ANSI-AIHA Z9-5-2003

American National Standard for

ANSI/AIHA Z9.5–2003

Laboratory Ventilation

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American National Standard — Laboratory Ventilation

Secretariat

American Industrial Hygiene Association

Approved September 30, 2002

American National Standards Institute, Inc.

Licensed to Forlab Deisgn & Engineering Co., Ltd./K.Kim ANSI Store order #X251746 Downloaded: 4/13/2006 9:31:03 AM ET Single user license only. Copying and networking prohibited.

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 CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time.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


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


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


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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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

2



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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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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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



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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• 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.

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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.

7



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



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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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



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 (<5% change) when the sash is fully closed. 3.2.2

Conventional Hoods

Conventional hoods shall meet the requirements in Section 3.3. The hood exhaust volume shall remain unchanged with the sash in full open or in the design open position. As the sash is lowered, the face velocity will increase. In the fully closed position, airflow would be through the airfoil only. 3.2.3

Auxiliary Supplied Air Hoods

Auxiliary air hoods are laboratory hoods that meet the requirements in Section 3.3.

Auxiliary supplied air hoods are not recommended unless special energy conditions or design circumstances exist. The information in this section is provided because many auxiliary air hoods are still used. The intent is not to discourage innovative design but current experience indicates these requirements are necessary. The rationale for using auxiliary supplied air hoods is that auxiliary air need not be conditioned as much (i.e., temperature, humidity) as room supply air, and that energy cost savings may offset the increased cost of installation, operation, and maintenance. However, if all the air from the auxiliary plenum is not captured at the hood face, the anticipated energy savings is not realized. With respect to temperature and humidity, workers may experience discomfort if it is necessary to spend appreciable time at the hood.

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In addition: • The supply plenum shall be located externally and above the top of the hood face; moreover, the auxiliary air shall be released outside the hood. • The supply jet shall be distributed so as not to affect containment. • The auxiliary air shall not disrupt hood containment or increase potential for escape.

If auxiliary air hoods are designed and operated properly, worker protection at the face may be enhanced because the downward airflow at the breathing zone suppresses body vortices. However, if the design and operation are improper, contamination control may be compromised and the air quality and condition inside the hood may be significantly different from the room air and may compromise the work conducted inside the hood. For retrofit projects, auxiliary air may be installed more cheaply with less disruption than by upgrading the main air supply system. If auxiliary air is conditioned to the same extent as room air, most of the potential advantages are lost while the disadvantages remain and the total system becomes more expensive to install, operate, and maintain. With a worker (or reasonable proportioned mannequin) at the full open hood face, the hood should capture >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



• 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 [<60 fpm (0.30 m/s)] may not adequately reflect containment under dynamic (realworld) conditions as room and operator dynamics have significant effect on containment at these low face velocities. Hoods with excellent containment characteristics may operate adequately below 80 fpm (0.41 m/s) while others may require higher face velocities. It is, therefore, inappropriate to prescribe a range of acceptable face velocities for all hoods. Face velocity can be divided into ranges with differing characteristics as shown below: Room and operator dynamics have significant effects on hood performance at low face velocities. Therefore, it is important to understand the effects of dynamic challenges on hood performance so that standard operating procedures and user restrictions can be established. Operating a hood below 60 fpm (0.30 m/s) is not recommended since containment cannot be reliably quantified at low velocities and significant risk of exposure may be present. 17



60–80 fpm (0.30–0.41 m/s): Hoods with excellent containment characteristics operating under relatively ideal environmental conditions (i.e., room design characteristics) and with prudent operating practices can provide adequate containment in this velocity range although at an increased level of risk. Containment must be verified quantitatively in this range and effective administrative controls should be in place and compliance must be enforced. 80–100 fpm (0.41–0.51 m/s): Most hoods can be operated effectively with relatively low risk in this velocity range although containment should still be quantitatively verified. Proper operator training and enforcement of administrative controls are still highly recommended. This is the range recommended for a majority of laboratory chemical hoods.

The mechanism that controls the exhaust fan speed or damper position to regulate the hood exhaust volume shall be designed to ensure a minimum exhaust volume in constant volume systems equal to the larger of 50 cfm/ft of hood width, or 25 cfm/ft2 of hood work surface area, except where a written hazard characterization indicates otherwise, or if the hood is not in use.

100–120 fpm (0.51–0.61 m/s): This velocity range has similar characteristics as 80–100 fpm (0.41–0.51 m/s) but at significantly higher operating costs. Containment may be slightly enhanced in this range and hoods that do not contain adequately in the 80–100 fpm (0.41–0.51 m/s) range may be improved by operating in this range. 120–150 fpm (0.61–0.76 m/s): Although most hoods can operate effectively in this range, performance is not significantly better than at the lower ranges of 80–100 fpm (0.41–0.51 m/s) and 100–120 fpm (0.51–0.61 m/s) and the operating cost penalty imposed by high face velocities in this rage is severe and is not recommended for this reason. >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 <10% of the applicable lower explosive limit. • Shall prevent transport of contaminants out of the glovebox.

Care should be exercised when placing certain hazardous liquids in an evacuated airlock or interior of a glovebox when a decrease in pressure could affect the boiling point of the liquid causing it to go to a gaseous state. Meeting the above requirements will depend on whether the glovebox is continuous flow or is sealed. The minimum exhaust flow rate is usually based on a glove being breached or an access door being intentionally opened. The air velocity into the open gloveport or door should be 125 ± 25 linear fpm (0.635 ± 0.13 m/s).

4.1.12 Medium Containment Glovebox A medium containment glovebox shall conform to all the mandatory requirements of Sections 4.1.1 through 4.1.10, is not provided with pass-through airlocks, and shall be provided with sufficient exhaust ventilation to maintain an inward air velocity of at least 100 fpm (0.51 m/s) through the open access ports, and create a negative pressure of at least 0.1 in.wg (25 Pa) when access ports are closed.

Examples include gloveboxes designed to prevent overexposure to acutely hazardous materials that are not highly volatile and/or where allowable exposure levels have been established and personnel exposure can be verified to be below the established allowable levels.

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4.1.13 Special Case Containment Glovebox A special case containment glovebox shall be designed for special situations, does not necessarily conform to the provisions of this standard, but has been tested for the intended use and found adequate for that purpose. 4.1.14 Controlled Atmosphere Containment Glovebox An isolation and containment glovebox shall be a controlled atmosphere containment glovebox required for special atmosphere work when either the controlled atmosphere and/or the contained agents are hazardous.

Examples include applications where an inert atmosphere is necessary to protect the work or when it provides an added measure of safety.

4.1.14.1 Design and Construction Design and construction, and materials shall conform to the requirements for high, medium, or special case containment gloveboxes as necessary.

Refer to the AGS-1998-001 for more details on construction.

If the controlled atmosphere gas is hazardous, the airlocks shall be provided with a purge air exhaust system that, by manipulation of valves, creates a purge flow of room air sufficient to provide at least 5 air changes per minute, with good mixing, to the interior space of the airlock. 4.1.14.2 Operation Operation of an isolation and containment glovebox shall conform to high, medium, or special case containment requirements as necessary, and the airlock purge system shall be operated for sufficient time to dilute any hazardous gas in the airlock to safe concentrations before the outer door is opened.

For the empty airlocks, a purge time of 3 min. at 5 air changes per minute with good mixing would reduce an atmosphere of 100% to less than 1 ppm. If an object in the airlock has cavities that would trap gas, or if the gas might be adsorbed in the object, more time would be required: Such time should be determined by sampling the exhaust stream upstream of the ACD.

Care shall be exercised when placing certain hazardous liquids in an evacuated airlock or interior of a glovebox when a decrease in pressure could affect the boiling point of the liquid, causing it to go to gaseous state.

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4.2

Ductless Hoods

Ductless hoods shall meet the general requirements of Sections 3.1 and 3.3 as applicable.

Ductless hoods have limited application because of the wide variety of chemicals used in most laboratories. The containment collection efficiency and retention for the air-cleaning system used in the ductless hood must be evaluated for each hazardous chemical.

A Hazard Evaluation and Analysis shall be conducted as directed in ANSI/AIHA Z9.7 and Section 2.1.1.

As referenced in ANSI/AIHA Z9.7, the hazard evaluation and analysis serve to ensure proper air quality, effective occupant protection, and satisfactory system performance.

Compliance with the general requirements of Sections 2, 3.3, and 5.3.6.2 shall be evaluated by qualified persons. Ductless hoods that do not meet the requirements specified in Sections 9.3 and 9.4 shall be used only for operations that normally would be performed on an open bench without presenting an exposure hazard.

Air-cleaning performance monitoring is typically limited for many hazardous materials. Chemical-specific detectors located downstream of adsorption media or pressure drop indicators for particulate filters are necessary for systems recirculating treated air from the ductless hood back into the laboratory.

Ductless hoods shall have signage prominently posted on the ductless hood to inform operators and maintenance personnel on the allowable chemicals used in the hood, type and limitations of filters in place, filter changeout schedule, and that the hood recirculates air to the room.

Ductless hoods may be appropriate if the contaminant is particulate and provision is made for changing filters without excessive contamination of the laboratory or potential exposure to personnel changing the filters. See Sections 9.3 and 9.4. Adsorption media such as activated charcoal are not efficient for fine particles and are predominately used for adsorbing gases or vapors. Many gases and vapors of low molecular weight will be stripped from the adsorption media and reenter the room air on continued flow of clean air through the ductless hood. When this happens, the ductless hood only serves to protect the worker at the hood face and to spread the contaminant release into the room air during a longer time span and at a lower concentration. Where multiple air contaminants may challenge the ductless hood air-cleaning system, the collection efficiency and breakthrough properties of such mixtures are complicated and are dependent on the nature of the specific mixture. Enhanced breakthrough of components should be especially considered as a part of the Hazard Evaluation and Analysis. Also the warning properties (i.e. odor, taste) of the chemical being filtered must be adequate to provide an early indication that the filtration media are not operating properly.

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4.2.1

Airborne Particulates

Ductless hoods that utilize air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates shall meet the requirements of Section 9.3.1. 4.2.2

Gases and Vapors

Ductless hoods utilizing adsorption or other filtration media for the collection or retention of gases and vapors shall be specified for a limited use and shall meet the requirements of Section 9.3.2. 4.2.3

Handling Contaminated Filters

Contaminated filters shall be unloaded from the aircleaning system following safe work practices to avoid exposing personnel to hazardous conditions and to ensure proper containment of the filters for final disposal. Airflow through the filter housing shall be shut down during filter change-out. 4.3

Special Purpose Hoods

Special laboratory chemical hoods shall be designed in accordance with ANSI/AIHA Z9.2 and ACGIH’s Industrial Ventilation: A Manual of Recommended Practice.

5

Laboratory Ventilation System Design

5.1

Laboratory Design

5.1.1

Differential Pressure and Airflow Between Rooms

As a general rule, airflow shall be from areas of low hazard to higher hazard unless the laboratory is used as a Clean Room (such as Class 10,000 or better), or an isolation or sterile laboratory, or other special-type laboratories. When flow from one area to another is critical to emission exposure control, airflow monitoring devices shall be installed to signal or alarm that there is a malfunction.

Special purpose hoods are defined as any not conforming to the specific types described in this standard. Special hoods may be used for operations for which other types are not suitable (e.g., enclosures for analytical balances, for histology processing machines, gas vents from atomic absorption, or gas chromatography equipment). Other applications might present opportunities to achieve contamination control with less bench space or less exhaust volume (such as special mixing stations, sinks, evaporating racks, heat sources, or ventilated work tables).

The intent of this section is to require the reader to carefully consider the critical need to maintain directional airflow between spaces and to understand how best to accomplish the desired outcome. Although it is true a difference in pressure is the driving force that causes air to flow through any openings from one room to another, specifying quantitative pressure differential is a poor basis for design. 27



Air shall be allowed to flow from laboratory spaces to adjoining spaces only if • There are no extremely dangerous and life-threatening materials used in the laboratory; • The concentrations of air contaminants generated by the maximum credible accident will be lower than the exposure limits required by 2.1.1. The desired directional airflow between rooms shall be identified in the design and operating specifications.

What really is desired is anoffset air volume (as defined below). Attempts to design using direct pressure differential measurement and control vs. controlling the offset volume may result in either short or extended periods of the loss of pressure when the doors are open or excessive pressure differentials when the doors are closed, sufficient to affect the performance of low pressure fans. (See information below on the need for directional airflow.) When the differential pressure design basis is used, the relative volumes of supply and exhaust air to each room should be set so that air flows through any opening, including open doorways, at a minimum velocity of 50 fpm (0.25 m/s) and a preferred velocity of 100 fpm (0.51 m/s) in the desired direction. NOTE: When an ordinary 3 ft × 7 ft = 21 ft2 (0.9 m × 2.1 m = 1.95 m2) door is open, under the above conditions, the airflow through the door would be from 1050 to 2100 cfm (496 to 991 L/s) and the differential pressure will be about 0.0001 to 0.0006 in.wg (0.025 to 0.15 Pa). If a differential pressure of only 0.01 in. wg (2.5Pa) was specified and actually maintained, when the door was open it would generate an air velocity and airflow through the door of 400 fpm (2.0 m/s) and 8400 cfm (3964 L/s) respectively. These latter values would be impractical in operation. Double door airlocks do not have the same difficulties as opening a normal door and do not require the 1050 cfm to 2100 cfm (496 to 991 L/s) mentioned above as long as only one door is opened at one time. Without an airlock, the actual opening of a door into a corridor will usually draw contaminants with it because of the speed of the door’s movement despite the effects of the negative pressurization. So, it is important to keep door openings to a minimum as well as the amount of time that the laboratory doors are kept open.

The desired directional airflow between rooms shall be identified in the design and operating specifications.

The need to maintain directional airflow at every instance and the magnitude or airflow needed will depend on individual circumstances. For example, “clean rooms” (designed primarily to protect the product not the worker) may have very strict requirements for directional airflow and pressure control to limit the movement of contaminants into the clean room. Pharmaceutical laboratories governed by the Food and Drug Administration (FDA) current Good Laboratory Practices (cGLP) are other examples of stricter control requirements.

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Some people recommend a 10% “offset” in ventilation rate with lab exhaust being 10% greater than the lab supply air as a means of maintaining negative pressurization in the laboratory and keeping air flowing from the corridor into the laboratory. For example a laboratory with 1000 cfm (472 L/s) of exhaust would have 900 cfm (425 L/s) of supply air and 100 cfm (47.2 L/s) coming from adjoining spaces. This 10% design offset is merely a rule of thumb and may not be adequate to maintain directional airflow and pressurization, especially when the laboratory door is open. The amount of offset should be based on two considerations: • The airflow required to keep the laboratory room negative with regard to surrounding air spaces. The 10% offset may be appropriate in some cases but has no general validity. • The “stringency” of the requirements for direction of airflow. Is the requirement really “stringent” as in “we really mean it!” or “most of the time,” or “except when the door is open?” If the requirement is stringent, two seldom considered factors become important. First, if there is any appreciable temperature difference between the laboratory and adjoining space, when a door is opened there will be a thermal exchange or warmer air at the top of the doorway and cooler air flowing in the opposite direction near the floor. An airflow velocity of at least 50 fpm (0.25 m/s) is needed to inhibit this exchange as calculated in the note above. Second, the air volume needed to control airflow through a door in this way is independent of the size of the room or its need for supply or exhaust air and is only related to the number and square footage of doors into the laboratory. Consequently, if the requirement is stringent, an airlock door is the only current available solution. In the absence of an airlock, an arbitrary 10% offset of the laboratory ventilation rate is not the proper basis for design.

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If the door phenomenon is not considered, there will be no safety isolation when the door is open. In many laboratories, momentary door opening to allow the movement of materials and personnel in and out of the laboratory will not cause a significant safety condition because of the short duration of time for any contaminants to escape from the laboratory to the corridor. Where the toxicity of the escaping contaminants would be a concern during the 15 sec opening of a door, then double door airlocks should be employed. However, for both fire contaminant reasons and hazardous materials contaminant, laboratory doors should be closed except when in actual use. The speed of response of the laboratory pressure controls should be in proportion to the danger of the hazardous materials contained in the laboratory. For most laboratories, speed of response should be in the range of 0.5 sec to 3 sec. 5.1.1.1 Airlocks Airlocks shall be utilized to prevent undesirable airflow from one area to another in high hazardous applications, or to minimize volume of supply air required by Section 5.1.1. An airlock shall consist of a vestibule or small enclosed area that is immediately adjacent to the laboratory room and having a door at each end for passage. Airlocks shall be applied in such a way that one door provides access into or out of the laboratory room, and the other door of the airlock provides passage to or from a corridor (or other nonlaboratory area). Airlock doors shall be arranged with interlocking controls so that one door must be fully closed before the other door may be opened. 5.1.1.2 Critical Air Balance If the direction of airflow between adjacent spaces is deemed critical, provision shall be made to locally indicate and annunciate inadequate airflow and improper airflow direction.

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5.1.2

Diversity

The following issues shall be evaluated in order to design for diversity: • • • • •

• • • • • • •

Use patterns of hoods Type, size, and operating times of facility Quantity of hoods and researchers Sash management (sash habits of users) Requirements to maintain a minimum exhaust volume for each hood on the system Type of ventilation system Type of laboratory chemical hood controls Minimum and maximum ventilation rates for each laboratory Capacity of any existing equipment Expansion considerations Thermal loads Maintenance department’s ability to perform periodic maintenance

The following conditions shall be met in order to design a system diversity: • Acceptance of all hood-use restrictions by the user groups. Designers must take into account the common work practices of the site users. • A training plan must be in place for all laboratory users to make them aware of any limitations imposed on their freedom to use the hoods at any time. • An airflow alarm system must be installed to warn users when the system is operating beyond capabilities allowed by diversity. • Restrictions on future expansions or flexibility must be identified.

Diversity is defined as operating a system at less capacity than the sum of the peak demands. With respect to laboratory chemical hoods, diversity can be defined as the percentage of full flow capacity on a manifolded system in active use at anytime. A system using 70% of the peak demand is said to operate at 70% Usage Factor or 70% diversity. A system that is designed with full flow capacity for all hoods is designed for 100% Usage Factor or 100% diversity. Both existing and new facilities can benefit from applying diversity to the HVAC design if laboratory chemical hoods are used for only a small portion of a day. Diversity may allow existing facilities to add laboratory chemical hood capacity without adding new mechanical equipment. In new construction, diversity allows the facility to reduce capital equipment expenditures and space requirements by downsizing equipment and other infrastructure. Diversity also reduces operating expenses due to lower airflow requirements. Common approaches for creating diversity include VAV hoods, sash management aids such as building management system trending and automated sash closers, and hood use detection. Designing with diversity may limit the number of hoods in use or limit the sash openings, thus creating potential for overexposures to personnel, and prevention of future expansion opportunities. Therefore, diversity should be applied carefully in all situations. Certain diversity approaches may be undesirable for certain circumstances: • Sash management is difficult to predict and often unreliable. Dependence on historical sash management patterns may be insufficient for any given facility. The use of building management systems to monitor sash management may help, but this requires significant commitment by operating personnel to effectively regulate the users. Automatic sash closers—designed to improve sash management habits—may be overridden and lose their effect on diversity. • Laboratories with extremely high use patterns— such as teaching labs—may be candidates for fullflow or very-high-usage factor designs.

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5.1.3 Noise Generation of excessive noise shall be avoided in laboratory ventilation systems. Fan location and noise treatment shall provide for sound pressure level (SPL) in conformance with local ambient noise criteria.

The acoustic character of the ventilation system should help create a pleasant working environment. Sound from the ventilation system should not interfere with laboratory operations. It may be used to mask undesirable noise such as vehicular traffic, noisy equipment, or low discourse. The primary references for design criteria and methods will be found in ASHRAE publications such as: • Chapter 7 on Sound and Vibration from the ASHRAE 2001 Handbook – Fundamentals. • Chapter 46 on Sound and Vibration Control from ASHRAE 1999 Handbook – HVAC Applications. Noise associated with mechanical ventilation and exhaust systems generally originates with fans, duct or damper vibration, and air noise caused by excessive air velocity or turbulence. Therefore, the primary design focus should be on preventing excessive noise generation. Where possible, it is good practice to locate high static pressure fans remote from occupied spaces. Use good duct design procedures. Avoid abrupt duct turns without turning vanes, change duct dimensions gradually, and generally follow procedures given in the latest ASHRAE Handbooks chapters on duct design. The careful use of vibration isolators, inertia blocks, and suitable fan speed and outlet velocities is indicated. Variable volume systems have found wide application in laboratories. However it is important to be aware that variable sound levels may focus unwanted attention on the ventilation system. Frequently laboratories have large and numerous fans, and then special care must be taken to comply with location regulations and good practice with regard to noise contamination of adjoining properties. NOTE: Such regulations vary but provide for sound pressure level (SPL) in the range of 50 dBA and limit the increase in SPL above background levels when the ventilation systems are operating. System design should provide for control of exhaust system noise (combination of fan-generated noise and air-generated noise) in the laboratory. Systems should be designed to achieve an acceptable SPL and frequency spectrum [room criteria, (RC), or noise criteria (NC)] as described in the ASHRAE 1999 Handbook – HVAC Applications. The recommended range for hospital laboratories is 50 – 35; higher RC ranges might be acceptable for other types of laboratories. NC curves above 55 might result in unacceptable speech interference in the laboratory. Use of porous or flammable sound-absorbing interior lining of exhaust ductwork usually is unacceptable.

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5.1.4

Laboratory Ventilation — Emergency Modes

When the type and quantity of chemicals or compressed gases that are present in a laboratory room could pose a significant toxic or fire hazard, the room shall be equipped with provision(s) to initiate emergency notification and initiate the operation of the ventilation system in a mode consistent with accepted safety practices. A hazard assessment (see Section 2.4) shall be performed to identify the credible emergency conditions that may occur.

Each laboratory room should be evaluated with respect to the potential for hazardous chemical spills, accidental gas release, or a fire occurrence. If the type and quantity of chemicals and gas present could pose a toxicity or fire hazard if accidentally spilled, released, or ignited, the room occupants should have a means to signal for an appropriate emergency response as well as initiate appropriate emergency ventilation.

Emergency situations (see NFPA 92A-2000) that shall be anticipated and the appropriate ventilation system responses shall include:

The intent of the chemical emergency provision is to utilize the ventilation system to maximize the dilution and removal of chemical fumes and vapors, and prevent migration of such fumes and vapors to other building areas. This response is intended to address a serious chemical spill or related incident that has the potential for releasing large amounts of hazardous fumes or vapors within the room.

• CHEMICAL EMERGENCY (Chemical Spill, Eye-Wash or Emergency Shower Activation, Flammable Gas Release, etc.) – A means such as a clearly marked wall switch, pull station, or other readily accessible device should enable the room occupants to initiate appropriate emergency notification and simultaneously activate the ventilation system’s chemical emergency mode of operation if one exists. For rooms served by VAV ventilation systems, the Chemical Emergency mode of operation should maximize the room ventilation (air change per hour) rate and, if appropriate, increase negative room pressurization. For rooms served by CAV ventilation systems that utilize a reduced ventilation level for energy savings, the Chemical Emergency mode of operation should ensure that the room ventilation and negative pressurization are at the maximum rate.

In addition to automatically initiating the emergency ventilation modes, it is highly desirable that the emergency situation be simultaneously and automatically indicated to appropriate facility personnel at one or more designated locations. The intent of the fire emergency ventilation mode is to utilize the ventilation system to maximize the negative pressurization of the room of fire origin in order to retard the spread of smoke and toxic fire gases to other parts of the facility. (Also refer to NFPA 92A-2000). In some facilities the nature of the chemicals used (flammability or toxicity) may be such that the risk of fire is heightened upon a spill or gas release. In such situations prudent safety precautions (and/or the local code) may justify initiating a fire alarm and summoning the local fire department to respond.

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Operation of the room ventilation system in a chemical emergency mode should not reduce the room ventilation rate, room negative pressurization level, or hood exhaust airflow rate.

NOTE: At the discretion of the facility and/or as a result of local ordinances, the occurrence of either a CHEMICAL EMERGENCY or a FIRE may initiate a fire emergency mode of operation for the room ventilation system.

• FIRE – A means such as a wall-mounted “FIRE ALARM” pull station should enable the room occupants to initiate a fire alarm signal and simultaneously activate an appropriate fire emergency mode of operation for the room and/or building ventilation system. For rooms served by VAV ventilation systems, the fire emergency mode of operation should maximize the exhaust airflow rate from the hoods and other room exhaust provisions, and also shut off the room supply makeup air. For rooms served by CAV ventilation systems that utilize a reduced ventilation level for energy savings, the fire emergency mode of operation should ensure that the maximum exhaust airflow rate from the hoods and other room exhaust provisions are in effect, and should also shut off the room supply makeup air. 5.2

Supply Air

5.2.1

Supply Air Volume

If laboratories are to be maintained with a negative pressurization and directional airflow from the corridor into the laboratory, supply air volume shall be less than the exhaust from the laboratory. When laboratories are to be maintained with a positive pressurization and directional airflow supply, air volume shall be more than the exhaust from the laboratory. 5.2.2

In general, return air is not used in laboratories with hazardous chemicals or biological hazards. The difference between the air supplied by the ventilation system and that exhausted should be transferred through small cracks under doors, in walls and ceilings, or in transfer grilles so as to provide a directional airflow to resist the escape of airborne hazardous materials from the laboratory room.

Supply Air Distribution

Supply air distribution shall be designed to keep air jet velocities less than half, preferably less than one-third of the capture velocity or the face velocity of the laboratory chemical hoods at their face opening.

For most laboratory chemical hoods, this requirement will mean 50 fpm (0.25 m/s) or less terminal throw velocity at 6 ft (1.8 m) above the floor. For laboratories with very small volumes of hood exhaust this may be achieved by correct selection and placement of conventional aspirating supply diffusers. For rooms with greater supply air requirements, either perforated ceilings or special large-capacity radial diffusers

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may be necessary. These special laboratory diffusers systems are preferable from a safety viewpoint to auxiliary air hoods because the ventilation air can also be used to sweep gases and vapors from the room into the laboratory chemical hoods. The large capacity radial diffusers are available from several manufacturers designed specifically for laboratory use. These diffusers have capacities of up to 100 cfm (47.2 L/s) per square foot of diffuser and come in 1ft × 1ft (0.3 m × 0.3 m), 2 ft × 2 ft (0.6 m × 0.6 m), 1 ft × 4 ft (0.3 m × 1.2 m), and 2 ft × 4 ft (0.6 m × 1.2 m) sizes with nonaspirating design and omnidirectional radial flow patterns. Supply air diffusers where practical should be located as close to the personnel corridor and entry door to the laboratory and as far from the major exhaust devices as is practical. This location will help to provide unidirectional flow, sweeping the contaminants into the exhaust devices and helping further protect the corridor from airborne hazardous materials. The ideal arrangement is to group the hoods and exhaust devices as far as possible from entry doors and exit corridors and locate supply air diffusers close to entry doors and exit corridors. 5.2.3

Supply Air Quality

Supply systems shall meet the technical requirements of the laboratory work and the requirements of the latest version of ANSI/ASHRAE 62. 5.3

Exhaust

5.3.1

Exhaust System Ductwork

Additional design information can be obtained using Computational Fluid Dynamics (see Memarzadeh, 1996).

5.3.1.1 Design Laboratory exhaust system ductwork shall comply with the appropriate sections of Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA, 1995) standards. Systems and ductwork shall be designed to maintain negative pressure within all portions of the ductwork inside the building when the system is in operation.

An exception applies to exhaust fans located in a normally unoccupied enclosed space such as a roof penthouse when the fan discharge ductwork is well sealed and the enclosed space is adequately ventilated.

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Exhaust ductwork shall be designed in accordance with ANSI/AIHA Z9.2-2001 and Chapter 34 on Duct Design of the ASHRAE 2001 Handbook – Fundamentals and Section 6-5 of NFPA 45-2000. Branch ducts shall enter a main duct so that the branch duct centerline is on a plane that includes the centerline of the main duct. For horizontal main ducts, branch ducts shall not enter a main duct on a plane below the horizontal traverse centerline of the main duct. Horizontal runs of branch ducts shall be kept at a minimum. Longitudinal sections of a duct shall be a continuous seamless tube or of a continuously welded formed sheet. Longitudinal seams that are formed mechanically shall be utilized only for light duty systems with no condensation or accretion inside the duct. Spiral ducts may be one gauge lighter than the required gauge of longitudinal seam duct, except the spiral duct gauge shall always meet the abrasive wear resistance requirements. Traverse joints shall be continuously welded or flanged with welded or Van Stone flanges. (When nonmetallic materials are used, joints shall be cemented in accordance with the manufacturer’s procedures.) If the duct is coated with a corrosion-resistant material, the coating shall extend from the inside of the duct to cover the entire face of the flange. Flange faces shall be gasketed or beaded with material suitable for service.

When nonmetallic materials are used, joints cemented in accordance with the manufacturer’s procedures may be considered equivalent to welding.

If condensation within the duct is likely, all horizontal duct runs shall be sloped downward at least 1 in. per 10 ft in the direction of the airflow to a suitable drain or sump.

Exhaust duct sizes should be selected to ensure sufficiently high airflow velocity to retard condensation of liquids or the adherence of solids within the exhaust system. In some cases, accumulation of solids material within the duct system may be prevented by providing water spray nozzles in the duct at frequent intervals and sloping the duct down to an appropriate receptor (e.g., a wet dust collector).

Exhaust airflow volume shall be sufficient to keep the temperature in the duct below 400°F (204°C) under all foreseeable circumstances.

This includes the ignition of a spill of flammable liquid that in turn requires an estimate of the maximum credible accident that would generate heat.

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If variable air volume (VAV) laboratory chemical hoods are used, satisfying this criteria might require a heat sensor arrangement to signal the VAV controls system to increase the exhaust airflow. An alternative solution would be to provide a higher temperature exhaust system design or a high-temperature combustion flue design for the portions of the exhaust system in which temperatures might exceed 400°F (204°C) in conjunction with NFPA 86-1999. All duct connections to the exhaust fan shall be consistent with good ventilation design practice. As an alternative, the duct connections may be made by means of inlet and outlet boxes. If circumstances such as space limitations prevent the implementation of the preceding requirements, then applicable speed and power corrections shall be made by applying the “System Effect Factor” (see AMCA 201-90).

For good inlet and outlet duct design refer to the Air Movement and Control Association’s Fan Application Manual Part 1, the ACGIH Laboratory Ventilation Manual, and Chapter 34 of the ASHRAE 2001 Handbook – Fundamentals.

Where optimum duct connections cannot be made due to space or other limitations, suitable alternative means shall be substituted to compensate for the space limitations.

An adequate outlet duct connection has the same requirements as an air inlet duct except it need be only 3 diameters in length and no vortex breaker is necessary.

If adequate duct connections cannot be provided at the fan, the fan shall be equipped with inlet and outlet boxes furnished by the fan manufacturer. The manufacturer shall furnish performance curves for the fan with the inlet and outlet box(es) as part of the fan.

Transition fittings at the inlet and outlet should have a 15o or less included angle in any plane. Computation of this factor requires data on the fan’s “blast area” and must typically be obtained from the manufacturer.

If neither adequate connections nor inlet/outlet boxes are present, the fan speed and power requirements represented in the fan rating table shall be corrected by the “System Effect Factor.” 5.3.1.2 Materials Exhaust system materials shall be in accordance with Chapter 5 of ACGIH’s Industrial Ventilation: A Manual of Recommended Practice, Chapter 34 on Duct Design of the ASHRAE 2001 Handbook – Fundamentals, and Chapter 6-5 of NFPA 45 – 2000. Exhaust system materials shall be resistant to corrosion by the agents to which they are exposed. Exhaust system materials shall be noncombustible if perchloric acid or similar oxidizing agents that pose a fire or explosive hazard are used.

Solid metal ductwork has good fire characteristics but in some cases has inferior corrosion resistance for some chemicals. Solid plastic ductwork generally has good corrosion resistance but may not be acceptable to the local fire authority. An economical material that can be used when appropriate and if proper care is used in installation and maintenance is a metal duct with a protective coating. However, because of the thin coatings generally used, pinhole defects in the coating may be relatively common, which would eventually lead to a very small amount 37



of leakage. Any mechanical damage or scratching of the coating in installation or maintenance would have to be immediately and properly repaired or the bare metal revealed in the scratch will be eaten away. Owner’s representatives must spend more time and money during installation to make sure contractor coats all exposed metal during initial installation and similar care must be exercised whenever the coated exhaust duct is modified during renovations. 5.3.2

Manifolds

5.3.2.1 Combined Exhaust Systems Two or more exhaust systems may be combined into a single manifold and stack, if the conditions of 5.3.2.2 are met. Manifold exhaust systems frequently have significant advantages over individual (single-hood/single-fan) systems and are encouraged. Manifold and individual systems have the following characteristics: Manifold Systems: Advantages: • High concentration discharges from individual hoods are diluted by the air from all the other hoods on the manifold before being released into the atmosphere. • The potential for installing redundant fans is increased and may only require one additional fan and the cost to provide redundancy is reduced. • The potential for installing emergency power is increased while the cost is reduced. • The potential to utilize diversity is increased. • The potential to efficiently utilize VAV controls is increased. • The potential to provide additional capacity for future expansion is increased. • Fan maintenance costs are reduced. • The number of roof penetrations and potential leaks are reduced. • Shaft space for ductwork is reduced. • First costs are lower. • Operating costs are lower. • Redundancy of exhaust fan becomes more feasible. • Energy recovery is financially feasible. • Fewer stacks to locate in ideal location (5.3.4, 5.3.5, Appendix 3). • High mass of discharge makes it less susceptible to wind. 38



Disadvantages: • Fan failure affects all hoods on the system and redundancy is required. • Changing the application of a single hood (i.e., from a standard laboratory chemical hood to radioisotope hood or perchloric acid hood) is difficult. • The ability to provide treatment (i.e., scrubbing, filtering, etc.) for an individual exhaust source requires an in-line scrubber and additional static pressure for the entire manifold or in the specific hood branch. • Controls for system static pressure, capacity control, etc., are more complex than individual systems. • May be difficult to apply in existing buildings. Individual Systems: Advantages: • Fan failure affects only a single hood. • Changing the application of a single hood (i.e., from a standard laboratory chemical hood to radioisotope hood or perchloric acid hood) is easily accomplished. • The ability to provide treatment (i.e., scrubbing, filtering, etc.) for an individual exhaust source is easily accomplished. • The system is less complex. Disadvantages: • There is no dilution of the source effluent before releasing it to the atmosphere. • Providing redundancy is difficult due to space limitations and is more expensive. • Providing emergency power is difficult and more expensive. • Applying diversity is difficult. • Providing future capacity for expansion requires additional ductwork, equipment, and utilities. • Maintenance costs are higher. • Requires a larger number of roof penetrations and roof leak potential is increased. • Shaft space requirements are higher. • First costs are higher. • Operating costs are higher. • Energy recovery is not financially feasible • Impossible to locate all stacks in ideal location (5.3.4, 5.3.5, Appendix 3) • Low mass of discharge makes it more susceptible to wind 39



Large Systems: Large and/or diverse systems that have several types of hoods often benefit from a hybrid approach where a manifold is designed to handle a majority of the hoods and individual exhaust systems are installed for those that cannot or should not be manifolded such as perchloric acid or radioisotope hoods. Adverse Chemical Reaction Potential: Contrary to popular belief, the probability of two or more reagents from different sources combining in the manifold to produce an explosion is extremely small but should be evaluated for special cases involving large quantities of materials. Consider the minimum manifold with two hoods connected to a single fan: Reagent A is spilled in Hood A, covering the entire work surface and producing maximum evaporation and duct concentration while Reagent B is similarly spilled in Hood B. Reactive chemistry experts attempting to devise worst-case binary reaction assure us that although these two chemicals, when mixed in liquid or solid form, will certainly explode, when mixed in concentrations less than 10,000 ppm (1%) in air, it is unlikely that an explosive reaction can be initiated or sustained (Hitchings, unpublished data). The last statement notwithstanding, assuming that a reaction can be initiated, the result would be only a slight adiabatic temperature increase in the duct. The ability of chemicals from different sources to form toxic products is similarly limited by low concentrations that become lower and lower the closer they get to the fan on manifolded systems. 5.3.2.2 Manifold Requirements Laboratory chemical hood ducts may be combined into a common manifold with the following exceptions and limitations: Each control branch shall have a flow-regulating device to buffer the fluctuations in pressure inherent in manifolds.

Flow regulating devices that are pressure-independent devices also allow changes to be made in the system without the need to rebalance the entire system.

Perchloric acid hoods shall not be manifolded with nonperchloric acid hoods unless a scrubber is installed between the hood and the manifold.

Manifolding of perchloric acid hoods is discouraged because nonvertical ductwork is implied by connecting one or more hoods together and nonvertical ducts are difficult to wash down properly using duct-mounted spray heads.

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Where there is a potential contamination from hood operations as determined from the Hazard Evaluation and Analysis of Section 2.4, radioisotope hoods shall not be manifolded with nonradioisotope hoods unless in-line HEPA filtration and/or another necessary aircleaning system is provided between the hood and the manifold.

Installing in-line filtration is impractical in most situations because it increases the overall static pressure for the entire system unless a booster fan is installed with the HEPA filters, which increases a leak potential. Manifolding of radioisotope hoods is discouraged due to the potential contamination of the entire exhaust system in the event of HEPA filtration failure and the possibility of pressurizing the exhaust manifold with the booster fan.

Carbon bed filters shall be added for gases.

HEPA filters only cover radioactive dust, not radioactive gases. Systems that use heavy digestions or other operations that could cause condensation in the duct may not be appropriate for a manifold system. The high potential of condensation imposes drainage problems throughout the system rather than just for the hoods that may have high condensation.

5.3.2.3 Compatibility of Sources Exhaust streams that contain concentrations of flammable or explosive vapors at concentrations above the Lower Explosion Limit (LEL) as well as those that might form explosive compounds (i.e., perchloric acid hood exhaust) shall not be connected to a centralized exhaust system. Exhaust streams comprised of radioactive materials shall be adequately filtered to ensure removal of radioactive material before being connected to a centralized exhaust system. Biological exhaust hoods shall be adequately filtered to remove all hazardous biological substances prior to connection to a centralized exhaust system. 5.3.2.4 Exhaust System Reliability Unless all individual exhausts connected to the centralized exhaust system can be completely stopped without creating a hazardous situation, provision shall be made for continuous maintenance of adequate negative static pressure (suction) in all parts of the system.

This requirement could be satisfied by one or both of the following provisions: •

Multiple operating fans so the loss of a single fan does not result in loss of total system negative static pressure • Spare centralized system exhaust fan(s) that will rapidly and automatically be put into service upon failure of an operating fan by repositioning isolation dampers and energizing the standby fan motor. Emergency backup power should be provided to all exhaust fans and the associated control system. 41



As an alternative, if the hood is completely turned off, the hood shall be emptied and decontaminated and provisions shall be implemented to prevent the hood from backdrafting.

Before considering complete shut down of the hood, the following considerations should be investigated: • Room air balance • Use of other chemicals in the space • Notification to occupants Under these conditions, the exhaust volume is independent of the sash position. Note this requires careful planning for a system less than 100% diversity (see Section 5.1.2).

The VAV hood shall be provided with an emergency switch that allows the hood exhaust volume to return to the maximum.

If the maximum exhaust volume of the variable air volume hoods in one room exceeds 10% of the room air supply volume, and if the laboratory is designed for controlled airflow between the laboratory and adjacent spaces, automatic flow control devices should be provided to reduce the supply air volume by the same amount that hood exhaust volume is reduced. At present, this system requires sophisticated testing equipment and training of maintenance personnel.

5.3.2.5 Biological Safety Cabinets Class II–Type A and Type B3 biological safety cabinets manifolded with chemical laboratory chemical hoods shall have either: 1) A thimble connection or

NOTE: Type A and Type B3 cabinets that have the cabinet exhaust flow directed into the thimble connection do not meet the hard duct connection requirement for Type B cabinet. Thimbles allow the exhaust flow to continue exhausting airflow from the room when the biological safety cabinet is off thus avoiding continuous dust loading of the biological safety cabinet filters. Secondly, this prevents the exhaust system from becoming positively pressurized by the internal fans in the biological safety cabinets in the event that the exhaust system should fail. Thirdly, continuous exhaust through the thimble connection may be important for room air balance as well as removing the heat load of laboratory equipment.

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2) A constant-volume control device and an interlock/alarm for these devices shall be installed between the cabinet outlet and the exhaust manifold. Where Hazard Evaluation and Analysis determines that the installation calls for direct connection (hard ducted) of the biological safety cabinet (e.g., Class II–Type B) to an exhaust manifold system to allow work with toxic chemicals or radionuclides, interlocks and alarms shall be provided to prevent the biological safety cabinet from operating its normal starting mode or to immediately warn the operator in the event of an exhaust system failure (CDC-NIH, 1999).

For direct (hard ducting) of Class II Type B cabinet, the exhaust flow balance is critical for the needed inflow velocity of the biological safety cabinet. Where the installation calls for direct connection of the biological safety cabinet (e.g., Class II–Type B), interlocks and alarms should be provided to prevent the biological safety cabinet from shutting down and to immediately warn the operator in the event of an exhaust system failure. Thimble connections can be improperly designed and are sometimes difficult to balance and draw in a small amount of room air. However, they are recommended over the direct connection and operation interlock design so that worker and product protection are maintained even in the event of an exhaust system failure. Interlocks, if activated during an exhaust system failure involving radioactive materials, could cause worker or product exposure. A nonmanifolded dedicated exhaust system connection directly vented to the atmosphere may be needed for work with these types of hazardous materials. Constant volume control devices maintain a constant exhaust rate from all types of biological safety cabinets due to changes in exhaust system static pressure. Refer to NSF 49 for testing and certification of biological safety cabinets.

5.3.2.6 Static Pressure The static pressure in the exhaust system shall be lower that the surrounding areas throughout the entire length, with the exception noted in Section 5.3.1.1.

This prevents contaminated air from leaking out of the duct into the building.

5.3.2.7 Exhaust Fan Location Exhaust systems shall have the exhaust fan located outside the building unless: • The fans are in an adequately ventilated penthouse or room adjacent to the outside and the discharge ductwork passes directly from the fan to the outside without passing through another room or space, and

Leakage from ducts, fittings, flex connections, and fan housings is a potential source of contamination in fan rooms and penthouses. Locating the fans outside eliminates the need for an additional ventilation system for the room housing the fans. In winter, maintenance may suffer, however.

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• There are no flexible connections on the discharge side of the fan and all ductwork in the discharge side of the fan is of welded and/or flanged and gasketed construction.

Leakage from flexible connections is a one of the largest contributors to fan room or penthouse contamination. The length of duct and number of fittings on the positive side of the fan should be minimized.

5.3.2.8 System Classification Laboratory hood exhaust systems shall not be classified as “Hazardous Exhaust Systems” as defined in Building Officials and Code Administrators International (BOCA), Uniform, or International Mechanical Codes.

Fire/Explosion Potential From Flammables: A common misconception that concerns many when considering manifolded systems is the possibility of fires or explosions produced by flammable materials used and released in the hoods. This concern is not supported by application experience. However, overly cautious code officials often rule that laboratory exhaust systems meet the definition of “Hazardous Exhaust Systems” as defined in the building/mechanical codes and require that sprinklers or other types of fire detection/suppression equipment be installed in laboratory chemical hood exhaust systems. The “Hazardous Exhaust Systems” definition is intended to include industrial ventilation systems where high concentrations of flammable materials within the explosive limits are conveyed through the duct. Laboratory exhaust systems do not meet this definition. Empirical studies using acetone, toluene, and methyl ethyl ketone (MEK) were conducted in worst-case scenarios (Hitchings, personal communication). The entire work surface was covered with solvent in a VAV hood with the sash down and minimum flow (maximum duct concentration). This produced duct solvent concentrations well below the LEL. Therefore, although the solvent itself is flammable, and a portion of the gradient from pure solvent at the work surface to duct concentration (occurring entirely in the hood itself) is in the flammable region, the mixture at all locations in the duct system is nonflammable. If the duct concentration is within the flammable region of the solvent between the hood and the manifold where it is diluted below the LEL, an ignition source is still required between the hood and the manifold to produce an explosion. Ignition sources in laboratory chemical hood ducts are hard to imagine. However, if an ignition source does exist, will the fire detection/suppression prevent an explosion? No. If an explosion occurs, all fuel is consumed and no fire can therefore exist and the activation of sprinklers or other types of fire suppression will probably only add to any capital damage that has already occurred.

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5.3.2.9 Fire Dampers Fire dampers shall not be installed in exhaust system ductwork (NFPA 45).

The accidental activation of a fire damper will shut off airflow from one or more laboratory chemical hoods and may cause worker injury or exposure. The activation of a fire damper caused by a fire in a laboratory chemical hood will shut off airflow from that hood making it impossible to remove the combustion products from the hood and forcing the hood to become positively pressurized. This condition makes it likely that the fire will escape the fire-resistant hood into the laboratory. With the exhaust flow from one or more hoods shut off, the laboratory may become positively pressurized with respect to the corridor, encouraging the spread of the combustion products, and perhaps the fire, from the laboratory to adjoining spaces.

5.3.2.10 Fire Suppression Fire sprinklers shall not be installed in laboratory chemical hood exhaust manifolds.

Studies of actual exhaust systems have demonstrated that the spray cone produced by sprinkler heads can actually act as a damper and reduce or prevent airflow in the duct past the sprinkler head (Hitchings and Deluga, personal communication). Like a fire damper, this may produce a lack of flow at one or more laboratory chemical hoods at the moment when it is needed most.

5.3.2.11 Continuous Operation Exhaust systems shall operate continuously to provide adequate ventilation for any hood at any time it is in use and to prevent backflow of air into the laboratory when the following conditions are present:

A “motorized damper” may need to be provided at the fan to isolate the system from a stack effect.

• Chemicals are present in any hood (opened or unopened). • Exhaust system operation is required to maintain minimum ventilation rates and room pressure control. • There are powered devices connected to the manifold. Powered devices include, but are not limited to: biological safety cabinets, in-line scrubbers, motorized dampers, and booster fans. 45



5.3.2.12 Constant Suction, Redundancy and Emergency Power Manifolds shall be maintained under negative pressure at all times and be provided with at least two exhaust fans for redundant capacity. Emergency power shall be connected to one or more of the exhaust fans where exhaust system function must be maintained even under power outage situations. 5.3.3

The manifold fans and controls should be designed so that sufficient static pressure is available to each connected exhaust source for all conditions that do not exceed the system diversity. Since each critical connected source (i.e., laboratory hoods) should have continuous performance monitors, exceeding system capacity should also result in flow alarms.

Exhaust Fans

Each fan applied to serve a laboratory exhaust system or to exhaust an individual piece of laboratory equipment (e.g., a laboratory chemical hood, biosafety cabinet, chemical storage, etc.) shall be adequately sized to provide the necessary amount of exhaust airflow in conjunction with the size, amount, and configuration of the connecting ductwork. In addition, each fan’s rotational speed and motor horsepower shall be sufficient to maintain both the required exhaust airflow and stack exit velocity and the necessary negative static pressure (suction) in all parts of the exhaust system. If flammable gas, vapor, or combustible dust is present in concentrations above 20% of the Lower Flammable Limit, fan construction shall be as recommended by AMCA’s 99-0401-86, Classification for Spark Resistant Construction. Laboratory exhaust fans shall be located as follows: • Physically outside of the laboratory building and preferably on the highest level roof of the building served. This is the preferred location since it generally minimizes risk of personnel coming into contact with the exhaust airflow. • In roof penthouse or a roof mechanical equipment room that is always maintained at a negative static pressure with respect to the rest of the facility, and provides direct fan discharge into the exhaust stack(s).

Under most operating conditions, centrifugal fans will leak small amounts of system gases at the fan shaft. Also, fan discharge ducts typically are under positive pressure and any air leaks would discharge into the room. Having laboratory exhaust fans in one of the above locations (Section 5.3.2.7) helps ensure that any fan leakage will be effectively removed and will not migrate within the building.

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All laboratory exhaust fans shall include provisions to allow periodic shutdown for inspection and maintenance. Such provisions include: • Ready access to all fans, motors, belts, drives, isolation dampers, associated control equipment, and the connecting ductwork. • Isolation dampers on the inlet side of all centralized exhaust system fans that have individual discharge arrangements or their own individual exhaust stacks. • Isolation dampers on both the inlet and outlet sides of all centralized exhaust system fans that discharge into a common exhaust stack or plenum. • Sufficient space to allow removal and replacement of a fan, its motor, and all other associated exhaust system components and equipment without affecting other mechanical equipment or the need to alter the building structure.

The requirements for inspection access and serviceability are intended to ensure that laboratory exhaust systems can be kept and maintained in proper operating condition. If a centralized exhaust system has multiple fans and a fan replacement is necessary, the process should not require disconnecting piping or removing other building encumbrances that might lead to an indefinite postponement of the required work.

See Section 8.1, Operations During Maintenance Shutdown, for necessary requirements and guidance. 5.3.4

Discharge of Contaminated Air

The discharge of potentially contaminated air that contains a concentration more than the allowable breathing air concentration shall be:

The in-stack concentrations of contaminants allowed under such regulations typically range from 100 to 1000 times higher than safe breathing concentrations.

• Direct to the atmosphere unless the air is treated to the degree necessary for recirculation (see Section 9.3); • In compliance with applicable federal, state, or local regulations with respect to air emissions; • Discharged in a manner and location to avoid reentry into the laboratory building or adjacent buildings at concentrations above 20% of allowable concentrations inside the laboratory for routine emissions or 100% of allowable concentrations for emergency emissions under wind conditions up to the 1%-wind speed for the site. 5.3.5

Exhaust Stack Discharge

The exhaust stack discharge shall be in accordance with the ASHRAE 1999 Handbook – HVAC Applications, Chapter 43.

Necessary measures must be taken to protect the laboratory building and adjacent buildings from toxic materials reentry. 47



In any event the discharge shall be a minimum of 10 ft (3 m) above adjacent roof lines and air intakes and in a vertical up direction.

The 10 ft (3 m) height above the adjacent roof line called for by this standard is primarily intended to protect maintenance workers from direct exposure from the top of the stack. However, this minimum 10 ft (3 m) height may be insufficient to guarantee that harmful contaminants won’t enter the outside air intake of the building or of nearby buildings. After initial installation, the exhaust stack is unchanged for the lifetime of the hood. It is uncertain that the lifetime hood usage can be accurately projected. In most cases, consistent discipline in safe hood procedures cannot be assured. Accordingly, it is prudent to use conservative guidelines in the location and arrangement of the hood discharge. The basic challenge in locating the hood discharge is to avoid re-entrainment of effluent into any building air intake or opening and to minimize exposure of the public. The selection of stack height is dependent on the building geometry and airflow pattern around the building and is as variable as meteorological conditions. An excellent resource is Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications. Among the factors to consider in establishing stack configuration, design, and height are: toxicity, corrosivity, and relative humidity of the exhaust, meteorological conditions, geometry of the building, type of stack head and cap design, adjacency of other discharged stacks and building intake, discharge velocity, and receptor population.

A minimum discharge velocity of 3000 fpm (15.2 m/s) is required unless it can be demonstrated that a specific design meets the dilution criteria necessary to reduce the concentration of hazardous materials in the exhaust to safe levels (see Section 2.1) at all potential receptors.

A discharge velocity of 2500 fpm (12.7 m/s) prevents downward flow of condensed moisture within the exhaust stack. It is good practice to make the terminal velocity at least 3000 fpm (15.2 m/s) to encourage plume rise and dilution.

Esthetic conditions concerning external appearance shall not supersede the requirements of Sections 5.3.4 and 5.3.5.

In case there is a conflict, the requirements of Section 5.3.4 take priority. Some solutions that may be used are:

These factors affect the dilution of the exhaust stream and the plume trajectory. High discharge velocity and temperature increase plume rise, but high velocity is generally less effective than increased stack height.

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Any architectural structure that protrudes to a height close to the stack-top elevation (i.e., architectural structure to mask unwanted appearance of stack, penthouses, mechanical equipment, nearby buildings, trees or other structures) shall be evaluated for its effects on re-entrainment The air intake or exhaust grilles shall not be located within the architectural screen or mask unless it is demonstrated to be acceptable.

5.3.6

• An evaluation of the stack design that will account for the effects of problem structures should be undertaken. The evaluation should provide estimates of the expected concentration levels of exhaust contaminants at surrounding air intakes. Appropriate physical modeling (wind tunnel, mockup or water flume) or numerical modeling using appropriate methods (Computational Fluid Dynamics or other advanced numerical methods) should be undertaken as discussed in Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications. The limitations of the technique utilized should be understood and evidence should be provided that the results are conservative or accurate for the case being modeled. When physical modeling is used, procedures discussed in the EPA Guideline for Modeling of Atmospheric Diffusion (Office of Air Quality Planning and Standards, EPA-600/8-81-009, April 1981) should be employed. • Treatment of the discharge gas may permit a lower and esthetically acceptable stack. The technology of gas-treating equipment is outside the scope of this standard except as described in Section 9.2. • Appendix 3 is provided to assist the designer in understanding stack height determination and evaluation methods.

Recirculation of Room Exhaust Air

Nonlaboratory air or air from building areas adjacent to the laboratory may be used as part of the supply air to the laboratory if its quality is adequate.

In many laboratory settings, the laboratory is purposely kept at a slight negative differential pressure with respect to adjacent building spaces. In this situation, air flows from the adjacent spaces into the laboratory through building cracks and doorways, at least when open. This may be highly desirable; if not, this flow can be reduced, but not completely eliminated, by use of double-door airlock vestibules, with corresponding consumption of interior space and some hindrance to traffic.

5.3.6.1 General Room Exhaust Air exhausted from the general laboratory space (as distinguished from laboratory chemical hoods) shall not be recirculated to other areas unless one of the following sets of criteria is met:

Many laboratories, especially those handling hazard materials, have a sufficient number of laboratory chemical hoods so that the entire flow of supply air to the room necessary for air-conditioning is exhausted through laboratory chemical hoods (in other words, there is no surplus supply to be exhausted or recirculated). 49



1) Criteria A • There are no extremely dangerous or lifethreatening materials used in the laboratory; • The concentration of air contaminants generated by maximum credible accident will be lower than short-term exposure limits required by 2.1.1; • The system serving the laboratory chemical hoods is provided with installed redundancy, emergency power, and other reliability features as necessary.

Devices that are intended to provide heating and/or cooling by recirculating the air within a laboratory space (i.e., fan coil units) are exempt from this requirement.

2) Criteria B • Recirculated air is treated to reduce contaminant concentrations to those specified in 2.1.1; • Recirculated air is monitored continuously for contaminant concentrations or provided with a secondary backup air-cleaning device that also serves as a monitor (via a HEPA filter in a series with a less efficient filter, for particulate contamination only). Refer to Section 9.3.1; • Provision of 100% outside air, whenever continuous monitoring indicates an alarm condition. 5.3.6.2 Exhaust Hood Air Exhaust air from laboratory hoods shall not be recirculated to other areas. Hood exhaust air meeting the same criteria as noted in Section 5.3.6.1 shall only be recirculated to the same work area where the hood operators have control of the hood work practices and can monitor the status of air cleaning.

For most laboratories, recirculation of laboratory chemical hood air should be avoided. Laboratory chemical hood air usually contains significant amounts of materials with differing requirements for removal. Providing air-cleaning equipment to permit safe recirculation represents a high capital and operating cost, especially when redundancy and monitoring requirements are considered. Note that NFPA 45-2000 prohibits recirculation of laboratory chemical hood air when using flammables. Some “single purpose” laboratories might find it practical to recirculate laboratory chemical hood air; the requirements are similar to those in Section 5.3.6.1 criteria B. See Section 4.2 for more information.

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6

Commissioning Tests

6.1

Commissioning of Laboratory Ventilation Systems

Commissioning Test Instrumentation: All test instrumentation utilized for the commissioning process shall be in good working order and shall have been factory calibrated within 1 year of the date of use. (See 8.6.1 Air Velocity, Air Pressure, Temperature and Humidity Instruments) 6.2

Commissioning Process

All newly installed, renovated, or moved hoods shall be commissioned to ensure proper operation prior to use by laboratory personnel.

6.2.1

Commissioning tests are conducted to ensure that laboratory ventilation systems operate according to design specifications and are capable of meeting control objectives under resulting operating conditions. The extent of the commissioning process depends on the complexity of the systems along with the anticipated risk associated with work to be conducted in the laboratory.

Commissioning Authority

The commissioning process shall be overseen by a responsible person or commissioning authority.

The commissioning authority should be someone who represents the interests of the system owner and should be knowledgeable in the design and operation of laboratory ventilation systems. In addition, the commissioning authority should be experienced with collection and analysis of test data. The commissioning authority may develop the commissioning plan in conjunction with information provided by potential equipment suppliers and contractors, owner personnel, and project design professionals. A commissioning team consisting of personnel directly involved in the design, installation, and use of the new or renovated systems should assist the commissioning authority. A commissioning team might include: • • • • • • • • • •

HVAC Design Engineers; Health and Safety Personnel; Maintenance Engineers; HVAC Controls Expert; TAB (Testing, Adjusting and Air Balance) Leader; Commissioning Consultant; Hood Performance Tester; Laboratory Managers; Principal Researchers or Hood Users; and Chemical Hygiene Officer. 51



6.2.2

Commissioning Plan

A written commissioning plan shall accompany design documents and be approved by the commissioning authority in advance of construction activities. The commissioning plan shall be available to all potential suppliers and contractors prior to bid along with the other project documents.

The conceptual design phase of the project generally includes a statement of performance objective and criteria for establishing proper operation of proposed systems. The statement of performance provides an operational definition of performance that can be measured after installation and startup to validate or verify proper operation. The commissioning plan describes the tests that will be conducted to verify proper operation of the systems.

A commissioning plan shall address operation of the entire ventilation system where the hoods, laboratories, and associated exhaust and air supply ventilation systems are considered subsystems. The plan shall include written procedures to verify or validate proper operation of all system components and include: • Laboratory Chemical Hood Specification and Performance Tests • Preoccupancy Hood and Ventilation System Commissioning Tests • Preoccupancy Laboratory Commissioning Tests

For example, an operational definition for proper performance of a new hood system might include: the new hood operated with the vertical sliding sash at a height of 28 in. (71.1 cm) must have an average face velocity between 80 – 120 fpm (0.41 to 0.61 m/s) and provide containment below a control level of AU 0.1 ppm as determined by methods described in the ANSI/ASHRAE 110-1995, Method of Testing Performance of Laboratory Fume Hoods. A laboratory chemical hood system includes all associated subsystems such as the hoods, ducts, dampers, automated controls, filtration, fan, motor, and exhaust stacks. In laboratories, the air supply system is considered part of the hood system when operation can affect hood performance. It is imperative that the commissioning plan be completed and that is part of the project design documents. It should not be developed after the bid process or signing of contracts because it may substantially impact the individual contractor laboratory costs and scheduling. If it is developed after the bid date, whatever requirements it imposes on a contractor could be contested as being invalid since it was not available at the time of bid. Design changes made subsequent to construction must be reflected in a revised commissioning plan.

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6.2.3

Commissioning Documentation

Preliminary and final commissioning documents shall be issued to the appropriate party(s) by the Commissioning Authority. The documents shall include: • Design Flow Specifications; • Laboratory and System Drawings for Final System Design; • Copy of Test and Balance Report; • Commissioning Test Data; • List of Ventilation System Deficiencies uncovered and the details of how (and if) they were satisfactorily resolved. Operational deficiencies and other problems uncovered by the commissioning process shall be communicated to the responsible party (i.e., installer, subcontractor, etc.) for prompt correction.

The documents should detail the status of the ventilation systems relative to maintaining a safe facility environment. The document should clearly indicate, based upon the ventilation system functionality, which laboratory rooms and equipment (i.e., chemical laboratory hoods, biosafety cabinets, etc.) are ready for safe use, any areas or equipment that are not safe for use or occupancy, and other safety-related ventilation system details.

Unreasonable delays or unsatisfactory follow-up should be communicated to the owner as well as any contractors in the tier to which this subcontractor is responsible.

6.3 Laboratory Chemical Hood Specification and “As Manufactured” ANSI/ASHRAE 110 Defined Performance Test Data Specification and procurement of laboratory chemical hoods shall be based on tests conducted on the hood (or prototype hood) that demonstrate adequate hood containment. The containment tests shall include: • • • • • • •

Exhaust Flow Measurements Hood Static Pressure Measurement Face Velocity Tests Auxiliary Air Velocity Tests (if applicable) Cross Drafts Velocity Tests Airflow Visualization Tests Tracer Gas Containment Tests

The tests shall be conducted under constant volume conditions where exhaust and air supply flow are stable and exhibit no more than 5% variation from set-point.

“As Manufactured” Containment Tests, usually performed at the manufacturer’s facility, are conducted to determine whether the hood is adequately designed to provide the required level of performance. In addition, the tests are conducted to determine appropriate operating specifications. It is only necessary to perform these tests on one hood for each unique hood design or mode. What is desired are credible catalog data on the fundamental performance and capabilities of a hood as it comes from the manufacturer. The designer can then specify the unit with confidence that it will perform as per the manufacturer’s catalog data. It is recommended that the manufacturers’ tests be conducted or witnessed by the laboratory owner and design professional, and/or independent third party. Proper containment of a laboratory chemical hood is affected by a number of factors including design of the hood, design of the laboratory, and design and operation of the ventilation systems. Controlled tests enable elimination of one variable: design of the hood. Therefore, performance problems encountered after installation can be attributed to other factors. 53



Where possible, containment tests should be conducted according to methods described in the most recent ANSI/ASHRAE 110 standard equal to or more challenging than the standardized test. ANSI/ASHRAE 110-1995 does not specify a face velocity. The standard yields a performance rating in the form of AM yy, AI yy, or AU yy where, AM means “as manufactured,” AI means “as installed,” and AU means “as used.” The symbol yy represents the average 5-minute concentration of tracer gas measured in the breathing zone of a mannequin used to simulate a hood user. The ANSI/ASHRAE 110-1995 standard recommends a gas generation rate of 4 L/m. However, other generation rates (i.e., 1 L/m or 8 L/m) can be specified by the design professional or responsible person (2.3) when deemed appropriate. The containment tests should be conducted over the range of possible operating configurations afforded by the hood design (i.e., sash position, baffle configurations, etc.) and at different target face velocities or exhaust flow rates to determine operational boundary conditions and hood limitations. Testing at different operating configurations will help to identify operational limitations or worst-case operating conditions. This information helps the design professional in their work and can then be relayed to the hood users to ensure proper work practices that minimize potential for exposure. 6.3.1

Exhaust Flow Measurement

The volumetric flow exhausted from a laboratory chemical hood shall be determined by measuring the flow in the exhaust duct using industry-approved methods.

See the most recent edition of ACGIH’s Industrial Ventilation: A Manual for Recommended Practice, or ANSI/ASHRAE 41.2-1987 (RA 92), for measuring flow. The hood exhaust flow should be adjusted to achieve the target average face velocity at the design opening. Typically, exhaust flow can be predicted from the area of the opening multiplied by the design face velocity. However, infiltration of air into the hood through openings other than the face may require approximately 5–10% more exhaust flow than calculated. The exhaust flow and variance from the calculated flow should be determined to enable proper specification of flows for design of the ventilation systems.

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Failure to determine the total exhaust flow required to achieve the desired average face velocity may result in undersizing of the exhaust system or improper specification of supply volume to achieve required lab pressurization or differential airflow. Calculation of exhaust flow from face velocity measurements multiplied by hood face area is not a measurement of exhaust flow and due to the reasons stated above, true exhaust flow can vary significantly from the calculated exhaust flow. In addition, the accuracy of face velocity measurements can affect the accuracy of the average face velocity used to calculate exhaust flow. Face velocities measured at the plane of the sash opening using hot-wire thermoanemometers or pressure grid assemblies can be subject to significant error due to turbulence at the opening and direction of airflow over the probes where average face velocities could vary from actual by 5–20%. 6.3.2

Hood Static Pressure

The hood static pressure shall be measured above the outlet collar of the hood at the flows required to achieve the design average face velocity.

6.3.3

For test method, refer to ANSI/ASHRAE 41.3-1989. Hood static pressure is a measure of the resistance imposed on the exhaust system by the hood. Determination of hood static pressure is required to ensure proper system design. Typical hood static pressures range from 0.1 to 0.75 in.wg (25 to 187 Pa) at face velocities between 80 to 120 fpm (0.41 to 0.61 m/s). However, the hood static pressure will depend on the hood design and exhaust flow.

Face Velocity Tests The average face velocity alone is inadequate to describe hood performance. Face velocity is not a measure of containment but only the speed of air entering the face opening. Hood performance should be determined from tests of hood containment. Average face velocity should only be used as an indicator of proper system operation. Refer to section 3.3.1, Face Velocity, for information about analysis of face velocity data and recommended criteria.

The average face velocity shall be determined by the method described in the ANSI/ASHRAE 110-1995 Method of Testing Performance of Laboratory Fume Hoods.

The accuracy of face velocity measurements can be affected by numerous factors including instrument accuracy, measurement technique, hood aerodynamics, room air conditions (cross drafts), and exhaust flow

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Face velocity measurements shall be made by dividing the hood opening into equal area grids with sides measuring no more than 12 in. (30.5 cm). The tip of the probe shall be positioned in the plane of the sash opening and fixed (not handheld) at the approximate center of each grid. Grid measurements around the perimeter of the hood opening shall be made at a distance of approximately 6 in. (15.2 cm) from the top, bottom, and sides of the opening enclosure.

stability. Average face velocities and grid velocities can be significantly affected by turbulence (temporal variation) and direction through the opening (spacial variation). Multiple readings taken over time at each grid location are recommended to provide more accurate velocity measurements. Cross drafts can also bias face velocity data by creating turbulence at the opening and variations in face velocity readings.

The average face velocity shall be the average of the grid velocity measurements. Each grid velocity shall be the average of at least 10 measurements made over at least 10 seconds.

Multiple readings at each grid point will help determine more accurate average face velocities when turbulent air is present at the hood opening. Multiple readings can be acquired with the use of time constants for meters so equipped or use of a data logger or data acquisition system attached to a computer.

The plane of the sash shall be located at the midpoint of the sash frame depth. 6.3.4

Auxiliary Air Velocity Tests

For auxiliary air hoods, the face velocity shall be measured with the auxiliary air turned off unless room pressurization would change significantly to affect exhaust flow. Where exhaust flow would be affected by turning off the auxiliary airflow, auxiliary air must be redirected from the hood opening so as not to interfere with flow into the hood while conducting the face velocity traverse.

Face velocity measurements should be determined with the supply air off or with special devices designed to eliminate the effect of the auxiliary air at the hood face.

The velocity of the auxiliary air exiting the auxiliary air plenum shall be measured to determine the magnitude and distribution of air supplied above the hood opening.

The auxiliary air supply plenum located above the top of the hood face and external to the hood should be designed to distribute air across the width of the hood opening so as not to affect containment. Excessive auxiliary air velocity can interfere or overcome air flowing into the hood opening and cause escape from the hood.

The average auxiliary air velocity shall be determined from the average of grid velocities measured across the plenum outlet.

The downflow velocities should be measured approximately 6 in. (15.2 cm) above the bottom edge of the sash positioned at the design opening height.

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6.3.5

Cross-Draft Velocity Tests

Cross-draft velocity measurements shall be made with the sashes open and the velocity probe positioned at several locations near the hood opening to detect potentially interfering room air currents (cross drafts). Record measurement locations. Over a period of 10–30 sec., cross-draft velocities shall be recorded approximately 1 reading per second using a thermal anemometer with an accuracy of ±5% at 50 fpm (0.25 m/s).

More test locations may be required or can be useful for determining cross-draft velocities past the hood opening. Vertical and horizontal components of cross-draft velocities should be measured at each location.

The average and maximum cross-draft velocities at each location shall be recorded and not be sufficient to cause escape from the hood.

Increasing face velocity may not make the hood more resistant to cross drafts. However, increasing face velocity may: • Increase the required volume of room air supply and increase difficulties with ensuring proper room air distribution. • Increase exhaust of expensive conditioned air.

Cross draft velocities shall not be of such magnitude and direction as to negatively affect containment.

Excessive cross-draft velocities (>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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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



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



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



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.


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



• 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, <5%; and • For electronic control system, ±2% of fullscale values. 8.6.3

Other Test Instruments

Other instruments (such as voltmeters and tachometers) shall be checked for function and accuracy against a “known source” before use and follow manufacturer’s recommendation, when provided, for periodic calibration. 69



8.7

Monitoring Blowers, Motors, and Drives

8.7.1

Visual Inspection

Fans, blowers, and drive mechanisms shall be visually inspected weekly. 8.7.2

V-belt drives

V-belt drives shall be stopped and inspected monthly for belt tension and signs of belt wear or checking. 8.7.3

Key problematic observations are abnormal noise or vibration, bearing noise, excessive temperature of motors, lubricant leaks, etc.

This will probably require removing the belt guard.

Lubrication

Blowers, drives, and other critical machine elements shall be lubricated at intervals and with lubricants recommended by the manufacturer. 8.8

Critical Service Spares

The ventilation system management plan shall address the need of providing for critical service issues and keeping spare parts on hand.

Preventive maintenance is intended to prevent unplanned breakdowns, but breakdowns will occur. In some cases, delivery time of replacement parts might be long enough to inhibit maintenance resulting from periodic inspection. Maintenance supplies and spares should be planned, taking into consideration the typical factors involved, such as: • Potential health or safety risk of breakdown; • Availability of spares or replacements; and • Economic cost of facility out of service.

8.9

Critical Service Instrumentation

All critical service instrumentation shall have contingency plans in place.

9

Air Cleaning

9.1

Supply Air Cleaning

For critical equipment of 100 horsepower (74.6 kW) or larger, consideration should be given to providing temperature and vibration sensors to give early warning of problems.

Laboratory air supply systems seldom require air cleaning for health and safety reasons. Supply air cleaning usually is provided, however, for technical reasons, usually to reduce the contamination from atmospheric dust and dirt. See ASHRAE 1999 Handbook – HVAC Applications. 70



9.2

Exhaust Air Cleaning

Air-cleaning systems for laboratory exhaust systems, where required, shall be designed or specified by a responsible person to ensure that air-cleaning systems will meet the performance criteria necessary for regulatory compliance. See ASHRAE 2001 Handbook – Fundamentals.

9.3

Air-cleaning performance monitoring is typically limited for many hazardous materials. Chemical specific detectors located downstream of adsorption media, pressure drop indicators for particulate filters, and/or periodic stack sampling for contaminant emissions may be required to monitor for regulatory compliance.

Filtration for Recirculation

Air-cleaning systems for recirculating general exhaust or hood exhaust from laboratories shall meet the design and installation requirements of ANSI/AIHA Z9.7-1998. Recirculation of process air shall be returned to the same room where the process is located and control of the process is supervised. 9.3.1

Exhaust air might require cleaning for one or more reasons (See Sections 4.2 and 5.3). Air-cleaning equipment covers a wide range of physical and chemical mechanisms beyond the scope of this standard and its proper application is, in general, not included.

In practical terms, recirculation of exhaust air usually is economical only if the air needs to be cleaned of low concentrations of: • Particulate material that can be removed by static (i.e., not self-cleaning) filters; • Hazardous or odorous gases and vapors that can be removed efficiently by adsorption media.

Airborne Particulates

Air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates shall be filtered through a two-stage particulate filtration system specified following the standard performance and design criteria of the ASHRAE Systems and Equipment to meet the objectives of 2.4.1.

The two stage filtration system should consist of:

Filter installations shall be tested for leaks and have all leaks repaired or the filter replaced before use.

The properties and behavior of airborne particulates cover a wide range and may include dusts, fumes, mists, smoke, etc. Special caution should be taken when utilizing recirculating particulate air-cleaning systems when condensation or evaporation of hazardous particulate materials can take place in the airstream.

• A primary high efficiency filter (85–95% efficiency). See ANSI/ASHRAE 52.1-1992, & 52.2-1999), followed by • An industrial-grade HEPA filter.

See the Institute of Environmental Sciences Recommended Practice for Laminar Flow Clean Air Devices. The flowrate through the filters shall be maintained at design specifications not to exceed 100% of the rated flow capacity of the filters.

The filter assembly should be provided with a damper and control that:

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• Indicate the static pressure differential separately across the primary and secondary filters and the pressure differential across both filters and the damper; • Actuate a damper motor (or allow manual activation) to open the damper from an initial partially closed position when filters are clean to a full-open position when filters are fully loaded; and • Actuate a signal or alarm when the pressure drop across either the primary or secondary filter reaches 0.01 in.wg (2.5 Pa) more than the rated-loaded pressure drop. Also see the ASHRAE 2001 Handbook – Fundamentals for additional information on the theory and need for application of aircleaning equipment for the emission control of hazardous materials from work operations. 9.3.2

Gases and Vapors

Adsorption or other filtration media used for the collection or retention of gases and vapors shall be specified for a limited use. Specific hazardous materials to be collected, airflow rate, temperature, and other relevant physical properties of the system shall be incorporated into the selection of filtration media.

The intent of this section is to specify the need to have a method for detecting filter breakthrough before a hazardous contaminant is released to the laboratory environment. Any method that provides early, accurate, and reproducible detection for the contaminants present is acceptable. Activated carbon and other adsorption media are available in a number of configurations as filter housings. Media may be sprayed onto another filtration media as a thin coat or be packed into thin panels less than 2 in. (5.1 cm) in depth. Also, deep- bed filters, typically cylindrical in shape and up to several feet in diameter and length, are utilized to provide adequate retention time for gas adsorption.

A reliable and adequately sensitive monitoring system shall be utilized to indicate adsorbent breakthrough. The sensitivity of the monitoring system shall be a predetermined fraction of the TLV® or appropriate health standard of the contaminant being adsorbed but shall not be more than 25% of the TLV®. The breakthrough time of the contaminant, before the effluent reaches no more than 50% of the TLV®, shall be sufficient, based upon system capacity design to allow a work operation shut down or parallel filter switch-over, thus proving a fresh filter.

An important characteristic of adsorption media is that upstream layers perform the adsorption function; with the result that breakthrough of unadsorbed gas occurs rather quickly without gradual reduction of adsorption efficiency. Prediction of breakthrough in deep beds can be accomplished by periodic withdrawal of media samples from incremental depths of the bed, but this is impractical in the shallow beds used in panels or in smaller cylindrical cartridges. Saturation of the active adsorption sites occurs progressively through the layer of carbon and depends on the burden of adsorbate, which typically is variable. Therefore, breakthrough of contaminant on the downstream side of the carbon layer is difficult to predict.

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For toxic gases and vapors, the filtration system shall be designed and sized for capacity to ensure adequate collection and retention for a worst-case scenario when in the event of a spill or other major release, adequate warning is provided for personnel to stop work or enact other emergency procedures. 9.3.3

Handling Contaminated Filters

When required, contaminated filters shall be unloaded from the air-cleaning system following safe work practices to avoid exposing personnel to hazardous conditions and to ensure proper containment of the filters for final disposal.

The Hazard Assessment should include recommended work practices and procedures to conduct filter change-outs when filters have been exposed to hazardous materials. Hazardous waste disposal requirements should be identified where needed.

Airflow through the filter housing shall be shut down during filter change-out.

Care should be taken during filter replacement to minimize the release of hazardous materials from the filters from being deposited downstream of the filter bank. The work area and, if necessary, the downstream duct interior should be cleaned by HEPA-equipped vacuum cleaner or wet methods as appropriate before reloading the clean filter.

9.3.4

Ductwork Contamination Care should be taken during filter replacement to minimize dirt from the filters being deposited downstream of the filter bank or the work area. If necessary, the duct should be decontaminated before and after the replacement. Users may want to consider use of bagout filters.

9.4

Testing and Monitoring

9.4.1

Air Filters

Recirculation air filters shall be inspected and tested as per Section 9.3.1 except that provisions are mandatory.

All air filters should be provided with differential pressure gauges. Gauges should be read at intervals of 1 week (or at other intervals, based on experience) and inspected visually at the same time. If the pressure differential equals or exceeds the rated maximum, the filters should be changed at the first opportunity.

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9.4.2

Recirculated Activated Carbon Beds

Activated carbon beds or panels shall be tested as per Section 9.3.2 at intervals no longer than 1 month initially and then based on experience with the particular installation a schedule shall be prepared. 9.4.3

Air Pollution Control Equipment

Air pollution control equipment shall be inspected visually at intervals no longer than 1 week and, if necessary, at shorter intervals. Specific tests and repairs shall be in accordance with the manufacturer’s recommendations or in compliance with applicable regulations.

The variety of generic types of pollution control equipment, combined with the many different configurations on the market, make it inappropriate to set forth specific requirements.

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APPENDIX 1

Definitions, Terms, Units

There are many terms and definitions associated with laboratory ventilation that have special meaning. The following are definitions of terms or units used in this document: A2.1 adjacent roof line: For the purposes of determining the laboratory chemical hood stack height, the adjacent roof will be within 6 ft (1.8 m) horizontally of the nearest outer point of the exhaust fan stack. This criterion is intended to protect maintenance workers from direct exposure to their breathing zone, hands, feet, and other parts of their body. Parts of the building that are within 6 ft (1.8 m) horizontally of the exhaust fan stack are exempted if it would be impossible for a person to stand or cling to the surface in question. A2.2 air changes per hour (ACH): A common means for expressing a volumetric airflow through a room. Each ACH for a room is intended to represent an amount of air equal to the gross volume of the air passing through the room each hour. An ACH rate for a room can be converted to volumetric airflow by multiplying the ACH number times the gross volume of the room and then dividing the product obtained by 60. For instance, for an ACH of 10, a room with a gross volume of 2400 cubic feet would require a volumetric airflow of 10 × 2400 ÷ 60 = 400 cfm (189 L/s). This term does not reflect actual mixing factors and therefore does not indicate the effective air exchange rate in the room. See ACGIH’s Industrial Ventilation: Manual of Recommended Practice for further information on mixing factors. A2.3 auxiliary air hood: A laboratory chemical hood with an external supply air plenum at the top of the laboratory chemical hood. The auxiliary air plenum provides a makeup airstream comprised of unconditioned or only minimally conditioned outside air to substantially reduce the amount of conditioned room air exhausted by the laboratory hood. A2.4 bypass hood (constant air volume bypass laboratory hood): A laboratory hood design that incorporates an opening (bypass area) in the upper portion of the laboratory hood structure. When the movable sash is fully open, the sash

blocks off this bypass area and all of the airflow into the laboratory hood must pass through the open face area. However, as the sash is being closed to reduce the open face area, at a specific point an amount of bypass area is being uncovered. The increase in the bypass area opening offsets the decrease in the face area opening, thus providing an alternate path (the uncovered bypass area) for air to flow into the laboratory hood. When utilized with a constant air volume ventilation system, the bypass area keeps the laboratory hood face velocity relatively constant and from increasing to an objectionably high value as the sash is lowered. A2.5 capture velocity: The air velocity at a point in space of sufficient magnitude to overcome room air currents and draw the air and any contaminants at that point into the hood. A2.6 chemical hygiene officer: An employee who is designated by the employer and who is qualified by training or experience to provide technical guidance in the development and implementation of the provisions of the Chemical Hygiene Plan. This definition is not intended to place restrictions on the position description or job classification that the designated individual shall hold within the employer’s organizational structure. A2.7 constant air volume (CAV) ventilation system: A ventilation system designed to maintain a constant quantity of airflow within its ductwork. The airflow quantity is typically based upon the amount required to handle the most extreme conditions of outdoor-weather-related heat gain or loss and internal building loading. Although relatively simple, a constant volume ventilation system typically requires the maximum ongoing energy usage since the system always operates at maximum capacity. A2.8 design sash position: The maximum open area of the hood face that achieves the desired face velocity during any work inside the hood that produces airborne contaminants. A2.9 dilution ventilation: Ventilation airflow that dilutes contaminant concentrations by mixing with contaminated air, as distinguished from capturing the contaminated air. 75



A2.10 discharge velocity: The speed of the exhaust air normally expressed in feet per minute (meters/second) at the point of discharge from a laboratory exhaust system. Since laboratory exhaust system fans may be configured to discharge into a vertical exhaust stack or may utilize fans specifically designed to discharge directly upward, the discharge velocity normally refers to the air velocity as it leaves the last element of the exhaust system. Since the top of an exhaust stack may be conical (or other type of configuration), the velocity of the exhaust air at the point of discharge may differ from the velocity of the air within the vertical stack itself. The term “stack velocity” is sometimes used when referring to the speed of the exhaust airstream as it is discharged into the outside air. A2.11 diversity factor: A percentage factor that is applied to establish the theoretical maximum exhaust airflow quantity that is required at any point in time. For example, in an exhaust system consisting of three hoods, the diversity factor would be 1/3 if at any point in time only one hood were being used. Applying a diversity factor to the theoretical maximum required capacity of an HVAC system is often considered in the design of a VAV system. Incorporating a diversity factor enables downsizing HVAC system components and thus results in a smaller capacity ventilation system. The overall intention of applying a diversity factor when designing a VAV ventilation system is to achieve a lower life cycle cost (e.g., lower system first cost and/or lower system energy costs). A2.12 ductless hood: A laboratory hood that is not connected to an exhaust system that discharges the laboratory hood exhaust outdoors. Rather, a ductless laboratory hood incorporates an exhaust fan and exhaust filters as an integral part of the laboratory hood and discharges the exhaust directly into the room. Ductless laboratory hoods are of limited size and capacity in comparison to conventional ducted laboratory hoods. A2.13 exhaust air: Air that is removed from an enclosed space and discharged into the atmosphere.

A2.14 face velocity: The air velocity at the plane of and perpendicular to the opening of a laboratory chemical hood. A2.15 floor-mounted hood (walk-in hood): A larger-size laboratory hood with sash and/or door arrangement that enables access from the floor to the top of the hood interior. The name unfortunately is a misnomer and although the design and height of these hoods may allow it, users should not walk into any hood that may represent a significant exposure hazard. Walk-in laboratory hoods enable larger equipment and apparatus (e.g., equipment on carts, gas cylinders, etc.) to be more readily put in and set up within the laboratory hood. A2.16 glovebox: A controlled environment work enclosure providing a primary barrier from the work area. Operations are performed through sealed gloved openings to protect the user, the environment, and/or the product. A2.17 HEPA: High Efficiency Particulate Air (filter) for air filters of 99.97% or higher collection efficiency for 0.3 (m diameter droplets of an approved test aerosol (e.g., Emory 3004) operating at a rated airflow. A2.18 laboratory: It is difficult to provide a strict definition for laboratory. Some entire institutions are formally named “Laboratory.” The general concept for application of this standard is a facility in which the amounts of chemicals handled are small [perhaps 22 or 44 lbs (10 or 20 kg), except for storage of supplies], where much of the work involves manual manipulation of small containers or benchtop apparatus, and where the work is not routine production of goods. When this standard is used as a reference document in specifying design and construction (or modification) of a facility, it is suggested that the parties involved in the activity agree whether the facility is to be considered a laboratory. The Occupational Safety and Health Administration, in 29 CFR 1910.1450 (subpart 2, paragraph 191.1450), provides a definition of “laboratory” for regulatory purposes.

76



A2.19 laboratory chemical hoods: A chemical hood is a box-like structure with one open side, intended for placement on a table or bench. The bench and the hood may be one integral structure. The open side is provided with a sash or sashes that move vertically and/or horizontally to close the opening. Provisions are made for exhausting air from the top or back of the hood, and adjustable or fixed internal baffles may be provided to obtain proper airflow distribution across the open face. Provisions may be made for utilities and lighting. A2.20 makeup air (replacement air): Air provided by a ventilation system to replace air being exhausted from a laboratory hood, canopy hood, room, or space. A2.21 perchloric acid hood: A laboratory hood constructed and specifically intended for use with perchloric acid or other reagents that may form flammable or explosive compounds with organic materials of construction. A perchloric acid hood as well as its exhaust system must be constructed of all inorganic materials and be equipped with a water washdown system that is regularly used to remove all perchloric salts that may precipitate and collect in the laboratory hood and in the exhaust system. The exhaust fan must also be of a sparkresistant design to ensure against ignition of any perchlorate deposits in the exhaust system. A2.22 recirculation: Air removed or exhausted from a building area and ducted back to an air-handling system where it is mixed with outside fresh air. This air mixture is then conditioned and utilized for ventilation. Since air removed from a space is more often close to the temperature and humidity of the building interior than outside air, the recirculation process enables achieving a greater reduction in heating and cooling energy than if 100% outside air was utilized (also see return air). A2.23 reentry: The flow of contaminated air that has been exhausted from a space back into the space through air intakes or openings in the walls of the space. A2.24 replacement air: See makeup air.

A2.25 responsible person: An individual who has the responsibility and authority for the design and implementation of the ventilation management plan. This person may be the Chemical Hygiene Officer or work in conjunction with the Chemical Hygiene Officer. A2.26 return air: Air being returned from a space to the ventilation fan that supplies air to a space. A2.27 room air balance: A general term describing the requirement that a laboratory room have the proper relationship with respect to the total exhaust airflow from the room and the supply makeup airflow. The relationship of these airflows also establishes the pressure differential between the laboratory room and adjacent rooms and spaces. A2.28 room ventilation: The volumetric airflow through a room expressed in terms of cfm or L/sec. A2.29 special purpose hood: An exhausted hood, not otherwise classified for a special purpose such as but not limited to capturing emissions from equipment such as atomic absorption gas chromatographs; liquid pouring, mixing, or weighing stations; and heat sources. These hoods might not meet the design description of various types of laboratory chemical hoods discussed here. They may be exterior hoods, receiving hoods, or enclosing hoods, as described in the latest ACGIH Industrial Ventilation: A Manual of Recommended Practice. A2.30 variable air volume—two-position ventilation system: A constant air volume ventilation system (sometimes also referred to as a “two-position variable air volume system”) that is designed to provide two separate levels of airflow. The higher level of airflow is provided when a facility is normally occupied such as during regular work hours. The lower level of airflow is utilized during unoccupied times (e.g., nighttime, holidays, etc.) when ventilation needs and internal loads require less airflow. A2.31 variable volume hood: A hood designed so the exhaust volume is varied in proportion to the opening of the hood face by changing the speed of the exhaust blower or by operating a damper or control valve in the exhaust duct. 77



A2.32 variable air volume (VAV) ventilation system: A type of HVAC system specifically designed to vary the amount of conditioned air supplied and exhausted from the spaces served. The amount of air supplied and intended to meet (but not exceed) the actual need of a space at any point in time. In general, the amount of air that is needed by a space is determined by the required rate and the amount of airflow necessary to maintain comfortable conditions (temperature and humidity).

CAV –

constant air volume

CFD –

computational fluid dynamics

cfm –

cubic feet per minute

dBA –

(A scale) decibels

dP –

differential pressure

fpm –

feet per minute

in.wg –

inches water column (gauge)

A2.33 velocity: Magnitude and direction of air motion. As used in this standard, if the direction is omitted it is implied to be perpendicular to the plane of the airflow cross section. If the direction is important, it will be stated.

I&M –

Inspection and Maintenance Program

JIC –

joint industry codes (hydraulic equipment)

LEED –

Leadership in Energy and Environmental Design, a rating system from the U.S. Green Building Council

MAK –

maximum allowable concentration

NFPA –

National Fire Protection Association

NC –

noise criteria curves

A2.34 volumetric airflow rate: The rate of airflow expressed in terms of volume (cubic feet or liters) per unit of time. These are commonly expressed as cubic feet per minute (cfm) in USCS units or liters per second (L/s) in SI units. (Also see room ventilation.) A2.35 Walk-in hood: See floor-mounted hood.

NEC –

National Electrical Code

A2.36 units and abbreviations:

NFC –

National Fire Code

ACD –

air-cleaning device

NIOSH –

AMCA –

Air Movement Control Association

National Institute for Occupational Safety and Health

ACGIH –

American Conference of Governmental Industrial Hygienists

PEL –

Permissible Exposure Limit

PPE –

personal protective equipment

AGS –

American Glovebox Society

RC –

room criteria curves

AIHA –

American Industrial Hygiene Association

REL –

Recommended Exposure Levels

SEFA –

ASME –

American Society of Mechanical Engineers

Scientific Equipment and Furniture Association

ASHRAE – American Society of Heating, Refrigerating and Air Conditioning Engineers AI –

as installed

AM –

as manufactured

AU –

as used

BOCA –

Building Officials and Code Administrators International

SMACNA – Sheet Metal and Air Conditioning Contractors National Association SPL –

sound pressure level

TAB –

testing, adjusting and air balancing

TLV® –

Threshold Limit Value

TWA –

time weighted average

VAV –

variable air volume

WEEL –

Workplace Environmental Exposure Levels

78



APPENDIX 2 Referenced Standards and Publications The following standards and associated publications, when referenced in this document, constitute provisions of this American National Standards Institute, Inc. At the time of publication, the editions indicated were the most current. However, since standards and associated publications are subject to periodic revision, parties to agreements based on this American National Standard are encouraged to ensure that they reference the most recent editions of these documents. ACGIH: Industrial Ventilation: A Manual of Recommended Practice, 24th Edition. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 2001. ACGIH: Threshold Limit Values (TLV®) For Chemical Substances and Physical Agents. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 2002. AGS-1998-001: Guideline for Gloveboxes, 2nd Edition. Santa Rosa, CA: American Glovebox Society, 1998. AMCA 99-0401-86: Classification for Spark Resistant Construction. Arlington Heights, IL: Air Movement and Control Association, 1986. AMCA 201-90: Fan Application Manual, Part I, Fans and Systems: AMCA Classification for Spark Resistant Construction. Arlington Heights, IL: Air Movement and Control Association, 1990.

ANSI/ASHRAE 41.2-1987 (RA 92): Standard Methods for Laboratory Air Flow Measurement. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1992. ANSI/ASHRAE 41.3-1989: Standard Method for Pressure Measurement. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1989. ANSI/ASHRAE 41.7-1984 (RA 00): Method of Test Measurement of Flow of Gas. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 2000. ANSI/ASHRAE 52.1-1992: Gravimetric and DustSpot Testing Procedure for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1992. ANSI/ASHRAE 52.2-1999: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1999. ANSI/ASHRAE 62-2001: Ventilation for Acceptable Indoor Air Quality. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 2001. ANSI/ASHRAE 110-1995: Method of Testing Performance of Laboratory Fume Hoods. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1995.

ANSI/AIHA Z9.2-2001: Fundamentals Governing the Design and Operation of Local Exhaust Systems. Fairfax, VA: American Industrial Hygiene Association, 2001.

ASHRAE 2001 Handbook – Fundamentals (InchPound edition). Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 2001.

ANSI/AIHA Z9.7-1998: Recirculation of Air from Industrial Process Exhaust Systems. Fairfax, VA: American Industrial Hygiene Association, 1998.

ASHRAE 1999 Handbook – HVAC Applications (Inch-Pound edition). Atlanta, GA: American Society of Heating, Refrigerating, and AirConditioning Engineers, Inc., 1999

ANSI/ASHRAE 41.1-1986 (RA 01): Standard Method for Temperature Measurement. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1991.

The BOCA National Mechanical Code. Country Club Hills, Ill: Building Official and Code Administrators International, 1993. 79



CDC-NIH: Biosafety in Microbiological and Biomedical Laboratories, Appendix A, CDC-NIH, 4th edition, Atlanta, GA: Centers for Disease Control and Prevention, 1999. EPA-600/8-81-009: Guideline for Modeling of Atmospheric Diffusion. Office of Air Quality Planning and Standards, April 1981. Fairfax, R. Letter to R. Morris, 4 April 2001. “Hazard Communication,” Code of Federal Regulations. Title 29, Part 1910.1200, 1988. IMC-2000: International Mechanical Code. Falls Church, VA: International Code Council, 2000. Institute of Environmental Sciences. Recommended Practice for Laminar Flow Clean Air Devices. Institute of Environmental Sciences, 1986. Ivany, R., First, M., DiBerardinis, L.J.: “A New Quantitative Method for In-Place Testing of Laboratory Hoods,” American Industrial Hygiene Association Journal 50 no.5: 275-280. (1989). Kolesnikov, A., Ryan, R., Walters, D.B.: Use of Computational Fluid Dynamics to Optimize Airflow and Energy Conservation in Laboratory Hoods and Vented Enclosures. Washington, DC: EPA Labs for the 21st Century, January 2002a. Kolesnikov, A., McNally, J., Ryan, R., Walters, D.B.: CFD-Driven Design of a Low AirFlow, Rapid Recovery System to Maximize Safety and Optimize Energy Efficiency, Durham, NC: EPA Labs for the 21st Century, October 2002b. LEED: Leadership in Energy and Environmental Design. U.S. Green Building Council. Memarzadeh, F.: Methodology for Optimization of Laboratory Hood Containment, Volumes I and II. Bethesda, MD: National Institutes of Health, 1996. NFPA 30-2000: Flammable and Combustible Liquids Code. Quincy, MA: National Fire Protection Association, 2000. NFPA 45-2000: Standard on Fire Protection for Laboratories Using Chemicals. Quincy, MA: National Fire Protection Association, 2000.

NFPA 86-1999: Standards for Ovens and Furnaces. Quincy, MA: National Fire Protection Association, 2000. NFPA 92A-2000: Recommended Practice for Smoke Control Systems. Quincy, MA: National Fire Protection Association, 2000. NSF 49-1992: Class II (Laminar Flow) Biohazard Cabinetry. Ann Arbor, MI: National Sanitation Foundation, International, 1992. “Occupational Exposure to Hazardous Chemicals in Laboratories,” Code of Federal Regulations Title 29, Part 1910.1450, 1988. Petersen, R.L., Cochran, B.C., LeCompte, J.: “Specifying Exhaust Systems that Avoid Fume Reentry and Adverse Health Effects.” Symposium Paper at ASHRAE Summer Meeting, Honolulu, HI, June 23-26, 2002. To be published in 2002 ASHRAE Transactions. Ratcliff and Sandru: “Dilution Calculations for determining Laboratory Exhaust Stack Heights,” (ASHRAE Transactions, 105, part 1, paper Ch-997-2, 1999). SEFA-1-2002: Scientific Equipment and Furniture Association, 2001. SMACNA. HVAC Duct Construction Standards: Metal and Flexible, Merrifield, VA: Sheet Metal and Air Conditioning Contractors’ National Association, 1995. Smith, T.C. and Crooks, S.M: “Implementing a Laboratory Ventilation Management Program.” Chemical Health Safety 3 (1996): 12. “Test Methods,” Code of Federal Regulations Title 40, Part 60, Appendix A, 1989. UMC-1997: Uniform Mechanical Code. Whittier, CA: International Conference of Building Officials and Los Angeles, CA: International Association of Plumbing and Mechanical Officials, 1997. U.S. Nuclear Regulatory Commission, U.S. Department of Energy, U.S. Environmental Protection Agency, and U.S. Department of Defense: Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) (EPA 402-R-97016), 1997.

80



APPENDIX 3 Selecting Laboratory Stack Designs Necessary measures must be taken to protect the laboratory building and adjacent buildings from reingestion of toxic laboratory chemical hood exhaust back into a building air supply system. The 10 ft (3.0 m) minimum stack height called for in the body of this standard is primarily intended to protect maintenance workers from direct contamination from the top of the stack. However, the minimum height of 10 ft (3.0 m) is not enough by itself to guarantee that harmful contaminants would not be reingested. Similarly, a minimum 3000 fpm (15.2 m/s) exit velocity is specified in the body of this standard, but this exit velocity does not guarantee that reingestion will not occur. This appendix describes general stack design guidelines and three analysis methods for determining an adequate stack design. The first analysis method is termed the “Geometric” method, which ensures that the lower edge of an exhaust plume stays above the emitting building and associated zones of turbulent airflow. The geometric method is fully described here and is accompanied by an example. The second analysis method, briefly described, predicts exhaust dilution at downwind locations. The dilution equations are not presented here but can be obtained from Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications. A dilution criterion is presented in this appendix to judge the adequacy of the predicted dilutions in minimizing reingestion. The third analysis method described is wind tunnel or water flume modeling. General Guidelines Laboratory chemical hood exhaust stacks should have vertical, unobstructed exhaust openings. Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications describes appropriate rain protection devices. Goosenecks, flapper dampers, and rain caps are unacceptable as they deflect the exhaust sideways or downward, making it much more likely that reingestion will occur.

For a given exhaust flow rate, reducing the exit diameter with an exhaust nozzle is recommended to increase the exit velocity and rise or throw of the exhaust over the building. However, exit velocities much larger than 3000–4000 fpm (15.24 to 20.32 m/s) may result in high noise and vibration. Too small of a nozzle, or one with too rapid a decrease in area, could result in excessive pressure loss in the exhaust and the resulting combination of reduced flow due to fan system effect and reduced dilution and safety. Combining exhausts into a common stack, either by manifolding exhausts or with very close grouping of stacks, will enhance the rise of the exhaust plume. Close grouping of stacks can be used for specialty exhausts that cannot be manifolded because of their chemical nature. Manifolding or combining exhausts can generally give greater benefit than installing an exhaust nozzle on a stack serving a single laboratory chemical hood. Manifolding of exhausts can also provide some internal dilution of laboratory chemical hood exhausts when the majority of chemical emissions are from an upset condition or large release from a single laboratory chemical hood. Such upset or large release conditions are the primary cause of odor complaints and potential health effects. However, this internal dilution is partially offset by the decreased atmospheric dilution due to the larger plume size. Nevertheless, manifolding of exhausts is still beneficial and recommended. Variable exhaust flow rates, used to reduce energy costs, can periodically result in low exit velocities. Minimum exit velocities below 1500 fpm (7.62 m/s) are discouraged because for such low exit velocities, high winds can cause the exhaust to travel down the side of the stack instead of rising vertically. Makeup air or variable nozzles are recommended to maintain high exit velocities. Adding makeup air is preferred because it provides the larger plume rise and some internal dilution. Air intake placement is as important as stack design. Intakes on the side of the building or at grade will usually provide greater protection from rooftop exhausts. Intakes on the roof may work if placed a sufficient distance from the exhausts. 81



When only a single tall stack is present, an intake location near the base of the stack may be a good location. The advantage of this location is diminished if there are sources of toxic or odorous exhausts at other locations on the roof. Nearby intakes elevated above a laboratory exhaust stack should be avoided. Rooftop obstacles, such as parapets or architectural fences, and penthouses on the same roof as the hazardous exhaust stack can also act as adjacent buildings causing wind flow disturbances that reduce the rise of the exhaust. Note that it is the difference in roof heights that is particularly important when analyzing the adjacent building effect. First Stack Design Method— The Geometric Method Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications describes the geometric method. This is a conservative simplified method most appropriate for use by laboratory building ventilation designers. The geometric method is designed for isolated rectangular buildings that do not have taller buildings, dense taller trees, or taller hills close to the laboratory building. Also air intakes on the emitting building should be no higher than the top of the physical exhaust stack opening. Provided these conditions are met, the geometric method can be applied as follows: 1) Calculate the length of the recirculation zone (R) downwind of the building for each of the four basic approach wind directions. For a given direction, R = (Bsmall0.67) (Blarge0.33), where Bsmall is the smaller of the building height and width, and Blarge is the larger of the two. As used here, the recirculation zone height is the height of the emitting building. Table A1 presents recirculation zone length for various building dimensions. 2) Calculate the added plume rise (throw) due to exhaust momentum and add it to the stack height, to obtain the effective stack height. The added plume rise due to momentum (h-added)

equals 3 × (stack diameter) × (stack exit velocity/1%-wind speed). The 1%-wind speed is a high wind speed exceeded only 1% of the time. These wind speeds are available for numerous locations in the ASHRAE 1997 Handbook – Fundamentals, Chapter 26. 3) The effective height of the stack is the physical stack height plus the added plume rise due to momentum. 4) The geometric method, as stated here, specifies that the bottom of an exhaust plume should clear the emitting building, including penthouses, and the recirculation zone downwind of the building. The bottom of the plume extends downward at a 5:1 slope (5 units horizontal and 1 unit downward) from the effective stack height (physical height plus added plume rise). This should be done for all four of the basic approach wind directions. Table A2 shows flowrates required to meet the geometric method, given a 10 ft (3.0 m) stack height and a 3000 fpm (15.2 m/s) exit velocity (as per this standard), a 1%-wind speed of 15 mph (24 km /h), and various horizontal distances to clear. The horizontal distance is the distance between the stack and the downwind building edge plus the recirculation zone length. The same method can be used to determine a taller stack that also complies. Example Calculation for the First Stack Design Method—The Geometric Method A laboratory building is 100 ft (30.5 m) wide, 200 ft (61.0 m) long, and 60 ft (18.3 m) high. A manifolded laboratory exhaust with a flowrate of 10,000 cfm (4719 L/s) is located in the center of the roof. For wind approaching the 100 ft (30.5 m) wide side, Bsmall is 60 ft (18.3 m) and Blarge is 100 ft (30.5 m). The length of the recirculation zone is R = (60 0.67)(100 0.33) = 71 ft (21.7 m). The horizontal distance that must be cleared by the plume equals 100 ft (30.5 m) from the center to the edge of the building plus 71 ft (21.6 m) for the recirculation zone, or 171 ft (52.1 m). The required effective stack height to clear the building and recirculation zone is 171/5 (using the 5:1 slope) = 34.2 ft (10.4 m).

82



The added stack height due to momentum is calculated next. The stack diameter is 2.06 ft (0.63 m) based on a 3000 fpm (15.2 m/s) exit velocity and a 10,000 cfm (4719 L/s) flow rate. Using a 15 mph (24.1 km/h), 1320 fpm (6.7 m/s) 1%-wind speed, the added stack height = 3 × 2.06 × 3000/1320 = 14 ft (4.3 m). Given a physical stack height of 10 ft (3.0 m) based on the minimum required to meet this standard, the effective stack height is 14 + 10 ft = 24 ft (7.32 m). The required effective height computed above is 34.2 ft (10.4 m), which is not met with a 10 ft (3.0 m) physical stack height. The designer can increase the physical height to 20 ft (6.1 m). As an alternative, the designer can increase the momentum of the air by introducing outside air to the system. If the physical stack height remains at 10 ft (3.0 m), the diameter would need to increase to 3.5 ft (1.1 m), increasing flow rate to about 30,000 cfm (14158 L/s). Also, Table A1

increasing to 30,000 cfm (14158 L/s) will increase in-stack dilution by a factor of 3:1. This in-stack dilution, whether achieved by manifolding exhausts in the building or by adding roof air, can be very valuable to achieving safe results. The other wind direction (aimed toward the long side of the building) should be checked, but for this example this wind direction is the worst case. High volume flow in itself is not a guarantee of adequate dilution. For a given source spill rate in kilograms/second, a higher exhaust volume flow Qe increases the in-stack dilution, but somewhat reduces the atmospheric dilution because the atmosphere is now presented with a larger volume of gas to disperse. The following Tables A1 and A2 allow for rapid estimates of required dilution to be made where numerical calculation is not possible at the time.

Length of Downstream Recirculation Zone (feet and meters) Each story is 15 ft (4.6 m) high

Bldg. Dimensions

1 Story

2 Stories

3 Stories

4 Stories

5 Stories

6 Stories

7 Stories

Height in Feet (meters)

15 ft (4.6 m)

30 ft (9.1 m)

45 ft (13.7 m)

60 ft (18.3 m)

75 ft (22.9 m)

90 ft (27.4 m)

105 ft (32.0 m)

50 ft (15.2 m)

22.3ft (6.8 m)

35.5 ft (10.8 m)

46.6 ft (14.2 m)

53.1 ft (16.2 m)

57.2 ft (17.4 m)

60.7 ft (18.5 m)

63.9 ft (19.5 m)

75 ft (22.9 m)

25.5 ft (7.8 m)

40.6 ft (12.4 m)

53.3 ft (16.2 m)

64.6 ft (19.7 m)

75.0 ft (22.9 m)

79.7 ft (24.3 m)

83.3 ft (25.4 m)

100 ft (30.5 m)

28.1 ft (8.6 m)

44.6 ft (13.6 m)

58.6 ft (17.9 m)

71.0 ft (21.6 m)

82.5 ft (25.1 m)

93.2 ft (28.4 m)

101.6 ft (31.0 m)

150 ft (45.7 m)

29.8 ft (9.1 m)

51.0 ft (15.5 m)

67.0 ft (20.4 m)

81.2 ft (24.7 m)

94.3 ft (28.7 m)

106.5 ft (32.5 m)

118.1 ft (36.0 m)

200 ft (61.0 m)

29.8 ft (9.1 m)

56.1 ft (17.1 m)

73.6 ft (22.4 m)

89.3 ft (27.2 m)

103.7 ft (31.6 m)

117.1 ft (35.7 m)

129.9 ft (39.6 m)

250 ft (76.2 m)

29.8 ft (9.1 m)

59.6 ft (18.2 m)

79.2 ft (24.1 m)

96.1 ft (29.3 m)

111.6 ft (34.0 m)

126.1 ft (38.4 m)

139.8 ft (42.6 m)

300 ft (91.4 m)

29.8 ft (9.1 m)

59.6 ft (18.2 m)

84.2 ft (25.7 m)

102.0 ft (31.1 m)

118.5 ft (36.1 m)

133.9 ft (40.8 m)

148.5 ft (45.3 m)

500 ft (152.4 m)

29.8 ft (9.1 m)

59.6 ft (18.2 m)

89.4 ft (27.2 m)

119.2 ft (36.3 m)

140.3 ft (42.8 m)

158.5 ft (48.3 m)

175.7 ft (53.6 m)

1000 ft (304.8 m)

29.8 ft (9.1 m)

59.6 ft (18.2 m)

89.4 ft (27.2 m)

119.2 ft (36.3 m)

149.0 ft (45.4 m)

178.8 ft (54.5 m)

208.5 ft (63.6 m)

Length or Width

83



Formula for figure is: Length of downstream recirculation zone is Bsmall(0.67) × Blarge(0.33) where Bsmall is the smaller of height and width or length and Blarge is the larger of the two (from ASHRAE, 2001). Where Blarge is > 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

84



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



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.

86



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.

(

)

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

(

) 2.3

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

(

) 2.4.1

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

(

)

Employers 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 are considered when specifying design features and performance criteria.

(

)

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

(

)

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



(

(

)

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


(

) 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.

(

) 3.1.1

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

(

(

)

Sashes are not removed when the hood is in use.

(

)

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

) 3.1.1.1

(

)

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



(

) 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.

(

) 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.

(

(

)

) 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:

(

(

)

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

(

)

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

(

)

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.

(

)

The hood exhaust volume remains essentially unchanged (<5% change) when the sash is fully closed.

(

) 3.2.2

Conventional hoods meet the requirements in Section 3.3.

(

) 3.2.3

Auxiliary air hoods meet the requirements in Section 3.3.

In addition: ( ( ( (

) ) )

) 3.2.4

The supply plenum is located externally and above the top of the hood face; The supply jet is distributed uniformly across the hood width; The auxiliary air does not disrupt hood containment or increase potential for escape. Perchloric acid hoods meet the requirements in Sections 3.2.1 and 3.3 and NFPA 45.

In addition: (

)

All inside hood surfaces 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 are equipped with water wash-down capabilities;

89



(

)

All ductwork is 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 is manifolded or joined to nonperchloric acid exhaust systems;

(

)

No organic materials, including gaskets are used in the hood construction unless they are known not to react with perchloric acid and/or its byproducts;

(

)

Perchloric acid hoods are prominently labeled, “Perchloric Acid Hood.”

(

) 3.2.5

Floor-mounted hoods (formerly called walk-in hoods) meet the requirements in Sections 3.2.1 and 3.3.

(

) 3.2.6

A variable air volume hood meets 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 supply and exhaust systems are balanced. If the laboratory uses variable air volume, the supply and exhaust modulate together to maintain this balance.

(

)

Modification of the hood exhaust does not compromise the total laboratory exhaust.

(

)

Any modification of the hood exhaust does not compromise other fundamental concerns.

) 3.3.1

(

(

(

The average face velocity of the hood produces sufficient capture and containment of hazardous chemicals generated under as-used conditions.

)

The mechanism that controls the exhaust fan speed or damper position to regulate the hood exhaust volume is designed to ensure a minimum exhaust volume of 50 cfm/ft of hood width, for a 24 in. (61 cm) deep hood (or 25 cfm/ft2 of hood work surface for different depth hoods) except where a written hazard characterization indicates otherwise.

) 3.3.2

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

(

)

Face velocity measurements are made with the sash in the Design Sash Position.

(

)

The sash position at which benchmark face velocity is measured is recorded with the face velocity measurement and reproduced each time measurements are taken.

(

)

Decreases in the average face velocity below 90% of the benchmark velocity are corrected prior to continued hood use.

(

)

) 3.3.3

Face velocity increases exceeding 20% of the benchmark are corrected. All hoods are equipped with a flow-measuring device or a face velocity alarm indicator or both.

90



(

(

)

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

(

)

The device is calibrated at least annually and whenever damaged.

) 3.3.4

( 4

)

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

Other Containment Devices

(

) 4.1.1

Gloveboxes are not used for manipulation of hazardous materials with the face or other panels open or removed.

(

) 4.1.2

Materials: Interior cracks, seams, and joints are eliminated or sealed.

(

) 4.1.3

Utility valves and switches are in conformance with applicable codes.

(

)

When control of utilities from inside the glovebox is required, additional valves and switches are provided outside the glovebox for emergency shutoff.

(

) 4.1.4

Proper application of ergonomic principles is met by referring to Chapter 5.10, “Guidelines for Gloveboxes,” AGS-G001-1998.

(

) 4.1.5

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

(

) 4.1.6

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

(

) 4.1.7

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

(

)

Air-cleaning equipment is 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 the air-cleaning device (ACD) is passive, provision is made for determining the status of the ACD, as noted in Section 9.3. If the ACD is active, instrumentation is provided to indicate its status.

(

)

The ACD is located to permit ready access for maintenance.

(

)

Provision is made for maintenance of the ACD without hazard to personnel or the environment and so not to contaminate the surrounding areas.

91



(

(

(

(

) 4.1.8

Exhaust piping is in accordance with the principles described in ACGIH Industrial Ventilation: A Manual of Recommended Practice, ANSI/AIHA Z9.2, and the ASHRAE 2001 Handbook – Fundamentals.

(

)

All piping within the occupied premises is under negative pressure when in operation.

(

)

Materials are resistant to corrosion by the agents to be used.

) 4.1.9

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

(

)

If audible alarms are not provided, documented training for users in determining safe pressure differentials is required.

(

)

Pressure monitoring devices are adjustable and subject to periodic calibration.

) 4.1.10

Before the access panel(s) of the glovebox are opened or removed, the interior contamination is reduced to a safe level.

(

)

If the contaminant is gaseous, the atmosphere in the box is adequately exchanged to remove the potentially hazardous gas.

(

)

If the contaminant is liquid, any liquid on surfaces is wiped with suitable adsorbent material or sponges until visibly clean and dry.

(

)

Used wipes are placed in a suitable container before being removed from the glovebox.

(

)

If the contaminant is a powder or dust, all internal surfaces are cleaned and wiped until visibly clean and the exterior surfaces of the gloves also are wiped clean.

(

)

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

(

)

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

) 4.1.11

A high containment glovebox conforms to all the mandatory requirements of 4.1.1 through 4.1.11, and

(

)

Is provided with one or more air-lock pass-through ports for inserting or removing objects or sealed containers without breaching the physical barrier between the inside and outside of the glovebox.

(

)

Maintains negative operating static pressure within the range of –0.5 to –1.5 in. wg (–125 to –374 Pa) such that contaminant escape due to “pinhole-type” leaks is minimized.

(

)

Maintains dilution of any flammable vapor-air mixtures to <10% of the applicable lower explosive limit.

92



(

)

Prevents transport of contaminants out of the glovebox.

(

) 4.1.12

A medium containment glovebox conforms to all the mandatory requirements of Sections 4.1.1 through 4.1.10, and is not provided with pass-through airlocks, and is provided with sufficient exhaust ventilation to maintain an inward air velocity of at least 100 fpm (0.51 m/s) through the open access ports, and creates a negative pressure of at least 0.1 in. wg (25 Pa) when access ports are closed.

(

) 4.1.13

Special case containment gloveboxes are tested for the intended use and found adequate for that purpose.

(

) 4.1.14

An isolation and containment glovebox is used to control special atmosphere work when either the controlled atmosphere and/or the contained agents are hazardous.

(

) 4.1.14.1 Design and construction, and materials conform to the requirements for high, medium, or special case containment gloveboxes as necessary. (

(

(

If the controlled atmosphere gas is hazardous, the airlocks are provided with a purge air exhaust system that, by manipulation of valves, creates a purge flow of room air sufficient to provide at least 5 air changes per minute, with good mixing, to the interior space of the airlock.

) 4.1.14.2 Operation of an isolation and containment glovebox conform to high, medium, or special case containment requirements as necessary and the airlock purge system is operated for sufficient time to dilute any hazardous gas in the airlock to safe concentrations before the outer door is opened. (

(

)

)

) 4.2

Care is exercised when placing certain hazardous liquids in an evacuated airlock or interior of a glovebox when a decrease in pressure could affect the boiling point of the liquid, causing it to go to gaseous state. Ductless hoods meet the general requirements of Sections 3.1 and 3.3 as applicable.

(

)

A Hazard Evaluation and Analysis is conducted as directed in ANSI/AIHA Z9.7 and Section 2.1.1 of this Standard.

(

)

Compliance with the general requirements of Sections 2, 3.3 and 5.3.6.2, are evaluated by qualified persons.

(

)

Ductless hoods that do not meet the requirements specified in Sections 9.3 and 9.4 are used only for operations that normally would be performed on an open bench without presenting an exposure hazard.

(

)

Ductless hoods have signage prominently posted on them to inform operators and maintenance personnel about the allowable chemicals used in the hood, type and limitations of filters in place, filter changeout schedule, and that the hood recirculates air to the room.

) 4.2.1

Ductless hoods utilizing air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates must meet the requirements of Section 9.3.1.

93



(

) 4.2.2

Ductless hoods utilizing adsorption or other filtration media for the collection or retention of gases and vapors are specified for a limited use.

(

) 4.2.3

Contaminated filters are unloaded from the air-cleaning system following safe work practices to avoid exposing personnel to hazardous conditions and to ensure proper containment of the filters for final disposal.

( ( 5 (

(

)

) 4.3

Airflow through the filter housing is shut down during filter change-out. Special laboratory chemical hoods are designed in accordance with ANSI/AIHA Z9.2 and ACGIH Industrial Ventilation: A Manual of Recommended Practice.

Laboratory Ventilation System Design ) 5.1.1

As a general rule, airflow is from areas of low hazard to higher hazard and exceptions are documented.

(

)

When flow from one area to another is critical to emission exposure control, airflow-monitoring devices are installed to signal or alarm a malfunction.

(

)

Air is allowed to flow from laboratory spaces to adjoining spaces only if:

(

)

There are no extremely dangerous and life-threatening materials used in the laboratory;

(

)

The concentrations of air contaminants generated by the maximum credible accident will be lower than the exposure limits required by 2.1.1.

(

)

The desired directional airflow between rooms is identified in the design and operating specifications.

) 5.1.1.1

Airlocks are utilized to prevent undesirable airflow from one area to another in high hazardous applications, or to minimize volume of supply air required by Section 5.1.1.

(

)

Airlocks are applied in such a way that one door provides access into or out of the laboratory room, and the other door of the airlock provides passage to or from a corridor (or other nonlaboratory area).

(

)

Airlock doors are arranged with interlocking controls so that one door must be fully closed before the other door may be opened.

(

) 5.1.1.2

If the direction of airflow between adjacent spaces is deemed critical, provision is made to locally indicate and annunciate inadequate airflow and improper airflow direction.

(

) 5.1.2

The following issues are evaluated in order to design for diversity:

( ( ( (

) ) ) )

Use patterns of hoods; Type, size, and operating times of facility; Quantity of hoods and researchers; Sash management (sash habits of users);

94



( ( ( ( ( ( ( ( ( (

) ) ) ) ) ) ) ) ) )

(

)

(

)

(

)

Requirements to maintain a minimum exhaust volume for each hood on the system; Type of ventilation system; Type of laboratory chemical hood controls; Minimum and maximum ventilation rates for each laboratory; Capacity of any existing equipment; Expansion considerations; Thermal loads; and Ability to perform periodic maintenance. The following conditions are met in order to design a system diversity: Acceptance of all hood-use restrictions by the user groups, which take into account the common work practices of the site users. A training plan is in place for all laboratory users to make them aware of any limitations imposed on their freedom to use the hoods at any time. An airflow alarm system is installed to warn users when the system is operating beyond capabilities allowed by diversity. Restrictions on future expansions or flexibility are identified.

(

) 5.1.3

Generation of excessive noise is avoided in laboratory ventilation systems. Fan location and noise treatment provide for SPL in conformance with local ambient noise criteria.

(

) 5.1.4

When the type and quantity of chemicals or compressed gases that are present in a laboratory room could pose a significant toxic or fire hazard, the room is equipped with provision(s) to initiate emergency notification and initiate the operation of the ventilation system in a mode consistent with accepted safety practices.

(

(

)

A hazard assessment is performed to identify the credible emergency conditions that may occur.

(

)

For rooms served by VAV ventilation systems, the chemical emergency mode of operation maximizes the room ventilation (air changes per hour) rate and, if appropriate, increases negative room pressurization.

(

)

For rooms served by CAV ventilation systems that utilize a reduced ventilation level for energy savings, the chemical emergency mode of operation ensures that the room ventilation and negative pressurization are at the maximum rate.

(

)

Operation of the room ventilation system in a chemical emergency mode does not reduce the room ventilation rate, room negative pressurization level, or hood exhaust airflow rate.

) 5.2.1

If laboratories are to be maintained with a negative pressurization and directional airflow from the corridor into the laboratory, supply air volume is less than the exhaust from the laboratory.

(

(

)

When laboratories are to be maintained with a positive pressurization and directional airflow, supply air volume is more than the exhaust from the laboratory.

) 5.2.2

Supply air distribution is designed to keep airjet velocities less than half, preferably onethird of the capture velocity or the face velocity of the laboratory chemical hoods at their face opening.

95



(

) 5.2.3

Supply systems meet the technical requirements of the laboratory work and the requirements of the latest version of ANSI/ASHRAE 62.

(

) 5.3.1.1

Laboratory exhaust system ductwork complies with the appropriate sections of Sheet Metal and Air-Conditioning Contractors National Association (SMACNA, 1995) Standards.

(

(

)

Systems and ductwork are designed to maintain negative pressure within all portions of the ductwork inside the building when the system is in operation.

(

)

Exhaust ductwork is designed in accordance with ANSI/AIHA Z9.2 and Chapter 34 of the ASHRAE 2001 Handbook – Fundamentals and Section 6-5 of NFPA 45.

(

)

Branch ducts enter a main duct so that the branch duct centerline is on a plane that includes the centerline of the main duct.

(

)

For horizontal main ducts, branch ducts do not enter a main duct on a plane below the horizontal traverse centerline of the main duct.

(

)

Horizontal runs of branch ducts are kept at a minimum.

(

)

Longitudinal sections of a duct are a continuous seamless tube or of a continuously welded formed sheet.

(

)

Longitudinal seams that are formed mechanically are utilized only for light duty systems with no condensation or accretion inside the duct.

(

)

Traverse joints are continuously welded or flanged with welded or Van Stone flanges.

(

)

If the duct is coated with a corrosion-resistant material, the coating extends from the inside of the duct to cover the entire face of the flange.

(

)

Flange faces are gasketed or beaded with material suitable for service.

(

)

If condensation within the duct is likely, all horizontal duct runs are sloped downward at least 1 in. per 10 ft in the direction of the airflow to a suitable drain or sump.

(

)

Exhaust airflow volume is sufficient to keep the temperature in the duct below 400°F (204°C) under all foreseeable circumstances.

) 5.3.1.2

Exhaust system materials are in accordance with Chapter 5 of ACGIH’s Industrial Ventilation: A Manual of Recommended Practice, Chapter 34 of the ASHRAE 2001 Handbook – Fundamentals, and Chapter 6-5 of NFPA 45.

(

)

Exhaust system materials are resistant to corrosion by the agents to which they are exposed.

(

)

Exhaust system materials are noncombustible if perchloric acid or similar oxidizing agents that pose a fire or explosive hazard are used.

96



(

(

(

) 5.3.2.2

(

)

Perchloric acid hoods are not manifolded with nonperchloric acid hoods unless a scrubber is installed between the hood and the manifold.

(

)

Where there is a potential contamination from hood operations as determined from the Hazard Evaluation and Analysis of Section 2.4, radioisotope hoods are not manifolded with nonradioisotope hoods unless in-line HEPA filtration and/or other necessary air- cleaning systems are provided between the hood and the manifold.

) 5.3.2.3

Exhaust streams that contain concentrations of flammable or explosive vapors at concentrations above the LEL as well as those that might form explosive compounds (i.e., perchloric acid hood exhaust) are not connected to a centralized exhaust system.

(

)

Exhaust streams comprised of radioactive materials are adequately filtered to ensure removal of radioactive material before being connected to a centralized exhaust system.

(

)

Biological exhaust hoods are adequately filtered to remove all hazardous biological substances prior to connection to a centralized exhaust system.

) 5.3.2.4

(

(

Laboratory chemical hood ducts combined into a common manifold adhere to the following exceptions and limitations:

)

) 5.3.2.5

Provision is made for continuous maintenance of adequate negative static pressure in all parts of the system, as necessary, or the hood is emptied and decontaminated and provisions are implemented to prevent the hood from back-drafting. The VAV hood is provided with an emergency switch that allows the hood exhaust volume to return to the maximum. Class II-Type A and Type B3 biological safety cabinets manifolded with chemical laboratory chemical hoods have either:

(

)

A thimble connection; or

(

)

A constant-volume control device and an interlock/alarm for these devices are installed between the cabinet outlet and the exhaust manifold.

(

)

Where Hazard Evaluation and Analysis determines that the installation calls for direct connection (hard-ducted) of the biological safety cabinet (e.g., Class II Type B) to an exhaust manifold system to allow work with toxic chemicals or radionuclides, interlocks and alarms are provided to prevent the biological safety cabinet from starting or to immediately warn the operator about an exhaust system failure.

(

) 5.3.2.6

The static pressure in the exhaust system is lower than the surrounding areas throughout the entire length, with the exception noted in Section 5.3.1.1.

(

) 5.3.2.7

Exhaust systems have the exhaust fan located outside the building unless:

(

)

The fans are in an adequately ventilated penthouse or room adjacent to the outside and the discharge ductwork passes directly from the fan to the outside without passing through another room or space. 97



(

)

There are no flexible connections on the discharge side of the fan and all ductwork in the discharge side of the fan is of welded and/or flanged and gasketed construction.

(

) 5.3.2.8

Laboratory hood exhaust systems are not classified as “Hazardous Exhaust Systems” as defined in BOCA, Uniform, or International Mechanical Codes.

(

) 5.3.2.9

Fire dampers are not installed in exhaust system manifolds.

(

) 5.3.2.10 Fire sprinklers are not installed in chemical hood exhaust manifolds.

(

) 5.3.2.11 Exhaust systems operate continuously to provide adequate ventilation for any hood at any time it is in use and to prevent backflow of air into the laboratory when the following conditions are present:

(

(

)

Chemicals are present in any hood (opened or unopened).

(

)

Exhaust system operation is required to maintain minimum ventilation rates and room pressure control.

(

)

There are powered devices connected to the manifold. Powered devices include, but are not limited to: biological safety cabinets, in-line scrubbers, and booster fans.

) 5.3.2.12 Manifolds are maintained under negative pressure at all times and are provided with at least two exhaust fans for redundant capacity. (

(

)

Emergency power is connected to one or more of the exhaust fans where exhaust system function must be maintained even under power outage situations.

) 5.3.3

Each fan applied to serve a centralized laboratory exhaust system or to exhaust an individual piece of laboratory equipment is adequately sized to provide the necessary amount of exhaust airflow in conjunction with the size, amount, and configuration of the connecting ductwork.

(

)

Each fan’s rotational speed and motor horsepower are sufficient to maintain both the required exhaust airflow and stack exit velocity.

(

)

If flammable gas, vapor, or combustible dust is present in concentrations above 20% of the Lower Flammable Limit, fan construction is as recommended by AMCA’s Classification for Spark Resistant Construction.

(

)

Laboratory exhaust fans are located as follows: ( ) Physically outside of the laboratory building and preferably on the highest level roof of the building served. ( ) In a roof penthouse or a roof mechanical equipment room that is always maintained at a negative static pressure with respect to the rest of the facility, and provides direct fan discharge into the exhaust stack(s).

98



(

)

All laboratory exhaust fans include provisions to allow periodic shutdown for inspection and maintenance. Such provisions include: ( ) Ready access to all fans, motors, belts, drives, isolation dampers, associated control equipment, and the connecting ductwork. ( ) Isolation dampers on the inlet side of all centralized exhaust system fans that have individual discharge arrangements or their own individual exhaust stacks. ( ) Isolation dampers on both the inlet and outlet sides of all centralized exhaust system fans that discharge into a common exhaust stack or plenum. ( ) Sufficient space to allow removal and replacement of a fan, its motor, and all other associated exhaust system components and equipment without affecting other mechanical equipment or the need to alter the building structure.

(

(

) 5.3.4

The discharge of potentially contaminated air to a concentration more than the allowable breathing air concentration is:

(

)

Direct to the atmosphere unless the air is treated to the degree necessary for recirculation (see Section 9.3);

(

)

In compliance with applicable federal, state, or local regulations with respect to air emissions;

(

)

Discharged in a manner and location to avoid reentry into the laboratory building or adjacent buildings at concentrations above 20% of allowable concentrations inside the laboratory for routine emissions or 100% of allowable concentrations for emerging emissions under wind conditions up to the 1%-wind speed for the site.

) 5.3.5

The exhaust stack discharge is in accordance with Chapter 43 of the ASHRAE 1999 Handbook – HVAC Applications.

(

)

The discharge is a minimum of 10 ft (3.0 m) above adjacent roof lines and air intakes and in a vertical-up direction.

(

)

A minimum discharge velocity of 3000 fpm (15.2 m/s) is used unless it has been demonstrated that a specific design meets the dilution criteria necessary to reduce the concentration of hazardous materials in the exhaust to safe levels (see Section 2.1) at all potential receptors.

(

)

Esthetic conditions concerning external appearance do not supersede the requirements of Sections 5.3.4 and 5.3.5.

(

)

Any architectural structure that protrudes to a height close to the stack top is evaluated for its effects on re-entrainment.

(

)

The air intake or exhaust grilles are not located within the architectural screen or mask unless this position is demonstrated to be acceptable.

99



(

) 5.3.6

Nonlaboratory air or air from building areas adjacent to the laboratory is used as part of the supply air to the laboratory only if its quality is adequate.

(

) 5.3.6.1

Air exhausted from the general laboratory space (as distinguished from exhaust hoods) is not recirculated to other areas unless one of the following sets of criteria is met:

1)

Criteria A • • •

2)

Criteria B • •

(

Recirculated air is treated to reduce contaminant concentrations to those specified in 2.1.1. Recirculated air is monitored continuously for contaminant concentrations or provided with a secondary backup air-cleaning device that also serves as a monitor (via a HEPA filter in a series with less efficient filter, for particulate contamination only). Refer to Section 9.3.1.

) 5.3.6.2 Exhaust air from laboratory hoods is not recirculated to other areas. (

6

There are no extremely dangerous of life-threatening materials used in the laboratory. The concentration of air contaminants generated by maximum credible accident will be lower than short-term exposure limits required by 2.1.1. The system serving the laboratory chemical hoods is provided with installed redundancy, emergency power, and other reliability features as necessary.

)

Hood exhaust air meeting the same criteria as noted in 5.3.6.1 is only recirculated to the same work area where the hood operators have control of the hood work practices and can monitor status of air cleaning.

Commissioning Tests

(

) 6.1

All test instrumentation utilized for the commissioning process is in good working order and has been factory calibrated within 1 year of the date of use. (See 8.6.1 Air Velocity, Air Pressure, Temperature and Humidity Instruments)

(

) 6.2

All newly installed, renovated, or moved hoods are commissioned to ensure proper operation prior to use by laboratory personnel.

(

) 6.2.1

The commissioning process is overseen by a responsible person or commissioning authority.

(

) 6.2.2

A written commissioning plan accompanies design documents and is approved by the commissioning authority in advance of construction activities.

(

)

The commissioning plan is available to all potential suppliers and contractors prior to bid along with the other project documents.

(

)

The commissioning plan addresses operation of the entire ventilation system where the hoods, laboratories, and associated exhaust and air supply ventilation systems are considered subsystems.

100



(

)

The plan includes written procedures to verify or validate proper operation of all system components and includes: ( ( (

(

) 6.2.3

) ) )

Laboratory Chemical Hood Specification and Performance Tests; Pre-occupancy Hood And Ventilation System Commissioning Tests; and Pre-occupancy Laboratory Commissioning Tests.

Preliminary and final commissioning documents are issued to the appropriate party(s) by the Commissioning Authority.

The documents include:

(

( ( ( ( (

) ) ) ) )

Design Flow Specifications; Laboratory and System Drawings for Final System Design; Copy of Test and Balance Report; Commissioning Test Data; and List of Ventilation System Deficiencies Uncovered and the details of how (and if) they were satisfactorily resolved.

(

)

Operational deficiencies and other problems uncovered by the commissioning process are communicated to the responsible party (i.e., installer, subcontractor, etc.) for prompt correction.

) 6.3

Specification and procurement of laboratory chemical hoods are based on performance tests conducted on the hood (or prototype hood) that demonstrate adequate hood containment.

( ( ( ( ( ( ( (

) ) ) ) ) ) ) )

The performance tests include: Exhaust Flow Measurements; Hood Static Pressure Measurement; Face Velocity Tests; Auxiliary Air Velocity Tests (if applicable); Cross-Drafts Velocity Tests; Airflow Visualization Tests; and Tracer Gas Containment Tests.

(

)

The tests are conducted under constant volume conditions where exhaust and air supply flow are stable and exhibit no more than 5% variation from set-point.

(

) 6.3.1

The volumetric flow exhausted from a laboratory chemical hood is determined by measuring the flow in the exhaust duct using industry-approved methods.

(

) 6.3.2

The hood static pressure is measured above the outlet collar of the hood at the flows required to achieve the design average face velocity.

(

) 6.3.3

The average face velocity is determined by the method described in the ANSI/ASHRAE 110, Method of Testing Performance of Laboratory Fume Hoods.

101



(

(

(

(

(

)

Face velocity measurements are made by dividing the hood opening into equal area grids with sides measuring no more than 12 in. ( 30.5 cm). The tip of the probe is positioned in the plane of the sash opening and fixed at the approximate center of each grid, and grid measurements around the perimeter of the hood opening are made at a distance of approximately 6 in. ( 15.24 cm) from the top, bottom, and sides of the opening enclosure.

(

)

The average face velocity is the average of the grid velocity measurements.

(

)

Each grid velocity is the average of at least 10 measurements made over at least 10 sec.

(

)

The plane of the sash is located at the midpoint of the sash frame depth.

) 6.3.4

For auxiliary air hoods, the face velocity is measured with the auxiliary air turned off unless room pressurization would change significantly to affect exhaust flow.

(

)

Where exhaust flow would be affected by turning off the auxiliary airflow, auxiliary air is redirected from the hood opening.

(

)

The velocity of the auxiliary air exiting the auxiliary air plenum is measured to determine the magnitude and distribution of air supplied above the hood opening.

(

)

The average auxiliary air velocity is determined from the average of grid velocities measured across the plenum outlet.

) 6.3.5

Cross-draft velocity measurements are made and recorded with the sashes open and the velocity probe positioned at several locations near the hood opening to detect potentially interfering room air currents (cross drafts).

(

)

Over a period of 10 – 30 sec., cross-draft velocities are recorded approximately at 1 reading per sec. using a thermal anemometer with an accuracy of +5% at 50 fpm (0.25 m/s).

(

)

The average and maximum cross-draft velocities at each location are recorded and are not sufficient to cause escape from the hood.

(

)

Cross-draft velocities are not of such magnitude and direction as to negatively affect containment.

) 6.3.6

Airflow visualization tests are conducted as described in ANSI/ASHRAE 110–1995, Method of Testing Performance of Laboratory Fume Hoods.

(

)

The tests consist of small-volume generation and large-volume generation smoke to identify areas of reverse flow, stagnation zones, vortex regions, escape, and clearance.

(

)

Visible escape beyond the plane of the sash when generated 6 in. (15.24 cm) into the hood constitute a failure during the performance test.

) 6.3.7

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

102



(

(

(

(

)

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

(

)

Escape at more than the control levels stated above is acceptable at the discretion of the design professional in agreement with the responsible person (2.4.2).

) 6.4

Routine performances tests are 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 is labeled as out of service or restricted use and corrective actions are taken to increase flow.

(

)

Each hood is 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 is posted with a restricted use or out of service notice.

(

)

The restricted use notice states the requisite precautions concerning the type of materials permitted or prohibited for use in the hood.

) 6.5.1

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

( ( ( (

) ) ) )

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

(

)

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

(

)

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

(

)

Hood performance tests consist of tests described in Sections 6.3.1 through 6.3.6.

(

)

The hood monitor is calibrated and adjusted after hood performance has been determined as satisfactory.

(

)

Safe operating points are clearly identified for the hood user.

) 6.5.2

( (

) )

In multiple hood CAV systems, commissioning of multiple hood, constant air volume systems 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 are recorded after final balancing is complete);

103



( ( (

) )

) 6.5.3

Hood Performance Tests as described above in Sections 6.3.1 through 6.3.6 ; and Hood and System Monitor Calibration. VAV hood systems are 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 include: ( ( ( (

) ) ) )

Verification of VAV Sensor Calibration; VAV Hood Performance Tests; VAV Laboratory and Ventilation System Tests; and Verification of System Diversity.

(

) 6.5.3.1

VAV sensors are capable of accurate measurement and control within 10% of actual at the design maximum and minimum flow conditions.

(

) 6.5.3.2

In addition to hood performance tests described for evaluation of CAV hood systems, commissioning tests on VAV hood systems include measurement of flow or face velocities at different sash configurations and VAV Response and Stability tests.

(

)

Flow or face velocity measurements are conducted at a minimum of two separate sash configurations.

(

)

VAV Response and Stability tests 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).

(

)

VAV Response is 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.

(

)

VAV Stability is sufficient to prevent flow variations in excess of 10% from design at each sash configuration or operating mode.

(

) 6.5.3.3

The VAV hood controls provide stable control of flow in the exhaust and supply ducts and variation of flow does not exceed 10% from design at each sash configuration or operating mode.

(

) 6.5.3.4

Systems diversity is verified prior to use of laboratory chemical hoods.

(

(

)

) 6.5.4 ( ( ( (

) ) ) )

The tests are designed to verify that users will be alerted when system capacity is exceeded and unsafe conditions may exist. Tests to verify and commission the laboratory 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.

104



(

(

(

)

) 6.5.4.1

All ventilation system alarm and monitoring provisions related to occupant safety are verified for proper functionality. CAV laboratory room tests 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.

(

)

If a specific room dP has been specified, the dP is measured to ensure that it is within its allowable range.

(

)

If a room differential airflow is specified, actual room differential airflow is 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 is enabled and applicable parameters (i.e., room supply, room total exhaust, etc.) are performed for each separate mode.

(

)

Room ambient conditions (temperature, humidity, air currents, etc.) are measured to ensure they are being maintained under the conditions specified.

) 6.5.4.2

VAV laboratory room tests ensure proper performance of theVAV ventilation system and its associated controls such that:

( ( (

) ) )

The room general exhaust provides the specified range of airflow; The room supply provides the specified range of airflow; and Room air cross currents at the laboratory hood face opening are within limits.

(

)

If a specified room dP has been specified, the dP is 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 is 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 are evaluated for each mode.

(

)

Room ambient conditions (temperature, humidity, air currents, etc.) are also measured to ensure they are being maintained under the conditions specified.

(

)

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

105



(

7 (

) 6.6

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

(

)

If flow measurement in the duct is not practical, velocity at the hood face or opening is 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 is taken.

Work Practices ) Hood users are trained in the proper operation and use of hood. (

)

The user establishes work practices that reduce emissions and employee exposures.

(

)

The user does 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.

(

)

The following work practices are followed when hazardous materials are used in the hood: ( ) The user does 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. ( ) Equipment and materials are not placed in the hood so that they block the slots or otherwise interfere with the smooth flow of air into the hood. (

)

All work is conducted at least 6 inches behind the plane of the sash (hood face).

(

)

The horizontal sash or panels are not removed.

(

)

The hood is not operated without the back baffles in place.

( ) Flammable liquids are not stored permanently in the hood or the cabinet under the hood unless that cabinet meets the requirements of NFPA 30 and NFPA 45 for flammable liquid storage. ( ) The sash or panels are closed to the maximum position possible while still allowing comfortable working conditions. (

)

Hood users are trained to close the sash or panels when the hood is not in use.

(

)

The hood user does not operate with the sashes opened beyond the design opening.

(

)

Pedestrian traffic is restricted near operating hoods.

(

)

Rapid movement within the hood is discouraged

(

)

The hood is not operated unless it is verified that it is working.

(

)

Rapid movement of the sash or panels is discouraged.

106



(

( 8

(

) 7.1 (

)

If the hood failed the performance test, it is taken out of service until repaired, or a restricted use notice is posted on the hood.

(

)

The notice states the partially closed sash position necessary for safe/normal operation and any other precaution concerning the type of work and materials permitted or prohibited.

) 7.2

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

Preventive Maintenance (

)

Inspection and maintenance follow a written I&M Program developed by the user.

(

)

Preventative maintenance is performed on a regularly scheduled basis.

) 8.1

( (

Each hood is posted with a notice giving the date of the last periodic field test.

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

) 8.2

(

Laboratory workers are notified in advance of inspection and maintenance operations. All toxic or otherwise dangerous materials on or in the vicinity of the subject equipment is removed or cleaned up before maintenance.

)

Any hazardous materials and any other debris are cleaned up before operations resume.

(

) 8.3

Maintenance personnel are trained and required to use appropriate PPE during work involving potential hazards.

(

) 8.4

A written work permit system is established whenever the integrity of a potentially contaminated ventilation system is to be breached.

(

)

Such work permits are designed to suit the circumstances, and at least address the following factors: ( ) The permit system is overseen by a Responsible Person, as defined in this standard, and is signed by the person(s) to do the work, their supervisor, and any other supervisors affected by the work; (

)

The nature of the work, and the health and safety precautions, are described;

(

)

The time and place of the work are described;

( ) The same persons who signed the permit (or their counterparts on a different shift) sign off when the work is complete; ( ) Completed work permits are filed by an appropriate management function and retained for a minimum of 3 years or as specified by individual organizational policy. 107



(

(

) 8.5

Records are maintained for all inspections and maintenance.

(

)

If testing involves quantitative values, the observed values are recorded.

(

)

Inspection forms designed for the several categories of testing are provided and include the normal values for the parameters tested.

) 8.6.1

Pressure instrumentation and measurement are in compliance with ANSI/ASHRAE 41.3(1989. Temperature instruments and measurement techniques are in compliance with ANSI/ASHRAE 41.1(1986(RA 01).

(

)

All instruments using electrical, electronic, or mechanical components are 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 meets the following requirements:

(

(

)

Velocity-fpm Below 100 fpm (0.51 m/s) 100 fpm (0.51 m/s) and higher

Accuracy 5 fpm (0.025 m/s) 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 and 125 Pa, interpolate linearly.

(

)

Pitot-static tube measurements are in accordance with ANSI/ASHRAE 41.7-1984 (RA 00).

(

)

Inclined manometers are selected so that the nominal value of the measured parameter is at least 5% of full scale. U-tube manometers should not be used for pressures less than 0.5 in. wg (125 Pa).

(

)

) 8.6.2

Pitot tubes other than standard are calibrated. Air contaminant monitors are tested at least monthly or more often, if experience or manufacturer¹s recommendation indicates.

(

)

Such testing includes the sensing element, zero drift, and actuation of signals, alarms, and controls.

(

)

Continuous air monitors are calibrated per manufacturer¹s specifications or more frequently if experience dictates.

(

) 8.6.3

Other instruments (such as voltmeters and tachometers) are checked for function and accuracy against a “known source” before use and follow manufacturer’s recommendation, when provided, for periodic calibration.

(

) 8.7.1

Fans, blowers, and drive mechanisms are visually inspected weekly.

108



(

) 8.7.2

V-belt drives are stopped and inspected monthly for belt tension and signs of belt wear or checking.

(

) 8.7.3

Blowers, drives, and other critical machine elements are lubricated at intervals and with lubricants recommended by the manufacturer.

(

) 8.8

Ventilation system management plan addresses the need to provide critical service issues and keep spare parts on hand.

(

) 8.9

All critical service instrumentation has contingency plans in place.

9 Air Cleaning (

) 9.2

Air-cleaning systems for laboratory exhaust systems, where required, are designed or specified by a Responsible Person to ensure that air-cleaning systems will meet the performance criteria necessary for regulatory compliance.

(

) 9.3

Air-cleaning systems for recirculating general exhaust or hood exhaust from laboratories meet the design and installation requirements of ANSI/AIHA Z9.7–1998.

(

(

(

)

Recirculation of process air is returned to the same room where the process is isolated and control of the process is supervised.

) 9.3.1

Air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates are filtered through a two-stage particulate filtration system specified as following the standard performance and design criteria of the ASHRAE systems and equipment to meet the objectives of 2.4.1.

(

)

Filter installations are tested for leaks and have all leaks repaired or the filter replaced before use.

(

)

The flowrate through the filters is maintained at design specifications and does not exceed 100% of the rated flow capacity of the filters.

) 9.3.2

Adsorption or other filtration media used for the collection or retention of gases and vapors are specified for a limited use.

(

)

Specific hazardous materials to be collected, airflow rate, temperature, and other relevant physical properties of the system are incorporated into the selection of filtration media.

(

)

A reliable and adequately sensitive monitoring system is utilized to indicate adsorbent breakthrough. The sensitivity of the monitoring system is a predetermined fraction of the TLV® or appropriate health standard of the contaminant being adsorbed but is not more than 25% of the TLV®.

(

)

The breakthrough time of the contaminant, before the effluent reaches no more then 50% of the TLV®, is sufficient, based upon system capacity design to allow a work operation shut down or parallel filter switch-over, thus proving a fresh filter.

109



(

(

)

For toxic gases and vapors, the filtration system is designed and sized to ensure adequate collection and retention for a worst case scenario when in the event of a spill or other major release.

(

)

Adequate warning is provided for personnel to stop work or enact other emergency procedures.

) 9.3.3

When required, contaminated filters are unloaded from the air-cleaning system following safe work practices to avoid exposing personnel to hazardous conditions and to ensure proper containment of the filters for final disposal.

(

)

Airflow through the filter housing is shut down during filter change-out.

(

) 9.4.1

Recirculation air filters are inspected and tested as per Section 9.3.1 except that provisions are mandatory.

(

) 9.4.2

Activated carbon beds or panels are tested as per Section. 9.3.2 at intervals no longer than 1 month initially and then, based on experience with the particular installation, a schedule is prepared.

(

) 9.4.3

Air pollution control equipment is inspected visually at intervals no longer than 1 week and, if necessary, at shorter intervals.

(

)

Specific tests and repairs are in accordance with the manufacturer’s recommendations or are in compliance with applicable regulations.

110



APPENDIX 5 Sample Table of Contents for Laboratory Ventilation Management Plan Foreword PART A - Standards and Procedures Section I - Characterizing Hazardous Procedures • • • • • •

Laboratory Chemical Hood Systems – General Review A Systems Approach to Safety Responsibilities Categorizing Laboratory Hazards and Procedures Effluent Characteristics Hazard Information Summary

Section II - Selection and Performance of Hoods • Laboratory Chemical Hoods – Minimum Specifications Section III - System Design and Operation • Laboratory Ventilation Systems – Minimum Specifications • Laboratory Design – Minimum Specifications • Laboratory Hood Systems – Selection, Design, and Renovations Section IV - Operational Tests and Maintenance • Laboratory Hood Systems – Installation and Commissioning • Recommended Performance Criteria • Test and Maintenance Management Section V - Proper Work Practices • Personnel Training Programs PART B - Laboratory Hood Systems – Description and Data Archive

111


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ANSI-AIHA Z9-5-2003

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