ANSI-AIHA Z9-5-2003

American National Standard for

ANSI/AIHA Z9.5–2003

Laboratory Ventilation

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ANSI/AIHA Z9.5–2003

American National Standard — Laboratory Ventilation

Secretariat

American Industrial Hygiene Association

Approved September 30, 2002

American National Standards Institute, Inc.

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American National Standard

Approval of an American National Standard requires verification by ANSI that the requirements for due process, consensus, and other criteria for approval have been met by the standard’s developer. Consensus is established when, in the judgment of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution. The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether he or she has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processors, or procedures not conforming to the standards. The American National Standards Institute does not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American National Standards Institute. Requests for interpretations should be addressed to the secretariat or sponsor whose name appears on the title page of this standard. CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of approval. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute.

Published by

American Industrial Hygiene Association 2700 Prosperity Avenue, Suite 250, Fairfax, Virginia 22031 www.aiha.org

Copyright © 2003 by the American Industrial Hygiene Association All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. Printed in the United States of America. ISBN 1–931504–35–0

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Contents Page Foreword

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

1

Scope, Purpose, and Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2

Laboratory Ventilation Management Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3

Laboratory Chemical Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4

Other Containment Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5

Laboratory Ventilation System Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6

Commissioning Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7

Work Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

8

Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

9

Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Appendices APPENDIX 1

Definitions, Terms, Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

APPENDIX 2

Referenced Standards and Publications. . . . . . . . . . . . . . . . . . . . . . . 79

APPENDIX 3

Selecting Laboratory Stack Designs . . . . . . . . . . . . . . . . . . . . . . . . . . 81

APPENDIX 4

Audit Form for ANSI/AIHA Z9.5–2003 . . . . . . . . . . . . . . . . . . . . . . . . 87

APPENDIX 5

Sample Table of Contents for Laboratory Ventilation Management Plan . . . . . . . . . . . . . . . . . . . . . 111

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Foreword (This foreword is not part of the American National Standard Z9.5–2003.) General coverage. This standard describes required and recommended practices for the design and operation of laboratory ventilation systems used for control of exposure to airborne contaminants. It is intended for use by employers, architects, industrial hygienists, safety engineers, Chemical Hygiene Officers, Environmental Health and Safety Professionals, ventilation system designers, facilities engineers, maintenance personnel, and testing and balance personnel. It is compatible with the ACGIH Industrial Ventilation: A Manual of Recommended Practices, ASHRAE ventilation standards, and other recognized standards of good practice. HOW TO READ THIS STANDARD. The standard is presented in a two-column format. The left column represents the requirements of the standard as expressed by the use of “shall.” The right column provides description and explanation of the requirements and suggested good practices or examples as expressed by the use of “should.” Appendices 1 and 2 provide supplementary information on definitions and references. Appendix 3 provides more detailed information on stack design. Appendix 4 provides a sample audit document and Appendix 5 presents a sample table of contents for a Laboratory Ventilation Management Plan. Flexibility. Requirements should be considered minimum criteria and can be adapted to the needs of the User establishment. It is the intent of the standard to allow and encourage innovation provided the main objective of the standard, “control of exposure to airborne contaminants,” is met. Demonstrably equal or better approaches are acceptable. When standard provisions are in conflict, the more stringent applies. Response and Update. Please contact the standards coordinator at AIHA, 2700 Prosperity Avenue, Suite 250, Fairfax, VA 22031, if you have questions, comments, or suggestions. As with all ANSI standards, this is a “work in progress.” Future versions of the standard will incorporate suggestions and recommendations submitted by its Users and others. This standard was processed and approved for submittal to ANSI by the Z9 Accredited Standards Committee on Health and Safety Standards for Ventilation Systems. Committee approval of the standard does not necessarily imply that all committee members voted for its approval. At the time it approved this standard the Z9 Committee had the following members: J. Lindsay Cook, Chair Lou DiBerardinis, Vice-chair Margaret Breida, Secretariat Representative At the time of publication, the Secretariat Representative was Jill Snyder. Organization Represented . . . . . . . . . . . . . . . . . . . . . . . .Name of Representative Alliance of American Insurers . . . . . . . . . . . . . . . . . . . . .F. K. Cichon American Conference of Governmental Industrial Hygienists . . . . . . . . . . . . . . . . . . . . . . . . . . .R.T. Hughes American Foundrymen’s Society . . . . . . . . . . . . . . . . . . .R. Scholz American Glovebox Society . . . . . . . . . . . . . . . . . . . . . . .S. Crooks American Industrial Hygiene Association . . . . . . . . . . . .L. Blair American Insurance Services Group . . . . . . . . . . . . . . . .M. T. Jones American Society of Heating, Refrigerating, and Air Conditioning Engineers . . . . . . . . . . . . . . . . . .H. F. Behls American Welding Society . . . . . . . . . . . . . . . . . . . . . . . .T. Pumphrey Chicago Transit Authority . . . . . . . . . . . . . . . . . . . . . . . . .E. L. Miller National Spray Equipment Manufacturers Association . . . . . . . . . . . . . . . . . . . . . .D. R. Scarborough iii

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US Department of Health and Human Services National Institute for Occupational Safety and Health . .J. W. Sheehy US Department of Labor Occupational Safety and Health Administration . . . . . .I. Wainless US Department of the Navy . . . . . . . . . . . . . . . . . . . . . . .G. Kramer Individual Members G. M. Adams D. J. Burton J. L. Cook L. J. DiBerardinis S. J. Gunsel R. L. Karbowski G. Knutson M. Loan K. Paulson J. M. Price J. C. Rock M. Rollins T. C. Smith L. K. Turner Subcommittee Z9.5 on Laboratory Ventilation, which developed this standard, had the following members: Lou DiBerardinis, Chair D. Jeff Burton Douglas Walters,* Associate Chair (American Chemical Society) Steve Crooks (American Glovebox Society) Gregory DeLuga* Edgar Galson* Daniel Ghidoni* Todd Hardwick* Ron Hill* Dale Hitchings* Gerhard Knutson Victor Neuman* John Price Gordon Sharp* Thomas Smith J. Lindsay Cook (ex-officio)

* Contributing member of Z9.5 subcommittee but not a voting member of the full Z9 Committee at the time of standard approval.

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AMERICAN NATIONAL STANDARD

ANSI/AIHA Z9.5–2003

American National Standard for Laboratory Ventilation 1

Scope, Purpose, and Application

1.1

Scope

This standard sets forth the requirements for the design and operation of laboratory ventilation systems. This standard does not apply to the following types of laboratories or hoods except as it may relate to general laboratory ventilation: • Explosives laboratories; • Radioisotope laboratories; • Laminar flow hoods (e.g., a clean bench for product protection, not employee protection); • Biological safety cabinets. 1.2

Purpose

The purpose of this standard is to establish minimum requirements and best practices for laboratory ventilation systems to protect personnel from overexposure to harmful or potentially harmful airborne contaminants generated within the laboratory. It does not apply to comfort or energy considerations unless they have an effect on contaminant control ventilation. This standard: • Sets forth ventilation requirements that will, combined with appropriate work practices, achieve acceptable concentrations of air contaminants; • Informs the designer of the requirements and conflicts among various criteria relative to laboratory ventilation; • Informs the User of information needed by designers. 1.3

Application

There is a growing need for laboratories to conduct teaching, research, quality control, and related

activities. Such laboratories should satisfy several general objectives, in addition to being suited for the intended use: • They should be safe places to work; • They should be in compliance with environmental, health, and safety regulations; • They should meet any necessary criteria for the occupants and technology involved in terms of control of temperature, humidity, and air quality; and • They should be as energy efficient as is practical while adhering to above objectives. This standard addresses the ventilation requirements to satisfy the first criterion: making the laboratory a safe place to work. When techniques and designs are available to reconcile conflicts between safety criteria and other, possibly conflicting demands, they are discussed. General laboratory safety practices are not included except when they may relate to the ventilation system’s proper function or effectiveness. Traditional ventilation system designs typically do not meet all of the foregoing criteria, and most importantly they very often do not ensure adequate safety for the laboratory occupants. Persons responsible for laboratory operations and those working within a laboratory are typically not very knowledgeable about how ventilation systems directly impact laboratory occupant health and safety. Thus, they may not be aware of inadequate ventilation or other ventilation system deficiencies. On the other hand, ventilation system design professionals cannot be expected to be fully aware of all the particular hazards posed by every type of operation that may occur in a laboratory room. Furthermore, the specific work and operations of some laboratory facilities may need to be kept more confidential and may even be highly secretive.

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ANSI/AIHA Z9.5–2003

REQUIREMENTS OF THE STANDARD 2

Laboratory Ventilation Management Program

2.1

General Requirements

Management shall establish a Laboratory Ventilation Management Plan to ensure proper selection, operation, use, and maintenance of laboratory ventilation equipment.

CLARIFICATION AND EXPLANATION OF THE REQUIREMENTS

Management participation in the selection, design, and operation of laboratory ventilation systems is important to the overall success of the effort. The program should be written and supported by top management. A sample Table of Contents for a Laboratory Ventilation Management Plan is included in Appendix 5. Management should understand that ventilation equipment is not furniture, but rather it is part of installed capital equipment. It must be interfaced to the building ventilation system.

2.1.1

Laboratory Chemical Hoods

Adequate laboratory chemical hoods, special purpose hoods, or other engineering controls shall be used when there is a possibility of employee overexposure to air contaminants generated by a laboratory activity.

The performance of a laboratory chemical hood is ultimately determined by its ability to control chemical exposure to within applicable standards.

The containment and capture of a laboratory hood shall be considered adequate if, in combination with prudent practice, laboratory worker chemical exposure levels are maintained below applicable in-house exposure limits as recommended in 2.1.1. When these containment sources are not adequate, the laboratory shall conduct a hazard determination to evaluate the situation.

If exposure limits [e.g., Occupational Safety and Health Administration Permissible Exposure Limits (OSHA PELs), National Institute for Occupational Safety and Health Recommended Exposure Limits (NIOSH RELs), American Conference of Governmental Industrial Hygienists threshold limit values (ACGIH TLVs®), American Industrial Hygiene Association Workplace Environmental Exposure Limits (AIHA WEELs), German MAKs, (maximum admissible concentrations)] or similar means of prescribing and/or assessing safe handling do not exist for chemicals used in the laboratory, the employers should establish comparable in-house guidelines. Qualified industrial hygienists and toxicologists working in conjunction may be best suited to accomplish this need. A Laboratory Design Professional must anticipate that toxic and hazardous substances may be used at some point during the lifetime use of the facility. “OSHA’s standards were designed to provide a baseline or minimum level of safety, one where worker exposure levels are below the permissible exposure limits (PELs) accepted by government and private occupational health

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ANSI/AIHA Z9.5–2003

research agencies, including the National Institute of Occupational Safety and Health (NIOSH). These exposure limits are listed in 29 CFR Subpart Z, Toxic and Hazardous Substances. Unless the employer determines, through periodic monitoring, that exposure levels for substances used in laboratory chemical hoods routinely exceed the action levels (or, in the absence of action levels, the PELs), employees are not likely to be overexposed. Please be aware that the employer is responsible for ensuring that laboratory chemical hoods are functioning properly and implementing feasible control measures to reduce employee exposures if the exposures exceed the PELs. If an employer discovers, through routine monitoring and/or employee feedback, that laboratory chemical hoods are not effectively reducing employee exposures, it is the employer’s responsibility to adjust controls or replace hoods as necessary. OSHA does not promulgate specific laboratory chemical hood testing protocols (Richard Fairfax, Director, Directorate of Compliance Programs, OSHA, letter to R. Morris, 4 April 2001). “Overexposure” to chemicals implies a means of being able to define both an unsafe limit and the analytical means of determining when such limits are exceeded, neither of which may be commonplace nor practical. “Hazard determination,” on the other hand, as defined by 29 CFR 1910.1200, Hazard Communication Standard, is a regulation. 2.1.2

Volume Flowrates/Room Ventilation Rate

The specific room ventilation rate shall be established or agreed upon by the owner or his/her designee.

2.1.3

Since a ventilation system designer cannot know all possible laboratory operations, chemicals to be utilized, and their potential for release of fumes and other toxic agents, one air exchange rate (air changes per hour) cannot be specified that will meet all conditions. Furthermore, air changes per hour is not the appropriate concept for designing contaminant control systems. Contaminants should be controlled at the source.

General Ventilation

The general ventilation system shall be designed to replace exhausted air and provide the temperature, humidity, and air quality required for the laboratory procedures without creating drafts at laboratory chemical hoods.

Replacement air is part of the general ventilation system. In addition there may be need for general room exhaust (not through a hood used for contaminant control).

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ANSI/AIHA Z9.5–2003

2.1.4

Dilution Ventilation

Dilution ventilation shall be provided to control the buildup of fugitive emissions and odors in the laboratory.

2.2

Control of hazardous chemicals by dilution alone, in the absence of adequate laboratory chemical hoods, seldom is effective in protecting laboratory users. Because the exhaust from that type of system must be discharged to the outside or treated intensively before being used as return air, these systems usually are not economical for controlling exposure to hazardous materials compared with use of local exhaust hoods.

Chemical Hygiene Plan

The laboratory shall develop a Chemical Hygiene Plan according to the OSHA Laboratory Standard (29 CFR 1910.1450).

Although some laboratories do not fall under the OSHA Standard, the Chemical Hygiene Plan or a Laboratory Safety Manual is necessary to establish proper work practices. Persons participating in writing the plan should be knowledgeable in industrial hygiene, laboratory procedures and chemicals, the design of the ventilation systems, and the system’s maintenance needs. The plan should be disseminated and become the basis of employee training.

The plan shall address the laboratory operations and procedures that might generate air contamination in excess of the requirements of Section 2.1.1. These operations shall be performed inside a hood adequate to attain compliance. 2.3

Responsible Person

In each operation using laboratory ventilation systems, the user shall designate a “responsible person.”

The responsible person may have as duties: • Ensuring that existing conditions and equipment comply with applicable standards and codes. Ensuring that testing and monitoring are done on schedule; • Maintaining adequate records; • Performing visual checks; • Training employees; and • Performing any other related task assigned by the employer. At a minimum, the responsible person should coordinate these activities.

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ANSI/AIHA Z9.5–2003

2.4

The Role of Hazard Assessment in Laboratory Ventilation Management Programs

2.4.1

General Requirements

Employers shall ensure the existence of an ongoing system for assessing the potential for hazardous chemical exposure.

Much of this standard addresses a generic approach to exposure control. This is necessary because many of the chemical hazards in a laboratory are chronic in nature and an employee’s ability to sense overexposure is subjective.

Employers shall promote awareness that laboratory hoods are not appropriate control devices for all potential chemical releases in laboratory work. The practical limits of knowing how each ventilation control is being used in the laboratory shall be considered when specifying design features and performance criteria (commissioning and routine monitoring). The responsible person as defined in Section 2.3 shall be consulted in making this judgment. Laboratory chemical hoods shall be functioning properly and specific measures shall be taken to ensure proper and adequate performance. The employer shall establish criteria for determining and implementing control measures to reduce employee exposure to hazardous chemicals; particular attention shall be given to the selection of control measures for chemicals that are known to be extremely hazardous.

The employer may recommend (2.4.2) that providing standard laboratory hoods tested to the ANSI/ASHRAE 110 standard and an “as installed” AI 0.1 rating are best for the types of chemical hazards and work being performed at the specific workplace. The assumption that follows is that users are trained to understand limitations of the hood’s control ability and would not use it for work that, for example, should be performed in a glovebox. Alternatively, ensuring all hoods are capable of meeting an AU 0.1 rating may not be necessary, for example, if the only chemical being handled has an 8-hr time-weighted average (TWA) – TLV® exposure limit of 250 ppm. The following briefly describes an approach used within laboratory ventilation management programs in assigning control measures given the ability (or inability) to assess specific day-to-day chemical exposure situations. Hazard assessments in general are geared toward identifying chemicals, their release potential, and their possible routes of entry into the body. The first step in the assessment is to identify what chemical(s) can be released including normally uncharacterized byproducts. After characterizing the inherent hazard potential (largely based on physical properties, toxicity, and routes of entry), the next step is to ascertain at least qualitatively, the release “picture.” At what points within the “control zone” will chemicals be evolved and at what release rate? Will the chemical release have velocity? How has the maximum credible accidental release been accounted for? Finally, how many employees are/could be exposed and what means are available for emergency response? 5

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ANSI/AIHA Z9.5–2003

2.4.2

“Programming” and Control Objectives for New Construction, Renovation, or Program Evaluation

The following items shall be considered and decisions made regarding each element’s relevance following the hazard assessment process: • Vendor qualification; • Adequate workspace; • Design sash opening and sash configuration (e.g., for laboratory chemical hoods); • Diversity factor in Variable Air Volume (VAV) controlled laboratory chemical hood systems; • Manifolded or individual systems; • Redundancy and emergency power; • Hood location; • Face velocity for laboratory chemical hoods; • The level of formality given to system commissioning; • Tracer gas containment “pass” criteria (e.g., AI 0.5, AI 0.1, AI 0.05, etc.); – AMYY and AIYY by Design Professional in agreement with responsible person (2.3); – AU YYY by responsible person (2.3); • Alarm system (local and central monitoring); • Air cleaning (exhaust pollution controls); • Exhaust discharge (stack design) and dilution factors; • Recirculation of potentially contaminated air; • Differential pressure and airflow between spaces and use of airlocks, etc.; • Fan selection; • Frequency of routine performance tests; • Preventive maintenance; and • Decommissioning. 2.5

Programming is a term commonly used in the context of a construction project whereby the needs of a user group are developed chemistry, biology, etc.,” are generically understood by most designers, knowledge of the chemistry and biology and, therefore, potential hazards, are generally beyond the knowledge base of most designers. The overall goal of providing a safe workspace for the end users can be greatly enhanced by the use of a hazard assessment and system design team. Quality of system design and quality of performance are enhanced by utilizing the most appropriate skills and resources available to an organization. The Laboratory Ventilation Management Plan should describe specific responsibilities for each department involved in the design, installation, operation, and use of ventilation systems (Table 1 provides some guidance). Laboratories life cycle should be planned for 30–50+ years. Laboratory chemical hood performance can impact life cycle sustainability. (See Leadership in Energy and Environmental Design (LEED), a rating system from the U.S. Green Building Council.) The primary design professional license holder (architect and/or engineer) with the laboratory standard duty of care responsibilities cannot delegate any of their liability to others. For example, the sealing license holders cannot delegate responsibility or liability on to laboratory planner, industrial hygienist, and/or commissioning agent even if licensed or certified.

Recordkeeping

Complete and permanent records shall be maintained for each laboratory ventilation system.

Only permanent records will allow a history of the system to be maintained.

Records shall include: • As-built drawings; • Commissioning report; • Testing and Balance reports; • Inspection reports; • Maintenance logs; • Reported problems;

Records should be maintained to establish a performance history of the system that can be used to optimize operation. Records should be kept for at least the life of the system or until the system is altered.

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ANSI/AIHA Z9.5–2003

• System modifications; and • Equipment replacement or modifications. Table 1

Major Responsibilities Recommended for Ensuring Effective Ventilation Systems

Group or Department

Management

Responsibility • • • • •

Remove barriers between departments Provide leadership Coordinate activities Allocate sufficient resources Ensure that hood operators are trained in good work practices

Researchers

• Provide information on potentially hazardous materials • Provide information on procedures, work habits, duration of use, changes in hazardous operations and materials, etc. • Indicate performance problems

Health and Safety

• • • • •

Engineering

• Ensure system capability • Ensure proper design, installation, and commissioning of systems • Maintain up-to-date system documentation

Conduct Hazard Evaluation Establish control objectives and safety requirements Determine suitable control strategies Conduct routine safety audits Maintain records of performance

Maintenance

• Ensure proper functioning of systems • Ensure system dependability • Conduct preventive and repair maintenance

Purchasing

• Ensure equipment is not purchased without safety approval

Space Planning

• Ensure safety and engineering issues are considered in any space allocation decisions

Note to Table 1: The responsible person could be part of any one of the above groups and departments.

3

Laboratory Chemical Hoods

3.1

Design and Construction

The design and construction of laboratory chemical hoods shall conform to the applicable guidelines presented in the latest edition of ACGIH Industrial Ventilation: A Manual of Recommended Practice, and the most current codes, guidelines, and standards and any other applicable regulations and recommendations (see Appendix 2).

It is the intent of the standard to establish design parameters and performance criteria and not to limit new and innovative designs.

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ANSI/AIHA Z9.5–2003

Although construction varies among models and manufacturers, the following are recognized as good design features: • Work surfaces should be recessed at least 3/8 in. (0.953 cm) below the front edge of the bench or surface; sides and back should be provided with a seamless vertical lip at least 3/8 in. (0.953 cm) high to contain spills. • Airfoils or other sidewall designs that reduce leakage and airflow eddies at the front edge of the work area should be provided at the front edge of the bench and on the front side posts external to the sash. Airfoils should not interfere with the hood’s ability to meet the criteria of performance testing defined in this standard. • Utilities (e.g., valves and switches) should be located at readily accessible locations outside the hood. If additional utilities are required, other than electrical, they may be located inside the hood provided they have outside cutoffs and can be connected and operated without potentially subjecting the hood operator to exposure from materials in the hood or other unsafe conditions. • Baffle design should provide for the capture of materials generated within the hood and distribute flow through the opening to minimize potential for escape. • The local fire authority will determine if the flammable liquid storage cabinet will be vented. This is acceptable as long as it does not compromise hood performance. 3.1.1

Sashes

The laboratory chemical hood shall be equipped with a safety viewing sash at the face opening.

Type of sashes available are as follows: • Vertical raised sash • Horizontal sliding sash • Combination vertical raising and horizontal sliding sash Refer to Figure 1 for diagrams of different sash configurations.

Sashes shall not be removed when the hood is in use. 8

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ANSI/AIHA Z9.5–2003

Sash-limiting devices (stops) shall not be removed if the design opening is less than full opening.

The design opening of the hood and the position of the sash-limiting device should be determined by the responsible person based on the needs of the hood user. In combination sashes, the horizontal sash panel may be guided in lower roller tracks and overhead guides. Sashes should be constructed of transparent shatterproof material suitable for the intended use. Sash movement should require no more than 5 lbs. of force to move through the full track of the sash and should remain stationery when force is removed.

3.1.1.1 Vertical Sashes Vertical sashes shall be designed and operated so as not to be opened more than the design opening when hazardous materials are being used within the hood.

The vertical raised sash provides for full-face opening in the open position. This would be the maximum design opening area used for airflow design and measurements. Contact the safety officer if it is necessary to manually override the sash stops.

Where the design sash opening area is less than the maximum sash opening area, the hood shall be equipped with a mechanical sash stop and alarm to indicate openings in excess of the design sash opening area.

The maximum sash opening area intended for use by laboratory personnel is called the design sash position.

3.1.1.2 Horizontal Sashes Horizontal sashes shall be designed so as not to be opened more than the design opening width when hazardous materials are being generated in the hood.

The horizontal sash should be designed to allow free movement of the sash. Accumulation of debris or other materials in the sash track can impede movement. The sash track can be designed to minimize this potential by hanging the sash from overhead. In any event, periodic maintenance is recommended to ensure proper sash management. Contact the safety officer if it is necessary to manually override the sash stops. Caution is advised when using a horizontal panel as a shield in front of the hood operator as high concentrations can accumulate behind the sash panel and escape along the Users’ arms protruding through the opening or escape when their arms are withdrawn (Ivany, 1989).

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ANSI/AIHA Z9.5–2003

3.1.1.3 Combination Sashes A combination sash has the advantages and disadvantages of both types of sashes. If a combination sash provides horizontally moving panels mounted in a frame that moves vertically, the above requirements in Sections 3.1.1 to 3.1.1.2 shall apply.

If three or more sash panels are provided, one panel should be no more than 14 in. (35.6 cm) wide if it is to serve as a safety shield narrow enough for a person to reach around to manipulate equipment.

The combination vertical raised and horizontal sliding sash, commonly referred to as a combination sash, is a combination of the vertical sash described in Section 3.1.1.1 and horizontal sash in Section 3.1.1.2. The combination sash may be raised to full vertical sash opening. In the closed vertical position, the horizontal sliding panels can be opened to provide access to the interior hood chamber. Care should be taken in determining the design opening of a combination sash. Remember to include the area beneath the airfoil sill and through the bypass if one exists. 3.1.1.4 Automatic Sash Closers As discussed in Section 7.1, good work practices require closing the sash when the hood is not in use. The following factors shall be considered before automatic sash closing devices are installed on a laboratory chemical hood: • The adverse effect on energy consumption when the operators feel it is their responsibility to close the sash; and • The adverse effect on energy consumption when the operators do not feel it is their responsibility to close the sash. The following conditions shall be met before using automatic sash closing devices: • All users must be aware of any limitations imposed on their ability to use the hood. • Automatic sash positioning systems shall have obstruction sensing capable of stopping travel during sash closing operations without breaking glassware, etc. • Automatic sash positioning shall allow manual override of positioning with forces of no more than 10 lbs (45 N) mechanical both when powered and during fault modes during power failures.

Automatic sash positioning systems have been developed to close the hood sash when the operator is not present. The purpose is to save energy on VAV systems without having to rely on users to close the sash when they leave. Having the sash closed is an additional measure of safety since this condition will provide additional containment in the event of a hazardous release. The decision to use such a device should be based on the ability to train users to close the sash when needed, the energy savings, and any adverse consequences. If the user feels it is his/her responsibility to close the sash and the culture is that they do close the sash, then an automatic sash closer may not be necessary. On the other hand, if the user does not close the sash, energy consumption will increase and an automatic sash closer may be advantageous.

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Figure 1 — Diagrams of different sash opening configurations. 11

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3.2

Hood Types

3.2.1

Bypass Hood

Bypass hoods are laboratory hoods with either vertical or horizontal moving sashes that shall meet the requirements in Section 3.3.

Bypass mechanisms should be designed so the bypass opens progressively and proportionally as the sash travels to the fully closed position. The face velocity at the hood opening should not exceed three times the nominal face velocity with the sash fully open. Excessive velocities [>300 fpm (1.5 m/s)] can disrupt equipment, materials, or operations in the hood possibly creating a hazardous condition. Baffles should be designed to minimize ejection of liquid or solid materials outside the hood in the event of eruption.

The hood exhaust volume shall remain essentially unchanged (90% of the auxiliary jet airflow when either: the auxiliary air is at least 20°F (–6.7°C) warmer or cooler than room air. This does not apply if the auxiliary air is designed to be conditioned the same as room air. Hood face velocity is usually defined as air speed in a direction normal to the plane of the hood face opening. For auxiliary air hoods in standard operation, the directional component of the air velocity is not normal to the hood face plane. Accurate determination of the flow direction and derivation of the horizontal and vertical components of the velocity vector require very sophisticated instrumentation because of the low air speeds involved. Hence, measuring the hood’s face velocity with the auxiliary air shut off is an acceptable measure of hood exhaust volume, if turning off the auxiliary air does not upset the room air balance enough to significantly reduce the volume extracted by the hood exhaust system. NOTE: The 90% capture efficiency should be tested by material balance by introducing a tracer gas into the auxiliary airsteam and sampling the hood exhaust. Flow volume and sampling should be in accordance with EPA methods 1, 2, and 17 (40 CFR 60, Appendix A) or by other methods mutually agreed on by all parties. Tests should be conducted until three runs meeting these criteria are obtained.

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3.2.4

Perchloric Acid Laboratory Chemical Hoods

Perchloric acid hoods are laboratory hoods that meet the requirements in Sections 3.2.1 and 3.3 and NFPA 45. • In addition: All inside hood surfaces shall use materials that will be stable and not react with perchloric acid to form corrosive, flammable, and/or explosive compounds or byproducts; • All interior hood, duct, fan, and stack surfaces shall be equipped with water wash-down capabilities; • All ductwork shall be constructed of materials that will be stable to and not react with perchloric acid and/or its byproducts and will have smooth welded seams; • No part of the system shall be manifolded or joined to nonperchloric acid exhaust systems; • No organic materials, including gaskets, shall be used in the hood construction unless they are known not to react with perchloric acid and/or its byproducts; • Perchloric acid hoods shall be prominently labeled “Perchloric Acid Hood.” 3.2.5

Perchloric acid is a strong oxidizer. It can produce corrosive, flammable, and/or explosive reaction products; hence, the name given to this type of hood. Other chemicals, less widely known and used, may have similar properties. In all cases, these materials should only be used in a perchloric acid hood by experienced, trained personnel, knowledgeable and informed about the hazards and properties of these substances, provided with appropriate protective equipment after suitable emergency contingency plans are in place. The immediate supervisor and institutional/corporate responsible person (e.g., Safety Officer/Chemical Hygiene Officer) always should be notified before these substances are used. The complications of wash-down features and corrosion resistance of the exhaust fan might be avoided by using an air ejector, with the supplier blower located so it is not exposed to perchloric acid.

Floor-Mounted Hoods (formerly called Walk-In Hoods)

A floor-mounted hood is a laboratory hood that shall meet the requirements in Sections 3.2.1 and 3.3.

Floor-mounted hoods are used when the vertical working space of a bench hood is inadequate for the work or apparatus to be contained in the hood. The base of the hood should provide for the containment of spills by means of a base contiguous with the sidewalls, and a vertical lip at least 1 in. (2.54 cm) or equivalent. Often the lip can be replaced by a ramp to allow wheeled carts to enter the hood. The hood should be furnished with distribution ductwork or interior baffles to provide uniform face velocity. Doors and panels on the lower portion should be capable of being opened for the installation of apparatus. If the lower doors are kept closed during operation, the hood and exhaust system design and operation may be similar to a laboratory chemical hood and

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the effectiveness of the control should be equivalent if all the provisions of Section 3.3 are implemented. However, in many floor-mounted hoods, the closed lower sash may cause significant turbulence and the hood may not perform as well as a bench-top hood (Knutson, unpublished data). If the lower panels are opened during operations, the hood loses much of its effectiveness, even if face velocities comply with Section 3.3. The design and task-specific applications of floor mounted (walk-in) hoods may make it difficult to comply with the work practices of Section 6 of this standard. Hence, consideration should be given to preparation and implementation of written standard operating procedures (SOPs) for use of floor-mounted hoods. For example, if manipulations below waist height are necessary, special provisions may be necessary such as armports or small openings strategically located at necessary access points. Small rooms with one wall constituting a supply plenum and the opposite wall constituting an exhaust plenum should not be called floor-mounted hoods. In such instances, workers are intended to be inside the hood and exposure control provisions are drastically different. This standard does not apply to such rooms. 3.2.6

Variable Air Volume (VAV) Hoods

A variable air volume hood is a laboratory hood that shall meet all mandatory requirements of Sections 3.2.1 and 3.3 and is designed so the exhaust volume is varied in proportion to the opening of the hood face.

The VAV hood is a conventional (restricted bypass) hood equipped with a VAV control system.

The supply and exhaust systems shall be balanced. If the laboratory uses variable air volume, the supply and exhaust shall modulate together to maintain this balance. In addition, modification of the hood exhaust shall not compromise the total laboratory exhaust. Any modification of the hood exhaust shall not compromise other fundamental concerns.

The variation in the exhaust volume can be achieved by changing the speed of the exhaust blower or by operating a damper or other control device in the exhaust duct. Note that additional commissioning requirements will be necessary for these systems (see Section 6). The balance can be achieved by maintaining a differential pressure between the room and a reference point, for example the corridor, typically accomplished by maintaining a fixed difference (offset) between the supply and exhaust volumes. Since modifications of the volumetric flow of a VAV hood could upset the balance, the supply and exhaust systems should be designed to accommodate the modification in the exhaust air. The laboratory exhaust is based on three components: 15

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• Replacement of the exhaust air; • Heat load considerations; andlower sash may cause significant turbulence and the hood may not perform as well as a bench-top hood (Knutson, unpublished data). • Minimum (refer to right-hand explanation in 2.1.2) airflow requirements for general or dilution ventilation within the laboratory. It is recommended that VAV systems be equipped with emergency overrides that permit full design flow even when the sash is closed. 3.3

Hood Design (Performance Specifications) Criteria

3.3.1

Face Velocity

The average face velocity of the hood shall produce sufficient capture and containment of hazardous chemicals generated under asused conditions.

According to the Scientific Equipment and Furniture Association (SEFA), “ Face velocity shall be adequate to provide containment. Face velocity is not a measure of safety.” (SEFA 1-2002).

An adequate face velocity is necessary but is not the only criterion to achieve acceptable performance and shall not be used as the only performance indicator.

Face velocity has been used as the primary indicator of laboratory hood performance for several decades. Recently, however, studies involving large populations of laboratory chemical hoods tested using a containment-based test like the ANSI/ASHRAE Standard 110, “Method of Testing the Performance of Laboratory Fume Hoods,” reveal that face velocity is actually an inadequate indicator of hood performance. In one published study, approximately 17% of the hoods tested using the method had “acceptable” face velocities in the range of 80-120 fpm, but “failed” the tracer gas containment test with control levels exceeding the ACGIH recommended control level of 0.1 ppm. (Smith and Crooks, 1996). Some of these tests were AI while others were AU. See Section 6 on hood testing and commissioning for additional information. Example: LABORATORY CHEMICAL HOOD FACE VELOCITIES IN PRESSURE (at standard temperature) are: • 120 fpm — 0.000898 in wc press • 100 fpm — 0.000623 in wc press • 80 fpm — 0.000399 in wc press

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LABORATORY CHEMICAL HOOD FACE VELOCITY IN MPH WIND • 120 fpm — 1.36 mph wind • 100 fpm — 1.13 mph wind • 80 fpm — 0.91 mph wind Design face velocities for laboratory chemical hoods in the range of 80(100 fpm (0.41(0.51m/s) will provide adequate face velocity for a majority of chemical hoods. Factors including the design of the hood, the laboratory layout, and cross-drafts created by supply air and traffic all influence hood performance as much as or more than the face velocity. However, containment must be verified for all hoods using visual methods such as smoke (minimum) or quantitative methods such as tracer gas containment testing (recommended). Most tracer gas containment test methods, including the ANSI/ASHRAE 110 “Method of Testing Performance of Laboratory Fume Hoods” have certain limitations that must be observed. The ANSI/ASHRAE 110 method is a static test under controlled conditions and at low face velocities [150 fpm (>0.76 m/s): Most laboratory experts agree that velocities above 150 fpm (0.76 m/s) at the design sash position are excessive at operating sash height and may cause turbulent flow creating more potential for leakage.

3.3.2

Periodic Face Velocity Measurement

Once adequate performance (see 2.1.1) has been established for a particular hood at a given benchmark face velocity using the methods described above, that benchmark face velocity shall be used as a periodic check for continued performance as long as no substantive changes have occurred to the hood.

Substantive changes include: changes in hood setup; hood face velocity control type, setpoint, range, and response time; exhaust system static pressure, control range and response time; the hood operating environment including lab/furniture geometry, supply air distribution patterns, and volume; and room pressure control range and response time.

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Face velocity measurements shall be made with the sash in the Design Sash Position. The Design Sash Position is the maximum opening or configuration allowed by user standards, SOPs, or the Chemical Hygiene Plan, whichever is applicable, and used in the design of the exhaust system to which the hood is connected. The sash position at which benchmark face velocity is measured shall be recorded with the face velocity measurement and reproduced each time measurements are taken.

The face velocity of a combination sash is sometimes determined with the sash closed and the horizontal windows open. For “set-up” conditions, the determination of the actual face velocity may not be unique. The face velocity of combination sash hoods should identify the sash position where the tests were conducted.

A decrease in the average face velocity below 90% of the benchmark velocity shall be corrected prior to continued hood use.

This magnitude of decrease may impair performance.

Face velocity increases exceeding 20% of the benchmark shall be corrected prior to continued use.

An increase in individual hood average face velocity not exceeding 20% of the benchmark face velocity will probably not significantly alter hood performance and is acceptable with no corrective action. It should be noted, however, that there is an unnecessary increase in operating cost with increased face velocities. Increases exceeding 20% and the accompanying increase in supply flowrates may degrade performance due to increased impingement and cross-draft velocities.

It is important to use the same sash position for successive periodic performance measurements. If because of environmental challenges, face velocity cannot be accurately measured then air flow measurement can replace face velocity (6.5).

In constant volume systems, the face velocity will increase with reduced sash height. Although the face velocity could be three times or more than the design face velocity, the hood performance does not usually deteriorate because the hood opening is reduced (which often improves performance) and the lowered sash acts as a partial barrier. Supply and exhaust system capacities should be observed in the event of hood face velocity increases as volume shifting may occur, depriving other hoods of adequate airflow. Periodic dynamic testing should be performed when significant changes have occurred or to evaluate the response of a VAV system.

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3.3.3

Flow-Measuring Device for Laboratory Chemical Hoods

All hoods shall be equipped with a flow indicator, flow alarm, or face velocity alarm indicator to alert users to improper exhaust flow.

The purpose of the flow-measuring device is to provide the hood user with continuous information about the hood’s airflow. One method is to measure the total volume flow through the hood. Another method is to measure the face velocity. One popular method for measuring total volume flow is the Hood Static Pressure measuring device (see ACGIH’s Industrial Ventilation: A Manual of Recommended Practices), which can be related to flow. This method measures static suction in the exhaust duct close to the hood throat and, if there are no adjustable dampers between the hood and the measuring station, is related to the flow volume. Other methods include various exhaust volume or flow velocity sensors.

The flow-measuring device shall be capable of indicating airflows at the design flow and ±20% of the design flow.

The means of alarm or warning chosen should be provided in a manner readily visible or audible to the hood user. The alarm should warn when the flow is 20% low, and that is 80% of the setpoint value. The choice of audible vs. visible alarms should be made considering the potential needs of a physically disabled user. Tissue paper and strings do not qualify as the sole means of warning.

The device shall be calibrated at least annually and whenever damaged. 3.3.4

Hood Location

Laboratory chemical hoods shall be located so their performance is not adversely affected by cross drafts. Windows in laboratories with hoods shall be fully closed while hoods are in use (emergency conditions excepted).

The location of laboratory chemical hoods and other hoods or vented openings with respect to open windows, doorways, and personnel traffic flow directly influences the containment ability. Cross currents, drafts, and spurious air currents from these sources may decrease a hood’s containment ability (Kolesnikov, 2002a; Kolesnikov, 2002b; Memarzadeh, 1996). Users should be aware that cross drafts may disturb capture efficiency even when the sash is partially closed.

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4

Other Containment Devices

4.1

Gloveboxes

4.1.1

General Description and Use

Gloveboxes shall not be used for manipulation of hazardous materials with the face or other panels open or removed. If the potential combinations of material properties with planned manipulations are so complex the hazard cannot be estimated, a glovebox may or may not be suitable. A hazard evaluation shall be employed in such complex cases. Gloveboxes shall be used when the properties of the hazardous materials, the planned manipulations, or a credible accident would generate hazardous personal exposures if the work were done in an ordinary laboratory hood.

Laboratory-scale gloveboxes, for which this standard applies, should have a maximum internal chamber volume of 50 ft3 (1.4 m3) (single-sided access) or 100 ft3 (2.8 m3) (double-sided access) respectively (pass-through chambers excluded). Larger gloveboxes may occasionally be found in laboratory settings but are beyond the scope of this standard. Gloveboxes may be used for any laboratory manipulations that can be conducted under the restraints imposed by working with gloves through armholes. Gloveboxes may be used when the manipulated substances must be handled in a controlled (e.g., inert) atmosphere or when they must be protected from the external environment.

4.1.1.1 Location There are no special requirements for location beyond those already noted for hoods. 4.1.2

Design, Construction, and/or Selection Materials

Interior cracks, seams, and joints shall be eliminated or sealed.

4.1.3

Since manipulations through glove ports are somewhat difficult, however, it is advisable to avoid high traffic areas.

Depending upon the nature of the hazard controlled, a glovebox may be constructed of material with favorable characteristics such as fire rating, radiation shielding, nonporous and/or impervious surfaces, corrosion-resistance for the intended use, and easily cleaned. Interior corners should be covered.

Utilities

Utility valves and switches shall be in conformance with applicable codes. When control of utilities from inside the glovebox is required, additional valves and switches shall be provided outside the glovebox for emergency shutoff.

Certain applications require that all valves be located inside of the glovebox containment and all lines exterior to the box be 100% welded.

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4.1.4

Ergonomic Design

Ergonomics shall be a significant consideration in the design, construction, and/or selection of gloveboxes. Frequency of use shall dictate the extent to which ergonomic principles will be applied. Proper application of ergonomic principles shall be met by referring to chapter 5.10, Guideline for Gloveboxes, AGS-G001-1998. 4.1.5

Provision for Spills

The design of the glovebox shall provide for retaining spilled liquids so the maximum volume of liquid permitted in the glovebox will be retained. 4.1.6

A system for draining the spilled liquid into a suitable sealed container should be provided if the properties of the spilled liquid or other circumstances prevent cleanup by working through the gloves.

Exhaust Ventilation

Containment gloveboxes shall be provided with exhaust ventilation to result in a negative pressure inside the box that is capable of containing the hazard at acceptable levels. 4.1.7

Frequent use versus infrequent use may dictate the extent to which ergonomic principles will be applied.

See Sections 4.1.11 through 4.1.14 for ventilation recommendations for specific glovebox types.

Exhaust Air Cleaning

The air or gas exhausted from the glovebox shall be cleaned and discharged to the atmosphere in accordance with the general provisions of this standard and pertinent environmental regulations.

If the glovebox is sealed tightly when closed, a pressure relief valve might be required to prevent excessive negative pressure in the glovebox, depending on the choice of air-cleaning equipment and exhaust blower.

Air-cleaning equipment shall be sized for the maximum airflow anticipated when hazardous agents are exposed in the glovebox and the glovebox openings are open to the extent permitted under that condition.

If an ACD is required, its operating efficiency should be relatively independent of airflow. A HEPA filter’s collection efficiency is relatively unaffected by changes in airflow rate, whereas the efficiency of a submerged orifice wet scrubber may drop substantially if airflow rate is increased or decreased. Where the airflow to a system like a submerged scrubber is decreased, additional air may be admitted to the system upstream of the ACD to maintain the rated volume flow at the ACD. On the other hand, if the airflow through the glovebox scrubber system increases to a point where the collection of the ACD is substantially impacted, then the airflow must either be reduced or the ACD redesigned, modified, or replaced to accommodate the higher flowrate velocity for particulate material.

If the air-cleaning device (ACD) is passive (i.e., a HEPA filter or activated carbon) provision shall be made for determining the status of the ACD, as noted in section 9.3. If the ACD is active (i.e., a packed-bed wet scrubber), instrumentation shall be provided to indicate its status.

The ACD shall be located to permit ready access for maintenance. Provision shall be made for maintenance of the ACD without hazard to personnel or the environment and so as not to contaminate the surrounding areas.

The ACD should be located as close as is practical to the glovebox to minimize the length of contaminated piping or the need for maintaining high transport velocity.

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4.1.8

Exhaust Ducting

Exhaust piping shall be in accordance with the principles described in the ACGIH Industrial Ventilation Manual, ANSI Z9.2, and the ASHRAE 2001 Handbook – Fundamentals. All piping within the occupied premises shall be under negative pressure when in operation. Materials shall be resistant to corrosion by the agents to be used. 4.1.9

Monitoring and Alarms

A glovebox pressure monitoring device with a means to locally indicate adequate pressure relationships to the user shall be provided on all gloveboxes.

Ergonomics principles indicate that the total number and types of alarms should be minimized. Alarms should also be clearly distinguished from each other.

If audible alarms are not provided, documented training for users in determining safe pressure differentials shall be required. Pressure monitoring devices shall be adjustable (i.e., able to be calibrated if not a primary standard) and subject to periodic calibration. 4.1.10 Decontamination Before the access panel(s) of the glovebox are opened or removed, the interior contamination shall have been reduced to a safe level.

Safe level is relative to the contaminant involved. Analytical techniques for determining surface contamination (mass/unit area, counts per minute/unit area) are helping to provide increasingly sensitive but not always specific risk information. Correlating surface contamination with exposure potential remains more of an art than a science.

If the contaminant is gaseous, the atmosphere in the box shall be adequately exchanged to remove the potentially hazardous gas. This can be affected by exhausting the box through its ventilation system, and where necessary providing an air inlet that is filtered if required. If the contaminant is liquid, any liquid on surfaces shall be wiped with suitable adsorbent material or sponges until visibly clean and dry. Used wipes shall be placed in a suitable container before being removed from the glovebox.

Many liquids and some solids have vapor pressures that might cause hazardous concentrations of vapor. A combination of the contamination reduction procedures discussed above might be necessary.

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Certain direct-reading instruments (e.g., combustible gas indicators) may lend themselves to such an assessment. If the contaminant is a powder or dust, all internal surfaces shall be cleaned and wiped until visibly clean. The exterior surfaces of the gloves also shall be wiped clean.

Neutralizing reagents should be used, if available.

Precautions to prevent hazards to personnel and contamination of the premises shall be made if the ducting is to be opened or dismantled.

The exhaust piping from the glovebox to the ACD may be contaminated, especially if a hazardous particulate is involved.

If there is any uncertainty about the effectiveness of contamination reduction procedures, personnel involved in opening the panels of the glovebox shall be provided with appropriate PPE or clothing.

Nonessential personnel should be excluded from the area. The contamination in the general work area should be reduced before use. For more information see EPA 402-R-97-016, MultiAgency Radiation Survey and Site Investigation Manual.

4.1.11 High Containment Glovebox A high containment glovebox shall conform to all the mandatory requirements of Sections 4.1.1 through 4.1.11, and

Examples include gloveboxes used for controlling exposures to acutely hazardous and highly volatile materials where any exposure may be harmful.

• Shall be provided with one or more airlock pass-through ports for inserting or removing objects or sealed containers without breaching the physical barrier between the inside and outside of the glovebox; • Shall maintain negative operating static pressure within the range of –0.5 to –1.5 in.wg (–125 Pa to –374 Pa) such that contaminant escape due to “pinhole-type” leaks is minimized. • Shall maintain dilution of any flammable vaporair mixtures to 50% of the average face velocity) have been demonstrated to significantly affect hood containment and should be identified and alleviated. Ideally, cross-draft velocities should be less than 30%. If the supply tracks the exhaust, measure the cross drafts at the maximum conditions.

6.3.6

Airflow Visualization Tests

Airflow visualization tests shall be conducted as described in the ANSI/ASHRAE 110-1995, Method of Testing Performance of Laboratory Fume Hoods. The tests shall consist of small-volume generation and large-volume generation smoke to identify areas of reverse flow, stagnation zones, vortex regions, escape, and clearance.

Smoke tests are valuable because they indicate the direction of airflow through the opening and within the hood enclosure when the smoke plume is visible. Smoke particles are rapidly diluted to the extent where they may not be visible even though significant concentrations may exist in the invisible plume. Smoke tests should be used only as an indication of flow direction and absence of visible smoke should not be interpreted as an absence of smoke. Users of smoke should note that smoke tubes and candles can be caustic and detrimental to the user, test equipment, and apparatus in the hood.

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Attempts to improve airflow patterns should be attempted by adjusting the baffles and slot widths, redirecting room air currents, or changing the opening configuration by moving the sash panels. Closure of the sashes resulting in an opening smaller than the design opening may represent a “restricted use” condition. Visible escape beyond the plane of the sash when generated 6 in. (15.2 cm) into the hood shall constitute a failure during the performance test.

Often the most devastating area for reverse flow is behind the airfoil sill on bench-top-mounted hoods. An improperly designed airfoil or lack of an airfoil will cause reverse flow along the work surface within 6 in. (15.2 cm) of the sash plane. Reverse flow in this region is particularly worrisome as the wake zone that develops in front of a hood user could overlap with the reverse flow zone. Dynamic challenges should be evaluated.

6.3.7

Tracer Gas Containment Tests

The tracer gas containment tests shall be conducted as described in the ANSI/ASHRAE 110-1995, Method of Testing Performance of Laboratory Fume Hoods or by a test recognized to be equivalent.

Tracer gas tests enable the ability to quantify the potential for escape from a laboratory chemical hood.

A control level for 5-minute average tests at each location conducted at a generation rate of 4 L/m shall be no greater than 0.05 ppm for “as manufactured” tests and 0.10 ppm for “as installed” (AM 0.05, AI 0.1).

Values for control level may not be suitable for establishing hood safety, as the tracer gas test methods may not adequately simulate actual material use, risk, or generation characteristics. In addition, the tracer gas test does not simulate a live operator, who may increase potential for escape due to operator size, movements near the hood opening, or improper hood use.

Escape more than the control levels stated above shall be acceptable at the discretion of the design professional in agreement with the responsible person (2.4.2). The “as used” 0.10 ppm level or more is at the discretion of the responsible person (2.3).

The test data need to be made available by the manufacturer for each specific model and type of hood so a potential buyer can verify proper containment or compare one manufacturer’s hood containment against another.

Hood containment should be evaluated at different mannequin heights to represent workers of different height. AM 0.05 can be achieved with a properly designed laboratory chemical hood. It should not be implied that this exposure level is safe. Safe exposure levels are application specific and should be evaluated by properly trained personnel (SEFA 1-2002).

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6.4

Ongoing or Routine Hood and System Tests

Routine performance tests shall be conducted at least annually or whenever a significant change has been made to the operational characteristics of the hood system. A hood that is found to be operating with an average face velocity more than 10% below the designated average face velocity shall be labeled as out of service or restricted use and corrective actions shall be taken to increase flow.

ANSI/ASHRAE 110-1995 may be used in the laboratory as an accepted test with specific values for the control levels (and the release rate if you depart from the standard). It also may be used for routine periodic testing, but it is somewhat expensive and other less rigorous tests may be adequate if conditions have not changed since commissioning tests. In addition to the hood tests, periodic testing at a minimum of 1-year intervals should ensure that: • All other room exhaust provisions are within specifications; • Room differential pressure is within specifications (if applicable); • Room differential airflow is within specifications (if applicable).

Each hood shall be posted with a notice giving the date of the routine performance test, and the measured average face velocity. If it is taken out of service it shall be posted with a restricted use or out- of-service notice. The restricted use notice shall state the requisite precautions concerning the type of materials permitted or prohibited for use in the hood.

6.5

Types of Systems

6.5.1

Single Hood CAV Systems

Commissioning tests on single hood, constant air volume (CAV) systems shall consist of: • • • •

Fan Performance Tests; Exhaust Duct Measurements; Hood Performance Tests; and Hood Monitor Calibration.

Fan Performance Tests shall include measurement of fan speed, fan static pressure, motor speed, and amp draw.

Periodic tests concerning face velocity or hood exhaust volume are valid indications of hood operation provided no changes have been made in that hood structure, supply air distribution, or other factors listed above that affect hood performance. The hood sash should not be lowered below design position to increase face velocity during routine tests. A decrease in face velocity at the design opening may be indicative of a problem with operation of the exhaust system.

Ensuring proper operation of a laboratory chemical hood requires proper design, installation, and operation of all components of the exhaust systems and many times the air supply systems as well.

Using a “top-down” approach, the fan should be adjusted to exhaust the specified volume of air.

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ANSI/AIHA Z9.5–2003

Exhaust duct measurements shall consist of exhaust flow measurement and hood static pressure measurement.

The exhaust flow should be measured in the exhaust duct according the methods described in ANSI/ASHRAE 41.2-1987 (RA 92) or as described above. Fan performance and exhaust measurements should be conducted by a certified Test-and-Balance firm.

Hood performance tests shall consist of tests described in Sections 6.3.1 through 6.3.6. The hood monitor shall be calibrated and adjusted after hood performance has been determined as satisfactory. Safe operating points shall be clearly identified for the hood user. 6.5.2

Multiple Hood CAV Systems

Commissioning of multiple hood, constant air volume systems shall include: • Fan Performance Tests; • Verification of proper test, adjustment, and balance of branch exhaust flow and static pressures (exhaust flow and static pressure for each branch shall be recorded after final balancing is complete); • Hood Performance tests as described above in Sections 6.3.1 through 6.3.6; and • Hood and System Monitor Calibration. 6.5.3

Multiple hood systems should be balanced using an iterative approach where dampers or controllers are adjusted until flow through each hood is in accordance with design specifications. Hood performance tests should follow completion of system balancing, measurement of branch exhaust flows, and branch static pressures. Determine that sash position of one hood does not affect flow through another hood.

VAV Laboratory Chemical Hood Systems

VAV hood systems shall be commissioned prior to use by laboratory personnel to ensure that all system components function properly and the system operates as designed under all anticipated operating modes (defined under the VAV section). The commissioning procedures for VAV systems shall include: • Verification of VAV Sensor Calibration; • VAV Hood Performance Tests; • VAV Laboratory and Ventilation System Tests; and • Verification of System Diversity.

Performance of laboratory chemical hoods connected to variable air volume systems (VAV) can be affected by numerous factors associated with proper design, calibration, and tuning of the control systems. It is imperative that all components of the VAV system be in proper operating condition to ensure proper hood performance. Commissioning tests should be specified to verify that the VAV systems operate according to design specifications. Some of the data, such as sensor calibrations, can be acquired through the process of installing the VAV controls or through the Testing, Adjustment and Air Balance process (TAB).

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Documentation collected outside the commissioning tests, such as manufacturer’s tests on system components, should be available in advance of commissioning tests for comparison with test data and inclusion with final commissioning documents. 6.5.3.1 VAV Sensor Calibration VAV sensors shall be capable of accurate measurement and control within 10% of actual at the design maximum and minimum flow conditions.

Numerous sensors can be employed in a typical VAV laboratory chemical hood systems such as sash position sensors and room differential pressure sensors, to name a few. The accuracy of the sensors depends on proper methods to measure the physical parameters and ability to adjust calibration. Sensors that report inaccurate information will not only be misleading when monitoring system operation but may result in unsafe hood and laboratory conditions. Part of the process of installing VAV controls and balancing system airflows should involve calibration of sensors and documentation of it. At a minimum, commissioning tests should test a representative sample of sensors to verify accurate reporting of information.

6.5.3.2 VAV Hood Performance Tests In addition to hood performance tests described for evaluation of CAV hood systems, commissioning tests on VAV hood systems shall include measurement of flow or face velocities at different sash configurations and VAV Response and Stability tests. Flow or face velocity measurements shall be conducted at a minimum of two separate sash configurations.

In the majority of VAV hood systems, the purpose of the VAV control system is to adjust airflows to compensate for changes in sash configurations or system operating mode (occupied/unoccupied, night setback, etc.). The VAV control system must be capable of quick and precise adjustment of flows without experiencing major overshoot or undershoot (10% of steady-state value).

VAV Response and Stability tests shall include continuous measurements and recording of flow while opening and closing the sashes for each hood (calibrated flow sensors or measurement of slot velocity within the hood can be used as an indicator of flow).

Commissioning tests should be used to verify that VAV systems provide satisfactory control of airflows in response to sash movement or changes in operating modes.

VAV Response shall be sufficient to increase or decrease flow within 90% of the target flow or face velocity in a manner that does not increase potential for escape.

A response time of < 3 sec. after the completion of the sash movement is considered acceptable for most operations. Faster response times may improve hood containment following the sash movement. 61

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VAV Stability shall be sufficient to prevent flow variations in excess of 10% from design at each sash configuration or operating mode. 6.5.3.3 VAV Ventilation System Tests The VAV hood controls shall provide stable control of flow in the exhaust and supply ducts and variation of flow must not exceed 10% from design at each sash configuration or operating mode.

On a plenum system determine what happens to exhaust flow when one fan is not operating.

6.5.3.4 Verification of System Diversity System diversity shall be verified prior to use of laboratory chemical hoods. The tests shall be designed to verify that users will be alerted when system capacity is exceeded and unsafe conditions may exist. 6.5.4

Laboratory Airflow Verification Tests

Tests to verify and commission the laboratory shall consist of: • Air supply measurements; • General room exhaust flow measurement (if applicable); • Room differential pressure measurement; and • Calculation of the difference between total area (laboratory, zone, etc.) supply and total exhaust. All ventilation system alarm and monitoring provisions associated with occupant safety shall be verified for proper functionality.

The laboratory commissioning tests are used to ensure proper air supply and exhaust for each laboratory or zone. TAB data once verified can be substituted where appropriate.

This includes local monitoring provisions for such items as hood airflow or room differential pressure as well as remote and central monitoring provisions for such parameters.

6.5.4.1 CAV Laboratory Room Tests These tests shall ensure that the ventilation system design airflow is being maintained within the allowable tolerance in: • All hood exhausts; • All other bench-top and equipment exhaust provisions that may be present; • The room general exhaust if present; • The room supply; and • Room air cross currents at the hood face opening. 62

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If a specific room differential pressure (dP) has been specified, the dP shall be measured to ensure that it is within its allowable range. If a room differential airflow is specified, actual room differential airflow shall be determined to ensure that is within allowable maximum and minimum limits and in the proper direction. If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.), each individual mode shall be enabled and applicable parameters (i.e., room supply, room total exhaust, etc.) shall be performed for each separate mode. Room ambient conditions (temperature, humidity, air currents, etc.) shall also be measured to ensure they are being maintained under the conditions specified. 6.5.4.2 VAV Laboratory Room Tests These tests shall ensure proper performance of the VAV ventilation system and its associated controls such that:

For most operations, 10 seconds will be an acceptable time to achieve the desired area pressurization but a Hazard Evaluation should be conducted to determine the acceptable time.

• The room general exhaust provides the specified range of airflow. • The room supply provides the specified range of airflow. • Room air cross currents at the laboratory hood face opening are within limits. If a specified room dP has been specified, the dP shall be measured to ensure that it is being controlled within its allowable range with all doors closed and at minimum and maximum room exhaust airflow. If a room differential airflow is specified, actual room differential airflow shall be determined to ensure that it is within allowable maximum and minimum limits and direction at minimum and maximum room exhaust airflow. If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.) conditions shall be evaluated for each mode. Room ambient conditions (temperature, humidity, air currents, etc.) shall also be measured to ensure they are being maintained under the conditions specified. 63

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ANSI/AIHA Z9.5–2003

The VAV systems shall be capable of maintaining the offset flow required between exhaust and supply to achieve the desired area pressurization within the desired time specified. 6.6

For most operations, 10 seconds will be an acceptable time to achieve the desired area pressurization but a Hazard Evaluation should be conducted to determine the acceptable time.

Laboratory Chemical Hoods

If practical, the exhaust flowrate from hoods shall be tested by measuring the flow in the duct by the hood throat suction method or by flow meter.

See the latest edition of the ACGIH-2001 Industrial Ventilation: A Manual of Recommended Practice. If a flowmeter is used, care should be taken to ensure that the element has not been compromised by chemical action or deposition of solids. NOTE: Fine dust, for example, might adhere to the throat of a venturi meter and change its inside dimension, which is critical to the measurement.

If flow measurement in the duct is not practical, velocity at the hood face or opening shall be measured at a sufficient number of points to obtain a realistic average velocity, and multiplied by the open area in the plane of the velocity measurements to obtain the flowrate. If the flowrate is more than 10% different from design, corrective action shall be taken. 7

Work Practices

Hood users shall be trained in the proper operation and use of a hood.

The laboratory’s Chemical Hygiene Plan should discuss proper work practices.

The user shall establish work practices that reduce emissions and employee exposures. The user shall not modify the interior or exterior components of the hood without the approval of the Chemical Hygiene Officer, Responsible Person, or other appropriate authority in the organization. Many work practices affect the overall safety and health in the laboratory. The following list concerns only those work practices that relate directly to hood performance and applies only when hazardous materials are to be used in the hood. • The user shall not lean into the hood so that his/her head is inside the plane of the hood, as defined by the sash, without adequate respiratory and personal protection.

During setup or hood maintenance, this provision is not necessary, provided there are no sources of chemicals in the hood and the hood is decontaminated.

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• Equipment and materials shall not be placed in the hood so that they block the slots or otherwise interfere with the smooth flow of air into the hood.

When large equipment must be placed in a laboratory chemical hood, placing the equipment on a stand to allow air to flow under the stand can reduce the significance of any airflow disturbance.

• All work shall be conducted at least 6 in. (15.2 cm) behind the plane of the sash (hood face).

Often marking the work surface with a tape or other means, to indicate the 6 in. (15.2 cm) line, will assist the user in identifying the limits of usable space.

• The horizontal sash or panels shall not be removed.

In some cases, while the hood is empty, the sash could be removed for setup procedures.

• The hood shall not be operated without the back baffles in place. • Flammable liquids shall not be stored permanently in the hood or the cabinet under the hood unless that cabinet meets the requirements of NFPA 30-2000 and NFPA 45-2000 for flammable liquid storage.

Although the storage of acids does not pose the same hazard as flammable solvents, the storage of acids under the hood should be in acid-resistant cabinets. Because of the high hazard associated with the storage of chemicals in front of the user at the hood, some laboratories prohibit the storage of flammable materials under the hood. Individual policies are often site specific; hence, the Chemical Hygiene Officer should always be consulted.

• The sash or panels shall be closed to the maximum position possible while still allowing comfortable working conditions.

In some laboratory design, the normal sash position is not full open. When the sash is raised above the design level, the hood could lose adequate control.

• Hood users shall be trained to close the sash or panels when the hood is not in use. • The hood user shall not operate with the sashes opened beyond the design opening. • Pedestrian traffic shall be restricted near operating hoods.

When a person walks past a laboratory chemical hood he or she sets up a wake that can aspirate contaminants from the laboratory chemical hood. Proper location of the hood and administrative controls are required to minimize this potential hazard.

• Rapid movement within the hood shall be discouraged. • The hood shall not be operated unless verified it is working. • Rapid movement of the sash or panels shall be discouraged.

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7.5

Posting

Each hood shall be posted with a notice giving the date of the last periodic field test. If the hood failed the performance test, it shall be taken out of service until repaired, or posted with a restricted use notice. The notice shall state the partially closed sash position necessary for safe/normal operation and any other precaution concerning the type of work and materials permitted or prohibited. 7.6

Other information that should be posted may include flowrates, fan numbers, an indication that the system is VAV or less than 100% diversity and an emergency phone number.

Operating Conditions

Hoods shall be in operation whenever hazardous volatile materials are being used or stored inside.

8

The intent is to ensure that those using the hood know its current status and where to get help or further information.

A hood that is more than 10% below the standard operating conditions, either because of inadequate face velocity, or poor distribution of the face velocity should be immediately reported to the responsible safety person. The hood should not be used unless specific conditions for safe use can be identified and posted such as its maximum sash opening. Hoods should only be turned off when all materials are removed from the interior and only if the hood does not provide general exhaust ventilation to the space.

Preventive Maintenance

Inspection and maintenance shall follow an Inspection and Maintenance (I&M) Program developed by the user.

I&M programs should be “preventive” in nature. The written I&M Program should identify potential hazards and problems associated with laboratory operations and designate appropriate I&M procedures to minimize such hazards and problems. This could include, for example, routine inspection of fan belts to ensure that hood exhaust ventilation fans are turning at the designed speeds, that hoods are being cleaned to minimize buildup of hazardous chemicals in the hoods, and so forth. The written program should identify standard operating procedures to be followed during I&M activities. The “responsible person” identified in Section 2.3 should be involved in the development and operation of the I&M program.

Preventive maintenance shall be performed on a regularly scheduled basis.

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8.1

Operations During Maintenance Shutdown

Operations served by equipment being shut down for inspection or maintenance shall be safely discontinued and secured during such maintenance.

“Secured” condition will vary from case to case. It might consist of ceasing operation, or requiring removal from the premises of all flammable and highly toxic materials.

Lock-out/tag-out procedures shall be implemented. Laboratory workers shall be notified in advance of inspection and maintenance operations. 8.2

Housekeeping Before and After Maintenance

All toxic or otherwise dangerous materials on or in the vicinity of the subject equipment shall be removed or cleaned up before maintenance. Any hazardous materials and any other debris shall be cleaned up before operations resume.

8.3

All ventilation equipment should be de-energized and labeled as such with appropriate signage before starting any repair work.

If possible, equipment to be removed to the shop should be decontaminated before removal. Also, a procedure should be established to notify hood users before any maintenance is to be performed so work in the hood can be halted during maintenance. If the maintenance activities involve contact with potentially contaminated parts of the system, these parts should be evaluated first by appropriate methods.

Safety for Maintenance Personnel

Maintenance personnel shall be trained and required to use appropriate PPE (such as respirators, goggles or faceshields, gloves, and protective clothing) during parts of the work involving potential hazard. 8.4

Work Permits

• A written work permit system shall be established whenever the integrity of a potentially contaminated ventilation system is to be breached. Such work permits shall be designed to suit the circumstances, and shall at least address the following factors: The permit system shall be overseen by a responsible person, as defined in this standard, and shall be signed by the person(s) to do the work, his/her supervisor, and any other supervisors affected by the work; • The nature of the work, and the health and safety precautions, shall be described; • The time and place of the work shall be described; 67

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• The same persons who signed the permit (or their counterparts on a different shift) shall sign off when the work is complete; and • Completed work permits shall be filed by an appropriate management function and retained for a minimum of 3 years or as specified by individual organizational policy. 8.5

Records

Records shall be maintained for all inspections and maintenance. If testing involves quantitative values (such as hood throat suction) the observed values shall be recorded. Inspection forms designed for the several categories of testing shall be provided and shall include the normal values for the parameters tested. 8.6

Testing and Monitoring Instruments

8.6.1

Air Velocity, Air Pressure, Temperature and Humidity Measurements

Pressure instrumentation and measurement shall be in compliance with ANSI/ASHRAE 41.3-1989. Temperature instruments and measurement techniques shall be in compliance with ANSI/ASHRAE 41.1-1986 (RA 01). All instruments using electrical, electronic, or mechanical components shall be calibrated no longer than 12 months before use or after any possible damage (including impacts with no apparent damage) since the last calibration. The accuracy of a scale used for a given parameter shall meet the following requirements:

Records should be kept for at least 1 year or until the next required test is performed.

Instruments of a “primary standard” nature (i.e., standard pitot tubes, flow tube manometers, draft gauges, etc.)—if used with fluids for which they are designed and tested for leaks—require no further calibration.

Accuracy Velocity-fpm Below 100 fpm (0.51 m/s) 5 fpm (0.025 m/s) 100 fpm (0.51 m/s) and higher 5% of signal Pressure- in. wg 0.1 in.wg (25 Pa) 0.5 in.wg (125 Pa) and higher

Accuracy 10% of signal 5% of signal

Between 25 Pa and 125 Pa, interpolate linearly.

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Pitot-static tube measurements shall be in accordance with ANSI/ASHRAE’s Method of Test Measurement of Flow of Gas, 41.7-1984 (RA 00). Inclined manometers shall be selected so that the nominal value of the measured parameter is at least 5% of full scale. U-tube manometers shall not be used for pressures less than 0.5 in.wg (125 Pa). Pitot tubes other than standard shall be calibrated. Temperature measurement instrumentation shall have an accuracy of ±0.5°F or ±1°C over the entire measurement range. Humidity measurement instrumentation shall have an accuracy of ±3.0% relative humidity over the entire measurement range. 8.6.2

Air Contaminant Monitors

Air contaminant monitors shall be tested at least monthly or more often, if experience or manufacturer’s recommendations so indicate. Such testing shall include the sensing element, zero drift, and actuation of signals, alarms, or controls. Continuous air monitors shall be calibrated per manufacturer’s specifications or more frequently if experience dictates. 8.6.2.1 Tolerance of Test Results Allowable variance from design conditions, or conditions determined otherwise satisfactory, shall be: • For air velocity, +10%; • For ventilation air pressure or differential pressure, +20%; For pneumatic control system air pressure, 8 Bsmall, use Blarge = 8 Bsmall

Table A2

Volume Necessary to Achieve Throw Off Edge of Building and Recirculation Zone, cfm and L/s Assume stack is 10 ft (3.0 m) high and fan exit velocity is 3000 fpm (15.2 m/s) with 15 mph

Distance to Edge of Building and Recirc. Zone

Feet to throw horizontally

Meters to throw horizontally

Flow needed, cfm

Flow needed, L/s

75

22.9

1,267

598.0

100

30.5

5,068

2392.0

150

45.7

20,272

9567.3

200

61.0

45,612

21526.5

250

76.2

81,088

38269.3

300

91.4

126,699

59795.3

Second Stack Design Method— The Numerical Method A more detailed analysis that accounts for dilution within the plume can be used if the required stack heights or flowrates are too large from the geometric method. Minimum dilution can be predicted using equations from Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications. The equations are not discussed in detail here. The equation numbers of most interest are equations 25 to 30 in Chapter 43. These equations apply only to intakes below stack top. The stack height used in these equations is the physical stack height only. “Effective stack height,” including the effect of plume rise, should not be used. The EPA screening dispersion model, SCREEN3, can also be used in certain situations to supplement the ASHRAE Handbook equations. For the example case discussed above [10 ft (3.0 m) stack, diameter = 2.06 ft (0.63 m), exit velocity =

3000 fpm (15.2 m/s), flowrate = 10,000 cfm (4719 L/s), receptor at end of wake recirculation zone 171 ft (52.1 m) away], the predicted minimum dilution from Chapter 43 is 455:1. If the diameter is increased to 3.5 ft (1.07 m) associated with a larger flow rate of 30,000 cfm (14152.4 L/s), the minimum dilution decreases to 264:1. At first glance, the smaller flowrate stack that yields the larger dilution would seem to be preferred. However, the larger 30,000 cfm (14152.4 L/s), flowrate provides an internal dilution of 3:1 compared to the original 10,000 cfm (4719 L/s). When comparing the two cases, the larger flowrate case has a total dilution of 3 × 264 = 792:1, which is better than the lower flowrate case and would provide lower chemical concentrations at an air intake for a given chemical release rate. Allowable spill rate to meet the 0.05 ppm at the receptor location would be 11.2 L/m of toxic vapor. The original design with d = 2.06 ft (0.63 m) has a higher dilution Dcrit of 455 but the reduced volume flow only allows a spill

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volume rate of 6.4 L/m. In effect, the factor of 3 volume flow increase in the stack with the fan allows about a factor of 1.75 increase in allowable spill rate. In conceptual terms, exit velocity and volume flow rate are “equal partners” in plume rise and the resulting increase in safety through greater dilution. However, in practical terms, exit velocities can only be increased by doubling or tripling while manifolding or adding roof air to the stack can easily result in a 10-fold increase in dilution. Dilution in the context of dispersion of laboratory exhaust is a deceptively difficult concept because one must account for both the dilution within the exhaust system, De, which is present at the stack and the dilution from the stack to a downwind location, D. The concept can be simplified by normalizing D by the volume flow rate through the exhaust stack, Q. By normalizing D, only the dispersion, which occurs between the exhaust stack and the downwind location, needs to be considered. The normalized value can be presented in one of two ways, either as a normalized dilution or a normalized concentration value. A normalized dilution value can be obtained by multiplying D by the ratio of the actual volume flow rate and a standardized volume flowrate [i.e., 1000 cfm (472 L/s) × (Qact / Qstd)]. The result is a dilution value that is independent of the actual volume flowrate through the exhaust stack, making it possible to compare the effectiveness of various exhaust stacks with different volume flowrates, because all of the values are referenced to the same 1000 cfm (0.47 m3/s) volume flowrate. A normalized concentration value is obtained by applying the definitions of concentration and dilution provided in the ASHRAE 1999 Handbook – HVAC Applications, Chapter 43 [C/m = 1/ (D × Q)]. The result is a normalized concentration value that is the ratio of the concentration present at the downwind location and the mass emission rate of the emitted chemical, expressed in units of µg/m3 per g/s. This value is completely independent of the volume flowrate through the exhaust stack, and thus can be used to readily compare the effectiveness of exhaust stacks with various volume

flowrates. Another advantage of this method is that if the emission rate of a chemical is known, you can simply multiply the emission rate by the C/m value to obtain a pollutant concentration. This concentration can then be compared directly with established health and odor limits. Design Criteria When designing stacks with the numerical method, it is necessary to have a design criterion for selecting a stack design. Development of a dilution criterion can be difficult since the types and quantities of laboratory chemicals can vary significantly from laboratory to laboratory. As a starting place, it is suggested here to have the stack provide protection similar to what a laboratory chemical hood would provide a worker standing at the hood. As described in this standard, a laboratory chemical hood should have an ANSI/ASHRAE 110 test performed by a manufacturer, and the ANSI/ASHRAE 110 rating should be AM 0.05 or lower. This rating translates to the worker being exposed to 0.05 ppm or lower of tracer gas while 4 L/min of tracer gas are being emitted from within the laboratory chemical hood. The same 4 L/min of tracer gas are being emitted from the laboratory chemical hood exhaust stack. The recommended design criterion is that the 0.05 ppm concentration also be the maximum concentration at the air intake. (The time constant for exposure concentrations mentioned in this standard is measuring over a 10-minute span of time.) The detailed calculations are not presented here, but it can be confirmed that the 4 L/min. emission rate and an allowable air intake concentration of 0.05 ppm corresponds to a normalized concentration design criterion of 750 µg/m3 per g/s or a 2800:1 dilution for a 1000 cfm (472 L/s) flowrate exhaust, 280:1 for a 10,000 cfm (4719 L/s) flow rate, and a 93:1 dilution for a 30,000 cfm (14158 L/s) exhaust. These suggested design criteria is somewhat more lenient than the smaller criteria suggested in the ASHRAE 1999 Handbook – HVAC Applications, Chapter 13, which recommend that air intake concentrations should be less than 3 ppm due to an evaporating liquid spill in a laboratory chemical hood and exhausted at a rate of 7.5 L/s. The ASHRAE criteria translate to a normalized concentration design criterion of 400 µg/m3 per g/s or a 85

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5000:1 dilution for a 1000 cfm (472 L/s) flowrate exhaust. For facilities with intense chemical utilization, design criteria specific for that facility can be developed using the chemical inventory. In the stack examples above, the 10,000 cfm (4719 L/s) case had a predicted dilution of 455:1, which meets the 280:1 criterion for a 10,000 cfm (4719 L/s) flowrate. The 30,000 cfm (14158 L/s) case had a predicted dilution of 264:1, which also meets the 93:1 criterion for this flowrate, by a larger margin than the 10,000 cfm (4719 L/s) stack. Graphical Solution Referenced for the Second Stack Design Method Using the Halitsky Criteria Two graphical solutions can be consulted that show a solution to the dilution calculations. The first is Ratcliff and Sandru (ASHRAE Transactions, 105, part 1, paper Ch-99-7-2, 1999) and the second is Petersen, Cochran, and LeCompte (to be published in 2002 ASHRAE Transactions). The solutions in both papers are for a Halitsky Criteria spill, 0.028 ppm, rather than the criterion derived from the ANSI/ASHRAE 110 test specification. Quite a bit of expertise is required to interpret the graphs. As an example, in the second paper, one point calculated and shown on the graph is that a zero height stack with a flow of 50,000 cfm (23597 L/s) and an exit velocity of 3000 fpm (15.2 m/s) would require an offset distance of 120 ft (36.6 m) to the nearest receptor site using the 0.028 ppm exposure limit at the receptor. These graphs were derived from Chapter 43 of ASHRAE 1999 Handbook – Applications equations for critical wind speeds and dilutions. Zero-height stacks are quite

common because stacks that end below parapet walls, below the height of adjacent penthouses, or that end below adjacent screen walls or screens will act as a zero-height stack. Receptor sites would include operable doors and windows, and any location where pedestrian access was allowed as well as to outside air intakes. Third Stack Design Method— Physical Modeling Using the Wind Tunnel or Water Flume If the stack heights determined from the first two methods described above are undesirable or if the geometry or topography of the building site makes simple analysis methods unreliable, a scale model of the building and surroundings should be physically modeled in an atmospheric wind tunnel or water flume. Physical modeling provides more accurate, and typically less conservative, predictions than the numerical or geometric methods. Physical modeling is the safest method to choose stack heights in new buildings or in buildings being retrofitted. It more accurately accounts for complex building geometries, taller nearby buildings, hills, architectural screens, and several stacks placed closely together. Physical modeling should follow the guidelines given in the ASHRAE 2001 Handbook – Fundamentals, Chapter 16. Dilution criteria are still necessary to evaluate the results of physical modeling. The design criteria discussed above provide initial guidance. A more complete evaluation of appropriate design criteria should be conducted when the chemical usage is expected to exceed minimal levels. In addition, the design criteria should take into account the 20% factor outlined in Section 5.3.4.

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APPENDIX 4

Audit Form for ANSI/AIHA Z9.5-2003

Laboratory Ventilation Audit item numbers refer to Standard paragraphs. Compliance with the Standard should only be claimed when all applicable provisions or elements of the Standard are met. Note: (X) all those that apply. 2 (

Laboratory Ventilation Management Program ) 2.1.1

(

Adequate laboratory chemical hoods, special purpose hoods, or other engineering controls are used when there is a possibility of employee overexposure to air contaminants generated by a laboratory activity.

)

Laboratory worker chemical exposures are maintained below applicable in-house exposure limits.

(

) 2.1.2

The specific room ventilation rate is established or agreed upon by the owner or their designee.

(

) 2.1.3

The general ventilation system is designed to replace exhausted air and provide the temperature, humidity, and air quality required for the laboratory procedures without creating drafts at exhaust hoods.

(

) 2.1.4

Dilution ventilation is provided to control the buildup of fugitive emissions and odors in the laboratory.

(

) 2.2

The laboratory develops a Chemical Hygiene Plan according to the OSHA Laboratory Standard (29 CFR 1910.1450).

(

)

The plan addresses the laboratory operations and procedures that might generate air contamination in excess of the requirements of Section 2.1.1.

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These operations are performed inside a hood adequate to attain compliance.

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) 2.3

In each operation using laboratory ventilation systems, the user designates a “responsible person.”

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) 2.4.1

Employers ensure an ongoing system for assessing the potential for hazardous chemical exposure.

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Employers promote awareness that laboratory hoods are not appropriate control devices for all potential chemical releases in laboratory work.

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The practical limits of knowing how each ventilation control is being used in the laboratory are considered when specifying design features and performance criteria.

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The responsible person defined in Section 2.3 is consulted in making these judgments.

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Laboratory chemical hoods are functioning properly and specific measures are taken to ensure proper and adequate performance. 87

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ANSI/AIHA Z9.5–2003

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The employer establishes criteria for determining and implementing control measures to reduce employee exposures to hazardous chemicals; particular attention is given to the selection of control measures for chemicals that are known to be extremely hazardous.

) 2.4.2

The following items are considered and decisions made regarding each element’s relevance following the hazard assessment process:

( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (

) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )

Vendor qualification; Adequate workspace; Design sash opening and sash configuration (e.g. , for laboratory chemical hoods); Diversity factor in VAV-controlled laboratory chemical hood systems; Manifolded or individual systems; Redundancy and emergency power; Hood location; Face velocity for laboratory chemical hoods; The level of formality given to system commissioning; Tracer gas containment “pass” criteria; Alarm system (local and central monitoring); Air cleaning (exhaust pollution controls); Exhaust discharge (stack design) and dilution factors; Recirculation of potentially contaminated air; Differential pressure and airflow between spaces and use of airlocks, etc.; Fan selection; Frequency of routine performance tests; Preventive maintenance; and Decommissioning.

2.5

Complete and permanent records are maintained for each laboratory ventilation system.

3

Laboratory Chemical Hoods

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) 3.1

The design and construction of laboratory chemical hoods conform to the applicable guidelines presented in the latest edition of ACGIH Industrial Ventilation: A Manual of Recommended Practice, and the most current codes, guidelines and standards, and any other applicable regulations and recommendations.

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) 3.1.1

The laboratory chemical hood is equipped with a safety viewing sash at the face opening.

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Sashes are not removed when the hood is in use.

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Sash-limiting devices (stops) are not removed if the design opening is less than full opening.

) 3.1.1.1

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Vertical sashes are designed so as not to be opened more than the design opening when hazardous materials are present within the hood. Where the design sash opening area is less than the maximum sash opening area, the hood is equipped with a mechanical sash stop or alarm to indicate openings in excess of the design opening area.

88

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ANSI/AIHA Z9.5–2003

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) 3.1.1.2

Horizontal sashes are designed so as not to be opened more than the design opening width when hazardous materials are being generated in the hood.

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) 3.1.1.3

If three or more sash panels are provided, one panel is no more than 14 inches (35.6 cm) wide to serve as a safety shield.

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) 3.1.1.4

If a combination sash provides horizontally moving panels mounted in a frame that moves vertically, the above requirements are met. The adverse consequences of the sash closing when the hood operator is not present to observe is considered before automatic sash closing devices are installed on a laboratory chemical hood.

The following conditions are met before using automatic sash closing devices:

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All users are aware of any limitations imposed on their ability to use the hood.

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Automatic sash positioning systems have obstruction sensing capable of stopping travel during sash closing operations without breaking glassware, etc.

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Automatic sash positioning allows manual override of positioning with forces of no more than 10 lbs (45 N) mechanical both when powered and during fault modes during power failures.

) 3.2.1

Bypass hoods with either vertical or horizontal moving sashes meet the requirements of Section 3.3.

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The hood exhaust volume remains essentially unchanged (