argument againstusing computer models. Many designs would be impossiblewithouttheiruse. Theyshould instead be read as a warning that computer models should notbe used by inexperiencedpeople as 'black boxes' alwaysassumedby themto givethe correct answer.Itis alwaysnecessaryforthe designerofa SHEVSto ensurethathe/shehas identifiedwhichmodel (or models— a designmayrequire the use ofmore than one) isappropriate to the circumstancesbeing considered. It isalways necessaryfor the designer ofa SHEVSto satisfy him/her selfthat the model isbeing usedwithin its prudentlimits.Andofcourseit is necessaryforthe Regulator assessingadesignproposal to become satisfiedthatthe designer ofthe system has considered thesefactors.

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17.5 Mistaken perceptionsof conflict betweenactive and passivefire precautions There often appears tobe awidespread misconception thatin some wayactive fireprecautions suchas aSHEVS and passivefire precautionssuchas fire-resisting partitions are competing one againsttheother. Such views can be seen to be the result oftoo narrow a focuson one partofthe wide range ofmeasures available. Similar problems exist inmisconceptions ofthe perceived conflict between differentactive measures (seesection 11.1,for example,concerningthe interactionsbetween smokeventilation and sprinklers). It canbe misleadingto contrast one form offire protection with anotheras iftheywere completely independent ofeachother. In practice, eachsystem influencesthe others. It is betterto regard the building itselfasthe system,withdifferentforms offireprot:ection sharing contributionstowards overall safety. The importance ofthis cannot be overstated. In fact virtuallyall formsofsmoke control depend on aspectsof'passive'fireprotection. Pressuredifferential systems aredesigned to protectagainst smokeleakage throughsmallgapsin whatis otherwisepassive protection enclosingthe escape route. The marketfor fire-resistingmaterials is essentiallyunaffected bythe presence ofsuchmethods ofsmoke control. Smoke and heat exhaust ventilationallowstheuse ofspacesmuch larger than a conventionalfire compartment. Usuallythis isthe result ofusing sprinklersas well.But even forthis casethere are still many requirements for 'passive'fire protection, eg all shop unitwalls exceptthe front, ofshop units opening onto amall wherea SHEVSis fitted into themall, or where smoke exhaust ducts passthrough neighbouringfirecompartments. Other examples include:

•• partitionmembranes, • ceiling downstandsfor smokereservoirsor smoke walls,

barriers.

Related 'passive'fire-protection measuresimportant for smoke control can also include intumescentseals forfire doors and fire-resistingglazing. As for all applications,there arethesame requirements for fire-resistingmaterialsto be ableto withstand thermal shocks,to be impermeableto smoke, andto bestable underdifferentenvironmental conditions includingthe abilityto resist humidity, fringal attack,thefreeze—thaw cycle,and ageingofthematerials.Ifthe material cracks,it could renderthe smokecontrol system unable to prevent thepassage ofsmoke. Alllarger openings,suchas holes madeforpipes, cables,ducting,etc., must beproperly sealed. This has to be aproperfire and smokeseal,riota patchwork usingwhatever materialis left on site (examplesexist ofthe failure offire-resistingwalls because ofsuch inadequate materials ascardboard and polystyrenehaving been used to seal holes madefor cables,pipes, etc. —thiskind offault is seen alltoo often duringpost-fire investigations).

96

__________

_______________

18 Smoke ventilation and enforcementof regulations

Thefinal decision as to whatis acceptable rests with those who are responsiblefor enforcingthe relevant fire safetyregulations. In large or complexbuildingsit is usuallyimpracticaltofollowthe prescriptiveguidelines given in the relevant standards and a fire safety engineeringapproach isneededto achieve a successful smoke and heat exhaust ventilation system so that the same level ofsafety is accomplished asfor amore conventionalbuildingwithoutthe same amountof compartmentation. The successor failureofthedesign will often depend on the details.The assumptionsand calculation procedures whichare correct forone scenario may not be correctfor another. It should also beclearlyunderstood thatthevarious publishedformulaewere derived from experimentsand maynotbe appropriate whenthe design scenario is very different. For example,aformula experimentallyderivedfrom a tall and narrow atrium maynotbe suitablefor SHEVSdesign ofa wide atrium with a relativelylow ceiling.Unfortunatelythereis often confusionaboutthevalidity ofvarious assumptionsand calculationformulaeusedin the designprocess It should be emphasized further that anySHEVS designprocedure has 'assumptions' built intoit. It is impossibleto do a smoke-control design from first principleswithoutanyassumptions.Thus, it follows that the enforcer ofregulations,and thebuilding'sowneror developer, should insistthat the designer ofa system should make all the assumptions explicit,and should state the sourcesfor methodology and/or data.It is often the case that the most worrying problemswith adesign arise from unreasonable assumptions.Although itmay sometimes be difficult to followthecalculation methodology itis usuallypossibleto make a commonsensejudgement about the validity ofthe assumptions.

As the buildingsbecome more complicated,both in

size and geometry and alsowiththe introduction ofnew

innovativematerials andconstruction techniques, formulaenormallyusedfor design ofsmoke control systemsbecome less reliableandparticular careis needed in the designprocess.In those scenariositmaybe desirableforthe enforcer ofregulationsto seek asecond opinion from an independent source ofexpertise.Ifthe buildingis so complex that confidencein the design process is low then it maybe desirableto do an 'in-situ' commissioningfiretest to check the SHEVS designand tofinetunethe system.A further advantage ofsuchatest is that it may clearlyshow some implementation faults,eg whetheradamper in a ducthas beeninstalledsuchthat opens in the 'wrong' direction in the eventofafire.The testinvolvestheuse ofoneor more alcohol fires to produce sufficient heat such that the hot buoyant gas layerflows can bemonitored and the effectivenessofthe SHEVScanbe assessed.Obviouslythe temperature must alsobekept low enough so as notto cause any damage to thebuilding.Non-toxic and non-corrosiveoil-mist theatrical smokemay be injected into the fire plume if visualizationofthe hot gas layer is desired. Such methods have beendeveloped andusedsuccessfullyin the last few

i

years.

One otherproblemwith a smoke-control system is maintenance and training ofstaffwhere needed. A regular check on the system is essentialto ensure that it will operate as designed,ifneeded. Also, intervention by trained staffis sometimesbeneficial or even necessaryto achieve satisfactoryevacuation oftheoccupants inthe eventofafire. For example,calculationsdone atFRS'°° indicated that the presenceoftrained stafftohelp with evacuation isofgreatbenefit in large single-storey buildings.Itis difficult to ensure that thereis a continual training programme, particularlywhenthe 'ownership' of a buildingchanges.

97

19 Acknowledgements

Theauthors ofthis bookwould like to record their indebtednesstoDr G 0 Hansell, co-author ofDesin approachesforsmokecontrolinatriumbuildizgsL'31, an earlier BRE publication,some ofwhose texthasbeen carried forwardintothispresentbook; and toMrJoris Verbeek of IFSET for his work on the Figuresand Plates.

Theywould alsolike to statetheirappreciation cfthe work ofCEN/TC191/SC1andoftherelated 'Mirror Groups' in the national Standards Institutesinprep:aring thedraftParts ofPrEN12101. Manyideas havedeveloped andhavebeenclarifiedasaresult oftheirdiscussions.

98

______

_____

20 References

[1] DepartmentoftheEnvironmentand the WelshOffice. BuildingRegulations1991. Approved DocumentB (1992edition). London,The StationeryOffice, 1991. [2] PublicHealthActs 1936and 1961. London,The Stationery Office. [3] TheFactories Act1961. London,The Stationery Office,1961. [4] Offices, Shopsand Railway PremisesAct 1963. London,The Stationery Office,1963.

[5] HomeOffice and Scottish Homeand HealthDepartment. Fireprecautions intowncentre redevelopment. FirePreventionGuide No 1. London,The Stationery Office,1972. [6] British StandardsInstitution. Fireprecautions inthe design and construction ofbuildings. Part 10: Code of practice for shopping complexes. British Standard BS 5588: Part 10: 1991. BSI, London, 1991. [7] British StandardsInstitution. Fireprecautions inthe design, construction and use ofbuildings. Part 7: Code ofpractice forthe incorporation of atria inbuildings. British Standard BS 5588: Part 7: 1997. BSI, London, 1997. [8] ThomasP H &Hinkley PL. Roof ventingtheory and the Vauxhall fire. Fire Protection Review1964: 27(282):208—209. [9] ThomasPH, Hinkley PL, TheobaldC R&Simms D L. Investigationsintotheflow ofhot gases in roofventing. FireResearch TechnicalPaper No. 7. London, TheStationery Office, 1963. [10] ThomasPH &Hinkley PL. Designofroof-ventingsystems for single-storeybuildings. FireResearchTechnicalPaper No. 10. London, TheStationery Office, 1964. [11] SilcockA& Hinkley P L. FireatWuIfrun shopping centre, Wolverhampton.FireResearchStation FireResearchNote878. Garston, BRE, 1971. [121 Morgan H P. Smokecontrolmethods inenclosed shopping centres ofone ormore storeys: a design summary. BRE Report. London, TheStationery Office, 1979. [13] HansellG & Morgan H P. Designapproachesfor smoke control inatriumbuildings. BRE Report BR 258. Garston, CRC, 1994. [14] Sharry J A.Anatrium fire. FireJournal 1973: 67(6): 39—41. [15] Morgan H P&SavageN P. A study ofalargefire in a covered shopping complex: StJohnsCentre 1977. BRE Current Paper CP 10/80. Garston, BRE, 1980. [16] SaxonR. Atrium buildings: developmentand design. London, TheArchitectural Press, 1983. [17] TheAndraeusBuilding Firein Sao Paulo, Brazil. FirePrecaution 1973: 97:37. [18] Lathrop JK. Atrium fire proves difficult toventilate. FireJournal 1979: 73(1): 30—31. [19] RobinsonP. Atrium buildings:a fire service view. FireSurveyor 1982: 11(4):42—47. [20] DegenkolbJG. Atriums. TheBuilding Official and Code Administrator 1983: XVIJ(6): 18—22.

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[21] Parnell AC &Butcher E G. Smoke movement in atria. Fire Protection(South Africa) 1984: 11(3): 4—6. [22] National Fire ProtectionAssociation. Smokemanagement systems in malls, atnaand large areas. 1995edition. PublicationNo. 92B. QuincyMA, USA, NFPA, 1995. [23] Fire Safety Bureau. Code ofpracticeforfire precautions in buildings,Paragraph 7.6.1, FireSafety Bureau,Singapore Civil DefenceForce, Singapore, 1997. [24] Morgan H P& GardnerJ R Design principles forsmoke ventilationinenclosed shopped centres. BRE Report BR 186. Garston CRC, 1990. [25] Morgan H P& Marshall N R. Smoke hazards in covered mutilevel shopping malls: an experimentally-basedtheory for smoke production. BRE Current Paper 48/75. Garston, BRE, 1975. [26] CoxG. Compartment fire modelling. Combustion fundament s offire. Chapter 6. London,Academic Press, 1995. pp 329—404. [27] Morgan HP& HansellG0.Atrium buildings: calculating smoke flows in atria for smoke control design. Fire Safety Journal 1987:12: 9—35. [28] Chartered Institution ofBuilding Services Engineers. CIBSE Guide VolumeE: Fire Engineering.London, CIBSE, 1997.

[29] British StandardsInstitution. Firesafety engineeringin buildings.Part 1: Guideto theapplication offire safety engineering principles. British Standard Draft for Development,DD 240: Part 1: 1997. London, BSI, 1997. [30] British StandardsInstitution. Fireprecautions inthe desigr. construction and use ofbuildings. Part 4: Codeof practice for smoke control using pressuredifferentials. British Standard BS 5588: Part4 1998. London, BSI, 1998. [311 RamachandranG & BengtsonS. Exponentialmodel offire growth. Proceedings stinternational Symposiumon FireSafety Science. Washington,USA, HemispherePublishingCorporation, 1986. 657—666. [32] Ghosh B K. Firesinreal scenarios. InternationalSymposiumon Fire Science and Technology,KoreanInstitute ofFire Science and Engineering,Seoul, Korea, November1997. 439—449. [33] Morgan P B E, Webb .15,Samme P & Ghosh B. Audit of company fire safety policy for J SSainsbury Plc. Phase2: Experimental studies. BRE ClientReportlCR213/96. Garston, BRE, 1996. [34] Morgan H P& HansellGO. Fire sizes and sprinkler effectiveness in offices - implicationsfor smoke control design. Fire SatetyJournal 1985:8(3):187—198. [35J Ghosh B K. Firedamage and sprinkler effectiveness in retail premises. BRE Chent Report CR 57/91. Garston, BRE, 1991. [36] RamachandranG. Trade-otis betweenfire safety measures: probabilistic evaluation. FireSurveyor 1990: 19(21: 4—13. [37] Morgan H P &Chandler S E. Firesizes and sprinkler effectiveness in shopping complexes and retail premises. Fire Surveior 1981: 10(5): 23--28.

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[38] HansellGO& Morgan H P. Firesizes in hotel bedrooms— implicationsfor smoke control design. FireSafety Journal 1985:8(3):

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[39] Smith PG & Murrell iv. A study ofsprinkler performance in a simulated 6-bed hospital room. Private communication.Garston, Fire ResearchStation, BRE, 1986. [40] Vincent BG, KungHC & Hill EE. Residentialside wall sprinkler firetestswith limited water supply. FireScience and Technology1988: 8(2): 41—53. [411 CoteAE. Highlightsof afield test ofa retrofit sprinkler system. Fire Journall983:77(31:93—103. [421 Proulx G&Sime JD. To prevent panic in anunderground emergency : why not tell peoplethe truth? Proceedings3rd InternationalSymposiumonFireSafety Science, 1991. pp843—852. [43] Hansell G 0. Heat and mass transfer process affecting smoke control in atrium buildings.PhDThesis, SouthBank University,London, 1993. [44] Zukoski EE, Kubota & CetegenB. Entrainmentinfire plumes. FireSafety Journal 1981: 3: 107. [45] Quintiere J G, RinkinenWJ &JonesWW. Theeffects of room openings onfire plumesentrainment. CombustionScience and Technologyl98l:26: 193. [461 Hinkley P L. Ratesofproduction ofhotgasesin roofventing experiments. FireSafety Journal 1986: 10: 57—65. [47] McCaffrey BJ, Quintiere J G&Harkleroad MF.Estimating room temperatures and the likelihoodofflashover using firetest data correlations. Fire Technology1981: 17(2): 98—119. [48] PorehM & Morgan H P. On power lawsfor estimating the mass flux inthe nearfield offires. FireSafety Journal 1996: 27: 159—1 78. [49] Heskestad G. Engineeringrelations forfire plumes. FireSafety

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Journall984:7(1): 25—32. [50] Morgan H P&Marshall N R.Smoke hazards incovered multi-levelshopping malls: amethod ofextracting smoke fromeach level separately. BRECurrentPaperCPl9/78. Garston, BRE, 1978. [51] HeseldenAiM. Fireproblems ofpedestrian precincts: Part1 The smoke production ofvarious materials. FireResearchNote 856. Borehamwood,Fire Research Station, 1971. [52] Morgan H P. Thehorizontal flowof buoyantgases toward an opening. FireSafety Journal 1986: 11: 193—200. [53] Morgan H P&Marshall NR. Thedepth ofvoid-edgescreens in shopping malls. FireEngineersJournal 1989:49(152):7—9. [54] HansellGO. Private communication,1991. [55] BosleyK. The effects ofwind speed on escape behaviour through emergency exits: Summary report. FROG ResearchReport Number 53. London,Home Office, 1992. [561 Ghosh B K. Effectofplug-holinginfire smoke ventilation. BREClient Report CR50/95. Garston, BRE, 1995. [57) Spratt D & HeseldenAiM.Efficient extraction ofsmoke from athin layer under a ceiling. FireResearchNote1001. Garston, Fire ResearchStation, 1974. [58] HeseldenAJ M. Privatecommunication.Garston, Fire ResearchStation, BRE, 1976. [591 Wraight H GH. Private communication.Garston, Fire ResearchStation, 1984. [60] Marshall N R, Feng S Q &Morgan HP. Theinfluence ofa perforated falseceiling onthe performance ofsmoke ventilation systems. FireSafety Journal 1984/85: 8: 227—237. [61] HansellG 0, Marshall N R & Morgan HP. Smokeflow experiments in a modelatrium. BREOccasionalPaper OP55. Garston, BRE, 1993. [62] Morgan H P& MarshallN R. Smokecontrol measuresin covered two-storey shopping mall having balconiesaspedestrian walkways. BRE Current Paper 11/79. Garston, BRE, 1979. [63] Poreh M, Morgan HP, Marshall NR M &Harrison R. Entrainmentbytwodimensional spill-plumesin malls and atria.Fire

1—19.

[64] Miles 5, Kumar S &CoxG. Thebalcony spill plume—some Safety Science, 1997. pp 237—247.

[65] ThomasPH, Morgan HP&MarshallNRM.The spill plume in smoke control design. FireSafety Journal 1998:30: 21—46.

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[66] Grella &FaethG M. Measurementsin atwo-dimensional thermal plume along a vertical adiabaticwall. Journal ofFluid Mechanics1975: 71(4): 701—710. [67] MarshallN R&Harrison R. Experimentalstudies ofthermal spill-plumes.BREOccasional Paper OP1. Garston, BRE, 1996. [68] Thomas P H. On the upward movementof smoke and related shopping mall problems. FireSafety Journal 1987: 12: 191—203. [69] Williams C. In situacceptance testing ofsmoke venti ation systems using real fires atthe EuropeanParliamentBuilding. Proceedings Eurofire '98, Firesafetybydesign, engineeringand management,Brussels, Belgium, 11—13 March 1998, Session 13, Paper S13 13 59. [CD-ROM). Asse, Belgium, IFSET, 1998. [70] PaulsJ. Calculatingescape times for tall buildings.SFPE Symposium:Quantitativemethods forlifesafetyanalysis,March 1986. Boston, MA, USA, SFPE, 1986. [71] HansellG & Morgan H P. Smokecontrol in atrium buildings using depressurisation.Part 1: Design principles. FireScience and Technologyl99O: 10(1 &2): 11—26. [72] HansellGO & MorganH P. Smokecontrol in atrium buildings using depressurisation.Part 2: Considerationsaffecting practical design.Fire Science and Technology1990: 10(1 & 2): 27—41. [73] BRE. The assessment ofwind loads. Part8: Internal pressures. Digest 346. Garston, CRC, 1990. [74] Douglas-BainesW. Effectsofvelocity distribution on wind loads andflowpattern on buildings.ProceedingsSymposiumNo 16: Wind effects on buildings and structures, NationalPhysical Laboratory, 1963. London,The Statioery OffIce, 1965. [75] Hinkley P1. Theeffectofsmoke ventingonthe operation of sprinklers subsequentto thefirst. FireSafety Journal 1989: 14(4):

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221—240. [76] Garrad G &Ghosh B K. Effectofairflowunder ahot gas layer in a simulated shopping mall. BRE Note N 30/96. Garston, BRE, 1996. [77] Garrad G & Ghosh B K. Effectofhot gas layervelocity infire smoke ventilation. BRENote N 109/95.Garston, BRE, 1995.

[78]

Ghosh B K. Some effects of crosswind on ventilators.

WorkshopPaper inEuropeanWorkshoponAerodynamics ofnatural heat and smoke ventilators. Journal ofWind EngineeringandIndustrial Aerodynamics 1993: 45(111): 247—270.

[79] Comitélechnique Permanentdu GroupdeIravaii Iricendiedu Comite Européendes Assurances.Proposals For

general rules forapproved automatic sprinkler installations.1968. [80] British StandardsInstitution. Fireextinguishinginstallations and equipment on premises. Part 2: Specificationfor sprinkler systems. BritishStandardBS 5306: Part2. London,BSI, 1990,, [81) HeskestadG. Modelstudy of automatic smoke and heatvent performance insprinklered tires. Factory MutualResearchCorporation Serial No. 21933, RC74-T-29. Norwood, Boston, USA, 1974. [82] Hinkley P L. Sprinkler operation and the effectofventing: studies using a zone model. BRE Report BR 213. Garston, BRE, 1992. [83] DavisWD&Cooper LY. Acomputer model forestimating the responseofsprinkler linksto compartment fires with draftcurtains and fusible-linkactuated ceiling vents. Fire Technology1991: 27: 113—127.

[84] CooperLV. Interaction of anisolated sprinkler spray and a two-layer compartment fire environment:phenomenaand model simulations. FireSafety Journal 1995: 25(2): 89—107. [85] GardinerAJ. Themathematical modelling ofthe interaction between sprinkler sprays and the thermally buoyant layer of gases from fires. PhDThesis,South Bank University, London, 1988.

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___ _______

___ _____

[86] Jackman LA. Sprinkler spray interactions with fire gases. PhDThesis, South BankUniversity, London, 1992. [87] Kumar S, Heywood G M, hew S K &Atkins W S. Superdrop modelling of a sprinkler spray in atwo-phaseCFD-particletracking model. Proceedings InternationalSymposiumonFire Safety Science, Melbourne,Australia, 1997. [881 Hinkley P L, HansellG 0, Marshall N R & HarrisonR. ExperimentsattheMu(tifunctioneelTrainingcentrum,Ghent,on the interaction betweensprinklers and smoke venting. BRE Report BR 224. Garston, CRC, 1992. [89] IngasonH & Olsson S. Interaction betweensprinklers and fire vents. SP Report 1992:11. Borfls, Sweden,SwedishNational Testing and ResearchInstitute, 1992. [90] Morgan H P. Combiningsprinklers and vents: an interim approach. Fire Surveyor1993:22(2): 10—14. [91] British StandardsInstitution. Loadingfor buildings. Part 2: Code ofpractice forwind loads. British StandardBS 6399: Part2. London, BSI, 1997. [92] British StandardsInstitution.Actions on structures. Wind actions (together with United Kingdom NationalApplication Document). ENV 1991-2-4: 1997. London, British Standards Institution, 1997. [93] UnderwritersLaboratory Inc. Leakage-rateddampers for usein smoke control systems. UL 555 5. USA, Underwriters Laboratory nc, 1993. [94] Atkinson B and Marchant R L. The DeedsRoad experiments: firesfor commissioningtests—a preliminaryreport.Proceedings InternationalFireSafety EngineeringConference: theconceptand the tools. Sydney,Australia,CSIRO, 1992

Design methodologies forSHEVS [95] StandardsAssociationofAustralia. Australian/New

ZealandStandard4391 lInt): 1996. Smoke managementsystems — hot smoke test. Sydney, Standards AssociationofAustralia, 1996.

[96] Morgan H P, Williams C, HarrisonR, ShippMP& De Smedti-C. BATC: hot smoke ventilationtest at BrusselsAirport. 1stInternationalConferenceonFire Safety ofLarge EnclosedSpaces, 25—27 September 1995, Lille, France. [97] Ghosh B K. Deflection of smoke curtains in real fire scenarios: theory and fullscaleexperiments. Proceedings Eurofire '98:Firesafety bydesign, engineeringand management,Brussels, Belgium, 11—13 March 1998. Session 13, PaperS13 1360,1998. [98] McCaffrey B J, QuintiereJ G& HarkleroadMF. Estimating room temperatures and the likelihood offlashover using firetest data correlations. Fire Technology1981: 17(2): 98—119. [99] Morgan H P. The influenceofwindow flows on the onset of flashover. SFSE/FRS Symposiumon Flowthrough openings, 13June 1989. Garston, BRE, 1989. [100] Ghosh BK. Private communication.Garston, Fire Research Station, BRE, 1994. [101] GarradG, MarshallN R & HarrisonR. Smoke leakage through gapsin smoke curtains: a small-scalestudy. &REFireNote2. Garston, CRC, 1997. [102] Shao-Lin Lee &EmmonsHW.A study of natural convection abovea line fire. Journal ofFluid Mechanics1961: 11(3): 353—368. [1031 British StandardsInstitution. Componentsfor smoke and heat control systems. Part3: Specificationfor smoke curtains. British StandardBS 7346: Part3. London,BSI, 1990.

101

Annex A: Design procedure with a growing design fire

Note: The principles described inAnnexBare applicable

hereaswell.

=

0 forthefirstiteration. • Set Identifythe location ofthe buoyant smokelayers base in thesmoke reservoiratthe end ofthe

A.1 Choosea design fire curve Thishasbeen discussedin moredetail in section 3.1.It will also be necessaryto identifythe averageheat release rate persquare metrefor the selected scenario.

•

A.2 Establish the required escapetime

• •

Thismustbe done usingmethodsfrom sources outside thefield ofsmoke ventilation.

A.3 Calculatetimes to danger, ie available escape time Useaniterative procedure basedontheprinciple ofa

'quasi-steady-state'calculation,wherethe growing fireis treated as ifitis asuccessionofsteady fires, eachinits owndefinedtimeinterval,with thewholeapproximating tothe actual curve.This lends itselfwell to converting intoa computer program, and can be muchmoregeneral in applicationthan afullyanalyticalsolution,since the latterwill yieldvery complicatedformulaefor all butthe simplestofbuilding geometries.

(a) Selecta time incrementfor calculation Toolargean increment will givepooraccuracy andcould result in the calculationbeingmathematicallyunstable, ie inherently unable to givethe correct answers.The smaller the increment the more accurate the resultsof this method ofcalculation,buttoo smallan increment canleadtoarithmetical errorsarisingin computerswhich specifynumbers byusing toofew digits.A one-second increment seemsto work well with computer programs inthe presentauthors' experience. (b) Iterativeprocedure

• Identify mass ofsmoky gasesresident inthe smoke reservoir atthe end ofthe previousiteration. =0 forthe firstiteration. • Set Identifytotal heatresident inthesmoky gasesinthe smokereservoir at the end ofthe iteration. previous

•

previous iteration. Set= ceiling height for the first iteration. Hence, identifythe height ofrise to the layer base at thestartofthe current iteration. Using the appropriate growth curve identifiedearlier, andthe heat-release rate identifiedearlier,calculate theaveragefireperimeter during thetime interval for thecurrentiteration. Calculatethe averageconvective heatfluxin the smoky gasesduringthe time interval for the current iteration. Usingthe heightofrise, the heat flux, and the fire perimeter calculatetheaverage massflow rate of smoky gasesentering the layer duringthe current iteration, usingthe samemethods as for asteady-.state designfire. Notethat thiswill cover both single-storey geometries andthe more complicated atrium-like geometries. Usingresults calculatedforthe layerfrom all previous iterationsand steady-stateformulaefortheventilators, calculatethe exhaust mass flow duringthe currenttime interval.

• Fromand the differencebetweenthemass entering the the mass calculatethe net • • •

layer being exhausted, mass ofsmokygases adding tothe layer duringthe current increment. Ifthe exhaust is greater than the flowrate entering the layer, defaultthe layer depthto the depth ofaceiling-jet. From the differencebetweentheheat carried intothe gasesand the heat being exhausted from the layer, calculatethe net heat addingto the layerduringthe current increment. Byadding the net addition ofmassto the massresident atthestartofthe increment,calculatethe mass of smoky gasesresident in the layer attheend ofthe current increment. By adding the net addition ofheat to the heat resident atthestartofthe increment,calculatethe heatresident in thelayerat the end ofthe current increment. Note that itis conventionalto ignoreheat lossesfrom the layer otherthan by the exhaust gases,but one could include the effectofsprinklercoolingifnecessary.

102

Design methodologies for SHEVS

Inclusionofheatlosses to the buildingstructure is difficult.

A.4 Acceptability criteria for calculated times

• Calculate the excesstemperature ofthe gasesresiding in the layer at the end ofthecurrentincrement. Apply • Wherethe layercriteria temperature ishigherthan the before the 'timerequiredfor the same 'maximumlayertemperature above ambient' 'steady-state' criteria as for the steady-state design:ifthe layeristoo safety',the designis not acceptable. the layer depthexceedsour 'steady-state' end theiterationand branch out to section • Where the mass of and the criteria earlier than the 'time required for safety',the •hot, smoky gases layer Using resident in the at the end of the is design not accpable. temperature, layer currentincrement, and theknown horizontal areaof • Whenneither criterion is exceeded earlier thanthe the smoke reservoir,calculatethe atthe 'time for the is A.4.

layerdepth end ofthe current increment. Notethat one can

• • •

introduce non-rectangular-section smoke reservoirsby making the areaa function ofheight. Using minimumclear heightsspecifiedas forthe steady-state designmethod, checkwhetherthe calculated layerdepth has reachedthe deepest acceptable limit. Ifit has, stop the iterativecalculation and branch outto section A.4. Check whetherthe total time tothe end ofthe current iteration has reached the 'time required forsafety'.Ifit has, stop the iterativecalculation and branch out to section A.4. Loop backtothe startofthe iterativeprocess and start the calculationsforthe nexttimeinterval.

required safety', design acceptable in principle,but stillhas tobe subjected to other criteria specifiedinthe 'steady-state'design methodology.

A.5 Further acceptability criteria The designershouldusethe layer depth and temperature, and the exhaust mass flow rate, calculated forthe final timeincrement to carry outthe same 'steadystate'calculations such as minimumpossiblelayer depth forflowto the exhaust ventilators,wind effects on ventilators,air speedat escape doorsbeingusedas inlets, etc.

103

Annex B: Design procedure with a steady-state design fire

B.1 General introduction Theflowofthermally buoyant gasesaway from afire, through a building,intoasmoke reservoir,andtheir exhaust from the buildingintothe surrounding atmosphere, is influencedby many factors.Theseinclude the shape ofthebuildingat eachpart oftheflow,and external factors suchas wind pressures,snow loads, etc. To be successfulasmoke exhaust ventilation system must be designed in a waywhichincludesconsideration ofall

suchinfluences.

B.2 Identification of 'design regions' needed in calculation The designproceduremustconsider a successionof zones(also called herein'design regions'),which correspond to successivestagesin the path followedby the smoky gases.

B.3 Zone-by-zonedeterministic calculation procedure: single-storeyspaces Forlargesingle-volumespaces (ie wheresmokerises directly from the burning fuel to the thermally buoyant layerin the smoke reservoir)thefollowingdesign regions

arenecessary. (a) The fire

The designshouldbe based on a steady-statefire ofa size appropriate to the buildingconcerned, as discussedin Chapter 3. (b)The plume above thefire, risingintothe smoke reservoir

The heighttothe smoke base mustbespecifiedforlifesafetyapplications.Somepossiblerequirements are listed in TableBi. Themass flow rate ofsmoky gases entering thereservoir is then calculated. Fortemperature control designsthe temperature ofthe buoyantsmoke layer must be specified; and the massflow rate entering the layerand the height ofrise ofthe plume arethen calculated.

Table Bi Minimum clear heightabove escape routes Minimum height Typeofbuilding Public buildings(eg single-storeymalls, exhibitionhalls)

3.Om

_______

_________ ____________ 2.5 m Non-publicbuilding (eg othces,

apartments, prisons) Carparks

_____________

____________

________

Smaller of2.5 m or

0.8 times ceiling height Note: These heightsapplyto single-storeysituations.Wheresmoke must rise throughanother storeybeforereachingthe fisalsmoke reservoir, isusualtoaddanother0.5 mtoeachvalve.

it

(c) The smoke reservoirand ventilators The smokereservoirmustbe ofsufficient depth; this requires calculation ofthe minimum depthoflayer necessaryfor gasestoflowfrom the plume's point of entrytothe layer towards theventilators. Thegases in thelayershallbe between acceptable high and low temperature limits:thehigh limitbeing200 °C to avoid painfulheatradiation on lightlyclad people beneaththe smoke layer,thelow limitbeingmore arbitrary buttypicallybeinga minimumdesignlayer temperature of2O °C to avoid loss ofbuoyant stabilicy of

the layer. Theareaofnatural ventilators (ie wherethegases are propelled through the ventilatorsby the buoyant pressure ofthe layerbeneaththe ventilator), or the capacity ofpoweredventilators (usuallyfans),must be calculatedto exhaust the same massflowrate as enters the layer in the plume risingfrom thefire. Note: Natural and powered smoke exhaust ventilators

should never be usedsimultaneouslyin the same smoke reservoir. (d) Effectof externalinfluences(eg wind and snow The effectofexternal influencesmust be allowedforin the design. This is particularlyimportant in decidingthe location ofnatural ventilators and in choosingbetween natural and powered smoke ventilators.In essence,n.o natural ventilator should be located whereitmight experience an overpressurefrom a wind.Wind-induced overpressuresoccuronthe upwind sidesofbuildings, and

104

Design methodologies for SHEVS

fora considerable distance on any lowersurfacesupwind ofahigherstructure. Thepossibilityofsnow orice affectingthe operation ofthe ventilators must also be takenintoaccount whenspecifyingequipment.

(b) Entrainment in, and flow outof, a side room Theplumeabovethe fire is as above,butcan be combined with the flowofsmoky gasesleavingthe fireroom intoa single calculation.

(e)Airinlets(including anydoors servingas air inlets) Thesemust allow sufficient replacement air to enterthe buildingtoreplace the gasesbeing exhausted as smoke.If they areusuallyclosed,theymust open on receipt ofthe same signalthatoperatesthe rest ofthe smoke ventilation system.The airspeed throughany inlets also serving as escape doors (acommondesign feature) must beless than 5 rn/sto avoid adverse effectson people escaping throughthose doors. All inlet air must bebelow the smoke layer and preferably moving at less than 1 rn/s whenit enters the affectedzone. Powered inlet fans should never beusedwith powered smokeexhaust fans, in orderto avoid changing pressureforces on escape doors asthe fire size changes.

(c) Smoke flowsbeneath a canopyor balcony, approaching a spilledge Wherea canopy (or the underside ofa balcony) projects beyondthe fireroom's opening,the effectonthe smoke flowatthe spilledge canbecalculated to find the mass flowrateflowingtowards that edge. Ifthe smokeexhaust ventilationdesign requires that smokebe contained beneaththe canopy or balcony, andbe prevented from spillingintothe adjacent space, the remainder ofthe design calculationis essentiallyas for section B.3.

Wherepresent,these shallallow forthe effectsof buoyancy-induceddeflection away from the vertical,and must meetthe criteria forminimum leakagewheninthe deflected position. Notethatthis aspect ofdesign and specificationofsmokecurtains hasbeen largely overlooked untilrecently, and doesnot feature in any earlier design guides.Nevertheless, it is clear from experiments at FRS971that deflectioncan be a serious problemcapable ofjeopardizing the successofthe entire smokeventilation design, especiallyfor lighter and deeper curtains, unless the problemis properly addressed by calculation duringthe designofthesystem andby specifyingthe equipment to compensate andthus reduce theproblemto harmless proportions.

(d) Thespillplume The mixingofair intothe spillplume as it risesto meet the buoyant smokelayerunderthe ceilingmust be calculated,to give the total massflow rateofgas entering the smoke layer. Forlife-safetyapplicationsthe heightof thebase ofthebuoyantlayerofsmoky gasesabove the highest escape route open to the same space as the fire, must be specified. It is usual to add 0.5 mto the minimum valueslisted inTable B1. For temperature control systemsthe temperature of thegases in the smokereservoir (ie in the layer)shall be specifiedand the mass flowentering the layercalculated. Thecalculationprocedures for the spillplume canbe usedtofind theheightto thesmoke layer base. Where thereare higher balconies above the spilledge the designmust takeintoaccount thebreadthofthe balconies,iethe distance betweenthe edgeofthe balcony and thewall (or glazedfacade).This affectsthe abilityof airto move betweenthe plume and the facade,and determines whetherthe plume willthrowitselfclear of the wall or be pulled backagainst it to smokelog the higherbalconies.

(g) Suspended ceilings Wherepresent,these can complicatetheflow ofsmoky gases, and must be allowedfor in the design.

All calculationsand requirements from sections B.3 (c)—(f) shallalso apply to the presentcase.

Note: Ifthe provision ofinlet air is inadequate,the entire smokeventilation system will be ineffective. (f) Free-hanging smokecurtains

BA Zone-by-zonedeterministic calculation

procedure: complex flow path involving spill plumes Buildings wherethe initialplume above the fire is

intercepted by aceiling andthe smoketravels laterally before spillingintoa higher adjacent space (egsee Figure 5), require additionalstepsin the calculationof smoke movement and ofthe entrainment ofair into smoky gases. Examplesinclude multistorey shopping malls, atriaand buildingswith mezzanine floors. (a) The fire The selectionofa designfire isas for the single-volume space above.

(e)Thesmoke reservoir

(f) Atriumdepressurization

Wherethe pressures in the smokelayerin an atrium are to be reduced belowambient to prevent smokemoving intorooms adjacent tothat atrium, theeffects ofwind pressures on the outsideofthebuildingmust be included in thedesign calculations.

B.5 Integrating the SHEVSinto the building Compatibilitywith other safety and buildingsystems in

the same buildingis essential.Itis also acommon

experience that any safetymeasures which interfere with the building'severyday use willbe 'deactivated' for the sake ofconvenience.This practicaland psychological problem can be greatly reduced ifthefire-safety measures are properly integrated intothe buildingdesign

AnnexB: Design procedure — steady-stateftre 105

atanearlystage. It is still common practice in all countries,unfortunately,to designthefire-safety

measures intothe buildingalmost as an afterthought. This reduces the chances ofthose measuresremaining effective over the building'slife, and is also likelyto increase the initialcostofthefire-safetymeasures.

B.6Computer-based design calculations Wherecomputer-based zonemodels areusedto carry outcalculationsaspart ofthe designprocess,all

mathematical formulaeusedin those models, assumptions made, and valuesofinputparameters should be explicitlyincludedinthe documentation made availabletotheownerofthebuilding,andto the enforcer ofregulationsiftheyrequire it. In addition,informationconcerningvalidationofthe computer-basedzone modelsusedin design should be included in the documentation.Wheresuch validation informationexistsinthepubliclyavailableliterature it oughtto be sufficient to cite appropriate references.

106

________

____

Annex C: Deflection of smoke curtains

C.1 Principle In SHEVSsmoke curtains areusedto create reservoirs whichwill contain smoke andhot gases.To fulfil that role theymustresist the sidewaysdeflection causedby the buoyancy-drivenforces due tohot gases, orthefaninduced forcesin mechanical exhaust systems. Iftheydo notresist those forces, gapsmight occur beneaththe curtain orbetweenthe curtain andthe building structure,leading to the flowofhot gases from thereservoir intoadjacent areas. Theoretical andexperimental workhas shown that the deflectionofasmoke curtain andthe flow ofhot gases through gapsin itcan berelated to the hot gas layer contained bythe curtain. ThisAnnex considers the deflectionoffree-hanging curtains only, as those whichare fixed atboth ceilingand floor and/orsidesare effectivelylocked inplace and will not be subjectto deflection.The methodofcalculationof the leakagethroughgaps inthe curtains is validfor all

d1

N

C

A

types ofcurtains. Free-hanging smoke curtainscan bedivided intotwo categories: those whichact to contain agas layer whichdoesnot extend below the bottom ofthe curtain (FigureCl) (eg reservoir screens and channelling screens), thosewhichfallto floor level and act completelyto seal areas from asmoke compartment in whichthe gas layer extends belowthe bottomofthe curtain (Figure C2) (such as mightbeinstalled along balconies to form a closed atrium). Thetypes will bereferred to as those which do notreach the floor andthosewhichclose an opening, respectively.

FigureCl Defleclionofa smoke curtainwhichdoes not reach

Thepressure ofgases acting onthesmoke curtain will cause it to deflect from the normal verticallyhanging position. Thathorizontal deflectionofthe curtain causes the bottomofthe curtain to rise, whichcould leadto leakage ofgasunderneath the curtain ifthe rise takes the bottomofthe curtain above thebase ofthegas layer. Because the curtainsare not rigid, they are alsolikelyto bowinuse, like a sail inthe wind. Such bowing will lead to afurther riseofthebottomofthe curtain.

p0

the floor

•

•

C.2Curtains not reaching the floor Thedeflectionofthe curtain is calculated following reference [97] (FigureCl):

d

=1.2

p061D 3T/(2Mb+MCLC)

(Ct)

where:

01

= deflection ofthe curtain (m), = density ofambient air (kgm3), = temperaturerise above ambient ofthegases in the

D1

= depthofthegas layer (m),

d

smokelayer (°C),

T = absolutetemperature ofthegas (K), Mb = mass per metrelengthofthe curtain'sbottombar (kgnf'),

M == mass per m2ofthecurtainfabric (kgm2), to bottom

L

length ofthe smoke curtain from top bar, measured along thefabric (m).

AnnexC: Deflection of smoke curtains

107

o

L=zd0+d

(C.5)

d0

Theprocedure is: 1 assumea valuefor L d0, 2 calculatedusingEqn (C.4), 3 calculateLusing Eqn (C.5).

\Lc

d1

Repeat steps 1—3withthenewvalueofL, until successivevaluesof differby 1% or less. The calculatedvaluefor L must thenbe modifiedby includinga termto allow forbowing ofthecurtain as for curtainsnot reachingthe floor,so that:

L

C floor window

= L+ 1.7 (L

—

L(fiflal)

FigureC2 Deflection ofa smoke curtainclosingan opening

The lengthofthe curtain to contain a gas layerofdepth D1 is calculated using an iterativeprocedure:

(C.6)

d0)

C.4 Smoke leakage through gaps in curtains The leakageofsmokeand hot gas throughverticalgaps at theedges ofsmokecurtains canbe related to thehot gas layer that they contain bythe followingequaticn101: 1/2

M =A 352.172gDiO1 l\ T )l T0 ) g

L=D1+d Theprocedure is:

(C.2)

L

1 assume astarting valuefor D1, 2 calculate usingEqn (Cl), 3 calculatenextvalue ofL usingEqn (C.2).

d

Repeatsteps1—3with the newvalue ofL, until successivevalues ofL differ by 1% orless. The calculated valuefor L must then be modifiedby includinga termto allow for bowing ofthe curtain9,so that:

L(fil)= L + 1.7 (L—D1)

(C.3)

C.3Curtains closing an opening The deflectionofthe curtain is calculatedfrom (see FigureC2):

d

C

12p0O(3D1—2d0)d 3T1(2Mb+MCLC)

where:

= Mg mass ofgas flowingthrough the gap (kgs), == Ag areaofthe gap (m2), T1 = absolutetemperature ofthe gasesinthe layer (K), T0 = absoluteambient temperature (K), = depth ofgas in reservoir (m), g = accelerationdue to gravity(ms), = temperaturerise above ambient ofthegas (°C). The gasesflowingthroughcurtain gaps will entrain air as theyrise totheceiling,and maycause the formation ofa smoky gas layerwithin the areawhichthe curtains are intended to protect. Suchagas layerwill be considerably cooler than that within the main reservoir.Wherea smoke layerforms within the areaintended tobe protectedbythesmoke curtains,then it maybe necessary to consider further measures toprotectoccupants.Such entrainment has notbeen closely studied,butpreliminary research'°'1 suggeststhatthe mass entrained can be related tothe mass flowingthroughthe gapsto give a conservativeestimate ofthe smokerisingto the ceiling. M

(C.4)

whered0 istheheightofthe opening (m) andother variablesare as definedabove. The required curtain length to contain agas layer of depthD1 is calculatedusing an iterativeprocedure:

(C.7)

= 6Mh g

(C.8)

where:

M = mass ofgas flowingintogas layer in protected area (kgsj,

= Mg mass ofgas flowingthroughagap in asmoke curtain

(kgs'), = of rise from the base ofthe hot gas layerin height h

108

__________

the reservoirto the ceilingin the protectedarea.

Note:This equation is derived from a smallnumber of

experiments'°1. It is desirableto extend thestudy further to confirmthe derived correlation.

Acalculationprocedure for thetemperature ofthe gas layerwithin the protected areais:

Design methodologies for SHEVS

=

NIg o

(K)

_____

(C.9)

where =temperature above ambient ofthe smoke layerinitiallyforming (ignoringanysubsequent cooling) inthe protected reservoir adjacent to the leakage (°C).

109

Annex D: A comparison of different spill-plume calculation methods

D.1 The example scenario Thespill-plumemethodsdescribedin section 6.3.2apply to differingscenarios.The limited shared features of these methods dictate that a comparisonmustbebased on a scenarioinvolvinga large-area smokereservoir,with afreeplume risingfrom thespill edge. Oneofthemost common ofsuchscenariosisamultistorey shopping mall, wherethe fire islocatedin ashopandthe smoke travels out ofthe shop and is channelledto alengthofspilledge. Thefollowingtypical example ofashopunitscenario is usedas the basisforcomparison. Shop width= 10m, having no downstand facia (chosen to remove amajor areaofuncertainty inthe calculation). Storeyheight=5 m, simplifiedforpurposes ofthis exampleso thatthe shop opening is takenas 5 mhigh. Assuming asteady-state designfire: Convectiveheatfiuxleaving the shop = 5000kW, coming from a 3 m x 3 mfire having aperimeter of12 m. Becausethe shop widthisless than 5 times the side ofthe fire (seesection 5.1) Ce inEqns (5.2) and (5.7) = 0.34. The smokeis channelleddirectly to the spilledge overa lengthofedge of10 m. Thereis no downstand atthe void edge.

reservoir,it is necessaryto specifythe heightofthe ceilingin the mall in orderto be ableto use the 'effective layer depth correction' in assessingthe effective heightof rise ofthe spillplume foruse inthe BRE method. ftdoes notaffectthe othermethods. Weconsider heretwo ceilingheights: 15 m above the floor, and 11 m above the floor. See FigureDl which illustratesthe dimensionsofthis example.

••

Itis nownecessaryto calculatethe mass flowentering a

visiblesmoke layer base atdifferentheights above the spilledge, within a smokereservoirformed beneaththe ceiling.Results are listedbelowand are shown graphicallyin FigureD2. The Thomas (1987) method has not beenincludedinits unmodifiedform in view ofthe uncertainties surroundingthe choiceofanappropriate value ofAforthe circumstancesofthisexample.The method has been usedinits modifiedform wherethe valueofAis calculatedusing Poreh's method.

UsingEqn (5.7): Massflowrateofgases approaching spilledge= 29.2 kg/s. Using Eqn (5.11): Depth ofsmokelayerapproaching spilledge = 1.19 m.

A more precise calculationispossibleusingEqn (E.3),

wherethetemperature dependence ofthe parameter KM can beincluded for still greater accuracy521,givinga

depthof1.14 m.This lastvaluehasbeen used inthe present calculation,although Eqn (5.11) alone is sufficiently accurate for normal designpurposes. Hence atthe spilledge we have for the approach flow:

Q= 5000kW M7= 29.2 kg/s D= 1.14m

Becausethe example stipulatesa large-areasmoke

FigureDl Idealized shopping mall:example for comparingspill plume calculation methods

110

Design methodologies for SHEVS

D.2 BRE method

D.3 Thomaset al (1998) method

(a) 15 m ceiling

Calculationswere done using Eqns 6.7and 6.8. Results arelisted inTable D.3 and areshown in FigureD2.

Theresultsofapplying section 6.3.2 (a) andAnnex Eare shown in TableD.1. Table D.1 Entrainment intothe example spill plume: BRE_method,_15_m_ceiling

Heightofvisible smoke base above spill edge (m)

Mass flow rateof

________

smoky gasesentering smoke layer

(kg/s)

3.6 5.24

6.83 8.41 10

105

2

146 189 239 285

4 6 8 10

(b) 11 m ceiling The resultsofapplying section 6.3.2 (a) and Annex E are showninTable D.2.

(m)

(kg/s)

2.04 2.83

84.3 105 124 146 167 189

6

75

___________

102 129

__________

156 183

_____

D.4 Poreh et al method

Table D.4 Entrainment intothe example spill plume: Poreh method Mass flowrate of Height ofvisible smoke base smoky gasesentering above spilledge smoke layer (m) (kg/s)

69 94

2

4 6 8

119 144 170

10

E

0 0

IL

15

> 0 .0 a) Co

10

-

a)

0 E

Cl) It)

.0

(It

> 0

5

x

BRE-method-iSm ceiling

o

gRE-method - lim ceiling

+

Thomas Ctal(1998) method

0

Poreh etal method

[odiiedThomas)l987)method

.0 It)

0 50

70

90

110 130 150 170 190 210 230 Mass FlowRate in Spill Plume (kg/s)

FigureD2 Spill plume entrainment: comparisonofcalculation

________ __________ __________

Calculationsweredone usingEqns 6.3 and 6.4. Results arelisted in TableD.4, and areplottedgraphicallyin FigureD2.

Table D.2 Entrainment into theexample spill plume: BRE method, 11 m ceiling Massflowrate of HeightofvisibJe smoke base smoky gasesentering above spilledge smoke layer

3.62 4.41 5.21

Table D.3 Entrainment into theexample spill plume: Thomas etal (1998) method Massflowrateof Height ofvisible smoke base smoky gasesentering above spill edge smoke layer (m) (kg/s)

methods

250

270

290

AnnexD: Spill-plume calculation methods

D.5 Thomas(1987) using Poreh method to calculate A. Calculationswere done usingEqns 6.5 and 6.6.Results arelisted in TableD.5 and areshown graphicallyin FigureD2.

111

theThomas (1987) method. It does, however,suggest thatthis method isnotready yetfor general

• application. TheThomas methodwith calculatedusing Poreh's method (Eqn isinclose agreement with theBRE methodsthroughout theheightrange. • The Thomas method isin reasonable the end-entrainment zX

(1987)

6.6)

(1998)

Table D.5Entrainment into theexample spill plume: Modified Thomas (1987)using Porehmethodto calculate A Massflowrate of Height ofvisible smoke base smokygases entering above spill edge smoke layer (m)

(kg/s)

2

4

97.5 136

6

177

8

219

10

263

Itis generallytruethat designsbased on thelarger massflowvalues are conservativein terms ofsafety. We can alsonote thatforthe verydifferentcircumstanceo:Fthe European Parliament hot smoketest (adhered plume

D.6 Discussionand conclusions It canbe seenfrom FigureD2that:

I The Porehmethod, while applicableto situations whereend effectsare to unimportant, appears

agreement (although contributionissurprisinglysmall) forlesserheights of rise (perhaps acceptablyso for heightsup to around 4 m for designpurposes). Thereis a large andgrowing discrepancycompared with the BREand the modified Thomas (1987) methods above this height.

predict

consistently the lowest entrainment. This is not surprisingin view ofthe absence ofanyendentrainment terms. This is unlikelyto matter where the plume is very narrow, suchas inthe 'virtual'partof

with end entrainment, 1 MWfire, twofiretrays, large smokereservoir)[69J (summarizedinAnnexJ), the BRE method predicted asmoke layerbase within measuring error ofthe observedvisualsmoke layerbase. Whilethis is not complete validationofthe BREmethod, this good agreement represents a major extension ofthe 'envelope' ofvalidationand as suchtendsto lend added confidence in that method. By extension,we caninferthat it also lends greaterconfidenceinthe modifiedThomas(1987) method for the freeplume example cited inthisAnnex. Noneofthe othermethods described in this bookcanbe applied to this hot-smoke test scenario.

112

______

______

_____________ ____

Annex E: User's guide to• BRE spill-plume calculations

Note: This Annex usesa differentnomenclature to the

rest ofthisbook:seethe nomenclature listatthe end of theAnnex. E 1 Introduction FRS has carried out anumberofstudies intothe movement ofsmokeinbuildings.Part ofthis bookhas resulted inthe development ofatheoryby Morgan & Marshall251 to estimate the amount ofair entrained into free(ordouble-sided) thermalspillplumes (Figure24b). Thiscalculation method is important forsmoke-control design in that it enables the designer to calculatethe required fan capacity or vent areafor asmoke ventilation system forlarge undividedvolume buildings(egmultilevel shoppingmallsand atria). Anumberofstudies have since been carried outwhichhave resulted in the

modificationofthe originaltheoryto include morerecen: workon thermally buoyant horizontal flows271and adhered (or attached, or wall, or single-sided) plumes2761 (Figure24a). The calculationscanbe done using an electronic calculator havingfrill scientificfunctions.This, however, maybetime-consuming,particularlywherethe designer wishes tolookata numberofgeometries or conditions. Thecalculationscaneasilybeincorporated in a computer program wherefrequent calculationsare required. An alternative method to FigureEl isgiven laterin this Annex in order to facilitatesuch programming. Many ofthe variablesusedin equations in this Annex do not appear in the main bodyofthebook. To avoid unnecessary complicationsfor the reader who doesnot wish to use this calculationprocedure, thisAnnex is providedwith a separate listofnomenclature.

———b

a >, 0 C—. a. 0—

— .i.

o a

CCC 000 CCC

EEE 000

0.5

1

1.5

2

2.5

3

3.5

Modifieddistanceabovevirtual

soinrceI (v)

FigureEl Graphical representation ofthe theoreticalsolution for a plume issuing from a restrainedsource F < 1

4

AnnexE: BRE spilplume calculations

113

Fortunately,these assumptions correspond tomany practical scenariosofinterest to designers. Further, it should be notedthatexperimental evidence611 suggeststhat the calculationprocedure whichis the subjectofthis guide should not be usedfor approach flow layertemperatures higher than about 350 °C. Accuratemethodsforhigher temperatures do not yetexist. Thepresentmethod significantly overpredicts the mixingofair intothe risinghotgases forhigher temperatures. In practice, the designer willhave arrived at thekey parameters oftheapproach flow by some calculation procedure independent ofthe presentguide. For example,byusingEqns(5.7) and (5.8)to calculatethe flowofsmoky gases passingfrom aroom intoan atrium void. Another example is whereasingle-storeymall allowssmoke to risethroughthevoid ofa two-storey mall: here,the flow in the single-storeymall canbe calculated in the usual wayusing, forexample, sections 5.2 and 5.3 ofthis book.

calculatethe remaining parameters ofthe flow. 3 Using theresultsfrom theprecedingstage, calcuLlate the entrainment into the flow as it rotates around the void edge, ieas the smoky gases change from a horizontallymoving flowto a verticallymovingflow. Bythe end ofthis stage thekeyparameters requiredfor thenextstage ofcalculationofthevertically moving gases willbeknown at the horizontal plane passing throughtheceiling/void edge. Theseparameters are the heatflux, the verticallymoving massflux, and the kinetic energy ofthe gases (this last is based only on the verticalcomponent ofvelocity). 4 Theplume at greater heightsbehaves asifit risesfrom an infinitelywide source located in thehorizontal plane passingthrough the ceiling/void edge, where that sourcehashorizontal profiles ofbothbuoyancy and (theverticalcomponent of) velocitywhichcanbe describedbyGaussianfunctions.This sourceis, of course,virtual. We have followedLee &Emmons102 in usingthis source, and indeed in the method of calculatingthe plume above this source.The BRE method follows Lee& Emmons in callingthis source an 'EquivalentGaussian Source'. Calculate the keyparameters ofthe Equivalent Gaussian Sourceby ensuringthat the three key parameters from stage 3 abovekeep the same values. 5 Knowingtheheightabove theceiling/void edge (eg this islikelyto bechosento be equal tothe smokelayer base inthe reservoirabove the void),calculatethe entrainment intothe spillplume. This calculation treats the plume as aperfect 2-D plume havinga Jength equalto the widthofthe channel ofthe approach flow. It is important thatthe designer firstidentifieswhether the'effective heightofrise' discussedin section 6.1 of the main textofthepresentworkapplies tohis/her circumstances. 6 Calculatetheadditional entrainment intothefree ends ofthe plume.This assumesthat the bulk ofthe plume is relativelyunaffectedbythese end effects; this is reasonablefor plume heightstypicallysmaller than or comparableto the plume length[62.

E.3 Outline of procedure

E.4 Detailed calculation procedure

The calculationproceedsin discrete stages: 1 Thedesigner mustknow: (a) the internalgeometry ofhis building,including

E.4.1Deriving key approach-flow parameters

E.2 Scenariosand assumptions The calculationmethodstrictlyonly appliesto fire scenarioswherea horizontallyflowing,thermally buoyant layer ofsmoky gases approaches avoid, through which those gases then rise. Morespecifically, the followingassumptions aremade. Thisapproachflow is assumedto be beneath aflat ceiling(ora downstand) atthe edge ofthe void. It is channelled bydownstands (which may be either walls or channellingscreens). Theflowhas flow-lineswhichareeverywhere parallel and which approach the edge ofthe void at a right-

• • • • Theapproach flowis also assumedto be developed. •• There is no immersed ceilingjet. It is alsoassumed that thevelocity ofthe clear air belowthe smoke has avalue smaller angle.

fully

the layer itself

2

layer

thanthat of

relevant channel widths, (b) at least two ofthe keyparameters ofthe approach flow;usefulpairs are: massflow/heatflux, massflow/meanlayertemperature, mass flow/ceiling temperature, heat flux/mean layertemperature, heat flux/ceilingtemperature, heatflux/layer depth, layer depth/meanlayertemperature, layer depth/ceiling temperature. Usingtheknown parameters for the approach flow,

Complete allnecessarypre-calculationsto derive the key parameters ofthe approach flow described in stage 1(b) above. E.4.2 Determingremaining approach-flow parameters Select from the followingEqns(from27)to determine the remaining parameters forthe approach flow from the initialknown parameters. — Calculatethe meanlayertemperature (0w): (K)

(E.1)

Calculatethe mass flowrate (Mw)at the opening52]:

114

_____ __________

M=

(2gO7)"2

C312

(kg s)

dW3/2cM

(E.2)

where:

= 1.22 kgm3for an ambient temperature T0of288K, = 0.6 for opening with a deep downstand or 1.0 for

p0 Cd

no dowristand, 9.81 ms2,

g

= 1.3 for most typicalflowinglayers.

Design methodologies for SHEVS anomalous entrainment above the spilledge as ifit occurred in the rotation region. Ifthe line plume issingle-sidedgo to E.4.7after completion ofthis step. E.4.4 Calculate the Equivalent GaussianSource: First convert Qand M into the corresponding parameters perunitlengthofplume (ie divide bythe channel width (W) to give and A). Then solve the followingEqns:

O

The depthofthelayer(d)at the opening is thengiven

1

by521:

[Notethe importance ofknowing whetherthereisa downstand running along the edgeofthe void (and thus at right angles to thedirection oftheflow), becausethis changes the valueofCd.]

r

d =[2C2Kwp(2gOT)1/2]

I

(m)

—

layer ist52:

Il+A2 ________ Q0 Tctl A+—

0[

2B

(E.4)

wherelcQ =0.95 for most typicalflowinglayers. Greater accuracycan be achievedby calculatingthe values ofthe profilecorrection factor 1M and KQusingthe temperature-dependent formulaein52, although this is usuallyunnecessary for mostpractical designs. Thelayer's characteristicvelocity (v) is given by271: v = 0.96 CdKM [ IC0

gQT

UG

and bG

]

____

-

(E.12)

(E.1)

=

(E.14)

1/3

(m s')

1

LCP0IW'o]

(E.5)

Fora deep downstand, whereCd = 0.6,this becomes: 1/3

= 0.761 gQT 1

Fe

PoL[]i32

K

(K)

T0c

wherethe empiricalthermalconstant'°21 2= 0.9:

c=

O —0

(E.1J)

F

(E.3)

The mass-weightedaveragetemperature O ofthe gas

—

[9J LT]G

,2/3

3M7

(E.1C

T0cjp0J

[

(m s')

(E.6)

[]

G U(; and bG are parameters ofthe Equivalent GaussianSource.

where

E.4.5 Calculate theentrainmentintotherising plume: The SourceFroudenumber(F) forthe line plume is251:

[cp0WT2o]

Withno downstand at the opening,Cd= 1.0, and

F=

1/3

V

= 1.271

gQT 1

(ms)

UG

(gb)

[2

1/2

(E.15)

(E.7)

LcP0WT2o] Calculatethehorizontal flux(B) ofvertical buoyant

potential energy27'251 (relativeto the voidedge):

wherea = 0.16 for double-sided'°2 and 0.077 for singlesided61 line plumes. Calculatethe transformed parameter (DG) forthe Equivalent GaussianSource: 1

B=1Q.gvd2

Vg

(Wm1)

(E.8)

E.4.3 Calculate themass flux (Mr) rising pastthevoid edge271: M3,

)2d

poWa'(2g

3/2

+M

(kgs1)

(E.9)

wheretheentrainment constant a = 1.1. Note: cC takes sucha large valueas aresult oftreatingall

(E.16)

(1— F2)'3

I

Determine the valueof (1g) by usingthe following procedure (or the alternative procedure ofE.6below): represents a valueon the vertical axisofFigure El. Lookacross to the middle solid curve and findthe correspondingvalueofIi(uc;) on the other axis. Calculate the transformed heightparameter ofx'

AnnexE: BRE spill-plumecalculations correspondingto the desired plume height (x), noting thatxmust be setequal totheappropriate effective heightofrise identifiedin section 6.1 ofChapter 6 ofthis book. 2 x x/ =—a—

(E.17)

SMr=4biia XPo

Al1(v) =

E= (ba +b)

(m)

(E.27)

(;±u)

(m)

(E.28)

(E.18)

[F2(1— F2)]113

and (E.19)

11(v)= 11(v0)+M1(v)

Determine valuesofb, p andu' correspondingto the calculated valueofT1(n) usingthe followingmethodor an alternativeprocedure which is setoutin E.7below. 11(u) represents a valueonthe horizontal axis ofFigure El. Usingthis valuefindthecorrespondingvalues (from allthree curves) foru, p and b. Then use the following equations todetermine u', p and b':

u'= u"F'1'3

(E.20)

1

(E.21)

(1—F2)1°p'

b'= b"[F2 (1— F2)]113

(E.22)

Nextdetermine thecharacteristichalf-width (b) ofthe line plume251atheightx:

E23"

b= b'bg

Then calculatethe axial vertical velocity component (u) ofthe gases at height x:

uscF

(E.24)

Calculate the massflow per unitplume length (mr) passingthe chosen height25x:

=

Poub[1

'[]

(E.26)

where: 2

Next calculateA11(u):

(kgs1)

115

Notethatwhile the originalderivation was semiempirical,thistreatmentis equivalentto regarding the freeends ofthe line plume as iftheywere themselvesline plumesoflength2b at eachend, although the parameter btakes its valuesfrom the properties ofthe main line plume itself Addthis to theplume entrainment result from E4.5 to obtain the total mass flowMrofsmokygases risingpast thespecifiedheight(x), ie: Mr=mrW + öMr (kg s')

(E.29)

It should benotedthat where both endsofa plume are bounded by sidewalls (egas in a shaft)then öMr=0. E.4.7 Modifications to the above procedure for singlesided27'611(or adhered) line plumes Convert both the Equivalent GaussianSource and the plume intoacomposite ofa real andanimaginary balf suchthatthe centreline ofthe composite lies along the verticalwallto whichthe plume is adhering. This is done bydoubling valuesfor B, M (and henceA), and Qfrom

E.4.3)before returning to E.4.4—E.4.6 above. Note that experiments [61] show thatthe valueofa needed in E.4.4—E.4.6 should change valuefrom 0.16 (valid for a free- or double-sidedplume) to 0.077 forthe adhered plume. Oncompleting E.4.6, halvethe final valueofmass flow Mrrisingpast thedesired plume height(x).

E.5 Limits to spill-plume entrainment calculations

(1 +A 2)112]

(kg s1

Convert tothetotalmassflow in the line plume (ignoringend-effects)bymultiplyingEqn (E.25) by the channel width(ie mrW). E.4.6 Calculate the entrainmentöMr125'62 intothe free ends ofthe line plume The widthoftheline plume (and alsoits axial velocity)

canbe taken asbeingapproximatelyconstantfor most of itsheightas a first-order approximation,and equal tothe meanofthevalues atthe EquivalentGaussian Source and atthechosen heightx. The entrainment öMrintoboth endsofthe line plume is then623:

It isknown from experimental studies with free plumes thatfor heights ofrisefrom the spilledgeto thevisible

smoke layer base ofless than 3 m, no current theory adequately describes the entrainment. The mass flow ratespredicted bytheoryaregreaterthan observed in practice. Whereheights ofrise less than 3 m occur,this over-prediction ofentrainment will usuallyprovide an additionalsafetymargin inthe provision ofsmoke exhaust ventilation.

E.6 Alternative method for determination Of l(Ug)

IfDg 1.549 then Ti(Ug) = (ug_ 0.75)/O.9607 IfDg 1.549 and

1.242

Design methodologies for SHEVS

116 then Ii(Dg) = (lJg— 0.843)/0.8594 If 1.242 andhg> 1.059 then11(Ug) = (hg— 0.9429)/0.6243 = — IfDg 1.896then u'

= 1.0

Cd

>0.786 and I1(D)

thenu'

IfI(u)

c

1.896 = 0.090811(u) + 0.821

d

0.786then u' =11(u)°35

E.7.2Determination of p" = 1f11(u) >0.832 then p' 0.960711(D) >0.464 and 0.832 1f11(i)

I()

F g

+ 0.75

Im

thenp' = 0.859411(D)+ 0.8429 If11(u) >0.186 and 11(D) 0.464 then p' =0.624311(o) + 0.9429 = 1f11(o) 0.186 then p' O.371411(u) + 1.0

6m

E.7.3Determination of b = 1f11(u) >2.161 then b' 0.93811(u) + 0.82

p

then b' =0.8911(u) + 0.95 1f11(D) 1.296 and I(u) >0.896 then b'=0.8111(v)+ 1.071 1f11(o) 0.896and 11(u) >0.65 then b" =0.619I(o)+ 1.214

Q0

1f11(i) 2.161 andI(ii) > 1.296

IfI(h)

0.65 and 11(u) >0.543

thenb"=0.33111(h)+ 1.414 1f11(i) 0.543 and11(u) > 0.421 thenb' = 0.062711(D) + 1.55 — = 1f11(u) 0.421 and 11(D) >0.348then b" 1821 0.6I(o) = 1f11('u) 0.348then b'

M

M Q

T u

u' v

W x x' cx

cx'

Now calculateu', p andb' from Eqns(E.20)—(E.22)in E.4.5

KM

? p 0 v

Upward mass flowrate per metreacross the horizontal planethroughthe balcony (kgs1m') Characteristichalf-width ofline plume at height x Dimensionlesshalf-width oflineplume Potential energy fluxpermetre ofhorizontal gas stream approaching spilledge (Wm1) Coefficientofdischarge Specific heatatconstantpressure ofgas (kJ kg'°C-1) Depthofgas stream beneathceiling (m) Source Froude number(for line plume) Accelerationdue togravity (ms2) Transformedheight(dimensionless) Mass flow rate per unitwidthofgas stream (kg m's') Mass per second per metreofair entrained intohot gas stream at corridor ceilingedge (kg ms1) Mass flow rate ofgases (kgs1) Mass persecond ofair entrained intofree endsof plume (kgs 1) Dimensionlessbuoyancy on plume axis Heat fluxin the gas (kW) Heatflux per second per unitwidthofgasflow (kWm1) Absolute gas temperature (K) Verticalgas velocity at height x (ms') Dimensionlessvertical gas velocity Horizontal velocitycomponentofgas (ms') Widthofgas flow (m) Heightofclear layerabovefire compartment/balcony (ie spill) edge (m) Dimensionlessvariable Entrainment constant for plume (0.077 and 0.16 for single-sidedand double-sided plumes) Entrainment constant for air mixingintogases rotating aroundahorizontal edge Profile correction factor for mass flow (approx. 1.3) Profilecorrection factorfor heat flux(approx.0.95) Anempiricalthermalplume constant(?= 0.9) Gasdensity (kgm3) Excess temperature ofgases above ambient temperature (°C) Transformedreciprocal ofbuoyancy (dimensionless) Function definedin Eqn (ElO) Function defined in Eqn (E12)

List of subscripts o Anambient property c Variableevaluated athighestpointin a flow (but outside anyboundary layer) g A propertyofthe equivalentGaussian source r Base ofceilingsmokereservoir w Variableevaluatedinthe horizontal flow at opening y Variable evaluated invertical flowpast top of opening

117

Annex F: 1977 fire at IMF building, Washington DC (based on reference [181)

Casehistory: Fire atIMF Building, WashingtonDC, in 1977 13-storey.square-shapedreinforced concrete Building office buildingwith penthouse, basementand

Atrium

4-storeyundergroundgarage Acentrally situated enclosed courtyard created the atrium. Thewindows otthe offices facingthe atrium were of6.35mm plate glass

Dateoffire 13May1977 Locationoffire 10th-floor office

Fire protection Two ventilationsystemsrecirculated air atthetop ofthe atrium, andatthe base oftheatrium therewas an airhandling unit. Smoke detectors wereprovided at the fans ofthe air-handlingunitand were arranged to shut down thefans whenthe detectors activated. Theunits could be manuallyrestarted and put on exhaust. The general office areawasfedbypenthouse air-handlingunits that could go intoa 'smoke-purge mode' iftheywererunning when afire occurred. Noneofthe above systemswas in operation at the time ofthe fire. Theroofofthe atrium was madeofclear plasticpanels. Sixcustom-made smokeventilators were provided in the atrium's roofcomprising clear plasticpanels onhinges

equipped with springsand release mechanisms.The release devicewas operated by one smokedetector locatedin theatrium roofFusiblelinks onindividual ventilators were alsofitted. Sprinklerswereprovided at rooflevel in the atrium andthe buildingwasequipped with manual fire-alarmpoints and hydrant valveson each floor.

The fire At 6.45 pma worker discovereda fire in asmalloffice (3 mx 4.6 m) onthe 10th floor (seeFigureFl for aplanof this floor).The Fire Brigadereceived the alarm at 7.01 pm. On arrival,firemen found fireventing from the office window into the atrium. The firefloor was hoi: and smoky andthis, coupled with the fact thatthe fire involvedaninner office, made locating the fire difficult. Thick black smokeissuingfrom the office hadbuiltclown from the roofofthe atrium tobelowthe 10thfloor. Although the smoke detectorhad operated, only two ofthe sixsmokeventilators had opened. TheotherIbur had released butthespringshad lostsufficientstrengthto open themfully. These units had to bemanuallyopened from outside. Smoke however did not vent effectively and atonestage completelysmoke-loggedthe atrium. Smoke extractors could notbeconnected to the smoke ventilators and so firemen usedlargeextractors pointed upward from the atrium ground floor to pull fresh air from the frontdoorsand pushsmoke upwards andout throughthe ventilators.Nobuildingengineeringstaff were availableto advisefiremen on the HVACsmokepurgecapabilityuntilmuchlater. It took2—3 hoursto finally removethesmoke from the atrium. Conclusions

• The firewasconfined to the room oforigin bythe closed doorandwall construction. • Windows facingtheatrium above the firefloor were crackedby heatbut fire andsmoke had not penetrated otherfloors. • The temperature ofthe gas layer in the atrium insufficienttoactivate the sprinklersin the atrium roof • Dueto ah ofreplacement air the existing office

was

FigureFl Plan ofthe 10th floor ofthe IMF building showing locationofthe office where the fire started

insufficiency

118

•

ventilation system designwas inappropriate for clearance ofsmokefrom the atrium, andthe 'dilution' ventilation approach usedby the Fire Brigadetook many hours to clear thesmoke. Ifthis had beenan atrium with balconies providing accessto escape ways, the smokemaywell have causedserious escape problemsfrom upperfloors.

Design methodologies for SHEVS

• Despite thefact that therewere unprotected openings onto the atrium, and thatatone theatrium was point

totally smokeAogged,smokedid notmigrate from the atrium to other parts ofthe building.This indicates that the existingventilation arrangements apparently 'depressurized' the atrium.

119

Annex G: Design procedure for hybrid systems

G.1 Mass-flow-basedsystems(Figure49)

• Determinetothe heightofrise ofthe smokeplume clear the

required openlevels,hb, with thedesign fire (seeChapter 3) chosenonthe lowest open level. This will alsoyield the smokelayer depth D, measured from thecentreline ofthe ventilator. From Figures28—3 9 or bydetailed calculationand with thedesiredchannellingscreen separation L, or opening widthW, determine the mass flowrateM1 entering the base ofthe layer.Ifthe fireis on the atrium floor, determine M1 usingsection 6.5. Calculatethe total surfaceareaofthe smokelayer (the atrium surface areain contactwith the smokelayer plus theareaofthe layer base),and determine the likelysmoke layertemperature usingChapter 9. Ifthe smoke layer temperature is below20 °C above ambient, then the numberofopen levels may needto be reconsidered, or some (or all) ofthelowerlevels vented independently from the atrium, usingthe procedures setout in Chapter 5. Setthe neutral pressure plane heightX, to that required abovethebase ofthe smokelayer, and determine the value of(AVCV/AC) from Eqn (7.1) or Figure46. Withthesevalues of(AC/A1C), D, M1 and 9 calculate the ventilationarearequired from Eqn (5.15), (or from Eqn 93 in reference [9]), and alsothe inlet area required. Followprocedure given in section G.3 below

•

•

6.3).

• With the designfireatthe lowestlevel (seeFigure and intoaccount the

• •

G.2Temperature-based systems (Figure 50)

• Decide on awith smokelayertemperature rise the facadematerial

0,

compatible employed.For float glassatemperature rise of70 °C above ambient will givea reasonablesafety margintothe system design.Toughened glassmaybe capable of withstanding higher temperature rises

• Calculate the totalsurfaceareaofthe smokelayer(the atrium surface (eg200—300°C).

areain contactwiththe smokelayer the area ofthe plus layerbase), and determine themass

50)

taking necessaryheight ofr[se hb for coolingpurposes,determine the maximum smoke layer depthDm Setthe neutral pressure plane height X,to that required above the base ofthis smokelayer depth,and determine the valueof(AC/A1C) from

•

•

flowrate requiredto givethe desiredtemperature rise, usingChapter 9. Asa simplificationincorporating a margin ofsafety,this stepcan beomittedand the mass flow ratecalculated usingEqn (5.10), By detailed calculationandwiththe channelling screen separation LoropeningwidthW, determine the height ofrise hb to thebase ofthe layer,necessary to givethe requiredmass flowrate (see sections 6.2 and

• Eqn Withthe same value ofhb,determine the shallowest smoke (7.2).

• •

layer depthD1, compatiblewiththe depressurizationconcept (this is often the second level beneaththe NPP). Withthesevaluesof(AVCV/AC),D1, M1 and 0 calculatethe ventilation areaandthe inlet area required using Eqn (5.15), (orfrom Eqn 93 of reference [9]). Followprocedure given in G.3 below.

G.3 Commonprocedure

• In the event that the actual inlet areaavailable thanthat

is

required bycalculation,then the ventilation areashould be increased to maintain the

greater

ratioof(AVCV/AiCI). Using Eqns (7.2) and (7.3) and the appropriate wind pressure coefficients(Cr's),checkthe system operation with regard to windeffects. Intheeventthatthe wind effectsmayadverselyaffect the operation ofanatural ventilationsystem, calculate the fan capacityrequired usingEqn (7.4),with the appropriatevalue ofdesignwindvelocity. Check that the anticipated suctionpressure and/orair inflowvelocitiesdo not in themselvesendanger the safeuse ofany escape routes away from the atrium(see

• • •

section 5.9).

120

________ ____________

_____

Annex H: Effect of a buoyant layer on the minimum pressure recommended for a pressure differential system

Uc

He/she will alsoknowthe ventilator andinlet parameters, including the mass exhaust rateofsmoky gases (Me)•

H.1.iWitha'dominant'air inlet

A 'dominant' air inlet occurswhenthe total areaofinlets belowthe smoke layer's base is morethantwicethe total area ofall openings,other thantheventilators themselves, above the smoke layer'sbase. Theheightofthe NPPabove the base ofthesmoke layeris for natural smokeand heat exhaust ventilators neglecting wind effects (seeFigure Hi):

x

d1Tambr2 Tambr

+ T1

()

Height

ofNPP

Air inlet

(Hi)

t

Smoke exhaust Me (A2Cvi) anatural ventilator)

H.1 Assessmentof height ofthe neutral pressure plane (NPP) Thedesignerofthe SHEVS willhavecalculated the depthD and temperature 01 ofthebuoyant smoke layer.

AiC1

Heightof highest leakage path to pressurized space

Pressurized

Figure Hi The NPF'and smokelayer buoyant pressure

where:

= CA0

using aflow network analysisconsideringall significant

CA

andC1A=total aerodynamicfreeareaofthe dominant Inlet (ie ofall inletsbelowthe smokelayer's base). Forpowered smokeand heatexhaust ventilators neglectingwind effects(see FigureHi): 2gO1

TM2 1 (CA.)2

p

(m)

(H.2)

H.i.2Withno dominant air inlet Wherethere is no dominant air inlet thereis no means of simple calculation,and the height must be calculated

leakage paths. This is beyondthe technical scope ofthe presentbook, and is not considered further herein.

H.2 The pressure rise at a specified height above the NPP The buoyantpressureat a height YNPPabove the NPP is:

Lp =--pOgyNPP

(Pa)

(H.3)

121

Annex I: Aspects of hot-smoke tests to confirm the performance

of SHEVS

1.1 Whydo hot-smoketests (HST5)? Hot-smoke tests (HSTs) are a form ofon-site acceptance testofthe entireSHEVS,in as close a form aspossibleto thefinal installedsystem. Itis not always necessaryto do

them.HSTs are desirablein the followingcircumstances. Wherethe designcalculationsfor the SHEVSare believed tobe inadequate bytheRegulatoryAuthority, whois neverthelesswillingto grant conditional approval subject to proofofperformance.Notethat this should not occur very often, as inadequate designs should be identifiedat an early stage inApprovals Procedures and the design corrected before installationofthe SHEVS equipment. Itmaybe considered wherea designisdefended bythe specialist designer,but is still not trusted bythe Regulatory

•

• Authority. Wherethe system,buildingshape,orequipment as installed doesnot matchthe on which

proposal approvalwas granted,butthe SHEVSdesigner nevertheless arguesthatthe system will work satisfactorily. This scenario oughtneverto happen, but occurs all too often. Wherethe circumstancesofthebuildingaresuch that the fundamentalassumptionsunderlyingthetheories uponwhich designsarebasedarenot valid, and approximationshad to be madeinthe design. Atypical casemightbe wherea spillplume rises past a strongly curved (inthe horizontal plane) spilledgewhereas the design methods are all basedonthe spilledge being straight. This canperhapsbe regarded as a special case ofthefirstcircumstance above,withno-onein a position ofblame in any way.In an ideal world, this oughtto be the only reasonforwanting HSTs.

•

1.2 Choosing the test location

It is possibleinmostbuildingsfitted with a SHEVSto imaginea real fire occurring in anyone ofmany locations.

Someofthese locationswill represent amore severe threatthan in otherplaces. For example,afireon the floor ofan atrium, notnear tothe walls,will entrain less air than the same firelocatedin aside-room whereby the smokeenters the atrium as a spillplume. The fan capacity

neededto maintain a smokelayerat a given height might for the latter casebetwicewhat is needed forthe former. Similardifferencescan occur betweenan adhered spill plume and a free spillplume. Another exampleis where

smoky gasesfrom a side-room (eg from a shop) can spread sidewaysunderneath aprojecting balcony before spillingintothe atrium, compared with another location wheresuchsidewaysspread cannot occur. It is generallytruethat a SHEVSshould be designed to cope with the worst-case location within any smokezone (ie within any areafeedingsmokeintoa singlesmoke reservoir). It istherefore necessaryto locate the test fire inthatsame location. Thefire should never be located in the easiestlocations simplybecause they aremore convenient.

1.3 Choosingthe test fire Thebasicrequirements for the HST are that: itmust notdamage the building,and itmust be as similaraspossibleto the designfire, in order tominimize the extent ofextrapolationrequired afterwards.

••

Reconcilingtheseconflictingrequirements inevitably means thattheHST must be specificallydesignedto matchthe chosen location in thebuilding.Thefollowing listgivesafew considerations. 1 The fuelmustburncleanly.Ethanol (either pure anhydrous, or as the almost-pure industrial methylated spirits)is excellentasitburns with no visiblesmoke, andleaves no deposits. 2 Theperimeter ofthe fire should beas closeaspossible to the designvalueinorderto obtain asimilar rate of entrainment. This may mean using more than one fire trayto simultaneouslysatisfy3,nextpoint below. 3 Theheat output ofthe HSTshould beas closeas possibleto the designvalue, subjecttothe gas temperatures being lowenough to avoid doingany damage.This must be calculated. 4 Heatinsulatingmaterialsmust be usedwherever the gaseswillbehot enough to causelocal damage. Typicallythis willinclude liningor simulatingasideroomand anybalcony projectingbeyondthe opening,

Designmethodologies for SHEVS

122 and/orany glazingabove the opening to aheightpre-

5

calculated asbeingnecessary. Atypical maximumlayer temperature inthe HST mustbebasedon themostvulnerable material (often PVC incable insulation,or otherwise, forwhichthe temperature must never exceed 70 °C). Good practice requires that asafety margin ofatleast20 °C beleft belowthatvalue. Themaximum heat output for point3 above is usuallyderivedby reverse-calculation from this layer temperature.

14 During the test Thermocouples should be usedto measure the layer temperature in the smoke reservoir,preferably as a vertical profile. 2 Height markers should be positionedto makeit easy and accurateto estimate theheightofthe smoke layer's base. 3 Thesmoke generators should be ofatypewhichleaves no deposits. 4 Thesmoke generators should be positioned so that the smoke is notdestroyed by the gas temperature (ie the smoke should not be introduced too close to the fire). 5 Enough smoke should beusedfor the layertobe visible—and forany smokeleakage elsewhere tobe visible. Notethatit is effectively impossiblefor the HSTsmoke tobe as optically denseas from areal fire. Itis betterto say that ifit ispossibleto see thetest smoke at all, the real firesmoke would be unacceptable!Calculationsofsmoke densities in real fires are possible,although difficult. 6 Observers should look for smoke leakagewhereit should notoccur. (Thisis cruciallyimportant.) 7 Thereshould be sufficient safety procedures for people presentduring theHST. Theseshould include having: — a fire-crew readywithhoselaid (or other extinguishingapparatus) in case oftrouble, — 'minders' for the inevitable crowds ofonlookers and VIPswithinstructions on how to guide themto 1

safety,

a safetyofficerin charge ofthe test with sole authority to demand evacuation ifconditions become unsafe,etc. 8 Thebuildingmust havebeen effectively cleared of peoplebeforetheHST (apart from thosetaking partin it, or being controlled spectators),especiallyat higher levels wheresmoke is expected to accumulate.Note that therewillbe enough CO2from the testfire in the smokelayerto be harmfulto anyonebreathing it. (Also notethat for one HSToneofBRE'sobservershad to —

orderone ofthe building'ssecuritystafftoleave the top floor against his will becausehe had beentoldby thebuildingownerto stand thereand keep people from entering that floor!). 9 Thereshould bea preliminaryHSTwith a smaller size offireto confirmthat the actual smokebehaviour safelymeetsthecalculated HST parameters. (Forone HSTthe testers had to abandon the originalfull fire size because in the preliminary test smokewas seen to beunexpectedly intercepted by aceilinghaving sprinklers.The fulloriginal size ofHST fire would have triggered several dozen ofthe sprinklerheads.) 1.5 The subsequentanalysis 1 Conclusionsshould not be based solely onvisible smokedensityThis is a major mistake,see section 1.4,

point S above. 2 Did theobserved resultsmatchthe predictionsforthe HST?

(a)Ifyes, has the same methodusedto calculatethe HSTbeenusedto extrapolate tothe full design condition?In this casethis can be donewith confidence. (b)Ifno, has a location-specificcorrection been derived and applied to the designscenario forthat same location?This is the bestthatcan bedone in the circumstances. 3 Were thereany otherproblems revealed bythe test whichrequire separate modificationsto the SHEVSor to otheraspects ofthebuilding?Examplesinthe past have included: — deflection of hanging smokecurtains, — of siphoning smokethroughHVAC/ACMVducts whichlackedsmoke dampers, — build-upofsmoke in 'stagnant corners' beneaththe smokelayer, — build-upofsmokein supposedlyprotectedspaces dueto unexpected leakage paths, — smokeatrooflevel which has already leftthe the smoke ventilators, re-entering buildingthrough plant-room intakes whichserve other parts ofthe building,etc. 4 Doesthe extrapolated designscenario, calculated as ir point 2(a) or 2(b)above, andconsidering any additionalproblems asin point3 above, represent a worsening ofsafety compared with the originaldesign criteriabeingtested? 5 Ifno, the SHEVShaspassed theHST. 6 Ifyes, the SHEVShasfailedtheHST.

123

AnnexJ: Case history smoke-control design in 'D3 Espace Leopold Building', European Parliament, Brussels Note: This design studywas carried outusing the

predecessor documents to the presentbook (ie two BRE Reports[24"3]), but usingmethods whichwere essentiallysimilarto the presentbook.

The 'D3Espace LeopoldBuilding'ofthe European Parliament in Brussels ishighly innovative and for

architecturalreasons required a performance-based approach to fire-safetydesign.The buildingincludes a 300 m longcovered 'lightstreet' or atrium, open to three tall storeys offoyers on one side, leadingto mostofthe meetingrooms, and to sixstoreys ofofficesontheother. Thefire-safetyengineered designdescribed in this Annex includes aSHEVSincorporating automatic smoke curtains to isolatethefoyer storeyopeningsaspart ofthe provision toprotectthe means ofescape,and to separate adjacent smokereservoirs.An extensiveanalysisof possiblefire scenariosled to specificationsfor programmingthe FireSafetyManagement system,and to writingevacuation procedures andfire intervention plans forthebuilding. At therequestoftheBrusselsFireService,ahot smoke testwas conducted in the 'light street', using a 1 MWfire in aspeciallyconstructed simulatedshopcompartment, to confirmtheproperfunctioningofthesmoke-control design.This test confirmedthe appropriatenessofthe basic smokeventilation design,but yielded important recommendations,especiallyfor finalizingthe installationofthe smokecurtains. This case studywill cover the followingtopics: Architect's design Code requirements for fire safetyin Belgium Achievement offire safetylevel inaccordance with the architect'sview FireBrigaderequest:hot-smoke test to verifythe function ofthe smoke-control system and to check whethersecondary problems could occur.

•• • •

J.1 Introduction Inmostofthecountries around theworld fire regulations

arestill very prescriptiveandvery little freedomfor designisgiven to architects to designspecial buildings'as the codes do not allowit'.

PlateJi External appearance of European Parliament buildings, Brussels

Belgiumalso has veryprescriptivecodes andwithouta Fire SafetyEngineeringapproach the designofthe new headquarters ofthe European Parliament would not have beenpossible. TheEuropean Parliamentbuildings(Plateji)in the heartofBrusselsaretoday'sand tomorrow's centres of important decisions.Onemajor decision,made4years ago, isalready in execution:theofficesand meetingroom complexfor Members ofthe European Parliament as well as for the administration (ie the D3 building)will be extensivelyequipped withactive fire protection, including aflexibleapproach to compartmentation, smoke detection, sprinklerswhereappropriate,and smoke-control installations.The authors wish to make it clear thatthe fire safetyengineeringdesign described herein wasdoneby IFSET, withFRS onlybecoming involvedwhenahot-smoke test was proposed.

J.2 A plan ofthe D3 complex The D3 complexis abuildingwith differentareas interconnected with eachothertocreate amaximum spatial effect. The buildingcomprisesthefollowingareas.

124

Design methodologies for SHEVS

Qr,

1Q

2Or

3O

4O

§O

FigureJi The light street'coveredwith a glass roof

J.2.1 Underground levels The buildinghasfive underground levelsofwhichLevels —5, —4 and —3 are usedforcar parking only. On average, thelevelshave the followingdimensions : length 273 m, width 77 m andheight2.4 m. Eachlevel has a parking capacityofabout 660 cars. Therearetwoentrances (North and South) open betweenthe differentlevels,connecting eachlevel to form a singleopenvolume. ParkingLevel—2 has the same overall dimensions althoughthatpart ofthe buildingbetweenaxes A andD (width=25 m) isusedfor other purposes. The north side is usedfor leisure activities, the southside for deliveries, both incoming and outgoing,and includesspace for storage.The numberofparking spacesis thus reduced to 360 cars. Level—1 is notusedas aparking areabuthas 20 deliveryquays forunloading andloading goods into/fromlarge and smalltransport vehicles.Thereis a largestorage hail aswell as aself-servicerestaurant.

J.2.2 Theinner street(covered with a glass roof) As canbe seen in FiguresJlandJ2, andinPlateJ2, thereis avoid betweenthe 7-storey-highconstruction atthe frontofthebuildingand the 16-storey-highconstruction at therear. This void is covered with aglazed roof forming a'lightstreet' so that the entire length(240 m) canbe considered as anatrium6storeys high, interrupted bya central forum betweenaxes N04 and S04. Atevery second level,3 walkways(bridges)cross the light streetfrom axis G to axisH.

At ground-le'el00 (FigureJ2),thecovered streetis a meeting place and circulationzone. The adjacent offices havesocialfunctions,andthere arealso a few shops located atthis level aswell asthe printing officeand the restaurant. TheFire SafetyPlan hadto consider thefollowing officesand meetingrooms whichare eitheradjacent to or haveescape routesopen tothe lightstreet. J.2.2.1. Conferenceblock 'Rue Wiertz'

Between axes A andG, a totalof39 conference rooms art locatedonthree levels: Level 01, Level 03 and Level 05. Each conference roomextends over two levels in height. At the entrance to each large conference room (140 seats there is alobbywhichis completely open to the covered lightstreet. Between Sli and S14 thereare some smaller offices whichhave glasstowards the inner street (FigureJ3).

J.2.2.2Office block 'RueMail' Between grid linesH and L smaller offices are situated on eachlevel (from 01 to 06). Some 40 offices on eachlevel areadjacentto thecovered lightstreetand separated from it byplain glasswindows (grid line I) (FigureJ3).

J.2.3 Thecentralregion The centralregionis mainly a circulationzone on Levels 01—04. The library is situated onLevels 05 and 06 and was includedin the study foractive fire-protection systems.

AnnexJ: Case history

125

;©

®

0 0 ci)

0 =

ci) ci) ci) ci)

>

-á

= 0 bJ

= 0

0 N

ci) ci)

=

0

0

0

0

= (ci

0

0= 00

0 0 ci)

-J ii) 0

(ci U,

0. uJ

= (ci = =

-o

00

0 0

ci) -J ci)

0 (ci

0.

ci,

U)

c()

cf-)

-)

-)a)

=

126

Design methodologies for SHEVS Exhaustvolumejiow

MrT/(1.22 T0) = 11.9 m3/s

(J.3)

where:

T0z=15+273 =288K, T1 01

PlateJ2 D3 Espace Leopold Building: the light street'

J.3 Fire risks and smoke control scenarios J.3.1 The underground levels (Plate J3} Thedesignfireforacovered car parkwas taken to be 12 m perimeter firewith a convectiveheat-release rateof 2500kW (2.5 MW). Theceilingareaneedsto be dividedintosmoke reservoirsby means ofautomatic curtains toprevent excessivecooling ofsmoke leading to smoke-loggingof the entirefloor area. Thevolume ofsmoky gases needingto be exhausted from the underground zonewas calculated as follows. Massflow Mf= 0.188 x P x (y)3/2

= 5.68 kg/s

(J.1)

where: P = 12 m perimeter, Y = 1.85 m heightofrise.

where:

= 2500 kWconvectiveheatflux.

PlateJ3 D3 Espace Leopold Building: carpark

440°, and

ambient temperature = 15 °C. This exhaust rateis the same forall fourunderground levels (Levels—5 to —2). Thereare no sprinkler installationsplanned for the car parkareas. The entrances on thenorth orsouthsidewill provide replacement air. At Level —1 thereis also astorage room for incoming goods. As thispart ofthe buildingcan contain flammable goods, thereis anappropriate quick-responsesprinkler installation.Itwas agreed that it would be appropriate to use the same fire size as before, andhenceEqns (J.1)—(J.3) also apply here, withthe same numerical valuesas above. As thesmoke temperature willbe affectedby cooling bythe sprinklers,the volumerate is reduced to 6.8 m3/s. At Level —1, however, the exhaust rate willbe determined bythepossibilityofa fire in a truck ata loadingquay or ofa fire in the stockroom orrestaurant. As thereis ahigh potential for risk to life in the restaurant, and toreduce the chance ofa severe lorry fire, the decision has been takento installquick-response sprinklersin both the restaurant and the deliveryquay. The followingfireparameters have beenadopted: Restaurant Intheabsence ofany specificdatafor restaurant fires, it was decided that adopting the BRE Reportt241 designfire for retail areas would be appropriately pessimistic, modifiedbythe more recentadvicefrom FRS thatthe size canbe halved whenquick-responsesprinklers are usedinstead ofstandard-response sprinklers. Area = 5 m2,

Q

Smoke layertemperature

= Q/(cM-)=440°

= 440 +288= 728 K,

=2.5MW.

(J.2)

Stock-holding areas In theabsence ofspecific dataforfires in the stockholding areas, it was decided to adopt the BRE Reportt241

127

AnnexJ: Case history designfireforstandard-response-sprinkleredretail areas. Area = 9 m2 (Note:thisshould notbeusedas a universalprecedent.), = 5MW. Q-

Deliveryquay In the absenceofspecificdataforsprinklered fires at deliveryquays, itwas decided to adopt adesignfiretwice as largeas the correspondingretail fireadvised by FRS forretail areas equipped with quick-responsesprinklers. Area = 9 m Q- =5MW According to Eqns(J.1)— (J.3) andapplying aheightrise of2 mintherestaurant and3.2 minthe deliveryquay, the followingsmokeexhaust rates are predicted: stock 6.8 m3/s, restaurant 4.8 m3/s, 13.2 m3/s. deliveryquay

J.3.2 Covered street

Itwasconsideredthat the covered light streetconstituted a largeatrium. Consequentlythe smoke control design

drewonthe guidelinesand calculationprocedures in a BRE Report1,which are similarto thoseinthis book. On the ground-floor (Level00),thefire risk in the streetitselfis negligible. However, the restaurant, adjacent shopsandprinting room havea fire risk. Asthe smokewill be exhaustedfrom the atrium(the covered lightstreet), the mass flowand the air-flowrates must be calculatedforthe worst case scenario on the ground floor. This isthecase for a fire in ashop with a shopfront of7m wide facingthe street. Quick-responsesprinklerswillbeinstalled toreduce

the designfire size and the amount ofsmoke produced. Thedesign fireparameters arethus: P = 9 m perimeter offire,

Q= 2500kW.

Withafurther heightrise of2.5 m afierthesmokehas left thecompartment (ie afurther height rise of2.5 mabove thetop oftheshop's opening intothe atrium), amass flowof37kg/swill enterthe smokelayerwith an average

temperature riseof67°C. (Thiswas calculated following the method in reference [131. Thatis, usingtheBREspill plume entrainment procedure but wihoutusingthe layer depthcorrection for alarge-area smokereservoir which hassubsequentlybeenshown to apply to atria such as this, and whichis recommended forthis and similar scenariosinsection 6.3. The effectofthis for thiscase study is thatthe smokeexhaust volumecould have been a little smallerthan was calculated,iethe designerred on theside ofsafety.) Thetotal smokeextract volume is 38 m3/s (FigureJ4). J.3.2.1 Conferenceblock'Rue Wiertz'

As this side isfullyopen to thelightstreet, thepotential danger existsthat all smokeentering the atrium will entrainlarge quantitiesofair so that alarge amount of coldsmokewillfill theatrium. Therefore, thesmoke should notenterthe atriumand must be exhausted directly from thefoyer withoutsignificantspillageinto the atrium. As thefire risk is low,itwasdecided that an unsprinkleredfire of9 m2 and 1 MWcould betakenas designfire parameters foruse with Eqns (J.1)—(J.3.This predicted a massflow of11.8 kg/s (equivalentto 13 m3/s)

tobe exhaustedseparatelyfrom thefoyers'

compartments on each appropriate level (FigureJ5). J.3.2.2Offices 'Rue Mail' Attheotherside ofthe atrium (covered Street)the situation is different.Here, thereare unsprinklered[, small officesonsix levels,whichare notopen totheatrium but areonly separated with awindow.Thesmoke is allowed to flowfrom thefire-levelintothe atrium (afterthefire has broken the window). The designusedthe principleof temperature-control,whereenough entrainment is

H8 5

I H SMOKE CURTAINS1

4

O

Of V

=67C = 37 kg/s = 38 rnYh = 36.800

I POSITIONED

AT THE BRIDGES

2 m3/h

Figure.14 SHEVSdesign: smoke in light street from a shop fire

MAIL

128

Design methodologies for SHEVS

FigureJ5 SHEVSdesign:

smoke in conference blockfoyer

allowedto reduce the average layer temperature in the atrium to a valuethat will notbreakany glazingexposed to the layer. This corresponded to a height ofrise of1.9 m above the fire-room's window to cool the smoketo 80 °C. Thecalculationprocedures were essentiallysimilarto thoseforashopfireinthe'covered street', but with a design firemore appropriate to the office scenario.The design solutionswere similarbut less onerous, andare notdetailedfurther herein.

J.3.3 Centralregion In thisarea,thefire risk is very lowbecause thereareno

shopsor offices.Therefore, this location is not sprinklered. Oneshould notehowever that,similarlyto the forums nearthe conference rooms, aspillageof smoke intothe atriumfrom lowerstoreys could cause highrisks forthepeople at higher levels.Theworst-case fire scenario is whenafirestarts beside one ofthe voids because smokewill rise throughthe voidsto a higher levelwhile coolinglargeamounts ofsurrounding air by entrainment. It was decided that an appropriate design fireforthis region would be: Area = 1 m2, Table

ii

= 500kW, with smoke allowedto spillintothe voidpast alengthofspill edge of5 m.

Inthis case, once againfollowingthe calculation procedures inreference [13], the smokevolume entering thevoid willbe 4.6 kg/s. After entering the void, a further heightofrise of2.5 m is calculated to allow people on the higherlevels to evacuate.The resultingmass flow ofsmoke entering the smoke reservoiris 24 kg/s while the temperature riseis 50 °C atthispoint. Hencethe volume rate = 22 m3/s according to Eqn (J.3).

.1.3.4Summary of smoke-control scenarios See Tableji.

J.4 Practical solutionsand installation Thefollowingaspectshad tobe taken intoconsideration whendesigninginteractivefire-protection systems. Smoke compartments (automatic smoke curtains) Automatic smoke detection systems Sprinklers(normal or quick-response)whereneeded Reliablesmoke exhaust fans.

•• ••

Summary ofsmoke-control scenarios

Zone

Level

Sprinklers?

Smoke exhaust

Volume

Temperature rise

{m/s)

(°C) 450 70

Carpark

—2to—5

No

Compartment

11.9

Storage Restaurant

—2

Yes

Compartment

—1

Deliveryquay

—1

Ground-level

00

Compartment Compartment Coveredstreet

RueWiertz

01—06

Yes(FRS)* Yes(FRS)* Yes(FRS)* No

6.8 4.8

No

Void

No

No

Centralpart Offices Quick-responsesprinklers

07—16

Compartment

13.2 38 13 22 —

70 70 67 92 50

—

129

AnnexJ: Case history J.4.1 Smoke and fire compartments J.4.11 Fixedfire compartment According to BelgianStandards,the buildingis divided into separate firecompartments. Afire-resistancerating (RI)is definedintermsofexposureto thetestfurnace heatingcurve. This means: thecomplex is compartmented horizontally,at every level (Rf=4h), rooms or places havingvoids over 1 or morelevels needto becompartmented from the otherplaces on

• Curtainshave beeninstalledwhich close offthe betweenthe andthe will

openings bridges corresponding levelsto prevent the smoke movingfrom one sideof the coveredstreetto theother.

Atotal length ofabout 1.5 kmofmovablesmokecurtains hasbeeninstalledintheD3building.

• J4.1.2.2 • Inthecentral areathere aretwo types ofmovablesmoke curtains: that curtainsthat lowerfor m andwhichform the • technical rooms (eg plantrooms) arecompartmented • lobbies compartment,not allowingthe smoke to enterthe h), adjacent to the conferencerooms, •• (Rf=2 staircasesandelevators are compartmented (Rf= • curtainsat Level 03 aroundthe voidto prevent from Levels 02 or passingthrough the void sprinklered andnon-sprinklered rooms are one from the other Level Centralregion

1

level,

1 h),

compartmented

(Rf= 1 h).

J.4.1.2Flexible smokecompartmentation Toprevent the smokedilutingtoo much andbecoming too cool(with the effectoflosingthe desired layering), automatic smoke curtainsare specifiedin the underground levels,the covered streetand aroundthe voids inthecentral region. The smokecurtains in theunderground carparkswill lower1 m to contain the smoketo a limited area. The smoke curtainsatthe entrances have two positions: ifthe fireoccurs at the same level (this willbe indicated by theaddressable smoke-detectioninstallation) the screen willlowerfor 1 m to allow replacement air to enter, ifthesmoke tends to risethroughtheentrances to a higher level,the screens can belowered further in order to prevent the smokefrom leaving the compartment.

• •

J.4.1.2.1 Coveredstreet

In theatriumthreetypes ofmovablesmoke curtainsare installed. Screenshavebeen installed along the balconies betweenthe covered streetand theforums infront of the threelarge conference rooms. These curtains can be lowered to two positions. — Ifthere isa fire on the samelevel the curtainswill lowerto halfposition. The smokewillbe keptinthe compartment andreplacement air can enterthe compartment (seeFigureJ5) — Ifthereis afire in the offices or shops atthe opposite sideofthe streetthe curtainswill lowerto the base oftheopeningsto the forumsto close those openingsand prevent smokepropagation towards the forums (seeFigureJ4). Curtains havebeen hungunderthe bridges across the coveredstreet. Thesescreens will alwayslower through the total height between the underside ofthe higher bridge tothe walkwayofthe lowerbridge directly beneath, to provide aboundary to the smoke compartment (smoke reservoir)inthe street.

•

•

entering

01 03.

smoke

smoke arid

J.4.1.2.3 Cert/ledquality

Themovablesmoke curtainsaretestedto British Standard BS 7346: Part3 whichindicatesa heat-proof fabric that cansurvivea smoky gas temperature of600 °C for halfan hour.

J.4.2Automaticsmokedetection Thewholecomplex is equipped with an appropriate smoke-detection system.Thesesmoke detectors are addressableso that the firelocation can be identifiedas quicklyas possible.The control panelmust perform the followingautomatic actions: close fire doors, open escape doors, lowersmokecurtainsto theirappropriate design height, activatethe emergencypowersupply, startthe smokeexhaust fans, open the air inletsfor replacement air, bring thelifts to evacuation level, stop the normal ventilation installations, activate the alarm signals.

•• • •• •• ••

J.4.3 Sprinklers As alreadymentionedin the descriptionofthe firerisks, sprinklersare only installedinplaces wherethereis a risk offast-growingfires. Quick-responsesprinklersare a'newgeneration'-type ofsprinklerwith alow response timeindex (RTI)value. Theyareusedin restaurantsand on deliveryquaysfor the trucks atLevel—1.

J.4.4 Smoke exhaust fans As indicatedinthe firescenarios allsmoke exhaust installationsare powered. Natural exhaust withsmoke vents was notapplicablebecause ofthe strongprobability ofadverse wind effectsaround such atall and complex building. Thefans,as well as the ductwork,mustwithstand the anticipated designtemperatures (seeTableji).

130

Design methodologies for SHEVS

The fans aretestedfollowingBritish Standard BS 7643: Part 2. It is obviousthat fans must operate without interruption in an emergency situation. Therefore, fireresisting cablingis usedat all times.

J.5 Hot-smoketest J.5.1 Introduction Inview ofthenovel features, and the limited full-scale validation ofcalculationprocedures foradheredspill plumes in atria, the BrusselsFireServicerequired a full scalehot-smoke test inthebuildingin orderto confirm both the designandtheoperation ofthe smoke-control system.This requirement was part ofthe conditions to obtain thebuildingpermit. The test wasscheduled fora dateas nearto completion ofthebuildingas was compatiblewiththe construction schedule. Temporary sheetingwas usedextensivelyto close offopenings, whichwere due to be closed more permanently before completion. InMarch1996 IFSET and FRS collaborated for the second time to carry out ahot-smoke test in abuilding (thefirsttestbeingBrusselsAirport Terminal).Thetest scenario agreed withthe Fire Servicewas afireina typicalshop opening out intothe atrium. Twotest fires were carried out, apreliminary onewith a 0.5 MWfire and themaintestwitha 1 MWfire in conjunctionwith theoretical calculationsto extrapolatethe experimental resultsto the fill design scenario. Afullreportwas presented to the client and to theFire Servicedescribingthe test givingtheresultsand conclusions.

FigureJ6 Schematicarrangement ofhot-smoke test

J.5.2 Description of the test Thetest followed the procedure developed byFRS. Industrialmethylated spiritswereburnedintrays, which inturn were floated onwater. A lightweightfire-resisting fire compartment was built to simulatethe shop geometry andtoprotectthe actual structure ofthe building.This protection was carried upthefacadeofthe atrium highenoughto ensureprotection ofthe structure and glazing directly above the opening to the fire compartment (FigureJ6and PlateJ4). Thetestfirewaschosentobelargeenoughto allow confident scalingofthe resultsto the full design scenario, butnotso large asto cause any damage to thebuilding.A preliminary test fire ofhalfthe calculated sizewasused first in order to confirmthe validityofthe design ofthe main test, and to confirmthat therewereno unexpected departures from the design assumptions. Temperature measurements were made inthe smoke layerformed in theatrium, as well as inthefire compartment. In addition,observations were made ofthe layer depth in the atriumas well as ofthebuild-up of smoke intheforums dueto leakage pastthesmoke curtains. The hot gaseswere madevisibleusing a synthetic oil-mist smokefrom commercialtheatricaltypesmokegenerators. Additionally,observationswere

PlateJ4 Hot-smoke test: lIre insimulated shop

AnnexJ: Case history madeby'rovingobservers' looking for any unexpected phenomena, suchas the appearance ofsmokein other parts ofthebuildingdueto leakage or siphoningthrough ventilation ducts. Safetyprotocols were agreed withthe Fire Service,and were applied very strictly. Calculationsofthe entrainment in the atriumwere made followingthe procedures set out inthisbook, includingthe 'effective layer depth'procedure. Calculationprocedures for extrapolatingthe observed build-up ofsmoke in the forums,and for deducing implicationsfor modificationsto ensurethedesired performance in the completed building,werededuced from firstprinciples.Reductions in smoke curtain gap widths were proposed.

J.5.3 Summary of conclusions from the test

•

• The testwassuccessfullycarried out without damage to thebuilding.Fires of4pproximatcly and MW were burnt in a simulatedshopunit. • • The powered SHEVSmaintained a smokelayerbase in the atrium reservoirwith abase at ± above ground-floor level.The predicted result agreed • within observational 0.5

1.0

15.5 0.5 m

•

•

• •

experimental uncertainty.By extrapolationfrom the test results,the SHEVSis expected to maintain the layer base unitat 10.4 m above ground-floor level,from a 2.5 MW, 2.2 mx 2.2 m quick-response-sprinkleredfire in a shop. There should be a seriesoffunctionaltestscarried out on thesmoke curtain system whenthebuildingis in its final stateandwhenthe permanent smoke curtain system is in place.These functionaltests should confirmthat all gaps are assmall as possibleand not larger(preferablysmaller)thanthoseproposed inthe calculations(notincluded inthe presentsummary). If largergapsremain whenthebuildingis completed it would benecessaryto recalculate the smokefilling timesforthefoyers and bridges.These functionaltests should alsotest the operation ofthe automatic detectionsystem and should confirmthatall the smoke curtains operate automaticallyon detection. Forthemaintest the curtain onBridge2, Level05 deflected 0.10 m. Forthedesign condition thecurtain on Bridge2, Level 05 was calculatedto deflectapproximately 0.38 m.The length ofthe fabric in the curtain should be enoughforthe bottombar to reston the walkwayeven whendeflected. (Notethatthe installershad needed to modif5rthese curtainspriorto the test toallow forthe relativelylarge buoyant pressuresexpected in this design). In thetest smoketravelled throughunforeseen leakage paths. All openings thatare likelyto be inthe smoke layer should be identifiedandremedied. For example, builders' work ducts to beclosed, doorgapsto be sealed, gaps around windowsto be sealed. In thetest smokeenteredotherreservoirsthrough edge gaps around the under-bridgesmoke curtains,but

131

was welllayered. It is desirablethatfans should be operated in adjacent reservoirs simultaneouslytothe one containingthe fire to remove this smoke, ifthe provisionforinlet air andfor electricalpower allows. Smoke entered the foyer on Level 05 mainlythrough gaps between the smokecurtains andreached dangerous conditionsafter approximately 6 minutes from ignition inthe maintest. This would havebeen perhaps 3 minutes from ignitionfor the design conditionswith real smokeand an ultra-fastgrowing fire. Reducingthe smoke curtain gaps could increase the time availablefor escape.Also, itwas recommended that early automatic detection and a voice alarm system be provided in these areas and a similarsystem in adjacent areas to warnpeoplenotto escapethroughthe foyer. Considerationcould be given to studyingthe possibilityofusing apowered dilution system in the foyers to extend the time availablefor evacuation. Consideration should begiven to providingearly automatic detection in the shop and office units to trigger both the smokeexhaust and alerting systems. Thewindows intheoffices opening ontothe atrium should be keptclosed atall times.

J.6 Fire safety management Asthebuildingis anopen construction relyingvery much onthe use ofactive fireprotection installations,fire scenarios havebeen written for the approximatetota][ of 400 compartments inthe building. These fire scenariosidentifr alltheautomatisms (ie the automaticallyinitiatedelectronic, electricaland/or mechanical operations) ofeach technical installation whichwill play arolein case offire. Allthe possible interactions have been definedsuchthat everything could be programmed onto the central management system forthe building.Itis intended that this will greatly simpliljithe degree ofcontrol ofthe building'ssystems required ofthe FireService. In additionto definingthefire scenariosand the consequent automatisms,itis intended to define and prepare evacuationprocedures and plans,andFire Serviceintervention plans in similardetail so that allthe actions,both automatic and byhuman agencies,required during afire emergency willbetakenin afullyintegrated manner. It is notenough to design systemsintoabuildingto ensure firesafety.It isimportant that those systemsmust stillbeworking, perhaps years later, whenafire actually occurs. For this reason, itis important that the building's management should be able to maintain the systemsand to trainkeystaffintheir operation. Itis alsoof considerablepracticalimportance thatthese fire safety management activitiesshould not involvetoo much inconveniencetothe normal use ofthe building. In this building,thefiresafety management procedures must beableto monitor andmaintain fourtypes ofactive fire-protectivesystems.As the control panels ofthe

132

Design methodologies for SHEVS

smokecurtains, fire detection, sprinkler installationand smoke-control installationare centralized in one control room, theirstatusand interactions can bechecked easily. Itis also easy to generate firesimulationsor scenarios, whichfacilitateseasy andfrequentfire training for the security staffwho usuallyman the Control Room.

J.7 Conclusions

• Aswiththethearchitecture ofthe buildingincouldnotcomply aFire •

prescriptiveregulations Belgium, SafetyEngineered approach has been applied leadin to anintegrated approach to the applicationoffire safetymeasures. The Fire Service Department have approved the active fire protection and fire safety management procedures, whichhave beendeveloped for this complex.

CI/SfB (68.5) 1999

Aboutthis book This book summarizesthe adviceavailablefromthe Fire ResearchStation, todesigners of Smoke and HeatExhaustVentilationSystems (SHEVS) for atria and other buildings. Itspurpose isto provide practical guidance onthe design ofsmoke-control systems. Itreflects current knowledgeand is based onthe results ofresearchwhere available,including as yetunpublishedresults ofexperiments.In addition, itdraws on theauthors' cumulative experience ofdesign features requiredfor regulatory purposes in many individualsmoke-control applications. Manyofthese design features have evolved overseveralyearsbyconsensus between regulatory authorities, developers and firescientists.

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BR368 ISBN 1 86081 289 9

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