ANSI-AIHA Z9-5-2003

LaboratoryVentilation

ANSI/AIHA Z9.5–2003

A Publication byAmerican Industrial Hygiene Association

®

American National Standard

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American National Standard —Laboratory Ventilation

Secretariat

American Industrial Hygiene Association

Approved September 30, 2002

American National Standards Institute, Inc.


Published by

American Industrial Hygiene Association2700 Prosperity Avenue, Suite 250, Fairfax, Virginia 22031www.aiha.org

Copyright © 2003 by the American Industrial Hygiene AssociationAll rights reserved.

No part of this publication may be reproduced in anyform, 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

AmericanNationalStandard

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ContentsPage

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 oper-ation of laboratory ventilation systems used for control of exposure to airborne contaminants. It is intend-ed for use by employers, architects, industrial hygienists, safety engineers, Chemical Hygiene Officers,Environmental Health and Safety Professionals, ventilation system designers, facilities engineers, mainte-nance 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 ofgood practice.

HOW TO READ THIS STANDARD. The standard is presented in a two-column format. The left col-umn represents the requirements of the standard as expressed by the use of “shall.” The right col-umn provides description and explanation of the requirements and suggested good practices orexamples as expressed by the use of “should.” Appendices 1 and 2 provide supplementary infor-mation on definitions and references. Appendix 3 provides more detailed information on stackdesign. Appendix 4 provides a sample audit document and Appendix 5 presents a sample table ofcontents for a Laboratory Ventilation Management Plan.

Flexibility. Requirements should be considered minimum criteria and can be adapted to the needs of theUser establishment. It is the intent of the standard to allow and encourage innovation provided the mainobjective of the standard, “control of exposure to airborne contaminants,” is met. Demonstrably equal orbetter 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, Suite250, Fairfax, VA 22031, if you have questions, comments, or suggestions. As with all ANSI standards, thisis a “work in progress.” Future versions of the standard will incorporate suggestions and recommendationssubmitted by its Users and others.

This standard was processed and approved for submittal to ANSI by the Z9 Accredited StandardsCommittee on Health and Safety Standards for Ventilation Systems. Committee approval of the standarddoes not necessarily imply that all committee members voted for its approval. At the time it approved thisstandard the Z9 Committee had the following members:

J. Lindsay Cook, ChairLou DiBerardinis, Vice-chairMargaret Breida, Secretariat RepresentativeAt the time of publication, the Secretariat Representative was Jill Snyder.

Organization Represented . . . . . . . . . . . . . . . . . . . . . . . .Name of RepresentativeAlliance of American Insurers . . . . . . . . . . . . . . . . . . . . .F. K. CichonAmerican Conference of Governmental

Industrial Hygienists . . . . . . . . . . . . . . . . . . . . . . . . . . .R.T. HughesAmerican Foundrymen’s Society . . . . . . . . . . . . . . . . . . .R. ScholzAmerican Glovebox Society . . . . . . . . . . . . . . . . . . . . . . .S. CrooksAmerican Industrial Hygiene Association . . . . . . . . . . . .L. BlairAmerican Insurance Services Group . . . . . . . . . . . . . . . .M. T. JonesAmerican Society of Heating, Refrigerating,

and Air Conditioning Engineers . . . . . . . . . . . . . . . . . .H. F. BehlsAmerican Welding Society . . . . . . . . . . . . . . . . . . . . . . . .T. PumphreyChicago Transit Authority . . . . . . . . . . . . . . . . . . . . . . . . .E. L. MillerNational Spray Equipment

Manufacturers Association . . . . . . . . . . . . . . . . . . . . . .D. R. Scarborough

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US Department of Health and Human ServicesNational Institute for Occupational Safety and Health . .J. W. Sheehy

US Department of LaborOccupational Safety and Health Administration . . . . . .I. Wainless

US Department of the Navy . . . . . . . . . . . . . . . . . . . . . . .G. Kramer

Individual MembersG. M. AdamsD. J. BurtonJ. L. CookL. J. DiBerardinisS. J. GunselR. L. KarbowskiG. KnutsonM. LoanK. PaulsonJ. M. PriceJ. C. RockM. RollinsT. C. SmithL. K. Turner

Subcommittee Z9.5 on Laboratory Ventilation, which developed this standard, had the following members:Lou DiBerardinis, Chair D. Jeff BurtonDouglas Walters,* Associate Chair (American Chemical Society) Steve Crooks (American Glovebox Society)

Gregory DeLuga*Edgar Galson*Daniel Ghidoni*Todd Hardwick*Ron Hill*Dale Hitchings*Gerhard KnutsonVictor Neuman*John PriceGordon Sharp*Thomas SmithJ. Lindsay Cook (ex-officio)

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


ANSI/AIHA Z9.5–2003AMERICAN NATIONAL STANDARD

American National Standard for Laboratory Ventilation

1 Scope, Purpose, and Application

1.1 Scope

This standard sets forth the requirements for thedesign and operation of laboratory ventilation sys-tems. This standard does not apply to the followingtypes of laboratories or hoods except as it mayrelate 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 mini-mum requirements and best practices for laborato-ry ventilation systems to protect personnel fromoverexposure to harmful or potentially harmful air-borne contaminants generated within the laborato-ry. It does not apply to comfort or energy consider-ations unless they have an effect on contaminantcontrol ventilation.

This standard:

• Sets forth ventilation requirements that will,combined with appropriate work practices,achieve acceptable concentrations of air cont-aminants;

• Informs the designer of the requirements andconflicts among various criteria relative to lab-oratory ventilation;

• Informs the User of information needed bydesigners.

1.3 Application

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

activities. Such laboratories should satisfy severalgeneral objectives, in addition to being suited forthe intended use:

• They should be safe places to work;• They should be in compliance with environ-

mental, health, and safety regulations;• They should meet any necessary criteria for

the occupants and technology involved interms of control of temperature, humidity, andair quality; and

• They should be as energy efficient as is practi-cal while adhering to above objectives.

This standard addresses the ventilation require-ments to satisfy the first criterion: making the labo-ratory a safe place to work. When techniques anddesigns are available to reconcile conflictsbetween safety criteria and other, possibly conflict-ing demands, they are discussed. General labora-tory safety practices are not included except whenthey may relate to the ventilation system’s properfunction or effectiveness.

Traditional ventilation system designs typically donot meet all of the foregoing criteria, and mostimportantly they very often do not ensure ade-quate safety for the laboratory occupants.Persons responsible for laboratory operations andthose working within a laboratory are typically notvery knowledgeable about how ventilation sys-tems directly impact laboratory occupant healthand safety. Thus, they may not be aware of inade-quate ventilation or other ventilation system defi-ciencies. On the other hand, ventilation systemdesign professionals cannot be expected to befully aware of all the particular hazards posed byevery type of operation that may occur in a labo-ratory room. Furthermore, the specific work andoperations of some laboratory facilities may needto be kept more confidential and may even behighly secretive.

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REQUIREMENTS OF THE STANDARD

2 Laboratory Ventilation Management Program

2.1 General Requirements

Management shall establish a LaboratoryVentilation Management Plan to ensureproper selection, operation, use, and mainte-nance of laboratory ventilation equipment.

2.1.1 Laboratory Chemical Hoods

Adequate laboratory chemical hoods, spe-cial purpose hoods, or other engineeringcontrols shall be used when there is a possi-bility of employee overexposure to air conta-minants generated by a laboratory activity.

The containment and capture of a laboratoryhood shall be considered adequate if, incombination with prudent practice, laborato-ry worker chemical exposure levels aremaintained below applicable in-house expo-sure limits as recommended in 2.1.1. Whenthese containment sources are not ade-quate, the laboratory shall conduct a hazarddetermination to evaluate the situation.

CLARIFICATION AND EXPLANATION OF THE REQUIREMENTS

Management participation in the selection, design, andoperation of laboratory ventilation systems is importantto the overall success of the effort. The program shouldbe written and supported by top management. A sampleTable of Contents for a Laboratory VentilationManagement Plan is included in Appendix 5.

Management should understand that ventilation equip-ment is not furniture, but rather it is part of installed cap-ital equipment. It must be interfaced to the building ven-tilation system.

The performance of a laboratory chemical hood is ulti-mately determined by its ability to control chemical expo-sure to within applicable standards.

If exposure limits [e.g., Occupational Safety and HealthAdministration Permissible Exposure Limits (OSHAPELs), National Institute for Occupational Safety andHealth Recommended Exposure Limits (NIOSH RELs),American Conference of Governmental IndustrialHygienists threshold limit values (ACGIH TLVs®),American Industrial Hygiene Association WorkplaceEnvironmental Exposure Limits (AIHA WEELs), GermanMAKs, (maximum admissible concentrations)] or similarmeans of prescribing and/or assessing safe handling donot exist for chemicals used in the laboratory, theemployers should establish comparable in-house guide-lines. Qualified industrial hygienists and toxicologistsworking in conjunction may be best suited to accomplishthis need.

A Laboratory Design Professional must anticipate thattoxic and hazardous substances may be used at somepoint during the lifetime use of the facility.

“OSHA’s standards were designed to provide a baselineor minimum level of safety, one where worker exposurelevels are below the permissible exposure limits (PELs)accepted by government and private occupational health



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2.1.2 Volume Flowrates/RoomVentilation Rate

The specific room ventilation rate shall beestablished or agreed upon by the owner orhis/her designee.

2.1.3 General Ventilation

The general ventilation system shall bedesigned to replace exhausted air and pro-vide the temperature, humidity, and air qual-ity required for the laboratory procedureswithout creating drafts at laboratory chemicalhoods.

research agencies, including the National Institute ofOccupational Safety and Health (NIOSH). These expo-sure limits are listed in 29 CFR Subpart Z, Toxic andHazardous Substances. Unless the employer deter-mines, through periodic monitoring, that exposure levelsfor substances used in laboratory chemical hoods rou-tinely exceed the action levels (or, in the absence ofaction levels, the PELs), employees are not likely to beoverexposed.

Please be aware that the employer is responsible forensuring that laboratory chemical hoods are functioningproperly and implementing feasible control measures toreduce employee exposures if the exposures exceed thePELs. If an employer discovers, through routine monitor-ing and/or employee feedback, that laboratory chemicalhoods are not effectively reducing employee exposures, itis the employer’s responsibility to adjust controls orreplace hoods as necessary. OSHA does not promulgatespecific laboratory chemical hood testing protocols(Richard Fairfax, Director, Directorate of CompliancePrograms, OSHA, letter to R. Morris, 4 April 2001).

“Overexposure” to chemicals implies a means of beingable to define both an unsafe limit and the analyticalmeans of determining when such limits are exceeded,neither of which may be commonplace nor practical.“Hazard determination,” on the other hand, as defined by29 CFR 1910.1200, Hazard Communication Standard, isa regulation.

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

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 con-trol the buildup of fugitive emissions andodors in the laboratory.

2.2 Chemical Hygiene Plan

The laboratory shall develop a ChemicalHygiene Plan according to the OSHALaboratory Standard (29 CFR 1910.1450).

The plan shall address the laboratory opera-tions and procedures that might generate aircontamination in excess of the requirementsof Section 2.1.1. These operations shall beperformed inside a hood adequate to attaincompliance.

2.3 Responsible Person

In each operation using laboratory ventilationsystems, the user shall designate a “respon-sible person.”

Control of hazardous chemicals by dilution alone, in theabsence of adequate laboratory chemical hoods, seldomis effective in protecting laboratory users. Because theexhaust from that type of system must be discharged tothe outside or treated intensively before being used asreturn air, these systems usually are not economical forcontrolling exposure to hazardous materials comparedwith use of local exhaust hoods.

Although some laboratories do not fall under the OSHAStandard, the Chemical Hygiene Plan or a LaboratorySafety Manual is necessary to establish proper workpractices.

Persons participating in writing the plan should beknowledgeable in industrial hygiene, laboratory proce-dures and chemicals, the design of the ventilation sys-tems, and the system’s maintenance needs. The planshould be disseminated and become the basis ofemployee training.

The responsible person may have as duties:

• Ensuring that existing conditions and equipmentcomply with applicable standards and codes.Ensuring that testing and monitoring are done onschedule;

• 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 coordinatethese activities.



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2.4 The Role of Hazard Assessmentin Laboratory VentilationManagement Programs

2.4.1 General Requirements

Employers shall ensure the existence of anongoing system for assessing the potentialfor hazardous chemical exposure.

Employers shall promote awareness thatlaboratory hoods are not appropriate controldevices for all potential chemical releases inlaboratory work.

The practical limits of knowing how eachventilation control is being used in the labo-ratory shall be considered when specifyingdesign features and performance criteria(commissioning and routine monitoring). Theresponsible person as defined in Section 2.3shall be consulted in making this judgment.

Laboratory chemical hoods shall be func-tioning properly and specific measures shallbe taken to ensure proper and adequateperformance.

The employer shall establish criteria fordetermining and implementing control mea-sures to reduce employee exposure to haz-ardous chemicals; particular attention shallbe given to the selection of control measuresfor chemicals that are known to be extreme-ly hazardous.

Much of this standard addresses a generic approach toexposure control. This is necessary because many of thechemical hazards in a laboratory are chronic in natureand an employee’s ability to sense overexposure is sub-jective.

The employer may recommend (2.4.2) that providingstandard laboratory hoods tested to the ANSI/ASHRAE110 standard and an “as installed” AI 0.1 rating are bestfor the types of chemical hazards and work being per-formed at the specific workplace.The assumption that fol-lows is that users are trained to understand limitations ofthe hood’s control ability and would not use it for workthat, for example, should be performed in a glovebox.Alternatively, ensuring all hoods are capable of meetingan AU 0.1 rating may not be necessary, for example, if theonly chemical being handled has an 8-hr time-weightedaverage (TWA) – TLV® exposure limit of 250 ppm.

The following briefly describes an approach used withinlaboratory ventilation management programs in assign-ing control measures given the ability (or inability) toassess specific day-to-day chemical exposure situations.

Hazard assessments in general are geared toward iden-tifying chemicals, their release potential, and their possi-ble routes of entry into the body.

The first step in the assessment is to identify what chem-ical(s) can be released including normally uncharacter-ized byproducts. After characterizing the inherent hazardpotential (largely based on physical properties, toxicity,and routes of entry), the next step is to ascertain at leastqualitatively, the release “picture.” At what points withinthe “control zone” will chemicals be evolved and at whatrelease rate? Will the chemical release have velocity?How has the maximum credible accidental release beenaccounted for? Finally, how many employees are/couldbe exposed and what means are available for emergencyresponse?



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2.4.2 “Programming” and Control Objectivesfor New Construction, Renovation, orProgram Evaluation

The following items shall be considered and deci-sions made regarding each element’s relevance fol-lowing 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 commis-

sioning;• 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 Recordkeeping

Complete and permanent records shall be main-tained for each laboratory ventilation system.

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

Programming is a term commonly used in thecontext of a construction project whereby theneeds of a user group are developed chemistry,biology, etc.,” are generically understood bymost designers, knowledge of the chemistry andbiology and, therefore, potential hazards, aregenerally beyond the knowledge base of mostdesigners.The overall goal of providing a safe workspace forthe end users can be greatly enhanced by theuse of a hazard assessment and system designteam.

Quality of system design and quality of perfor-mance are enhanced by utilizing the most appro-priate skills and resources available to an organi-zation. The Laboratory Ventilation ManagementPlan should describe specific responsibilities foreach department involved in the design, installa-tion, operation, and use of ventilation systems(Table 1 provides some guidance).

Laboratories life cycle should be planned for30–50+ years. Laboratory chemical hood perfor-mance can impact life cycle sustainability. (SeeLeadership in Energy and Environmental Design(LEED), a rating system from the U.S. GreenBuilding Council.)

The primary design professional license holder(architect and/or engineer) with the laboratorystandard duty of care responsibilities cannot del-egate any of their liability to others. For example,the sealing license holders cannot delegateresponsibility or liability on to laboratory planner,industrial hygienist, and/or commissioning agenteven if licensed or certified.

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

Records should be maintained to establish a per-formance history of the system that can be usedto optimize operation. Records should be kept forat least the life of the system or until the systemis altered.



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Table 1 Major Responsibilities Recommended for Ensuring Effective Ventilation Systems

Group or Department Responsibility

Management

• 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

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

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

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 allo-

cation decisions

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

• System modifications; and• Equipment replacement or modifications.

3 Laboratory Chemical Hoods

3.1 Design and Construction

The design and construction of laboratory chemicalhoods shall conform to the applicable guidelinespresented in the latest edition of ACGIH IndustrialVentilation: A Manual of Recommended Practice,and the most current codes, guidelines, and stan-dards and any other applicable regulations andrecommendations (see Appendix 2).

It is the intent of the standard to establish designparameters and performance criteria and not tolimit new and innovative designs.



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3.1.1 Sashes

The laboratory chemical hood shall beequipped with a safety viewing sash at the faceopening.

Sashes shall not be removed when the hood isin use.

Although construction varies among models and man-ufacturers, the following are recognized as good designfeatures:

• Work surfaces should be recessed at least 3/8 in.(0.953 cm) below the front edge of the bench orsurface; sides and back should be provided with aseamless vertical lip at least 3/8 in. (0.953 cm) highto contain spills.

• Airfoils or other sidewall designs that reduce leak-age and airflow eddies at the front edge of the workarea should be provided at the front edge of thebench and on the front side posts external to thesash. Airfoils should not interfere with the hood’sability to meet the criteria of performance testingdefined in this standard.

• Utilities (e.g., valves and switches) should be locat-ed at readily accessible locations outside the hood.If additional utilities are required, other than electri-cal, they may be located inside the hood providedthey have outside cutoffs and can be connectedand operated without potentially subjecting thehood operator to exposure from materials in thehood or other unsafe conditions.

• Baffle design should provide for the capture ofmaterials generated within the hood and distributeflow through the opening to minimize potential forescape.

• The local fire authority will determine if the flam-mable liquid storage cabinet will be vented. This isacceptable as long as it does not compromisehood performance.

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 config-urations.



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Sash-limiting devices (stops) shall not beremoved if the design opening is less than fullopening.

3.1.1.1 Vertical Sashes

Vertical sashes shall be designed and operat-ed so as not to be opened more than thedesign opening when hazardous materials arebeing used within the hood.

Where the design sash opening area is lessthan the maximum sash opening area, thehood shall be equipped with a mechanicalsash stop and alarm to indicate openings inexcess of the design sash opening area.

3.1.1.2 Horizontal Sashes

Horizontal sashes shall be designed so as notto be opened more than the design openingwidth when hazardous materials are beinggenerated in the hood.

The design opening of the hood and the position of thesash-limiting device should be determined by theresponsible person based on the needs of the hooduser.

In combination sashes, the horizontal sash panel maybe guided in lower roller tracks and overhead guides.

Sashes should be constructed of transparent shatter-proof material suitable for the intended use. Sashmovement should require no more than 5 lbs. of forceto move through the full track of the sash and shouldremain stationery when force is removed.

The vertical raised sash provides for full-face openingin the open position. This would be the maximumdesign opening area used for airflow design and mea-surements.

Contact the safety officer if it is necessary to manuallyoverride the sash stops.

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

The horizontal sash should be designed to allow freemovement of the sash. Accumulation of debris or othermaterials in the sash track can impede movement. Thesash track can be designed to minimize this potentialby hanging the sash from overhead. In any event, peri-odic maintenance is recommended to ensure propersash management.

Contact the safety officer if it is necessary to manuallyoverride the sash stops.

Caution is advised when using a horizontal panel as ashield in front of the hood operator as high concentra-tions can accumulate behind the sash panel andescape along the Users’ arms protruding through theopening 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 anddisadvantages of both types of sashes. If acombination sash provides horizontally movingpanels mounted in a frame that moves verti-cally, the above requirements in Sections 3.1.1to 3.1.1.2 shall apply.

3.1.1.4 Automatic Sash Closers

The following factors shall be consideredbefore automatic sash closing devices areinstalled on a laboratory chemical hood:

• The adverse effect on energy consump-tion when the operators feel it is theirresponsibility to close the sash; and

• The adverse effect on energy consump-tion when the operators do not feel it istheir responsibility to close the sash.

The following conditions shall be met beforeusing automatic sash closing devices:

• All users must be aware of any limitationsimposed on their ability to use the hood.

• Automatic sash positioning systems shallhave obstruction sensing capable of stop-ping travel during sash closing operationswithout breaking glassware, etc.

• Automatic sash positioning shall allowmanual override of positioning with forcesof no more than 10 lbs (45 N) mechanicalboth when powered and during faultmodes during power failures.

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

The combination vertical raised and horizontal slidingsash, commonly referred to as a combination sash, isa combination of the vertical sash described in Section3.1.1.1 and horizontal sash in Section 3.1.1.2. Thecombination sash may be raised to full vertical sashopening. In the closed vertical position, the horizontalsliding panels can be opened to provide access to theinterior hood chamber. Care should be taken in deter-mining the design opening of a combination sash.Remember to include the area beneath the airfoil silland through the bypass if one exists.

As discussed in Section 7.1, good work practicesrequire closing the sash when the hood is not in use.

Automatic sash positioning systems have been devel-oped to close the hood sash when the operator is notpresent. The purpose is to save energy on VAV sys-tems without having to rely on users to close the sashwhen they leave. Having the sash closed is an addi-tional measure of safety since this condition will pro-vide additional containment in the event of a hazardousrelease.

The decision to use such a device should be based onthe ability to train users to close the sash when need-ed, the energy savings, and any adverse conse-quences.

If the user feels it is his/her responsibility to close thesash 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 automaticsash closer may be advantageous.



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Figure 1 — Diagrams of different sash opening configurations.



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3.2 Hood Types

3.2.1 Bypass Hood

Bypass hoods are laboratory hoods with eithervertical or horizontal moving sashes that shallmeet the requirements in Section 3.3.

The hood exhaust volume shall remain essen-tially unchanged (<5% change) when the sashis fully closed.

3.2.2 Conventional Hoods

Conventional hoods shall meet the require-ments in Section 3.3. The hood exhaust vol-ume shall remain unchanged with the sash infull open or in the design open position. As thesash is lowered, the face velocity will increase.In the fully closed position, airflow would bethrough the airfoil only.

3.2.3 Auxiliary Supplied Air Hoods

Auxiliary air hoods are laboratory hoods thatmeet the requirements in Section 3.3.

Bypass mechanisms should be designed so thebypass opens progressively and proportionally as thesash travels to the fully closed position. The face veloc-ity at the hood opening should not exceed three timesthe nominal face velocity with the sash fully open.Excessive velocities [>300 fpm (1.5 m/s)] can disruptequipment, materials, or operations in the hood possi-bly creating a hazardous condition. Baffles should bedesigned to minimize ejection of liquid or solid materi-als outside the hood in the event of eruption.

Auxiliary supplied air hoods are not recommendedunless special energy conditions or design circum-stances exist. The information in this section is provid-ed because many auxiliary air hoods are still used. Theintent is not to discourage innovative design but currentexperience indicates these requirements are neces-sary.

The rationale for using auxiliary supplied air hoods isthat auxiliary air need not be conditioned as much (i.e.,temperature, humidity) as room supply air, and thatenergy cost savings may offset the increased cost ofinstallation, operation, and maintenance. However, if allthe air from the auxiliary plenum is not captured at thehood face, the anticipated energy savings is not real-ized. With respect to temperature and humidity, work-ers may experience discomfort if it is necessary tospend appreciable time at the hood.



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In addition:

• The supply plenum shall be located exter-nally and above the top of the hood face;moreover, the auxiliary air shall bereleased outside the hood.

• The supply jet shall be distributed so asnot to affect containment.

• The auxiliary air shall not disrupt hoodcontainment or increase potential forescape.

If auxiliary air hoods are designed and operated prop-erly, worker protection at the face may be enhancedbecause the downward airflow at the breathing zonesuppresses body vortices. However, if the design andoperation are improper, contamination control may becompromised and the air quality and condition insidethe hood may be significantly different from the roomair and may compromise the work conducted inside thehood.

For retrofit projects, auxiliary air may be installed morecheaply with less disruption than by upgrading themain air supply system. If auxiliary air is conditioned tothe same extent as room air, most of the potentialadvantages are lost while the disadvantages remainand the total system becomes more expensive toinstall, 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 auxil-iary air is at least 20°F (–6.7°C) warmer or cooler thanroom air. This does not apply if the auxiliary air isdesigned to be conditioned the same as room air.

Hood face velocity is usually defined as air speed in adirection normal to the plane of the hood face opening.For auxiliary air hoods in standard operation, the direc-tional component of the air velocity is not normal to thehood face plane. Accurate determination of the flowdirection and derivation of the horizontal and verticalcomponents of the velocity vector require very sophis-ticated instrumentation because of the low air speedsinvolved. Hence, measuring the hood’s face velocitywith the auxiliary air shut off is an acceptable measureof hood exhaust volume, if turning off the auxiliary airdoes not upset the room air balance enough to signifi-cantly reduce the volume extracted by the hoodexhaust system.

NOTE: The 90% capture efficiency should be tested bymaterial balance by introducing a tracer gas into theauxiliary airsteam and sampling the hood exhaust.Flow volume and sampling should be in accordancewith EPA methods 1, 2, and 17 (40 CFR 60, AppendixA) or by other methods mutually agreed on by all par-ties. Tests should be conducted until three runs meet-ing these criteria are obtained.



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3.2.4 Perchloric Acid Laboratory ChemicalHoods

Perchloric acid hoods are laboratory hoods thatmeet the requirements in Sections 3.2.1 and 3.3and NFPA 45.

• In addition: All inside hood surfaces shall usematerials that will be stable and not react withperchloric acid to form corrosive, flammable,and/or explosive compounds or byproducts;

• All interior hood, duct, fan, and stack surfacesshall be equipped with water wash-downcapabilities;

• All ductwork shall be constructed of materialsthat will be stable to and not react with per-chloric acid and/or its byproducts and willhave smooth welded seams;

• No part of the system shall be manifolded orjoined to nonperchloric acid exhaust systems;

• No organic materials, including gaskets, shallbe used in the hood construction unless theyare known not to react with perchloric acidand/or its byproducts;

• Perchloric acid hoods shall be prominentlylabeled “Perchloric Acid Hood.”

3.2.5 Floor-Mounted Hoods (formerly calledWalk-In Hoods)

A floor-mounted hood is a laboratory hood thatshall meet the requirements in Sections 3.2.1 and3.3.

Perchloric acid is a strong oxidizer. It can producecorrosive, flammable, and/or explosive reactionproducts; hence, the name given to this type ofhood. Other chemicals, less widely known andused, may have similar properties. In all cases,these materials should only be used in a perchloricacid hood by experienced, trained personnel,knowledgeable and informed about the hazardsand properties of these substances, provided withappropriate protective equipment after suitableemergency contingency plans are in place. Theimmediate supervisor and institutional/corporateresponsible person (e.g., Safety Officer/ChemicalHygiene Officer) always should be notified beforethese substances are used.

The complications of wash-down features and cor-rosion resistance of the exhaust fan might be avoid-ed by using an air ejector, with the supplier blowerlocated so it is not exposed to perchloric acid.

Floor-mounted hoods are used when the verticalworking space of a bench hood is inadequate forthe work or apparatus to be contained in the hood.

The base of the hood should provide for the con-tainment of spills by means of a base contiguouswith the sidewalls, and a vertical lip at least 1 in.(2.54 cm) or equivalent. Often the lip can bereplaced by a ramp to allow wheeled carts to enterthe hood. The hood should be furnished with distri-bution ductwork or interior baffles to provide uni-form face velocity.

Doors and panels on the lower portion should becapable of being opened for the installation of appa-ratus.

If the lower doors are kept closed during operation,the hood and exhaust system design and operationmay be similar to a laboratory chemical hood and



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3.2.6 Variable Air Volume (VAV) Hoods

A variable air volume hood is a laboratoryhood that shall meet all mandatory require-ments of Sections 3.2.1 and 3.3 and isdesigned so the exhaust volume is varied inproportion to the opening of the hood face.

The supply and exhaust systems shall bebalanced. If the laboratory uses variable airvolume, the supply and exhaust shall mod-ulate together to maintain this balance. Inaddition, modification of the hood exhaustshall not compromise the total laboratoryexhaust. Any modification of the hoodexhaust shall not compromise other funda-mental concerns.

the effectiveness of the control should be equivalent if allthe provisions of Section 3.3 are implemented. However,in many floor-mounted hoods, the closed lower sash maycause significant turbulence and the hood may not performas well as a bench-top hood (Knutson, unpublished data).

If the lower panels are opened during operations, the hoodloses much of its effectiveness, even if face velocities com-ply with Section 3.3.

The design and task-specific applications of floor mounted(walk-in) hoods may make it difficult to comply with thework practices of Section 6 of this standard. Hence, con-sideration should be given to preparation and implementa-tion of written standard operating procedures (SOPs) foruse of floor-mounted hoods. For example, if manipulationsbelow waist height are necessary, special provisions maybe necessary such as armports or small openings strate-gically located at necessary access points.

Small rooms with one wall constituting a supply plenumand the opposite wall constituting an exhaust plenumshould not be called floor-mounted hoods. In suchinstances, workers are intended to be inside the hood andexposure control provisions are drastically different. Thisstandard does not apply to such rooms.

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

The variation in the exhaust volume can be achieved bychanging the speed of the exhaust blower or by operatinga damper or other control device in the exhaust duct.

Note that additional commissioning requirements will benecessary for these systems (see Section 6).

The balance can be achieved by maintaining a differentialpressure between the room and a reference point, forexample the corridor, typically accomplished by maintain-ing a fixed difference (offset) between the supply andexhaust volumes. Since modifications of the volumetricflow of a VAV hood could upset the balance, the supplyand exhaust systems should be designed to accommo-date the modification in the exhaust air. The laboratoryexhaust is based on three components:



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3.3 Hood Design (PerformanceSpecifications) Criteria

3.3.1 Face Velocity

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

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

• Replacement of the exhaust air;• Heat load considerations; andlower sash may

cause significant turbulence and the hood may notperform 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 ventila-tion within the laboratory.

It is recommended that VAV systems be equipped withemergency overrides that permit full design flow evenwhen the sash is closed.

According to the Scientific Equipment and FurnitureAssociation (SEFA), “ Face velocity shall be adequateto provide containment. Face velocity is not a measureof safety.” (SEFA 1-2002).

Face velocity has been used as the primary indicator oflaboratory hood performance for several decades.Recently, however, studies involving large populationsof laboratory chemical hoods tested using a contain-ment-based test like the ANSI/ASHRAE Standard 110,“Method of Testing the Performance of LaboratoryFume Hoods,” reveal that face velocity is actually aninadequate indicator of hood performance.

In one published study, approximately 17% of thehoods tested using the method had “acceptable” facevelocities in the range of 80-120 fpm, but “failed” thetracer gas containment test with control levels exceed-ing the ACGIH recommended control level of 0.1 ppm.(Smith and Crooks, 1996). Some of these tests were AIwhile others were AU.

See Section 6 on hood testing and commissioning foradditional information.

Example:LABORATORY CHEMICAL HOOD FACE VELOCITIESIN 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 VELOCITYIN 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 inthe range of 80(100 fpm (0.41(0.51m/s) will provideadequate face velocity for a majority of chemicalhoods.

Factors including the design of the hood, the laborato-ry layout, and cross-drafts created by supply air andtraffic all influence hood performance as much as ormore than the face velocity.

However, containment must be verified for all hoodsusing visual methods such as smoke (minimum) orquantitative methods such as tracer gas containmenttesting (recommended).

Most tracer gas containment test methods, includingthe ANSI/ASHRAE 110 “Method of TestingPerformance of Laboratory Fume Hoods” have certainlimitations that must be observed. The ANSI/ASHRAE110 method is a static test under controlled conditionsand at low face velocities [<60 fpm (0.30 m/s)] may notadequately reflect containment under dynamic (real-world) conditions as room and operator dynamics havesignificant effect on containment at these low facevelocities.

Hoods with excellent containment characteristics mayoperate adequately below 80 fpm (0.41 m/s) while oth-ers may require higher face velocities. It is, therefore,inappropriate to prescribe a range of acceptable facevelocities for all hoods.

Face velocity can be divided into ranges with differingcharacteristics as shown below:

Room and operator dynamics have significant effectson hood performance at low face velocities. Therefore,it is important to understand the effects of dynamicchallenges on hood performance so that standardoperating procedures and user restrictions can beestablished. Operating a hood below 60 fpm (0.30 m/s)is not recommended since containment cannot be reli-ably quantified at low velocities and significant risk ofexposure may be present.



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The mechanism that controls the exhaustfan speed or damper position to regulate thehood exhaust volume shall be designed toensure a minimum exhaust volume in con-stant volume systems equal to the larger of50 cfm/ft of hood width, or 25 cfm/ft2 of hoodwork surface area, except where a writtenhazard characterization indicates otherwise,or if the hood is not in use.

3.3.2 Periodic Face VelocityMeasurement

Once adequate performance (see 2.1.1)has been established for a particular hoodat a given benchmark face velocity using themethods described above, that benchmarkface velocity shall be used as a periodiccheck for continued performance as long asno substantive changes have occurred tothe hood.

60–80 fpm (0.30–0.41 m/s): Hoods with excellent con-tainment characteristics operating under relativelyideal environmental conditions (i.e., room designcharacteristics) and with prudent operating practicescan provide adequate containment in this velocityrange although at an increased level of risk.Containment must be verified quantitatively in thisrange and effective administrative controls should bein place and compliance must be enforced.

80–100 fpm (0.41–0.51 m/s): Most hoods can be operat-ed effectively with relatively low risk in this velocityrange although containment should still be quantita-tively verified. Proper operator training and enforce-ment of administrative controls are still highly recom-mended. This is the range recommended for amajority of laboratory chemical hoods.

100–120 fpm (0.51–0.61 m/s): This velocity range has sim-ilar characteristics as 80–100 fpm (0.41–0.51 m/s) butat significantly higher operating costs. Containmentmay be slightly enhanced in this range and hoods thatdo not contain adequately in the 80–100 fpm(0.41–0.51 m/s) range may be improved by operatingin this range.

120–150 fpm (0.61–0.76 m/s): Although most hoods canoperate effectively in this range, performance is notsignificantly better than at the lower ranges of80–100 fpm (0.41–0.51 m/s) and 100–120 fpm(0.51–0.61 m/s) and the operating cost penaltyimposed by high face velocities in this rage is severeand is not recommended for this reason.

>150 fpm (>0.76 m/s): Most laboratory experts agree thatvelocities above 150 fpm (0.76 m/s) at the designsash position are excessive at operating sash heightand may cause turbulent flow creating more potentialfor leakage.

Substantive changes include: changes in hood setup;hood face velocity control type, setpoint, range, andresponse time; exhaust system static pressure, controlrange and response time; the hood operating environ-ment including lab/furniture geometry, supply air distribu-tion patterns, and volume; and room pressure controlrange and response time.



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Face velocity measurements shall be madewith the sash in the Design Sash Position. TheDesign Sash Position is the maximum openingor configuration allowed by user standards,SOPs, or the Chemical Hygiene Plan,whichever is applicable, and used in thedesign of the exhaust system to which thehood is connected. The sash position at whichbenchmark face velocity is measured shall berecorded with the face velocity measurementand reproduced each time measurements aretaken.

A decrease in the average face velocity below90% of the benchmark velocity shall be cor-rected prior to continued hood use.

Face velocity increases exceeding 20% of thebenchmark shall be corrected prior to contin-ued use.

The face velocity of a combination sash is sometimesdetermined with the sash closed and the horizontalwindows open. For “set-up” conditions, the determina-tion of the actual face velocity may not be unique. Theface velocity of combination sash hoods should identi-fy the sash position where the tests were conducted.

It is important to use the same sash position for suc-cessive periodic performance measurements.

If because of environmental challenges, face velocitycannot be accurately measured then air flow measure-ment can replace face velocity (6.5).

This magnitude of decrease may impair performance.

An increase in individual hood average face velocitynot exceeding 20% of the benchmark face velocity willprobably not significantly alter hood performance andis acceptable with no corrective action. It should benoted, however, that there is an unnecessary increasein operating cost with increased face velocities.Increases exceeding 20% and the accompanyingincrease in supply flowrates may degrade performancedue to increased impingement and cross-draft veloci-ties.

In constant volume systems, the face velocity willincrease with reduced sash height. Although the facevelocity could be three times or more than the designface velocity, the hood performance does not usuallydeteriorate because the hood opening is reduced(which often improves performance) and the loweredsash acts as a partial barrier.

Supply and exhaust system capacities should beobserved in the event of hood face velocity increasesas volume shifting may occur, depriving other hoods ofadequate airflow.

Periodic dynamic testing should be performed whensignificant changes have occurred or to evaluate theresponse of a VAV system.



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3.3.3 Flow-Measuring Device forLaboratory Chemical Hoods

All hoods shall be equipped with a flow indica-tor, flow alarm, or face velocity alarm indicatorto alert users to improper exhaust flow.

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

The device shall be calibrated at least annual-ly and whenever damaged.

3.3.4 Hood Location

Laboratory chemical hoods shall be located sotheir performance is not adversely affected bycross drafts. Windows in laboratories withhoods shall be fully closed while hoods are inuse (emergency conditions excepted).

The purpose of the flow-measuring device is to providethe hood user with continuous information about thehood’s airflow. One method is to measure the total vol-ume flow through the hood. Another method is to mea-sure the face velocity.

One popular method for measuring total volume flow isthe Hood Static Pressure measuring device (seeACGIH’s Industrial Ventilation: A Manual ofRecommended Practices), which can be related toflow. This method measures static suction in theexhaust duct close to the hood throat and, if there areno adjustable dampers between the hood and themeasuring station, is related to the flow volume. Othermethods include various exhaust volume or flow veloc-ity sensors.

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

The location of laboratory chemical hoods and otherhoods or vented openings with respect to open win-dows, doorways, and personnel traffic flow directlyinfluences the containment ability. Cross currents,drafts, and spurious air currents from these sourcesmay decrease a hood’s containment ability (Kolesnikov,2002a; Kolesnikov, 2002b; Memarzadeh, 1996).

Users should be aware that cross drafts may disturbcapture efficiency even when the sash is partiallyclosed.



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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 ofhazardous materials with the face or other panelsopen or removed.

If the potential combinations of material proper-ties with planned manipulations are so complexthe hazard cannot be estimated, a glovebox mayor may not be suitable. A hazard evaluation shallbe employed in such complex cases.

Gloveboxes shall be used when the properties ofthe hazardous materials, the planned manipula-tions, or a credible accident would generate haz-ardous personal exposures if the work were donein an ordinary laboratory hood.

4.1.1.1 Location

There are no special requirements for locationbeyond those already noted for hoods.

4.1.2 Design, Construction, and/or Selection Materials

Interior cracks, seams, and joints shall be elimi-nated or sealed.

4.1.3 Utilities

Utility valves and switches shall be in confor-mance with applicable codes. When control of util-ities from inside the glovebox is required, addi-tional valves and switches shall be provided out-side the glovebox for emergency shutoff.

Laboratory-scale gloveboxes, for which this stan-dard applies, should have a maximum internalchamber volume of 50 ft3 (1.4 m3) (single-sidedaccess) or 100 ft3 (2.8 m3) (double-sided access)respectively (pass-through chambers excluded).Larger gloveboxes may occasionally be found inlaboratory settings but are beyond the scope of thisstandard.

Gloveboxes may be used for any laboratory manip-ulations that can be conducted under the restraintsimposed by working with gloves through armholes.

Gloveboxes may be used when the manipulatedsubstances must be handled in a controlled (e.g.,inert) atmosphere or when they must be protectedfrom the external environment.

Since manipulations through glove ports are some-what difficult, however, it is advisable to avoid hightraffic areas.

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

Certain applications require that all valves be locat-ed inside of the glovebox containment and all linesexterior to the box be 100% welded.



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4.1.4 Ergonomic Design

Ergonomics shall be a significant considerationin the design, construction, and/or selection ofgloveboxes. Frequency of use shall dictate theextent to which ergonomic principles will beapplied. Proper application of ergonomic princi-ples 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 forretaining spilled liquids so the maximum volumeof liquid permitted in the glovebox will be retained.

4.1.6 Exhaust Ventilation

Containment gloveboxes shall be provided withexhaust ventilation to result in a negative pres-sure inside the box that is capable of containingthe hazard at acceptable levels.

4.1.7 Exhaust Air Cleaning

The air or gas exhausted from the glovebox shallbe cleaned and discharged to the atmosphere inaccordance with the general provisions of thisstandard and pertinent environmental regulations.

Air-cleaning equipment shall be sized for themaximum airflow anticipated when hazardousagents are exposed in the glovebox and theglovebox openings are open to the extent per-mitted under that condition.

If the air-cleaning device (ACD) is passive (i.e., aHEPA filter or activated carbon) provision shallbe 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), instrumentationshall be provided to indicate its status.

The ACD shall be located to permit ready accessfor maintenance. Provision shall be made formaintenance of the ACD without hazard to per-sonnel or the environment and so as not to con-taminate the surrounding areas.

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

A system for draining the spilled liquid into a suitablesealed container should be provided if the propertiesof the spilled liquid or other circumstances preventcleanup by working through the gloves.

See Sections 4.1.11 through 4.1.14 for ventilation rec-ommendations for specific glovebox types.

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

If an ACD is required, its operating efficiency shouldbe relatively independent of airflow. A HEPA filter’s col-lection efficiency is relatively unaffected by changes inairflow rate, whereas the efficiency of a submergedorifice wet scrubber may drop substantially if airflowrate is increased or decreased. Where the airflow to asystem like a submerged scrubber is decreased, addi-tional air may be admitted to the system upstream ofthe ACD to maintain the rated volume flow at the ACD.On the other hand, if the airflow through the gloveboxscrubber system increases to a point where the col-lection of the ACD is substantially impacted, then theairflow must either be reduced or the ACD redesigned,modified, or replaced to accommodate the higherflowrate velocity for particulate material.

The ACD should be located as close as is practical tothe glovebox to minimize the length of contaminatedpiping or the need for maintaining high transportvelocity.



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4.1.8 Exhaust Ducting

Exhaust piping shall be in accordance with theprinciples described in the ACGIH IndustrialVentilation Manual, ANSI Z9.2, and theASHRAE 2001 Handbook – Fundamentals. Allpiping within the occupied premises shall beunder negative pressure when in operation.

Materials shall be resistant to corrosion by theagents to be used.

4.1.9 Monitoring and Alarms

A glovebox pressure monitoring device with ameans to locally indicate adequate pressurerelationships to the user shall be provided onall gloveboxes.

If audible alarms are not provided, document-ed training for users in determining safe pres-sure differentials shall be required.

Pressure monitoring devices shall beadjustable (i.e., able to be calibrated if not aprimary standard) and subject to periodic cali-bration.

4.1.10 Decontamination

Before the access panel(s) of the glovebox areopened or removed, the interior contaminationshall have been reduced to a safe level.

If the contaminant is gaseous, the atmospherein the box shall be adequately exchanged toremove the potentially hazardous gas. Thiscan be affected by exhausting the box throughits ventilation system, and where necessaryproviding an air inlet that is filtered if required.

If the contaminant is liquid, any liquid on sur-faces shall be wiped with suitable adsorbentmaterial or sponges until visibly clean and dry.Used wipes shall be placed in a suitable con-tainer before being removed from the glove-box.

Ergonomics principles indicate that the total numberand types of alarms should be minimized.

Alarms should also be clearly distinguished from eachother.

Safe level is relative to the contaminant involved.Analytical techniques for determining surface contami-nation (mass/unit area, counts per minute/unit area)are helping to provide increasingly sensitive but notalways specific risk information. Correlating surfacecontamination with exposure potential remains more ofan art than a science.

Many liquids and some solids have vapor pressuresthat might cause hazardous concentrations of vapor. Acombination of the contamination reduction proceduresdiscussed above might be necessary.



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If the contaminant is a powder or dust, all internalsurfaces shall be cleaned and wiped until visiblyclean. The exterior surfaces of the gloves also shallbe wiped clean.

Precautions to prevent hazards to personnel andcontamination of the premises shall be made if theducting is to be opened or dismantled.

If there is any uncertainty about the effectivenessof contamination reduction procedures, personnelinvolved in opening the panels of the gloveboxshall be provided with appropriate PPE or clothing.

4.1.11 High Containment Glovebox

A high containment glovebox shall conform to allthe mandatory requirements of Sections 4.1.1through 4.1.11, and

• Shall be provided with one or more airlockpass-through ports for inserting or removingobjects or sealed containers without breachingthe physical barrier between the inside andoutside of the glovebox;

• Shall maintain negative operating static pres-sure within the range of –0.5 to –1.5 in.wg (–125 Pa to –374 Pa) such that contaminantescape due to “pinhole-type” leaks is minimized.

• Shall maintain dilution of any flammable vapor-air mixtures to <10% of the applicable lowerexplosive limit.

• Shall prevent transport of contaminants out ofthe glovebox.

4.1.12 Medium Containment Glovebox

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

Certain direct-reading instruments (e.g., combustiblegas indicators) may lend themselves to such anassessment.

Neutralizing reagents should be used, if available.

The exhaust piping from the glovebox to the ACD maybe contaminated, especially if a hazardous particulateis involved.

Nonessential personnel should be excluded from thearea. The contamination in the general work areashould be reduced before use.

For more information see EPA 402-R-97-016, Multi-Agency Radiation Survey and Site Investigation Manual.

Examples include gloveboxes used for controllingexposures to acutely hazardous and highly volatilematerials where any exposure may be harmful.

Care should be exercised when placing certain haz-ardous liquids in an evacuated airlock or interior of aglovebox when a decrease in pressure could affect theboiling point of the liquid causing it to go to a gaseousstate.

Meeting the above requirements will depend onwhether the glovebox is continuous flow or is sealed.The minimum exhaust flow rate is usually based on aglove being breached or an access door being inten-tionally opened. The air velocity into the open glove-port or door should be 125 ± 25 linear fpm (0.635 ±0.13 m/s).

Examples include gloveboxes designed to preventoverexposure to acutely hazardous materials that arenot highly volatile and/or where allowable exposurelevels have been established and personnel exposurecan be verified to be below the established allowablelevels.



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4.1.13 Special Case Containment Glovebox

A special case containment glovebox shall bedesigned for special situations, does not neces-sarily conform to the provisions of this standard,but has been tested for the intended use andfound adequate for that purpose.

4.1.14 Controlled Atmosphere ContainmentGlovebox

An isolation and containment glovebox shall be acontrolled atmosphere containment gloveboxrequired for special atmosphere work when eitherthe controlled atmosphere and/or the containedagents are hazardous.

4.1.14.1 Design and Construction

Design and construction, and materials shall con-form to the requirements for high, medium, or spe-cial case containment gloveboxes as necessary.

If the controlled atmosphere gas is hazardous, theairlocks shall be provided with a purge air exhaustsystem that, by manipulation of valves, creates apurge flow of room air sufficient to provide at least5 air changes per minute, with good mixing, to theinterior space of the airlock.

4.1.14.2 Operation

Operation of an isolation and containment glove-box shall conform to high, medium, or specialcase containment requirements as necessary,and the airlock purge system shall be operated forsufficient time to dilute any hazardous gas in theairlock to safe concentrations before the outerdoor is opened.

Care shall be exercised when placing certain haz-ardous liquids in an evacuated airlock or interior ofa glovebox when a decrease in pressure couldaffect the boiling point of the liquid, causing it togo to gaseous state.

Examples include applications where an inertatmosphere is necessary to protect the work orwhen it provides an added measure of safety.

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

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



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4.2 Ductless Hoods

Ductless hoods shall meet the generalrequirements of Sections 3.1 and 3.3 asapplicable.

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

Compliance with the general requirements ofSections 2, 3.3, and 5.3.6.2 shall be evaluat-ed by qualified persons.

Ductless hoods that do not meet the require-ments specified in Sections 9.3 and 9.4 shallbe used only for operations that normallywould be performed on an open bench with-out presenting an exposure hazard.

Ductless hoods shall have signage prominent-ly posted on the ductless hood to inform oper-ators and maintenance personnel on theallowable chemicals used in the hood, typeand limitations of filters in place, filter change-out schedule, and that the hood recirculatesair to the room.

Ductless hoods have limited application because of thewide variety of chemicals used in most laboratories. Thecontainment collection efficiency and retention for theair-cleaning system used in the ductless hood must beevaluated for each hazardous chemical.

As referenced in ANSI/AIHA Z9.7, the hazard evaluationand analysis serve to ensure proper air quality, effectiveoccupant protection, and satisfactory system perfor-mance.

Air-cleaning performance monitoring is typically limitedfor many hazardous materials. Chemical-specific detec-tors located downstream of adsorption media or pres-sure drop indicators for particulate filters are necessaryfor systems recirculating treated air from the ductlesshood back into the laboratory.

Ductless hoods may be appropriate if the contaminant isparticulate and provision is made for changing filterswithout excessive contamination of the laboratory orpotential exposure to personnel changing the filters. SeeSections 9.3 and 9.4.

Adsorption media such as activated charcoal are not effi-cient for fine particles and are predominately used foradsorbing gases or vapors. Many gases and vapors oflow molecular weight will be stripped from the adsorptionmedia and reenter the room air on continued flow ofclean air through the ductless hood. When this happens,the ductless hood only serves to protect the worker atthe hood face and to spread the contaminant release intothe room air during a longer time span and at a lowerconcentration.

Where multiple air contaminants may challenge the duct-less hood air-cleaning system, the collection efficiencyand breakthrough properties of such mixtures are com-plicated and are dependent on the nature of the specificmixture. Enhanced breakthrough of components shouldbe especially considered as a part of the HazardEvaluation and Analysis.

Also the warning properties (i.e. odor, taste) of the chemi-cal being filtered must be adequate to provide an early indi-cation that the filtration media are not operating properly.



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4.2.1 Airborne Particulates

Ductless hoods that utilize air-cleaning filtrationsystems for recirculating exhaust air contaminat-ed with toxic particulates shall meet the require-ments of Section 9.3.1.

4.2.2 Gases and Vapors

Ductless hoods utilizing adsorption or other filtra-tion media for the collection or retention of gasesand vapors shall be specified for a limited use andshall meet the requirements of Section 9.3.2.

4.2.3 Handling Contaminated Filters

Contaminated filters shall be unloaded from the air-cleaning system following safe work practices toavoid exposing personnel to hazardous conditionsand to ensure proper containment of the filters forfinal disposal. Airflow through the filter housingshall be shut down during filter change-out.

4.3 Special Purpose Hoods

Special laboratory chemical hoods shall bedesigned in accordance with ANSI/AIHA Z9.2 andACGIH’s Industrial Ventilation: A Manual ofRecommended Practice.

5 Laboratory Ventilation System Design

5.1 Laboratory Design

5.1.1 Differential Pressure and AirflowBetween Rooms

As a general rule, airflow shall be from areas of lowhazard to higher hazard unless the laboratory isused as a Clean Room (such as Class 10,000 orbetter), or an isolation or sterile laboratory, or otherspecial-type laboratories. When flow from one areato another is critical to emission exposure control,airflow monitoring devices shall be installed to sig-nal or alarm that there is a malfunction.

Special purpose hoods are defined as any not con-forming to the specific types described in this stan-dard. Special hoods may be used for operations forwhich other types are not suitable (e.g., enclosuresfor analytical balances, for histology processingmachines, gas vents from atomic absorption, or gaschromatography equipment). Other applicationsmight present opportunities to achieve contaminationcontrol with less bench space or less exhaust volume(such as special mixing stations, sinks, evaporatingracks, heat sources, or ventilated work tables).

The intent of this section is to require the reader tocarefully consider the critical need to maintain direc-tional airflow between spaces and to understandhow best to accomplish the desired outcome.Although it is true a difference in pressure is the dri-ving force that causes air to flow through any open-ings from one room to another, specifying quantita-tive pressure differential is a poor basis for design.



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Air shall be allowed to flow from laboratoryspaces to adjoining spaces only if

• There are no extremely dangerous andlife-threatening materials used in the labo-ratory;

• The concentrations of air contaminantsgenerated by the maximum credible acci-dent will be lower than the exposure limitsrequired by 2.1.1.

The desired directional airflow between roomsshall be identified in the design and operatingspecifications.

The desired directional airflow between roomsshall be identified in the design and operatingspecifications.

What really is desired is anoffset air volume (as definedbelow). Attempts to design using direct pressure differ-ential measurement and control vs. controlling the off-set volume may result in either short or extended peri-ods of the loss of pressure when the doors are open orexcessive pressure differentials when the doors areclosed, sufficient to affect the performance of low pres-sure fans. (See information below on the need fordirectional airflow.)

When the differential pressure design basis is used,the relative volumes of supply and exhaust air to eachroom should be set so that air flows through any open-ing, including open doorways, at a minimum velocity of50 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 condi-tions, the airflow through the door would be from 1050to 2100 cfm (496 to 991 L/s) and the differential pres-sure will be about 0.0001 to 0.0006 in.wg (0.025 to0.15 Pa). If a differential pressure of only 0.01 in. wg(2.5Pa) was specified and actually maintained, whenthe door was open it would generate an air velocity andairflow through the door of 400 fpm (2.0 m/s) and 8400cfm (3964 L/s) respectively. These latter values wouldbe impractical in operation.

Double door airlocks do not have the same difficultiesas opening a normal door and do not require the 1050cfm to 2100 cfm (496 to 991 L/s) mentioned above aslong as only one door is opened at one time. Withoutan airlock, the actual opening of a door into a corridorwill usually draw contaminants with it because of thespeed of the door’s movement despite the effects of thenegative pressurization. So, it is important to keep dooropenings to a minimum as well as the amount of timethat the laboratory doors are kept open.

The need to maintain directional airflow at everyinstance and the magnitude or airflow needed willdepend on individual circumstances. For example,“clean rooms” (designed primarily to protect the prod-uct not the worker) may have very strict requirementsfor directional airflow and pressure control to limit themovement of contaminants into the clean room.Pharmaceutical laboratories governed by the Food andDrug Administration (FDA) current Good LaboratoryPractices (cGLP) are other examples of stricter controlrequirements.



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Some people recommend a 10% “offset” in ventilationrate with lab exhaust being 10% greater than the labsupply air as a means of maintaining negative pressur-ization in the laboratory and keeping air flowing fromthe corridor into the laboratory. For example a labora-tory 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 offsetis merely a rule of thumb and may not be adequate tomaintain directional airflow and pressurization, espe-cially when the laboratory door is open.

The amount of offset should be based on two consid-erations:

• The airflow required to keep the laboratory roomnegative with regard to surrounding air spaces.The10% offset may be appropriate in some cases buthas no general validity.

• The “stringency” of the requirements for directionof airflow. Is the requirement really “stringent” as in“we really mean it!” or “most of the time,” or “exceptwhen the door is open?”

If the requirement is stringent, two seldom consideredfactors become important. First, if there is any appre-ciable temperature difference between the laboratoryand adjoining space, when a door is opened there willbe a thermal exchange or warmer air at the top of thedoorway and cooler air flowing in the opposite directionnear the floor. An airflow velocity of at least 50 fpm(0.25 m/s) is needed to inhibit this exchange as calcu-lated in the note above.

Second, the air volume needed to control airflowthrough a door in this way is independent of the size ofthe room or its need for supply or exhaust air and isonly related to the number and square footage of doorsinto the laboratory.

Consequently, if the requirement is stringent, an airlockdoor is the only current available solution. In theabsence of an airlock, an arbitrary 10% offset of thelaboratory ventilation rate is not the proper basis fordesign.



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5.1.1.1 Airlocks

Airlocks shall be utilized to prevent undesirableairflow from one area to another in high haz-ardous applications, or to minimize volume ofsupply air required by Section 5.1.1.

An airlock shall consist of a vestibule or smallenclosed area that is immediately adjacent tothe laboratory room and having a door at eachend for passage. Airlocks shall be applied insuch a way that one door provides access intoor out of the laboratory room, and the otherdoor of the airlock provides passage to or froma corridor (or other nonlaboratory area).Airlock doors shall be arranged with interlock-ing controls so that one door must be fullyclosed before the other door may be opened.

5.1.1.2 Critical Air Balance

If the direction of airflow between adjacentspaces is deemed critical, provision shall bemade to locally indicate and annunciate inade-quate airflow and improper airflow direction.

If the door phenomenon is not considered, there will beno safety isolation when the door is open. In many lab-oratories, momentary door opening to allow the move-ment of materials and personnel in and out of the lab-oratory will not cause a significant safety conditionbecause of the short duration of time for any contami-nants to escape from the laboratory to the corridor.Where the toxicity of the escaping contaminants wouldbe a concern during the 15 sec opening of a door, thendouble door airlocks should be employed. However, forboth fire contaminant reasons and hazardous materi-als contaminant, laboratory doors should be closedexcept when in actual use. The speed of response ofthe laboratory pressure controls should be in propor-tion to the danger of the hazardous materials containedin the laboratory. For most laboratories, speed ofresponse should be in the range of 0.5 sec to 3 sec.



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5.1.2 Diversity

The following issues shall be evaluated inorder 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 sys-tem

• 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 per-

form periodic maintenance

The following conditions shall be met in orderto design a system diversity:

• Acceptance of all hood-use restrictions bythe user groups. Designers must take intoaccount the common work practices of thesite users.

• A training plan must be in place for all lab-oratory users to make them aware of anylimitations imposed on their freedom touse the hoods at any time.

• An airflow alarm system must be installedto warn users when the system is operat-ing beyond capabilities allowed by diversi-ty.

• Restrictions on future expansions or flexi-bility must be identified.

Diversity is defined as operating a system at lesscapacity than the sum of the peak demands. Withrespect to laboratory chemical hoods, diversity can bedefined as the percentage of full flow capacity on amanifolded system in active use at anytime. A systemusing 70% of the peak demand is said to operate at70% Usage Factor or 70% diversity. A system that isdesigned with full flow capacity for all hoods isdesigned for 100% Usage Factor or 100% diversity.

Both existing and new facilities can benefit from apply-ing diversity to the HVAC design if laboratory chemicalhoods are used for only a small portion of a day.Diversity may allow existing facilities to add laboratorychemical hood capacity without adding new mechani-cal equipment. In new construction, diversity allows thefacility to reduce capital equipment expenditures andspace requirements by downsizing equipment andother infrastructure. Diversity also reduces operatingexpenses due to lower airflow requirements. Commonapproaches for creating diversity include VAV hoods,sash management aids such as building managementsystem trending and automated sash closers, andhood use detection.

Designing with diversity may limit the number of hoodsin use or limit the sash openings, thus creating poten-tial for overexposures to personnel, and prevention offuture expansion opportunities. Therefore, diversityshould be applied carefully in all situations. Certaindiversity approaches may be undesirable for certaincircumstances:

• Sash management is difficult to predict and oftenunreliable. Dependence on historical sash man-agement patterns may be insufficient for any givenfacility. The use of building management systemsto monitor sash management may help, but thisrequires significant commitment by operating per-sonnel to effectively regulate the users. Automaticsash closers—designed to improve sash manage-ment habits—may be overridden and lose theireffect on diversity.

• Laboratories with extremely high use patterns—such as teaching labs—may be candidates for full-flow or very-high-usage factor designs.



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5.1.3 Noise

Generation of excessive noise shallbe avoided in laboratory ventilationsystems.

Fan location and noise treatmentshall provide for sound pressurelevel (SPL) in conformance withlocal ambient noise criteria.

The acoustic character of the ventilation system should help cre-ate a pleasant working environment. Sound from the ventilationsystem should not interfere with laboratory operations. It may beused to mask undesirable noise such as vehicular traffic, noisyequipment, or low discourse.

The primary references for design criteria and methods will befound in ASHRAE publications such as:

• Chapter 7 on Sound and Vibration from the ASHRAE 2001Handbook – Fundamentals.

• Chapter 46 on Sound and Vibration Control from ASHRAE1999 Handbook – HVAC Applications.

Noise associated with mechanical ventilation and exhaust sys-tems generally originates with fans, duct or damper vibration, andair noise caused by excessive air velocity or turbulence.Therefore,the primary design focus should be on preventing excessive noisegeneration. Where possible, it is good practice to locate high stat-ic pressure fans remote from occupied spaces.

Use good duct design procedures. Avoid abrupt duct turns with-out turning vanes, change duct dimensions gradually, and gener-ally follow procedures given in the latest ASHRAE Handbookschapters on duct design. The careful use of vibration isolators,inertia blocks, and suitable fan speed and outlet velocities is indi-cated. Variable volume systems have found wide application inlaboratories. However it is important to be aware that variablesound levels may focus unwanted attention on the ventilation sys-tem. Frequently laboratories have large and numerous fans, andthen special care must be taken to comply with location regula-tions and good practice with regard to noise contamination ofadjoining properties.

NOTE: Such regulations vary but provide for sound pressure level(SPL) in the range of 50 dBA and limit the increase in SPL abovebackground 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) inthe laboratory. Systems should be designed to achieve an accept-able SPL and frequency spectrum [room criteria, (RC), or noisecriteria (NC)] as described in the ASHRAE 1999 Handbook –HVAC Applications. The recommended range for hospital labora-tories is 50 – 35; higher RC ranges might be acceptable for othertypes of laboratories. NC curves above 55 might result in unac-ceptable speech interference in the laboratory.

Use of porous or flammable sound-absorbing interior lining ofexhaust ductwork usually is unacceptable.



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5.1.4 Laboratory Ventilation —Emergency Modes

When the type and quantity of chemicals orcompressed gases that are present in a labo-ratory room could pose a significant toxic orfire hazard, the room shall be equipped withprovision(s) to initiate emergency notificationand initiate the operation of the ventilation sys-tem in a mode consistent with accepted safetypractices.

A hazard assessment (see Section 2.4) shallbe performed to identify the credible emer-gency conditions that may occur.

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

• CHEMICAL EMERGENCY (ChemicalSpill, Eye-Wash or Emergency ShowerActivation, Flammable Gas Release, etc.)– A means such as a clearly marked wallswitch, pull station, or other readily acces-sible device should enable the room occu-pants to initiate appropriate emergencynotification and simultaneously activatethe ventilation system’s chemical emer-gency mode of operation if one exists.

For rooms served by VAV ventilation systems,the Chemical Emergency mode of operationshould maximize the room ventilation (airchange per hour) rate and, if appropriate,increase negative room pressurization. Forrooms served by CAV ventilation systems thatutilize a reduced ventilation level for energysavings, the Chemical Emergency mode ofoperation should ensure that the room ventila-tion and negative pressurization are at themaximum rate.

Each laboratory room should be evaluated with respectto the potential for hazardous chemical spills, acciden-tal gas release, or a fire occurrence. If the type andquantity of chemicals and gas present could pose atoxicity or fire hazard if accidentally spilled, released, orignited, the room occupants should have a means tosignal for an appropriate emergency response as wellas initiate appropriate emergency ventilation.

The intent of the chemical emergency provision is toutilize the ventilation system to maximize the dilutionand removal of chemical fumes and vapors, and pre-vent migration of such fumes and vapors to other build-ing areas. This response is intended to address a seri-ous chemical spill or related incident that has thepotential for releasing large amounts of hazardousfumes or vapors within the room.

In addition to automatically initiating the emergencyventilation modes, it is highly desirable that the emer-gency situation be simultaneously and automaticallyindicated to appropriate facility personnel at one ormore designated locations.

The intent of the fire emergency ventilation mode is toutilize the ventilation system to maximize the negativepressurization of the room of fire origin in order toretard the spread of smoke and toxic fire gases to otherparts 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 offire is heightened upon a spill or gas release. In suchsituations prudent safety precautions (and/or the localcode) may justify initiating a fire alarm and summoningthe local fire department to respond.



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Operation of the room ventilation system in achemical emergency mode should not reducethe room ventilation rate, room negative pressur-ization level, or hood exhaust airflow rate.

• FIRE – A means such as a wall-mounted“FIRE ALARM” pull station should enablethe room occupants to initiate a fire alarmsignal and simultaneously activate an appro-priate fire emergency mode of operation forthe room and/or building ventilation system.

For rooms served by VAV ventilation sys-tems, the fire emergency mode of operationshould maximize the exhaust airflow ratefrom the hoods and other room exhaust pro-visions, and also shut off the room supplymakeup air. For rooms served by CAV venti-lation systems that utilize a reduced ventila-tion level for energy savings, the fire emer-gency mode of operation should ensure thatthe maximum exhaust airflow rate from thehoods and other room exhaust provisionsare in effect, and should also shut off theroom supply makeup air.

5.2 Supply Air

5.2.1 Supply Air Volume

If laboratories are to be maintained with a nega-tive pressurization and directional airflow from thecorridor into the laboratory, supply air volumeshall be less than the exhaust from the laboratory.

When laboratories are to be maintained with apositive pressurization and directional airflowsupply, air volume shall be more than theexhaust from the laboratory.

5.2.2 Supply Air Distribution

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

NOTE: At the discretion of the facility and/or as aresult of local ordinances, the occurrence of either aCHEMICAL EMERGENCY or a FIRE may initiate afire emergency mode of operation for the room venti-lation system.

In general, return air is not used in laboratories withhazardous chemicals or biological hazards. The dif-ference between the air supplied by the ventilationsystem and that exhausted should be transferredthrough small cracks under doors, in walls and ceil-ings, or in transfer grilles so as to provide a direction-al airflow to resist the escape of airborne hazardousmaterials from the laboratory room.

For most laboratory chemical hoods, this requirementwill mean 50 fpm (0.25 m/s) or less terminal throwvelocity at 6 ft (1.8 m) above the floor. For laborato-ries with very small volumes of hood exhaust this maybe achieved by correct selection and placement ofconventional aspirating supply diffusers. For roomswith greater supply air requirements, either perforat-ed ceilings or special large-capacity radial diffusers



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5.2.3 Supply Air Quality

Supply systems shall meet the technicalrequirements of the laboratory work and therequirements of the latest version ofANSI/ASHRAE 62.

5.3 Exhaust

5.3.1 Exhaust System Ductwork

5.3.1.1 Design

Laboratory exhaust system ductwork shallcomply with the appropriate sections of SheetMetal and Air Conditioning Contractors’National Association (SMACNA, 1995) stan-dards.

Systems and ductwork shall be designed tomaintain negative pressure within all portionsof the ductwork inside the building when thesystem is in operation.

may be necessary. These special laboratory diffuserssystems are preferable from a safety viewpoint to aux-iliary air hoods because the ventilation air can also beused to sweep gases and vapors from the room intothe laboratory chemical hoods. The large capacity radi-al diffusers are available from several manufacturersdesigned specifically for laboratory use. These dif-fusers have capacities of up to 100 cfm (47.2 L/s) persquare 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 omnidirectionalradial flow patterns.

Supply air diffusers where practical should be locatedas close to the personnel corridor and entry door to thelaboratory and as far from the major exhaust devicesas is practical. This location will help to provide unidi-rectional flow, sweeping the contaminants into theexhaust devices and helping further protect the corri-dor from airborne hazardous materials. The idealarrangement is to group the hoods and exhaustdevices as far as possible from entry doors and exitcorridors and locate supply air diffusers close to entrydoors and exit corridors.

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

An exception applies to exhaust fans located in a nor-mally unoccupied enclosed space such as a roof pent-house when the fan discharge ductwork is well sealedand the enclosed space is adequately ventilated.



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Exhaust ductwork shall be designed in accor-dance with ANSI/AIHA Z9.2-2001 and Chapter34 on Duct Design of the ASHRAE 2001Handbook – Fundamentals and Section 6-5 ofNFPA 45-2000.

Branch ducts shall enter a main duct so that thebranch duct centerline is on a plane that includesthe centerline of the main duct. For horizontalmain ducts, branch ducts shall not enter a mainduct on a plane below the horizontal traversecenterline of the main duct. Horizontal runs ofbranch ducts shall be kept at a minimum.

Longitudinal sections of a duct shall be a contin-uous seamless tube or of a continuously weldedformed sheet. Longitudinal seams that areformed mechanically shall be utilized only forlight duty systems with no condensation oraccretion inside the duct. Spiral ducts may beone gauge lighter than the required gauge of lon-gitudinal seam duct, except the spiral duct gaugeshall always meet the abrasive wear resistancerequirements.

Traverse joints shall be continuously welded orflanged with welded or Van Stone flanges.(When nonmetallic materials are used, jointsshall be cemented in accordance with the man-ufacturer’s procedures.) If the duct is coated witha corrosion-resistant material, the coating shallextend from the inside of the duct to cover theentire face of the flange. Flange faces shall begasketed or beaded with material suitable forservice.

If condensation within the duct is likely, all hori-zontal duct runs shall be sloped downward atleast 1 in. per 10 ft in the direction of the airflowto a suitable drain or sump.

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

When nonmetallic materials are used, joints cement-ed in accordance with the manufacturer’s proce-dures may be considered equivalent to welding.

Exhaust duct sizes should be selected to ensure suf-ficiently high airflow velocity to retard condensationof liquids or the adherence of solids within theexhaust system.

In some cases, accumulation of solids material with-in the duct system may be prevented by providingwater spray nozzles in the duct at frequent intervalsand sloping the duct down to an appropriate recep-tor (e.g., a wet dust collector).

This includes the ignition of a spill of flammable liq-uid that in turn requires an estimate of the maximumcredible accident that would generate heat.



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All duct connections to the exhaust fan shall beconsistent with good ventilation design practice. Asan alternative, the duct connections may be madeby means of inlet and outlet boxes. If circum-stances such as space limitations prevent theimplementation of the preceding requirements,then applicable speed and power corrections shallbe made by applying the “System Effect Factor”(see AMCA 201-90).

Where optimum duct connections cannot be madedue to space or other limitations, suitable alterna-tive means shall be substituted to compensate forthe space limitations.

If adequate duct connections cannot be providedat the fan, the fan shall be equipped with inlet andoutlet boxes furnished by the fan manufacturer.Themanufacturer shall furnish performance curves forthe fan with the inlet and outlet box(es) as part ofthe fan.

If neither adequate connections nor inlet/outletboxes are present, the fan speed and powerrequirements represented in the fan rating tableshall be corrected by the “System Effect Factor.”

5.3.1.2 Materials

Exhaust system materials shall be in accordancewith Chapter 5 of ACGIH’s Industrial Ventilation: A Manual of Recommended Practice, Chapter 34on Duct Design of the ASHRAE 2001 Handbook –Fundamentals, and Chapter 6-5 of NFPA 45 – 2000.

Exhaust system materials shall be resistant to cor-rosion by the agents to which they are exposed.Exhaust system materials shall be noncombustibleif perchloric acid or similar oxidizing agents thatpose a fire or explosive hazard are used.

If variable air volume (VAV) laboratory chemicalhoods are used, satisfying this criteria might requirea heat sensor arrangement to signal the VAV controlssystem to increase the exhaust airflow. An alternativesolution would be to provide a higher temperatureexhaust system design or a high-temperature com-bustion flue design for the portions of the exhaustsystem in which temperatures might exceed 400°F(204°C) in conjunction with NFPA 86-1999.

For good inlet and outlet duct design refer to the AirMovement and Control Association’s FanApplication Manual Part 1, the ACGIH LaboratoryVentilation Manual, and Chapter 34 of the ASHRAE2001 Handbook – Fundamentals.

An adequate outlet duct connection has the samerequirements as an air inlet duct except it need beonly 3 diameters in length and no vortex breaker isnecessary.

Transition fittings at the inlet and outlet should havea 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 themanufacturer.

Solid metal ductwork has good fire characteristicsbut in some cases has inferior corrosion resistancefor some chemicals. Solid plastic ductwork general-ly has good corrosion resistance but may not beacceptable to the local fire authority. An economicalmaterial that can be used when appropriate and ifproper care is used in installation and maintenanceis a metal duct with a protective coating. However,because of the thin coatings generally used, pinholedefects in the coating may be relatively common,which would eventually lead to a very small amount



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5.3.2 Manifolds

5.3.2.1 Combined Exhaust Systems

of leakage. Any mechanical damage or scratching of thecoating in installation or maintenance would have to beimmediately and properly repaired or the bare metal revealedin the scratch will be eaten away. Owner’s representativesmust spend more time and money during installation to makesure contractor coats all exposed metal during initial installa-tion and similar care must be exercised whenever the coatedexhaust duct is modified during renovations.

Two or more exhaust systems may be combined into a singlemanifold and stack, if the conditions of 5.3.2.2 are met.

Manifold exhaust systems frequently have significant advan-tages over individual (single-hood/single-fan) systems andare encouraged.

Manifold and individual systems have the following charac-teristics:

Manifold Systems:

Advantages:

• High concentration discharges from individual hoods arediluted by the air from all the other hoods on the manifoldbefore being released into the atmosphere.

• The potential for installing redundant fans is increasedand may only require one additional fan and the cost toprovide redundancy is reduced.

• The potential for installing emergency power is increasedwhile 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.



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Disadvantages:

• Fan failure affects all hoods on the system andredundancy is required.

• Changing the application of a single hood (i.e., froma standard laboratory chemical hood to radioisotopehood or perchloric acid hood) is difficult.

• The ability to provide treatment (i.e., scrubbing, filter-ing, etc.) for an individual exhaust source requires anin-line scrubber and additional static pressure for theentire 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 radioisotopehood or perchloric acid hood) is easily accomplished.

• The ability to provide treatment (i.e., scrubbing, filter-ing, etc.) for an individual exhaust source is easilyaccomplished.

• The system is less complex.

Disadvantages:

• There is no dilution of the source effluent beforereleasing it to the atmosphere.

• Providing redundancy is difficult due to space limita-tions and is more expensive.

• Providing emergency power is difficult and moreexpensive.

• 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



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5.3.2.2 Manifold Requirements

Laboratory chemical hood ducts may becombined into a common manifold with thefollowing exceptions and limitations:

Each control branch shall have a flow-reg-ulating device to buffer the fluctuations inpressure inherent in manifolds.

Perchloric acid hoods shall not be mani-folded with nonperchloric acid hoodsunless a scrubber is installed between thehood and the manifold.

Large Systems:

Large and/or diverse systems that have several types ofhoods often benefit from a hybrid approach where a man-ifold is designed to handle a majority of the hoods and indi-vidual exhaust systems are installed for those that cannotor should not be manifolded such as perchloric acid orradioisotope hoods.

Adverse Chemical Reaction Potential:

Contrary to popular belief, the probability of two or morereagents from different sources combining in the manifoldto produce an explosion is extremely small but should beevaluated for special cases involving large quantities ofmaterials.

Consider the minimum manifold with two hoods connectedto a single fan: Reagent A is spilled in Hood A, covering theentire work surface and producing maximum evaporationand duct concentration while Reagent B is similarly spilledin Hood B. Reactive chemistry experts attempting to deviseworst-case binary reaction assure us that although thesetwo chemicals, when mixed in liquid or solid form, will cer-tainly explode, when mixed in concentrations less than10,000 ppm (1%) in air, it is unlikely that an explosive reac-tion can be initiated or sustained (Hitchings, unpublisheddata). The last statement notwithstanding, assuming that areaction can be initiated, the result would be only a slightadiabatic temperature increase in the duct.

The ability of chemicals from different sources to form toxicproducts is similarly limited by low concentrations thatbecome lower and lower the closer they get to the fan onmanifolded systems.

Flow regulating devices that are pressure-independentdevices also allow changes to be made in the system with-out the need to rebalance the entire system.

Manifolding of perchloric acid hoods is discouragedbecause nonvertical ductwork is implied by connecting oneor more hoods together and nonvertical ducts are difficultto wash down properly using duct-mounted spray heads.



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Where there is a potential contamination fromhood operations as determined from theHazard Evaluation and Analysis of Section2.4, radioisotope hoods shall not be manifold-ed with nonradioisotope hoods unless in-lineHEPA filtration and/or another necessary air-cleaning system is provided between thehood and the manifold.

Carbon bed filters shall be added for gases.

5.3.2.3 Compatibility of Sources

Exhaust streams that contain concentrationsof flammable or explosive vapors at concen-trations above the Lower Explosion Limit(LEL) as well as those that might form explo-sive compounds (i.e., perchloric acid hoodexhaust) shall not be connected to a central-ized exhaust system. Exhaust streams com-prised of radioactive materials shall be ade-quately filtered to ensure removal of radioac-tive material before being connected to a cen-tralized exhaust system. Biological exhausthoods shall be adequately filtered to removeall hazardous biological substances prior toconnection to a centralized exhaust system.

5.3.2.4 Exhaust System Reliability

Unless all individual exhausts connected tothe centralized exhaust system can be com-pletely stopped without creating a hazardoussituation, provision shall be made for continu-ous maintenance of adequate negative staticpressure (suction) in all parts of the system.

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

HEPA filters only cover radioactive dust, not radioactivegases.

Systems that use heavy digestions or other operationsthat could cause condensation in the duct may not beappropriate for a manifold system. The high potential ofcondensation imposes drainage problems throughoutthe system rather than just for the hoods that may havehigh condensation.

This requirement could be satisfied by one or both ofthe following provisions:

• Multiple operating fans so the loss of a single fandoes not result in loss of total system negative sta-tic pressure

• Spare centralized system exhaust fan(s) that willrapidly and automatically be put into service uponfailure of an operating fan by repositioning isolationdampers and energizing the standby fan motor.

Emergency backup power should be provided to allexhaust fans and the associated control system.



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As an alternative, if the hood is completelyturned off, the hood shall be emptied anddecontaminated and provisions shall beimplemented to prevent the hood from back-drafting.

The VAV hood shall be provided with an emer-gency switch that allows the hood exhaust vol-ume to return to the maximum.

5.3.2.5 Biological Safety Cabinets

Class II–Type A and Type B3 biological safetycabinets manifolded with chemical laboratorychemical hoods shall have either:

1) A thimble connection or

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 inde-pendent of the sash position.

Note this requires careful planning for a system lessthan 100% diversity (see Section 5.1.2).

If the maximum exhaust volume of the variable air vol-ume hoods in one room exceeds 10% of the room airsupply volume, and if the laboratory is designed forcontrolled airflow between the laboratory and adjacentspaces, automatic flow control devices should be pro-vided to reduce the supply air volume by the sameamount that hood exhaust volume is reduced.

At present, this system requires sophisticated testingequipment and training of maintenance personnel.

NOTE: Type A and Type B3 cabinets that have the cab-inet exhaust flow directed into the thimble connectiondo not meet the hard duct connection requirement forType B cabinet.

Thimbles allow the exhaust flow to continue exhaustingairflow from the room when the biological safety cabi-net is off thus avoiding continuous dust loading of thebiological safety cabinet filters.

Secondly, this prevents the exhaust system frombecoming positively pressurized by the internal fans inthe biological safety cabinets in the event that theexhaust system should fail.

Thirdly, continuous exhaust through the thimble con-nection may be important for room air balance as wellas removing the heat load of laboratory equipment.



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2) A constant-volume control device and aninterlock/alarm for these devices shall beinstalled between the cabinet outlet and theexhaust manifold.

Where Hazard Evaluation and Analysis deter-mines that the installation calls for direct con-nection (hard ducted) of the biological safetycabinet (e.g., Class II–Type B) to an exhaustmanifold system to allow work with toxic chem-icals or radionuclides, interlocks and alarmsshall be provided to prevent the biologicalsafety cabinet from operating its normal start-ing mode or to immediately warn the operatorin the event of an exhaust system failure(CDC-NIH, 1999).

5.3.2.6 Static Pressure

The static pressure in the exhaust system shallbe lower that the surrounding areas through-out the entire length, with the exception notedin Section 5.3.1.1.

5.3.2.7 Exhaust Fan Location

Exhaust systems shall have the exhaust fanlocated outside the building unless:

• The fans are in an adequately ventilatedpenthouse or room adjacent to the outsideand the discharge ductwork passes direct-ly from the fan to the outside without pass-ing through another room or space, and

For direct (hard ducting) of Class II Type B cabinet, theexhaust flow balance is critical for the needed inflowvelocity of the biological safety cabinet.

Where the installation calls for direct connection of thebiological safety cabinet (e.g., Class II–Type B), inter-locks and alarms should be provided to prevent the bio-logical safety cabinet from shutting down and to imme-diately warn the operator in the event of an exhaustsystem failure. Thimble connections can be improper-ly designed and are sometimes difficult to balance anddraw in a small amount of room air. However, they arerecommended over the direct connection and opera-tion interlock design so that worker and product pro-tection are maintained even in the event of an exhaustsystem failure. Interlocks, if activated during an exhaustsystem failure involving radioactive materials, couldcause worker or product exposure. A nonmanifoldeddedicated exhaust system connection directly ventedto the atmosphere may be needed for work with thesetypes of hazardous materials.

Constant volume control devices maintain a constantexhaust rate from all types of biological safety cabinetsdue to changes in exhaust system static pressure.

Refer to NSF 49 for testing and certification of biologi-cal safety cabinets.

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

Leakage from ducts, fittings, flex connections, and fanhousings is a potential source of contamination in fanrooms and penthouses. Locating the fans outside elim-inates the need for an additional ventilation system forthe room housing the fans. In winter, maintenance maysuffer, however.



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• There are no flexible connections onthe discharge side of the fan and allductwork in the discharge side of thefan is of welded and/or flanged andgasketed construction.

5.3.2.8 System Classification

Laboratory hood exhaust systems shall notbe classified as “Hazardous ExhaustSystems” as defined in Building Officialsand Code Administrators International(BOCA), Uniform, or InternationalMechanical Codes.

Leakage from flexible connections is a one of the largestcontributors to fan room or penthouse contamination.

The length of duct and number of fittings on the positiveside of the fan should be minimized.

Fire/Explosion Potential From Flammables:

A common misconception that concerns many when con-sidering manifolded systems is the possibility of fires orexplosions produced by flammable materials used andreleased in the hoods. This concern is not supported byapplication experience. However, overly cautious codeofficials often rule that laboratory exhaust systems meetthe definition of “Hazardous Exhaust Systems” as definedin the building/mechanical codes and require that sprin-klers or other types of fire detection/suppression equip-ment be installed in laboratory chemical hood exhaustsystems.

The “Hazardous Exhaust Systems” definition is intendedto include industrial ventilation systems where high con-centrations of flammable materials within the explosivelimits are conveyed through the duct. Laboratory exhaustsystems do not meet this definition.

Empirical studies using acetone, toluene, and methyl ethylketone (MEK) were conducted in worst-case scenarios(Hitchings, personal communication). The entire work sur-face was covered with solvent in a VAV hood with the sashdown and minimum flow (maximum duct concentration).This produced duct solvent concentrations well below theLEL. Therefore, although the solvent itself is flammable,and a portion of the gradient from pure solvent at the worksurface to duct concentration (occurring entirely in thehood itself) is in the flammable region, the mixture at alllocations in the duct system is nonflammable.

If the duct concentration is within the flammable region ofthe solvent between the hood and the manifold where it isdiluted below the LEL, an ignition source is still requiredbetween the hood and the manifold to produce an explo-sion. Ignition sources in laboratory chemical hood ductsare hard to imagine. However, if an ignition source doesexist, will the fire detection/suppression prevent an explo-sion? No. If an explosion occurs, all fuel is consumed andno fire can therefore exist and the activation of sprinklersor other types of fire suppression will probably only add toany capital damage that has already occurred.



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5.3.2.9 Fire Dampers

Fire dampers shall not be installed in exhaustsystem ductwork (NFPA 45).

5.3.2.10 Fire Suppression

Fire sprinklers shall not be installed in laborato-ry chemical hood exhaust manifolds.

5.3.2.11 Continuous Operation

Exhaust systems shall operate continuously toprovide adequate ventilation for any hood at anytime it is in use and to prevent backflow of airinto the laboratory when the following conditionsare present:

• Chemicals are present in any hood (openedor unopened).

• Exhaust system operation is required tomaintain minimum ventilation rates androom pressure control.

• There are powered devices connected tothe manifold. Powered devices include, butare not limited to: biological safety cabinets,in-line scrubbers, motorized dampers, andbooster fans.

The accidental activation of a fire damper will shut offairflow from one or more laboratory chemical hoodsand may cause worker injury or exposure.

The activation of a fire damper caused by a fire in alaboratory chemical hood will shut off airflow from thathood making it impossible to remove the combustionproducts from the hood and forcing the hood tobecome positively pressurized. This condition makesit likely that the fire will escape the fire-resistant hoodinto the laboratory.

With the exhaust flow from one or more hoods shutoff, the laboratory may become positively pressurizedwith respect to the corridor, encouraging the spreadof the combustion products, and perhaps the fire,from the laboratory to adjoining spaces.

Studies of actual exhaust systems have demonstrat-ed that the spray cone produced by sprinkler headscan actually act as a damper and reduce or preventairflow in the duct past the sprinkler head (Hitchingsand Deluga, personal communication). Like a firedamper, this may produce a lack of flow at one ormore laboratory chemical hoods at the moment whenit is needed most.

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



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5.3.2.12 Constant Suction, Redundancyand Emergency Power

Manifolds shall be maintained under negativepressure at all times and be provided with atleast two exhaust fans for redundant capacity.

Emergency power shall be connected to one ormore of the exhaust fans where exhaust systemfunction must be maintained even under poweroutage situations.

5.3.3 Exhaust Fans

Each fan applied to serve a laboratory exhaustsystem or to exhaust an individual piece of lab-oratory equipment (e.g., a laboratory chemicalhood, biosafety cabinet, chemical storage, etc.)shall be adequately sized to provide the neces-sary amount of exhaust airflow in conjunctionwith the size, amount, and configuration of theconnecting ductwork. In addition, each fan’srotational speed and motor horsepower shall besufficient to maintain both the required exhaustairflow and stack exit velocity and the neces-sary negative static pressure (suction) in allparts of the exhaust system.

If flammable gas, vapor, or combustible dust ispresent in concentrations above 20% of theLower Flammable Limit, fan construction shallbe as recommended by AMCA’s 99-0401-86,Classification for Spark Resistant Construction.

Laboratory exhaust fans shall be located as fol-lows:

• Physically outside of the laboratory buildingand preferably on the highest level roof ofthe building served. This is the preferredlocation since it generally minimizes risk ofpersonnel coming into contact with theexhaust airflow.

• In roof penthouse or a roof mechanicalequipment room that is always maintainedat a negative static pressure with respect tothe rest of the facility, and provides directfan discharge into the exhaust stack(s).

The manifold fans and controls should be designed sothat sufficient static pressure is available to each con-nected exhaust source for all conditions that do notexceed the system diversity. Since each critical con-nected source (i.e., laboratory hoods) should havecontinuous performance monitors, exceeding systemcapacity should also result in flow alarms.

Under most operating conditions, centrifugal fans willleak small amounts of system gases at the fan shaft.Also, fan discharge ducts typically are under positivepressure and any air leaks would discharge into theroom. Having laboratory exhaust fans in one of theabove locations (Section 5.3.2.7) helps ensure thatany fan leakage will be effectively removed and will notmigrate within the building.



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All laboratory exhaust fans shall include provisionsto allow periodic shutdown for inspection and main-tenance. Such provisions include:

• Ready access to all fans, motors, belts, drives,isolation dampers, associated control equip-ment, and the connecting ductwork.

• Isolation dampers on the inlet side of all cen-tralized exhaust system fans that have individ-ual discharge arrangements or their own indi-vidual exhaust stacks.

• Isolation dampers on both the inlet and outletsides of all centralized exhaust system fansthat discharge into a common exhaust stack orplenum.

• Sufficient space to allow removal and replace-ment of a fan, its motor, and all other associat-ed exhaust system components and equip-ment without affecting other mechanical equip-ment or the need to alter the building structure.

See Section 8.1, Operations During MaintenanceShutdown, for necessary requirements and guid-ance.

5.3.4 Discharge of Contaminated Air

The discharge of potentially contaminated air thatcontains a concentration more than the allowablebreathing air concentration shall be:

• Direct to the atmosphere unless the air is treat-ed to the degree necessary for recirculation(see Section 9.3);

• In compliance with applicable federal, state, orlocal regulations with respect to air emissions;

• Discharged in a manner and location to avoidreentry into the laboratory building or adjacentbuildings at concentrations above 20% ofallowable concentrations inside the laboratoryfor routine emissions or 100% of allowableconcentrations for emergency emissions underwind conditions up to the 1%-wind speed forthe site.

5.3.5 Exhaust Stack Discharge

The exhaust stack discharge shall be in accor-dance with the ASHRAE 1999 Handbook – HVACApplications, Chapter 43.

The requirements for inspection access and ser-viceability are intended to ensure that laboratoryexhaust systems can be kept and maintained inproper operating condition. If a centralized exhaustsystem has multiple fans and a fan replacement isnecessary, the process should not require discon-necting piping or removing other building encum-brances that might lead to an indefinite postpone-ment of the required work.

The in-stack concentrations of contaminantsallowed under such regulations typically rangefrom 100 to 1000 times higher than safe breathingconcentrations.

Necessary measures must be taken to protect thelaboratory building and adjacent buildings fromtoxic materials reentry.



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

A minimum discharge velocity of 3000 fpm (15.2 m/s) is required unless it can be demon-strated that a specific design meets the dilutioncriteria necessary to reduce the concentrationof hazardous materials in the exhaust to safelevels (see Section 2.1) at all potential recep-tors.

Esthetic conditions concerning externalappearance shall not supersede the require-ments of Sections 5.3.4 and 5.3.5.

The 10 ft (3 m) height above the adjacent roof linecalled for by this standard is primarily intended to pro-tect maintenance workers from direct exposure fromthe top of the stack. However, this minimum 10 ft (3 m)height may be insufficient to guarantee that harmfulcontaminants won’t enter the outside air intake of thebuilding or of nearby buildings.

After initial installation, the exhaust stack is unchangedfor the lifetime of the hood. It is uncertain that the life-time hood usage can be accurately projected. In mostcases, consistent discipline in safe hood procedurescannot be assured. Accordingly, it is prudent to useconservative guidelines in the location and arrange-ment of the hood discharge.

The basic challenge in locating the hood discharge isto avoid re-entrainment of effluent into any building airintake or opening and to minimize exposure of the pub-lic. The selection of stack height is dependent on thebuilding geometry and airflow pattern around the build-ing and is as variable as meteorological conditions.

An excellent resource is Chapter 43 of the ASHRAE1999 Handbook – HVAC Applications. Among the fac-tors to consider in establishing stack configuration,design, and height are: toxicity, corrosivity, and relativehumidity of the exhaust, meteorological conditions,geometry of the building, type of stack head and capdesign, adjacency of other discharged stacks andbuilding intake, discharge velocity, and receptor popu-lation.

A discharge velocity of 2500 fpm (12.7 m/s) preventsdownward flow of condensed moisture within theexhaust stack. It is good practice to make the terminalvelocity at least 3000 fpm (15.2 m/s) to encourageplume rise and dilution.

These factors affect the dilution of the exhaust streamand the plume trajectory. High discharge velocity andtemperature increase plume rise, but high velocity isgenerally less effective than increased stack height.

In case there is a conflict, the requirements of Section5.3.4 take priority. Some solutions that may be usedare:



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Any architectural structure that protrudes to aheight close to the stack-top elevation (i.e.,architectural structure to mask unwantedappearance of stack, penthouses, mechanicalequipment, nearby buildings, trees or otherstructures) shall be evaluated for its effects onre-entrainment

The air intake or exhaust grilles shall not belocated within the architectural screen or maskunless it is demonstrated to be acceptable.

5.3.6 Recirculation of Room Exhaust Air

Nonlaboratory air or air from building areasadjacent to the laboratory may be used as partof the supply air to the laboratory if its qualityis adequate.

5.3.6.1 General Room Exhaust

Air exhausted from the general laboratoryspace (as distinguished from laboratory chem-ical hoods) shall not be recirculated to otherareas unless one of the following sets of crite-ria is met:

• An evaluation of the stack design that will accountfor the effects of problem structures should beundertaken. The evaluation should provide esti-mates of the expected concentration levels ofexhaust contaminants at surrounding air intakes.Appropriate physical modeling (wind tunnel, mock-up or water flume) or numerical modeling usingappropriate methods (Computational FluidDynamics or other advanced numerical methods)should be undertaken as discussed in Chapter 43of the ASHRAE 1999 Handbook – HVACApplications. The limitations of the technique uti-lized should be understood and evidence shouldbe provided that the results are conservative oraccurate for the case being modeled. When phys-ical modeling is used, procedures discussed in theEPA Guideline for Modeling of AtmosphericDiffusion (Office of Air Quality Planning andStandards, EPA-600/8-81-009, April 1981) shouldbe employed.

• Treatment of the discharge gas may permit a lowerand esthetically acceptable stack. The technologyof gas-treating equipment is outside the scope ofthis standard except as described in Section 9.2.

• Appendix 3 is provided to assist the designer inunderstanding stack height determination andevaluation methods.

In many laboratory settings, the laboratory is purpose-ly kept at a slight negative differential pressure withrespect to adjacent building spaces. In this situation,air flows from the adjacent spaces into the laboratorythrough building cracks and doorways, at least whenopen. This may be highly desirable; if not, this flow canbe reduced, but not completely eliminated, by use ofdouble-door airlock vestibules, with correspondingconsumption of interior space and some hindrance totraffic.

Many laboratories, especially those handling hazardmaterials, have a sufficient number of laboratorychemical hoods so that the entire flow of supply air tothe room necessary for air-conditioning is exhaustedthrough laboratory chemical hoods (in other words,there is no surplus supply to be exhausted or recircu-lated).



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1) Criteria A

• There are no extremely dangerous or life-threatening materials used in the laborato-ry;

• The concentration of air contaminantsgenerated by maximum credible accidentwill be lower than short-term exposure lim-its required by 2.1.1;

• The system serving the laboratory chemi-cal hoods is provided with installed redun-dancy, emergency power, and other relia-bility features as necessary.

2) Criteria B

• Recirculated air is treated to reduce cont-aminant concentrations to those specifiedin 2.1.1;

• Recirculated air is monitored continuouslyfor contaminant concentrations or provid-ed with a secondary backup air-cleaningdevice that also serves as a monitor (via aHEPA filter in a series with a less efficientfilter, for particulate contamination only).Refer to Section 9.3.1;

• Provision of 100% outside air, whenevercontinuous monitoring indicates an alarmcondition.

5.3.6.2 Exhaust Hood Air

Exhaust air from laboratory hoods shall not berecirculated to other areas.

Hood exhaust air meeting the same criteria asnoted in Section 5.3.6.1 shall only be recircu-lated to the same work area where the hoodoperators have control of the hood work prac-tices and can monitor the status of air clean-ing.

Devices that are intended to provide heating and/orcooling by recirculating the air within a laboratoryspace (i.e., fan coil units) are exempt from this require-ment.

For most laboratories, recirculation of laboratory chem-ical hood air should be avoided. Laboratory chemicalhood air usually contains significant amounts of mate-rials with differing requirements for removal. Providingair-cleaning equipment to permit safe recirculation rep-resents a high capital and operating cost, especiallywhen redundancy and monitoring requirements areconsidered.

Note that NFPA 45-2000 prohibits recirculation of labo-ratory chemical hood air when using flammables.

Some “single purpose” laboratories might find it practi-cal to recirculate laboratory chemical hood air; therequirements are similar to those in Section 5.3.6.1 cri-teria B. See Section 4.2 for more information.



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6 Commissioning Tests

6.1 Commissioning of LaboratoryVentilation Systems

Commissioning Test Instrumentation:

All test instrumentation utilized for the commis-sioning process shall be in good working orderand shall have been factory calibrated within 1year of the date of use. (See 8.6.1 Air Velocity,Air Pressure, Temperature and HumidityInstruments)

6.2 Commissioning Process

All newly installed, renovated, or moved hoodsshall be commissioned to ensure proper oper-ation prior to use by laboratory personnel.

6.2.1 Commissioning Authority

The commissioning process shall be overseenby a responsible person or commissioningauthority.

Commissioning tests are conducted to ensure that labo-ratory ventilation systems operate according to designspecifications and are capable of meeting control objec-tives under resulting operating conditions. The extent ofthe commissioning process depends on the complexityof the systems along with the anticipated risk associatedwith work to be conducted in the laboratory.

The commissioning authority should be someone whorepresents the interests of the system owner andshould be knowledgeable in the design and operationof laboratory ventilation systems. In addition, the com-missioning authority should be experienced with col-lection and analysis of test data.

The commissioning authority may develop the com-missioning plan in conjunction with information provid-ed by potential equipment suppliers and contractors,owner personnel, and project design professionals.

A commissioning team consisting of personnel directlyinvolved in the design, installation, and use of the newor renovated systems should assist the commissioningauthority. 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.



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6.2.2 Commissioning Plan

A written commissioning plan shall accompanydesign documents and be approved by thecommissioning authority in advance of con-struction activities.

The commissioning plan shall be available toall potential suppliers and contractors prior tobid along with the other project documents.

A commissioning plan shall address operationof the entire ventilation system where thehoods, laboratories, and associated exhaustand air supply ventilation systems are consid-ered subsystems.

The plan shall include written procedures toverify or validate proper operation of all systemcomponents and include:

• Laboratory Chemical Hood Specificationand Performance Tests

• Preoccupancy Hood and VentilationSystem Commissioning Tests

• Preoccupancy Laboratory CommissioningTests

The conceptual design phase of the project generallyincludes a statement of performance objective and cri-teria for establishing proper operation of proposed sys-tems. The statement of performance provides an oper-ational definition of performance that can be measuredafter installation and startup to validate or verify properoperation. The commissioning plan describes the teststhat will be conducted to verify proper operation of thesystems.

For example, an operational definition for proper per-formance of a new hood system might include: the newhood operated with the vertical sliding sash at a heightof 28 in. (71.1 cm) must have an average face velocitybetween 80 – 120 fpm (0.41 to 0.61 m/s) and providecontainment below a control level of AU 0.1 ppm as determined by methods described in theANSI/ASHRAE 110-1995, Method of TestingPerformance of Laboratory Fume Hoods.

A laboratory chemical hood system includes all associ-ated subsystems such as the hoods, ducts, dampers,automated controls, filtration, fan, motor, and exhauststacks. In laboratories, the air supply system is consid-ered part of the hood system when operation can affecthood performance.

It is imperative that the commissioning plan be com-pleted and that is part of the project design documents.It should not be developed after the bid process orsigning of contracts because it may substantiallyimpact the individual contractor laboratory costs andscheduling. If it is developed after the bid date, what-ever requirements it imposes on a contractor could becontested as being invalid since it was not available atthe time of bid.

Design changes made subsequent to constructionmust be reflected in a revised commissioning plan.



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6.2.3 Commissioning Documentation

Preliminary and final commissioning documentsshall be issued to the appropriate party(s) by theCommissioning 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 problemsuncovered by the commissioning process shall becommunicated to the responsible party (i.e.,installer, subcontractor, etc.) for prompt correction.

6.3 Laboratory Chemical Hood Specificationand “As Manufactured” ANSI/ASHRAE110 Defined Performance Test Data

Specification and procurement of laboratorychemical hoods shall be based on tests conduct-ed on the hood (or prototype hood) that demon-strate 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 vol-ume conditions where exhaust and air supplyflow are stable and exhibit no more than 5% vari-ation from set-point.

The documents should detail the status of the venti-lation systems relative to maintaining a safe facilityenvironment.

The document should clearly indicate, based uponthe ventilation system functionality, which laboratoryrooms and equipment (i.e., chemical laboratoryhoods, biosafety cabinets, etc.) are ready for safeuse, any areas or equipment that are not safe for useor occupancy, and other safety-related ventilationsystem details.

Unreasonable delays or unsatisfactory follow-upshould be communicated to the owner as well as anycontractors in the tier to which this subcontractor isresponsible.

“As Manufactured” Containment Tests, usually per-formed at the manufacturer’s facility, are conductedto determine whether the hood is adequatelydesigned to provide the required level of perfor-mance. In addition, the tests are conducted to deter-mine appropriate operating specifications. It is onlynecessary to perform these tests on one hood foreach unique hood design or mode.

What is desired are credible catalog data on the fun-damental performance and capabilities of a hood asit comes from the manufacturer. The designer canthen specify the unit with confidence that it will per-form as per the manufacturer’s catalog data. It is rec-ommended that the manufacturers’ tests be con-ducted or witnessed by the laboratory owner anddesign professional, and/or independent third party.

Proper containment of a laboratory chemical hood isaffected by a number of factors including design ofthe hood, design of the laboratory, and design andoperation of the ventilation systems. Controlled testsenable elimination of one variable: design of thehood. Therefore, performance problems encounteredafter installation can be attributed to other factors.



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6.3.1 Exhaust Flow Measurement

The volumetric flow exhausted from a labo-ratory chemical hood shall be determined bymeasuring the flow in the exhaust duct usingindustry-approved methods.

Where possible, containment tests should be conductedaccording to methods described in the most recentANSI/ASHRAE 110 standard equal to or more challeng-ing than the standardized test.

ANSI/ASHRAE 110-1995 does not specify a face veloc-ity. The standard yields a performance rating in the formof AM yy, AI yy, or AU yy where, AM means “as manu-factured,” AI means “as installed,” and AU means “asused.” The symbol yy represents the average 5-minuteconcentration of tracer gas measured in the breathingzone of a mannequin used to simulate a hood user.

The ANSI/ASHRAE 110-1995 standard recommends agas generation rate of 4 L/m. However, other generationrates (i.e., 1 L/m or 8 L/m) can be specified by the designprofessional or responsible person (2.3) when deemedappropriate.

The containment tests should be conducted over therange of possible operating configurations afforded bythe hood design (i.e., sash position, baffle configura-tions, etc.) and at different target face velocities orexhaust flow rates to determine operational boundaryconditions and hood limitations.

Testing at different operating configurations will help toidentify operational limitations or worst-case operatingconditions. This information helps the design profession-al in their work and can then be relayed to the hoodusers to ensure proper work practices that minimizepotential for exposure.

See the most recent edition of ACGIH’s IndustrialVentilation: A Manual for Recommended Practice, orANSI/ASHRAE 41.2-1987 (RA 92), for measuring flow.

The hood exhaust flow should be adjusted to achieve thetarget average face velocity at the design opening.

Typically, exhaust flow can be predicted from the area ofthe opening multiplied by the design face velocity.However, infiltration of air into the hood through openingsother than the face may require approximately 5–10%more exhaust flow than calculated. The exhaust flow andvariance from the calculated flow should be determinedto enable proper specification of flows for design of theventilation systems.



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6.3.2 Hood Static Pressure

The hood static pressure shall be measuredabove the outlet collar of the hood at theflows required to achieve the design averageface velocity.

6.3.3 Face Velocity Tests

The average face velocity shall be deter-mined by the method described in theANSI/ASHRAE 110-1995 Method of TestingPerformance of Laboratory Fume Hoods.

Failure to determine the total exhaust flow required toachieve the desired average face velocity may result inundersizing of the exhaust system or improper specifi-cation of supply volume to achieve required lab pressur-ization or differential airflow.

Calculation of exhaust flow from face velocity measure-ments multiplied by hood face area is not a measure-ment of exhaust flow and due to the reasons statedabove, true exhaust flow can vary significantly from thecalculated exhaust flow. In addition, the accuracy of facevelocity measurements can affect the accuracy of theaverage face velocity used to calculate exhaust flow.Face velocities measured at the plane of the sash open-ing using hot-wire thermoanemometers or pressure gridassemblies can be subject to significant error due to tur-bulence at the opening and direction of airflow over theprobes where average face velocities could vary fromactual by 5–20%.

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

The average face velocity alone is inadequate todescribe hood performance. Face velocity is not a mea-sure of containment but only the speed of air enteringthe face opening. Hood performance should be deter-mined from tests of hood containment. Average facevelocity should only be used as an indicator of propersystem operation.

Refer to section 3.3.1, Face Velocity, for informationabout analysis of face velocity data and recommendedcriteria.

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



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Face velocity measurements shall be made bydividing the hood opening into equal area gridswith sides measuring no more than 12 in.(30.5 cm). The tip of the probe shall be posi-tioned in the plane of the sash opening andfixed (not handheld) at the approximate centerof each grid. Grid measurements around theperimeter of the hood opening shall be madeat a distance of approximately 6 in. (15.2 cm)from the top, bottom, and sides of the openingenclosure.

The average face velocity shall be the averageof the grid velocity measurements.

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

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

6.3.4 Auxiliary Air Velocity Tests

For auxiliary air hoods, the face velocity shallbe measured with the auxiliary air turned offunless room pressurization would change sig-nificantly to affect exhaust flow. Where exhaustflow would be affected by turning off the auxil-iary airflow, auxiliary air must be redirectedfrom the hood opening so as not to interferewith flow into the hood while conducting theface velocity traverse.

The velocity of the auxiliary air exiting the aux-iliary air plenum shall be measured to deter-mine the magnitude and distribution of air sup-plied above the hood opening.

The average auxiliary air velocity shall bedetermined from the average of grid velocitiesmeasured across the plenum outlet.

stability. Average face velocities and grid velocities canbe significantly affected by turbulence (temporal varia-tion) and direction through the opening (spacial varia-tion). Multiple readings taken over time at each gridlocation are recommended to provide more accuratevelocity measurements. Cross drafts can also bias facevelocity data by creating turbulence at the opening andvariations in face velocity readings.

Multiple readings at each grid point will help determinemore accurate average face velocities when turbulentair is present at the hood opening. Multiple readingscan be acquired with the use of time constants formeters so equipped or use of a data logger or dataacquisition system attached to a computer.

Face velocity measurements should be determinedwith the supply air off or with special devices designedto eliminate the effect of the auxiliary air at the hoodface.

The auxiliary air supply plenum located above the topof the hood face and external to the hood should bedesigned to distribute air across the width of the hoodopening so as not to affect containment.

Excessive auxiliary air velocity can interfere or over-come air flowing into the hood opening and causeescape from the hood.

The downflow velocities should be measured approxi-mately 6 in. (15.2 cm) above the bottom edge of thesash positioned at the design opening height.



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6.3.5 Cross-Draft Velocity Tests

Cross-draft velocity measurements shall bemade with the sashes open and the velocityprobe positioned at several locations near thehood opening to detect potentially interferingroom air currents (cross drafts). Record mea-surement locations.

Over a period of 10–30 sec., cross-draft veloc-ities shall be recorded approximately 1 read-ing per second using a thermal anemometerwith an accuracy of ±5% at 50 fpm (0.25 m/s).

The average and maximum cross-draft veloci-ties at each location shall be recorded and notbe sufficient to cause escape from the hood.

Cross draft velocities shall not be of suchmagnitude and direction as to negatively affectcontainment.

6.3.6 Airflow Visualization Tests

Airflow visualization tests shall be conductedas described in the ANSI/ASHRAE 110-1995,Method of Testing Performance of LaboratoryFume Hoods.

The tests shall consist of small-volume gener-ation and large-volume generation smoke toidentify areas of reverse flow, stagnationzones, vortex regions, escape, and clearance.

More test locations may be required or can be useful fordetermining cross-draft velocities past the hood open-ing. Vertical and horizontal components of cross-draftvelocities should be measured at each location.

Increasing face velocity may not make the hood moreresistant to cross drafts. However, increasing facevelocity may:

• Increase the required volume of room air supplyand increase difficulties with ensuring proper roomair distribution.

• Increase exhaust of expensive conditioned air.

Excessive cross-draft velocities (>50% of the averageface velocity) have been demonstrated to significantlyaffect hood containment and should be identified andalleviated. Ideally, cross-draft velocities should be lessthan 30%.

If the supply tracks the exhaust, measure the crossdrafts at the maximum conditions.

Smoke tests are valuable because they indicate thedirection of airflow through the opening and within thehood enclosure when the smoke plume is visible. Smokeparticles are rapidly diluted to the extent where they maynot be visible even though significant concentrationsmay exist in the invisible plume. Smoke tests should beused only as an indication of flow direction and absenceof visible smoke should not be interpreted as anabsence of smoke. Users of smoke should note thatsmoke tubes and candles can be caustic and detrimen-tal to the user, test equipment, and apparatus in thehood.



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Visible escape beyond the plane of the sashwhen generated 6 in. (15.2 cm) into the hoodshall constitute a failure during the perfor-mance test.

6.3.7 Tracer Gas Containment Tests

The tracer gas containment tests shall be con-ducted as described in the ANSI/ASHRAE110-1995, Method of Testing Performance ofLaboratory Fume Hoods or by a test recog-nized to be equivalent.

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

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

Attempts to improve airflow patterns should beattempted by adjusting the baffles and slot widths, redi-recting room air currents, or changing the opening con-figuration by moving the sash panels.

Closure of the sashes resulting in an opening smallerthan the design opening may represent a “restricteduse” condition.

Often the most devastating area for reverse flow isbehind the airfoil sill on bench-top-mounted hoods. Animproperly designed airfoil or lack of an airfoil willcause reverse flow along the work surface within 6 in.(15.2 cm) of the sash plane. Reverse flow in this regionis particularly worrisome as the wake zone that devel-ops in front of a hood user could overlap with thereverse flow zone.

Dynamic challenges should be evaluated.

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

The test data need to be made available by the manu-facturer for each specific model and type of hood so apotential buyer can verify proper containment or com-pare one manufacturer’s hood containment againstanother.

Values for control level may not be suitable for estab-lishing hood safety, as the tracer gas test methods maynot adequately simulate actual material use, risk, orgeneration characteristics. In addition, the tracer gastest does not simulate a live operator, who mayincrease potential for escape due to operator size,movements near the hood opening, or improper hooduse.

Hood containment should be evaluated at differentmannequin heights to represent workers of differentheight.

AM 0.05 can be achieved with a properly designed lab-oratory chemical hood. It should not be implied that thisexposure level is safe. Safe exposure levels are appli-cation specific and should be evaluated by properlytrained personnel (SEFA 1-2002).



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6.4 Ongoing or Routine Hood andSystem Tests

Routine performance tests shall be conductedat least annually or whenever a significantchange has been made to the operationalcharacteristics of the hood system.

A hood that is found to be operating with anaverage face velocity more than 10% belowthe designated average face velocity shall belabeled as out of service or restricted use andcorrective actions shall be taken to increaseflow.

Each hood shall be posted with a notice givingthe date of the routine performance test, andthe measured average face velocity. If it istaken out of service it shall be posted with arestricted use or out- of-service notice. Therestricted use notice shall state the requisiteprecautions concerning the type of materialspermitted or prohibited for use in the hood.

6.5 Types of Systems

6.5.1 Single Hood CAV Systems

Commissioning tests on single hood, constantair volume (CAV) systems shall consist of:

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

Fan Performance Tests shall include measure-ment of fan speed, fan static pressure, motorspeed, and amp draw.

ANSI/ASHRAE 110-1995 may be used in the labora-tory as an accepted test with specific values for thecontrol levels (and the release rate if you depart fromthe standard). It also may be used for routine periodictesting, but it is somewhat expensive and other less rig-orous tests may be adequate if conditions have notchanged since commissioning tests.

In addition to the hood tests, periodic testing at a mini-mum of 1-year intervals should ensure that:

• All other room exhaust provisions are within speci-fications;

• Room differential pressure is within specifications(if applicable);

• Room differential airflow is within specifications (ifapplicable).

Periodic tests concerning face velocity or hood exhaustvolume are valid indications of hood operation provid-ed no changes have been made in that hood structure,supply air distribution, or other factors listed above thataffect hood performance.

The hood sash should not be lowered below designposition to increase face velocity during routine tests. Adecrease in face velocity at the design opening may beindicative of a problem with operation of the exhaustsystem.

Ensuring proper operation of a laboratory chemicalhood requires proper design, installation, and opera-tion of all components of the exhaust systems andmany times the air supply systems as well.

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



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Exhaust duct measurements shall consist ofexhaust flow measurement and hood staticpressure measurement.

Hood performance tests shall consist of testsdescribed in Sections 6.3.1 through 6.3.6.

The hood monitor shall be calibrated andadjusted after hood performance has beendetermined as satisfactory. Safe operatingpoints shall be clearly identified for the hooduser.

6.5.2 Multiple Hood CAV Systems

Commissioning of multiple hood, constant airvolume systems shall include:

• Fan Performance Tests;• Verification of proper test, adjustment, and

balance of branch exhaust flow and staticpressures (exhaust flow and static pres-sure for each branch shall be recordedafter final balancing is complete);

• Hood Performance tests as describedabove in Sections 6.3.1 through 6.3.6; and

• Hood and System Monitor Calibration.

6.5.3 VAV Laboratory Chemical HoodSystems

VAV hood systems shall be commissionedprior to use by laboratory personnel to ensurethat all system components function properlyand the system operates as designed under allanticipated operating modes (defined underthe VAV section).

The commissioning procedures for VAV sys-tems shall include:

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

Tests; and• Verification of System Diversity.

The exhaust flow should be measured in the exhaustduct according the methods described inANSI/ASHRAE 41.2-1987 (RA 92) or as describedabove.

Fan performance and exhaust measurements shouldbe conducted by a certified Test-and-Balance firm.

Multiple hood systems should be balanced using aniterative approach where dampers or controllers areadjusted until flow through each hood is in accordancewith design specifications.

Hood performance tests should follow completion ofsystem balancing, measurement of branch exhaustflows, and branch static pressures.

Determine that sash position of one hood does notaffect flow through another hood.

Performance of laboratory chemical hoods connectedto variable air volume systems (VAV) can be affectedby numerous factors associated with proper design,calibration, and tuning of the control systems. It isimperative that all components of the VAV system be inproper operating condition to ensure proper hood per-formance.

Commissioning tests should be specified to verify thatthe VAV systems operate according to design specifi-cations. Some of the data, such as sensor calibrations,can be acquired through the process of installing theVAV controls or through the Testing, Adjustment andAir Balance process (TAB).



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6.5.3.1 VAV Sensor Calibration

VAV sensors shall be capable of accuratemeasurement and control within 10% of actualat the design maximum and minimum flowconditions.

6.5.3.2 VAV Hood Performance Tests

In addition to hood performance testsdescribed for evaluation of CAV hood systems,commissioning tests on VAV hood systemsshall include measurement of flow or facevelocities at different sash configurations andVAV Response and Stability tests.

Flow or face velocity measurements shall beconducted at a minimum of two separate sashconfigurations.

VAV Response and Stability tests shall includecontinuous measurements and recording offlow while opening and closing the sashes foreach hood (calibrated flow sensors or mea-surement of slot velocity within the hood canbe used as an indicator of flow).

VAV Response shall be sufficient to increaseor decrease flow within 90% of the target flowor face velocity in a manner that does notincrease potential for escape.

Documentation collected outside the commissioningtests, such as manufacturer’s tests on system compo-nents, should be available in advance of commission-ing tests for comparison with test data and inclusionwith final commissioning documents.

Numerous sensors can be employed in a typical VAVlaboratory chemical hood systems such as sash posi-tion sensors and room differential pressure sensors, toname a few. The accuracy of the sensors depends onproper methods to measure the physical parametersand ability to adjust calibration. Sensors that reportinaccurate information will not only be misleading whenmonitoring system operation but may result in unsafehood and laboratory conditions.

Part of the process of installing VAV controls and bal-ancing system airflows should involve calibration ofsensors and documentation of it.

At a minimum, commissioning tests should test a rep-resentative sample of sensors to verify accurate report-ing of information.

In the majority of VAV hood systems, the purpose ofthe VAV control system is to adjust airflows to compen-sate for changes in sash configurations or systemoperating mode (occupied/unoccupied, night setback,etc.). The VAV control system must be capable of quickand precise adjustment of flows without experiencingmajor overshoot or undershoot (10% of steady-statevalue).

Commissioning tests should be used to verify that VAVsystems provide satisfactory control of airflows inresponse to sash movement or changes in operatingmodes.

A response time of < 3 sec. after the completion of thesash movement is considered acceptable for mostoperations. Faster response times may improve hoodcontainment following the sash movement.



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VAV Stability shall be sufficient to prevent flowvariations in excess of 10% from design at eachsash configuration or operating mode.

6.5.3.3 VAV Ventilation System Tests

The VAV hood controls shall provide stable controlof flow in the exhaust and supply ducts and varia-tion of flow must not exceed 10% from design ateach sash configuration or operating mode.

6.5.3.4 Verification of System Diversity

System diversity shall be verified prior to use oflaboratory chemical hoods. The tests shall bedesigned to verify that users will be alerted whensystem capacity is exceeded and unsafe condi-tions may exist.

6.5.4 Laboratory Airflow Verification Tests

Tests to verify and commission the laboratoryshall 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 totalexhaust.

All ventilation system alarm and monitoring provi-sions associated with occupant safety shall beverified for proper functionality.

6.5.4.1 CAV Laboratory Room Tests

These tests shall ensure that the ventilation sys-tem design airflow is being maintained within theallowable 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.

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

The laboratory commissioning tests are used toensure proper air supply and exhaust for each lab-oratory or zone.

TAB data once verified can be substituted whereappropriate.

This includes local monitoring provisions for suchitems as hood airflow or room differential pressureas well as remote and central monitoring provisionsfor such parameters.



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If a specific room differential pressure (dP) has beenspecified, the dP shall be measured to ensure that it iswithin its allowable range.

If a room differential airflow is specified, actual roomdifferential airflow shall be determined to ensure that iswithin allowable maximum and minimum limits and inthe proper direction.

If the room has more than one ventilation control mode(i.e., occupied/unoccupied, etc.), each individual modeshall be enabled and applicable parameters (i.e., roomsupply, room total exhaust, etc.) shall be performed foreach separate mode.

Room ambient conditions (temperature, humidity, aircurrents, etc.) shall also be measured to ensure theyare being maintained under the conditions specified.

6.5.4.2 VAV Laboratory Room Tests

These tests shall ensure proper performance of theVAV ventilation system and its associated controlssuch that:

• The room general exhaust provides the specifiedrange of airflow.

• The room supply provides the specified range ofairflow.

• Room air cross currents at the laboratory hoodface opening are within limits.

If a specified room dP has been specified, the dP shallbe measured to ensure that it is being controlled with-in its allowable range with all doors closed and at min-imum and maximum room exhaust airflow.

If a room differential airflow is specified, actual roomdifferential airflow shall be determined to ensure that itis within allowable maximum and minimum limits anddirection at minimum and maximum room exhaust air-flow.

If the room has more than one ventilation control mode(i.e., occupied/unoccupied, etc.) conditions shall beevaluated for each mode.

Room ambient conditions (temperature, humidity, aircurrents, etc.) shall also be measured to ensure theyare being maintained under the conditions specified.

For most operations, 10 seconds will be anacceptable time to achieve the desired areapressurization but a Hazard Evaluation shouldbe conducted to determine the acceptable time.



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The VAV systems shall be capable of maintain-ing the offset flow required between exhaustand supply to achieve the desired area pres-surization within the desired time specified.

6.6 Laboratory Chemical Hoods

If practical, the exhaust flowrate from hoodsshall be tested by measuring the flow in theduct by the hood throat suction method or byflow meter.

If flow measurement in the duct is not practical,velocity at the hood face or opening shall bemeasured at a sufficient number of points toobtain a realistic average velocity, and multi-plied by the open area in the plane of the veloc-ity measurements to obtain the flowrate.

If the flowrate is more than 10% different fromdesign, corrective action shall be taken.

7 Work Practices

Hood users shall be trained in the proper oper-ation and use of a hood.

The user shall establish work practices thatreduce emissions and employee exposures.The user shall not modify the interior or exteri-or components of the hood without theapproval of the Chemical Hygiene Officer,Responsible Person, or other appropriateauthority in the organization. Many work prac-tices affect the overall safety and health in thelaboratory.

The following list concerns only those workpractices that relate directly to hood perfor-mance and applies only when hazardous mate-rials are to be used in the hood.

• The user shall not lean into the hood sothat his/her head is inside the plane of thehood, as defined by the sash, without ade-quate respiratory and personal protection.

For most operations, 10 seconds will be an acceptabletime to achieve the desired area pressurization but aHazard Evaluation should be conducted to determinethe acceptable time.

See the latest edition of the ACGIH-2001 IndustrialVentilation: A Manual of Recommended Practice. If aflowmeter is used, care should be taken to ensure thatthe element has not been compromised by chemicalaction or deposition of solids.

NOTE: Fine dust, for example, might adhere to thethroat of a venturi meter and change its inside dimen-sion, which is critical to the measurement.

The laboratory’s Chemical Hygiene Plan should dis-cuss proper work practices.

During setup or hood maintenance, this provision is notnecessary, provided there are no sources of chemicalsin the hood and the hood is decontaminated.



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• Equipment and materials shall not beplaced in the hood so that they block theslots or otherwise interfere with the smoothflow of air into the hood.

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

• The horizontal sash or panels shall not beremoved.

• The hood shall not be operated without theback baffles in place.

• Flammable liquids shall not be stored per-manently in the hood or the cabinet underthe hood unless that cabinet meets therequirements of NFPA 30-2000 and NFPA45-2000 for flammable liquid storage.

• The sash or panels shall be closed to themaximum position possible while still allow-ing comfortable working conditions.

• Hood users shall be trained to close thesash or panels when the hood is not in use.

• The hood user shall not operate with thesashes opened beyond the design opening.

• Pedestrian traffic shall be restricted nearoperating hoods.

• Rapid movement within the hood shall bediscouraged.

• The hood shall not be operated unless ver-ified it is working.

• Rapid movement of the sash or panels shallbe discouraged.

When large equipment must be placed in a laboratorychemical hood, placing the equipment on a stand toallow air to flow under the stand can reduce the sig-nificance of any airflow disturbance.

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

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

Although the storage of acids does not pose the samehazard as flammable solvents, the storage of acidsunder the hood should be in acid-resistant cabinets.Because of the high hazard associated with the stor-age of chemicals in front of the user at the hood, somelaboratories prohibit the storage of flammable materi-als under the hood. Individual policies are often sitespecific; hence, the Chemical Hygiene Officer shouldalways be consulted.

In some laboratory design, the normal sash position isnot full open. When the sash is raised above thedesign level, the hood could lose adequate control.

When a person walks past a laboratory chemical hoodhe or she sets up a wake that can aspirate contami-nants from the laboratory chemical hood. Proper loca-tion of the hood and administrative controls arerequired to minimize this potential hazard.



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7.5 Posting

Each hood shall be posted with a notice givingthe date of the last periodic field test. If thehood failed the performance test, it shall betaken out of service until repaired, or postedwith a restricted use notice.

The notice shall state the partially closed sashposition necessary for safe/normal operationand any other precaution concerning the typeof work and materials permitted or prohibited.

7.6 Operating Conditions

Hoods shall be in operation whenever haz-ardous volatile materials are being used orstored inside.

8 Preventive Maintenance

Inspection and maintenance shall follow anInspection and Maintenance (I&M) Programdeveloped by the user.

Preventive maintenance shall be performed ona regularly scheduled basis.

The intent is to ensure that those using the hood knowits current status and where to get help or further infor-mation.

Other information that should be posted may includeflowrates, fan numbers, an indication that the system isVAV or less than 100% diversity and an emergencyphone number.

A hood that is more than 10% below the standard oper-ating conditions, either because of inadequate facevelocity, or poor distribution of the face velocity shouldbe immediately reported to the responsible safety per-son. The hood should not be used unless specific con-ditions for safe use can be identified and posted suchas its maximum sash opening. Hoods should only beturned off when all materials are removed from theinterior and only if the hood does not provide generalexhaust ventilation to the space.

I&M programs should be “preventive” in nature.

The written I&M Program should identify potential haz-ards and problems associated with laboratory opera-tions and designate appropriate I&M procedures tominimize such hazards and problems. This couldinclude, for example, routine inspection of fan belts toensure that hood exhaust ventilation fans are turning atthe designed speeds, that hoods are being cleaned tominimize buildup of hazardous chemicals in the hoods,and so forth.

The written program should identify standard operatingprocedures to be followed during I&M activities.

The “responsible person” identified in Section 2.3should be involved in the development and operation ofthe I&M program.



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8.1 Operations During MaintenanceShutdown

Operations served by equipment being shut downfor inspection or maintenance shall be safely dis-continued and secured during such maintenance.

Lock-out/tag-out procedures shall be implemented.

Laboratory workers shall be notified in advance ofinspection and maintenance operations.

8.2 Housekeeping Before and AfterMaintenance

All toxic or otherwise dangerous materials on or inthe vicinity of the subject equipment shall beremoved or cleaned up before maintenance. Anyhazardous materials and any other debris shall becleaned up before operations resume.

8.3 Safety for Maintenance Personnel

Maintenance personnel shall be trained andrequired to use appropriate PPE (such as respira-tors, goggles or faceshields, gloves, and protectiveclothing) during parts of the work involving poten-tial hazard.

8.4 Work Permits

• A written work permit system shall be estab-lished whenever the integrity of a potentiallycontaminated ventilation system is to bebreached. Such work permits shall bedesigned to suit the circumstances, and shallat least address the following factors: The per-mit system shall be overseen by a responsibleperson, as defined in this standard, and shallbe signed by the person(s) to do the work,his/her supervisor, and any other supervisorsaffected by the work;

• The nature of the work, and the health andsafety precautions, shall be described;

• The time and place of the work shall bedescribed;

“Secured” condition will vary from case to case. Itmight consist of ceasing operation, or requiringremoval from the premises of all flammable andhighly toxic materials.

All ventilation equipment should be de-energizedand labeled as such with appropriate signagebefore starting any repair work.

If possible, equipment to be removed to the shopshould be decontaminated before removal. Also, aprocedure should be established to notify hoodusers before any maintenance is to be performedso work in the hood can be halted during mainte-nance. If the maintenance activities involve contactwith potentially contaminated parts of the system,these parts should be evaluated first by appropri-ate methods.



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• The same persons who signed the permit (ortheir counterparts on a different shift) shallsign off when the work is complete; and

• Completed work permits shall be filed by anappropriate management function andretained for a minimum of 3 years or as spec-ified by individual organizational policy.

8.5 Records

Records shall be maintained for all inspectionsand maintenance. If testing involves quantitativevalues (such as hood throat suction) theobserved values shall be recorded. Inspectionforms designed for the several categories of test-ing shall be provided and shall include the normalvalues for the parameters tested.

8.6 Testing and Monitoring Instruments

8.6.1 Air Velocity, Air Pressure, Temperatureand Humidity Measurements

Pressure instrumentation and measurement shallbe in compliance with ANSI/ASHRAE 41.3-1989.Temperature instruments and measurement tech-niques shall be in compliance withANSI/ASHRAE 41.1-1986 (RA 01). All instru-ments using electrical, electronic, or mechanicalcomponents shall be calibrated no longer than 12months before use or after any possible damage(including impacts with no apparent damage)since the last calibration. The accuracy of a scaleused for a given parameter shall meet the follow-ing requirements:

Velocity-fpm AccuracyBelow 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 Accuracy0.1 in.wg (25 Pa) 10% of signal0.5 in.wg (125 Pa) and higher 5% of signal

Between 25 Pa and 125 Pa, interpolate linearly.

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

Instruments of a “primary standard” nature (i.e.,standard pitot tubes, flow tube manometers, draftgauges, etc.)—if used with fluids for which they aredesigned and tested for leaks—require no furthercalibration.



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Pitot-static tube measurements shall be in accor-dance with ANSI/ASHRAE’s Method of TestMeasurement of Flow of Gas, 41.7-1984 (RA 00).Inclined manometers shall be selected so that thenominal value of the measured parameter is atleast 5% of full scale. U-tube manometers shallnot be used for pressures less than 0.5 in.wg (125 Pa). Pitot tubes other than standard shall becalibrated.

Temperature measurement instrumentation shallhave an accuracy of ±0.5°F or ±1°C over theentire measurement range.

Humidity measurement instrumentation shallhave an accuracy of ±3.0% relative humidity overthe entire measurement range.

8.6.2 Air Contaminant Monitors

Air contaminant monitors shall be tested at leastmonthly or more often, if experience or manufac-turer’s recommendations so indicate. Such testingshall include the sensing element, zero drift, andactuation of signals, alarms, or controls.

Continuous air monitors shall be calibrated permanufacturer’s specifications or more frequently ifexperience dictates.

8.6.2.1 Tolerance of Test Results

Allowable variance from design conditions, or con-ditions determined otherwise satisfactory, shallbe:

• For air velocity, +10%;• For ventilation air pressure or differential pres-

sure, +20%; For pneumatic control system airpressure, <5%; and

• For electronic control system, ±2% of full-scale values.

8.6.3 Other Test Instruments

Other instruments (such as voltmeters andtachometers) shall be checked for function andaccuracy against a “known source” before useand follow manufacturer’s recommendation, whenprovided, for periodic calibration.



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8.7 Monitoring Blowers, Motors, andDrives

8.7.1 Visual Inspection

Fans, blowers, and drive mechanisms shall bevisually inspected weekly.

8.7.2 V-belt drives

V-belt drives shall be stopped and inspectedmonthly for belt tension and signs of belt wearor checking.

8.7.3 Lubrication

Blowers, drives, and other critical machine ele-ments shall be lubricated at intervals and withlubricants recommended by the manufacturer.

8.8 Critical Service Spares

The ventilation system management plan shalladdress the need of providing for critical ser-vice issues and keeping spare parts on hand.

8.9 Critical Service Instrumentation

All critical service instrumentation shall havecontingency plans in place.

9 Air Cleaning

9.1 Supply Air Cleaning

Key problematic observations are abnormal noise orvibration, bearing noise, excessive temperature ofmotors, lubricant leaks, etc.

This will probably require removing the belt guard.

Preventive maintenance is intended to preventunplanned breakdowns, but breakdowns will occur. Insome cases, delivery time of replacement parts mightbe long enough to inhibit maintenance resulting fromperiodic inspection. Maintenance supplies and sparesshould be planned, taking into consideration the typicalfactors involved, such as:

• Potential health or safety risk of breakdown;• Availability of spares or replacements; and • Economic cost of facility out of service.

For critical equipment of 100 horsepower (74.6 kW) orlarger, consideration should be given to providing tem-perature and vibration sensors to give early warning ofproblems.

Laboratory air supply systems seldom require aircleaning for health and safety reasons. Supply aircleaning usually is provided, however, for technical rea-sons, usually to reduce the contamination from atmos-pheric dust and dirt. See ASHRAE 1999 Handbook –HVAC Applications.



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9.2 Exhaust Air Cleaning

Air-cleaning systems for laboratory exhaustsystems, where required, shall be designed orspecified by a responsible person to ensurethat air-cleaning systems will meet the perfor-mance criteria necessary for regulatory com-pliance. See ASHRAE 2001 Handbook –Fundamentals.

9.3 Filtration for Recirculation

Air-cleaning systems for recirculating generalexhaust or hood exhaust from laboratoriesshall meet the design and installation require-ments of ANSI/AIHA Z9.7-1998.

Recirculation of process air shall be returnedto the same room where the process is locat-ed and control of the process is supervised.

9.3.1 Airborne Particulates

Air-cleaning filtration systems for recirculatingexhaust air contaminated with toxic particu-lates shall be filtered through a two-stage par-ticulate filtration system specified following thestandard performance and design criteria ofthe ASHRAE Systems and Equipment to meetthe objectives of 2.4.1.

Filter installations shall be tested for leaks andhave all leaks repaired or the filter replacedbefore use.

The flowrate through the filters shall be main-tained at design specifications not to exceed100% of the rated flow capacity of the filters.

Exhaust air might require cleaning for one or more rea-sons (See Sections 4.2 and 5.3). Air-cleaning equip-ment covers a wide range of physical and chemicalmechanisms beyond the scope of this standard and itsproper application is, in general, not included.

Air-cleaning performance monitoring is typically limitedfor many hazardous materials. Chemical specificdetectors located downstream of adsorption media,pressure drop indicators for particulate filters, and/orperiodic stack sampling for contaminant emissions maybe required to monitor for regulatory compliance.

In practical terms, recirculation of exhaust air usually iseconomical only if the air needs to be cleaned of lowconcentrations of:

• Particulate material that can be removed by static(i.e., not self-cleaning) filters;

• Hazardous or odorous gases and vapors that canbe removed efficiently by adsorption media.

The two stage filtration system should consist of:

• A primary high efficiency filter (85–95% efficiency).See ANSI/ASHRAE 52.1-1992, & 52.2-1999), fol-lowed by

• An industrial-grade HEPA filter.

The properties and behavior of airborne particulatescover a wide range and may include dusts, fumes,mists, smoke, etc. Special caution should be takenwhen utilizing recirculating particulate air-cleaning sys-tems when condensation or evaporation of hazardousparticulate materials can take place in the airstream.

See the Institute of Environmental Sciences Recom-mended Practice for Laminar Flow Clean Air Devices.

The filter assembly should be provided with a damperand control that:



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9.3.2 Gases and Vapors

Adsorption or other filtration media used forthe collection or retention of gases and vaporsshall be specified for a limited use. Specifichazardous materials to be collected, airflowrate, temperature, and other relevant physicalproperties of the system shall be incorporatedinto the selection of filtration media.

A reliable and adequately sensitive monitoringsystem shall be utilized to indicate adsorbentbreakthrough. The sensitivity of the monitoringsystem shall be a predetermined fraction ofthe TLV® or appropriate health standard of thecontaminant being adsorbed but shall not bemore 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 uponsystem capacity design to allow a work opera-tion shut down or parallel filter switch-over,thus proving a fresh filter.

• Indicate the static pressure differential separatelyacross the primary and secondary filters and thepressure differential across both filters and thedamper;

• Actuate a damper motor (or allow manual activa-tion) to open the damper from an initial partiallyclosed position when filters are clean to a full-openposition when filters are fully loaded; and

• Actuate a signal or alarm when the pressure dropacross either the primary or secondary filter reach-es 0.01 in.wg (2.5 Pa) more than the rated-loadedpressure drop.

Also see the ASHRAE 2001 Handbook – Fundamentalsfor additional information on the theory and need forapplication of aircleaning equipment for the emissioncontrol of hazardous materials from work operations.

The intent of this section is to specify the need to havea method for detecting filter breakthrough before a haz-ardous contaminant is released to the laboratory envi-ronment. Any method that provides early, accurate, andreproducible detection for the contaminants present isacceptable.

Activated carbon and other adsorption media are avail-able in a number of configurations as filter housings.Media may be sprayed onto another filtration media asa thin coat or be packed into thin panels less than 2 in.(5.1 cm) in depth. Also, deep- bed filters, typically cylin-drical in shape and up to several feet in diameter andlength, are utilized to provide adequate retention timefor gas adsorption.

An important characteristic of adsorption media is thatupstream layers perform the adsorption function; withthe result that breakthrough of unadsorbed gas occursrather quickly without gradual reduction of adsorptionefficiency. Prediction of breakthrough in deep beds canbe accomplished by periodic withdrawal of media sam-ples from incremental depths of the bed, but this isimpractical in the shallow beds used in panels or insmaller cylindrical cartridges. Saturation of the activeadsorption sites occurs progressively through the layerof carbon and depends on the burden of adsorbate,which typically is variable. Therefore, breakthrough ofcontaminant on the downstream side of the carbonlayer is difficult to predict.



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For toxic gases and vapors, the filtration sys-tem shall be designed and sized for capacity toensure adequate collection and retention for aworst-case scenario when in the event of aspill or other major release, adequate warningis provided for personnel to stop work or enactother emergency procedures.

9.3.3 Handling Contaminated Filters

When required, contaminated filters shall beunloaded from the air-cleaning system follow-ing safe work practices to avoid exposing per-sonnel to hazardous conditions and to ensureproper containment of the filters for final dis-posal.

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

9.3.4 Ductwork Contamination

9.4 Testing and Monitoring

9.4.1 Air Filters

Recirculation air filters shall be inspected andtested as per Section 9.3.1 except that provi-sions are mandatory.

The Hazard Assessment should include recommendedwork practices and procedures to conduct filterchange-outs when filters have been exposed to haz-ardous materials. Hazardous waste disposal require-ments should be identified where needed.

Care should be taken during filter replacement to min-imize the release of hazardous materials from the fil-ters from being deposited downstream of the filterbank.The work area and, if necessary, the downstreamduct interior should be cleaned by HEPA-equippedvacuum cleaner or wet methods as appropriate beforereloading the clean filter.

Care should be taken during filter replacement to min-imize dirt from the filters being deposited downstreamof the filter bank or the work area. If necessary, the ductshould be decontaminated before and after thereplacement. Users may want to consider use of bag-out filters.

All air filters should be provided with differential pres-sure gauges. Gauges should be read at intervals of 1 week (or at other intervals, based on experience) andinspected visually at the same time. If the pressure dif-ferential equals or exceeds the rated maximum, the fil-ters should be changed at the first opportunity.



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9.4.2 Recirculated Activated CarbonBeds

Activated carbon beds or panels shall be test-ed as per Section 9.3.2 at intervals no longerthan 1 month initially and then based on expe-rience with the particular installation a sched-ule shall be prepared.

9.4.3 Air Pollution Control Equipment

Air pollution control equipment shall beinspected visually at intervals no longer than 1 week and, if necessary, at shorter intervals.Specific tests and repairs shall be in accor-dance with the manufacturer’s recommenda-tions or in compliance with applicable regula-tions.

The variety of generic types of pollution control equip-ment, combined with the many different configurationson the market, make it inappropriate to set forth spe-cific requirements.



APPENDIX 1 Definitions, Terms, Units

There are many terms and definitions associatedwith laboratory ventilation that have special mean-ing. The following are definitions of terms or unitsused in this document:

A2.1 adjacent roof line: For the purposes ofdetermining the laboratory chemical hood stackheight, the adjacent roof will be within 6 ft (1.8 m)horizontally of the nearest outer point of theexhaust fan stack. This criterion is intended to pro-tect maintenance workers from direct exposure totheir breathing zone, hands, feet, and other parts oftheir body. Parts of the building that are within 6 ft(1.8 m) horizontally of the exhaust fan stack areexempted if it would be impossible for a person tostand or cling to the surface in question.

A2.2 air changes per hour (ACH): A commonmeans for expressing a volumetric airflow through aroom. Each ACH for a room is intended to representan amount of air equal to the gross volume of the airpassing through the room each hour. An ACH ratefor a room can be converted to volumetric airflow bymultiplying the ACH number times the gross volumeof the room and then dividing the product obtainedby 60. For instance, for an ACH of 10, a room witha gross volume of 2400 cubic feet would require avolumetric airflow of 10 × 2400 ÷ 60 = 400 cfm (189 L/s). This term does not reflect actual mixingfactors and therefore does not indicate the effectiveair exchange rate in the room. See ACGIH’sIndustrial Ventilation: Manual of RecommendedPractice for further information on mixing factors.

A2.3 auxiliary air hood: A laboratory chemicalhood with an external supply air plenum at the topof the laboratory chemical hood. The auxiliary airplenum provides a makeup airstream comprised ofunconditioned or only minimally conditioned out-side air to substantially reduce the amount of con-ditioned room air exhausted by the laboratoryhood.

A2.4 bypass hood (constant air volumebypass laboratory hood): A laboratory hooddesign that incorporates an opening (bypass area)in the upper portion of the laboratory hood struc-ture. When the movable sash is fully open, the sash

blocks off this bypass area and all of the airflow intothe laboratory hood must pass through the openface area. However, as the sash is being closed toreduce the open face area, at a specific point anamount of bypass area is being uncovered. Theincrease in the bypass area opening offsets thedecrease in the face area opening, thus providingan alternate path (the uncovered bypass area) forair to flow into the laboratory hood. When utilizedwith a constant air volume ventilation system, thebypass area keeps the laboratory hood face veloc-ity relatively constant and from increasing to anobjectionably high value as the sash is lowered.

A2.5 capture velocity: The air velocity at apoint in space of sufficient magnitude to overcomeroom air currents and draw the air and any conta-minants at that point into the hood.

A2.6 chemical hygiene officer: An employeewho is designated by the employer and who isqualified by training or experience to provide tech-nical guidance in the development and implemen-tation of the provisions of the Chemical HygienePlan. This definition is not intended to place restric-tions on the position description or job classifica-tion that the designated individual shall hold withinthe employer’s organizational structure.

A2.7 constant air volume (CAV) ventilationsystem: A ventilation system designed to maintaina constant quantity of airflow within its ductwork.The airflow quantity is typically based upon theamount required to handle the most extreme con-ditions of outdoor-weather-related heat gain or lossand internal building loading. Although relativelysimple, a constant volume ventilation system typi-cally requires the maximum ongoing energy usagesince the system always operates at maximumcapacity.

A2.8 design sash position: The maximumopen area of the hood face that achieves thedesired face velocity during any work inside thehood that produces airborne contaminants.

A2.9 dilution ventilation: Ventilation airflowthat dilutes contaminant concentrations by mixingwith contaminated air, as distinguished from cap-turing the contaminated air.

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A2.10 discharge velocity: The speed of theexhaust air normally expressed in feet per minute(meters/second) at the point of discharge from alaboratory exhaust system. Since laboratoryexhaust system fans may be configured to dis-charge into a vertical exhaust stack or may utilizefans specifically designed to discharge directlyupward, the discharge velocity normally refers tothe air velocity as it leaves the last element of theexhaust system. Since the top of an exhaust stackmay be conical (or other type of configuration), thevelocity of the exhaust air at the point of dischargemay differ from the velocity of the air within the ver-tical stack itself. The term “stack velocity” is some-times used when referring to the speed of theexhaust airstream as it is discharged into the out-side air.

A2.11 diversity factor: A percentage factor thatis applied to establish the theoretical maximumexhaust airflow quantity that is required at any pointin time. For example, in an exhaust system con-sisting of three hoods, the diversity factor would be1/3 if at any point in time only one hood were beingused. Applying a diversity factor to the theoreticalmaximum required capacity of an HVAC system isoften considered in the design of a VAV system.Incorporating a diversity factor enables downsizingHVAC system components and thus results in asmaller capacity ventilation system. The overallintention of applying a diversity factor when design-ing a VAV ventilation system is to achieve a lowerlife cycle cost (e.g., lower system first cost and/orlower system energy costs).

A2.12 ductless hood: A laboratory hood that isnot connected to an exhaust system that dis-charges the laboratory hood exhaust outdoors.Rather, a ductless laboratory hood incorporates anexhaust fan and exhaust filters as an integral partof the laboratory hood and discharges the exhaustdirectly into the room. Ductless laboratory hoodsare of limited size and capacity in comparison toconventional ducted laboratory hoods.

A2.13 exhaust air: Air that is removed from anenclosed space and discharged into the atmos-phere.

A2.14 face velocity: The air velocity at the planeof and perpendicular to the opening of a laborato-ry chemical hood.

A2.15 floor-mounted hood (walk-in hood): Alarger-size laboratory hood with sash and/or doorarrangement that enables access from the floor tothe top of the hood interior. The name unfortunate-ly is a misnomer and although the design andheight of these hoods may allow it, users shouldnot walk into any hood that may represent a signif-icant exposure hazard. Walk-in laboratory hoodsenable larger equipment and apparatus (e.g.,equipment on carts, gas cylinders, etc.) to be morereadily put in and set up within the laboratory hood.

A2.16 glovebox: A controlled environment workenclosure providing a primary barrier from the workarea. Operations are performed through sealedgloved openings to protect the user, the environ-ment, and/or the product.

A2.17 HEPA: High Efficiency Particulate Air (fil-ter) for air filters of 99.97% or higher collection effi-ciency for 0.3 (m diameter droplets of an approvedtest aerosol (e.g., Emory 3004) operating at a ratedairflow.

A2.18 laboratory: It is difficult to provide a strictdefinition for laboratory. Some entire institutionsare formally named “Laboratory.” The general con-cept for application of this standard is a facility inwhich the amounts of chemicals handled are small[perhaps 22 or 44 lbs (10 or 20 kg), except for stor-age of supplies], where much of the work involvesmanual manipulation of small containers or bench-top apparatus, and where the work is not routineproduction of goods.

When this standard is used as a reference docu-ment in specifying design and construction (ormodification) of a facility, it is suggested that theparties involved in the activity agree whether thefacility is to be considered a laboratory. TheOccupational Safety and Health Administration, in29 CFR 1910.1450 (subpart 2, paragraph191.1450), provides a definition of “laboratory” forregulatory purposes.

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A2.19 laboratory chemical hoods: A chemicalhood is a box-like structure with one open side,intended for placement on a table or bench. Thebench and the hood may be one integral struc-ture. The open side is provided with a sash orsashes that move vertically and/or horizontally toclose the opening. Provisions are made forexhausting air from the top or back of the hood,and adjustable or fixed internal baffles may beprovided to obtain proper airflow distributionacross the open face. Provisions may be made forutilities and lighting.

A2.20 makeup air (replacement air): Air provid-ed by a ventilation system to replace air beingexhausted from a laboratory hood, canopy hood,room, or space.

A2.21 perchloric acid hood: A laboratory hoodconstructed and specifically intended for use withperchloric acid or other reagents that may formflammable or explosive compounds with organicmaterials of construction. A perchloric acid hood aswell as its exhaust system must be constructed ofall inorganic materials and be equipped with awater washdown system that is regularly used toremove all perchloric salts that may precipitate andcollect in the laboratory hood and in the exhaustsystem. The exhaust fan must also be of a spark-resistant design to ensure against ignition of anyperchlorate deposits in the exhaust system.

A2.22 recirculation: Air removed or exhaustedfrom a building area and ducted back to an air-han-dling system where it is mixed with outside freshair. This air mixture is then conditioned and utilizedfor ventilation. Since air removed from a space ismore often close to the temperature and humidityof the building interior than outside air, the recircu-lation process enables achieving a greater reduc-tion in heating and cooling energy than if 100%outside air was utilized (also see return air).

A2.23 reentry: The flow of contaminated air thathas been exhausted from a space back into thespace through air intakes or openings in the wallsof the space.

A2.24 replacement air: See makeup air.

A2.25 responsible person: An individual whohas the responsibility and authority for the designand implementation of the ventilation managementplan. This person may be the Chemical HygieneOfficer or work in conjunction with the ChemicalHygiene Officer.

A2.26 return air: Air being returned from a spaceto the ventilation fan that supplies air to a space.

A2.27 room air balance: A general term describ-ing the requirement that a laboratory room have theproper relationship with respect to the total exhaustairflow from the room and the supply makeup air-flow. The relationship of these airflows also estab-lishes the pressure differential between the labora-tory room and adjacent rooms and spaces.

A2.28 room ventilation: The volumetric airflowthrough a room expressed in terms of cfm or L/sec.

A2.29 special purpose hood: An exhaustedhood, not otherwise classified for a special purposesuch as but not limited to capturing emissions fromequipment such as atomic absorption gas chro-matographs; liquid pouring, mixing, or weighingstations; and heat sources. These hoods might notmeet the design description of various types oflaboratory chemical hoods discussed here. Theymay be exterior hoods, receiving hoods, or enclos-ing hoods, as described in the latest ACGIHIndustrial Ventilation: A Manual of RecommendedPractice.

A2.30 variable air volume—two-position venti-lation system: A constant air volume ventilationsystem (sometimes also referred to as a “two-posi-tion variable air volume system”) that is designed toprovide two separate levels of airflow. The higherlevel of airflow is provided when a facility is normal-ly occupied such as during regular work hours. Thelower level of airflow is utilized during unoccupiedtimes (e.g., nighttime, holidays, etc.) when ventila-tion needs and internal loads require less airflow.

A2.31 variable volume hood: A hood designedso the exhaust volume is varied in proportion to theopening of the hood face by changing the speed ofthe exhaust blower or by operating a damper orcontrol valve in the exhaust duct.

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A2.32 variable air volume (VAV) ventilationsystem: A type of HVAC system specificallydesigned to vary the amount of conditioned air sup-plied and exhausted from the spaces served. Theamount of air supplied and intended to meet (butnot exceed) the actual need of a space at any pointin time. In general, the amount of air that is neededby a space is determined by the required rate andthe amount of airflow necessary to maintain com-fortable conditions (temperature and humidity).

A2.33 velocity: Magnitude and direction of airmotion. As used in this standard, if the direction isomitted it is implied to be perpendicular to theplane of the airflow cross section. If the direction isimportant, it will be stated.

A2.34 volumetric airflow rate: The rate of air-flow expressed in terms of volume (cubic feet orliters) per unit of time. These are commonlyexpressed as cubic feet per minute (cfm) in USCSunits or liters per second (L/s) in SI units. (Alsosee room ventilation.)

A2.35 Walk-in hood: See floor-mounted hood.

A2.36 units and abbreviations:

ACD – air-cleaning device

AMCA – Air Movement Control Association

ACGIH – American Conference ofGovernmental Industrial Hygienists

AGS – American Glovebox Society

AIHA – American Industrial HygieneAssociation

ASME – American Society of MechanicalEngineers

ASHRAE – American Society of Heating,Refrigerating and Air ConditioningEngineers

AI – as installed

AM – as manufactured

AU – as used

BOCA – Building Officials and CodeAdministrators International

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)

I&M – Inspection and MaintenanceProgram

JIC – joint industry codes (hydraulic equipment)

LEED – Leadership in Energy andEnvironmental Design, a rating sys-tem from the U.S. Green BuildingCouncil

MAK – maximum allowable concentration

NFPA – National Fire Protection Association

NC – noise criteria curves

NEC – National Electrical Code

NFC – National Fire Code

NIOSH – National Institute for OccupationalSafety and Health

PEL – Permissible Exposure Limit

PPE – personal protective equipment

RC – room criteria curves

REL – Recommended Exposure Levels

SEFA – Scientific Equipment and FurnitureAssociation

SMACNA – Sheet Metal and Air ConditioningContractors 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 ExposureLevels

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APPENDIX 2 Referenced Standards and Publications

The following standards and associated publica-tions, when referenced in this document, constituteprovisions of this American National StandardsInstitute, Inc. At the time of publication, the editionsindicated were the most current. However, sincestandards and associated publications are subjectto periodic revision, parties to agreements basedon this American National Standard are encour-aged to ensure that they reference the most recenteditions of these documents.

ACGIH: Industrial Ventilation: A Manual ofRecommended Practice, 24th Edition. Cincinnati,OH: American Conference of GovernmentalIndustrial Hygienists, 2001.

ACGIH: Threshold Limit Values (TLV®) ForChemical Substances and Physical Agents.Cincinnati, OH: American Conference ofGovernmental Industrial Hygienists, 2002.

AGS-1998-001: Guideline for Gloveboxes, 2ndEdition. Santa Rosa, CA: American GloveboxSociety, 1998.

AMCA 99-0401-86: Classification for SparkResistant Construction. Arlington Heights, IL: AirMovement and Control Association, 1986.

AMCA 201-90: Fan Application Manual, Part I,Fans and Systems: AMCA Classification for SparkResistant Construction. Arlington Heights, IL: AirMovement and Control Association, 1990.

ANSI/AIHA Z9.2-2001: Fundamentals Governingthe Design and Operation of Local ExhaustSystems. Fairfax, VA: American Industrial HygieneAssociation, 2001.

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

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

ANSI/ASHRAE 41.2-1987 (RA 92): StandardMethods for Laboratory Air Flow Measurement.Atlanta, GA: American Society of Heating,Refrigerating and Air Conditioning Engineers, 1992.

ANSI/ASHRAE 41.3-1989: Standard Method forPressure Measurement. Atlanta, GA: AmericanSociety of Heating, Refrigerating and AirConditioning Engineers, 1989.

ANSI/ASHRAE 41.7-1984 (RA 00): Method of TestMeasurement of Flow of Gas. Atlanta, GA:American Society of Heating, Refrigerating and AirConditioning Engineers, 2000.

ANSI/ASHRAE 52.1-1992: Gravimetric and Dust-Spot Testing Procedure for Testing Air-CleaningDevices Used in General Ventilation for RemovingParticulate Matter. Atlanta, GA: American Societyof Heating, Refrigerating and Air ConditioningEngineers, 1992.

ANSI/ASHRAE 52.2-1999: Method of TestingGeneral Ventilation Air-Cleaning Devices forRemoval Efficiency by Particle Size. Atlanta, GA:American Society of Heating, Refrigerating and AirConditioning Engineers, 1999.

ANSI/ASHRAE 62-2001: Ventilation for AcceptableIndoor Air Quality. Atlanta, GA: American Societyof Heating, Refrigerating and Air ConditioningEngineers, 2001.

ANSI/ASHRAE 110-1995: Method of TestingPerformance of Laboratory Fume Hoods. Atlanta,GA: American Society of Heating, Refrigeratingand Air Conditioning Engineers, 1995.

ASHRAE 2001 Handbook – Fundamentals (Inch-Pound edition). Atlanta, GA: American Society ofHeating, Refrigerating, and Air-ConditioningEngineers, Inc., 2001.

ASHRAE 1999 Handbook – HVAC Applications(Inch-Pound edition). Atlanta, GA: AmericanSociety of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1999

The BOCA National Mechanical Code. CountryClub Hills, Ill: Building Official and CodeAdministrators International, 1993.

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CDC-NIH: Biosafety in Microbiological andBiomedical Laboratories, Appendix A, CDC-NIH,4th edition, Atlanta, GA: Centers for DiseaseControl and Prevention, 1999.

EPA-600/8-81-009: Guideline for Modeling ofAtmospheric Diffusion. Office of Air QualityPlanning and Standards, April 1981.

Fairfax, R. Letter to R. Morris, 4 April 2001.

“Hazard Communication,” Code of FederalRegulations. Title 29, Part 1910.1200, 1988.

IMC-2000: International Mechanical Code. FallsChurch, VA: International Code Council, 2000.

Institute of Environmental Sciences.Recommended Practice for Laminar Flow Clean AirDevices. Institute of Environmental Sciences, 1986.

Ivany, R., First, M., DiBerardinis, L.J.: “A NewQuantitative Method for In-Place Testing ofLaboratory Hoods,” American Industrial HygieneAssociation Journal 50 no.5: 275-280. (1989).

Kolesnikov, A., Ryan, R., Walters, D.B.: Use ofComputational Fluid Dynamics to Optimize Airflowand Energy Conservation in Laboratory Hoods andVented Enclosures. Washington, DC: EPA Labs forthe 21st Century, January 2002a.

Kolesnikov, A., McNally, J., Ryan, R., Walters, D.B.:CFD-Driven Design of a Low AirFlow, RapidRecovery System to Maximize Safety andOptimize Energy Efficiency, Durham, NC: EPALabs for the 21st Century, October 2002b.

LEED: Leadership in Energy and EnvironmentalDesign. U.S. Green Building Council.

Memarzadeh, F.: Methodology for Optimization ofLaboratory Hood Containment, Volumes I and II.Bethesda, MD: National Institutes of Health, 1996.

NFPA 30-2000: Flammable and CombustibleLiquids Code. Quincy, MA: National Fire ProtectionAssociation, 2000.

NFPA 45-2000: Standard on Fire Protection forLaboratories Using Chemicals. Quincy, MA:National Fire Protection Association, 2000.

NFPA 86-1999: Standards for Ovens andFurnaces. Quincy, MA: National Fire ProtectionAssociation, 2000.

NFPA 92A-2000: Recommended Practice forSmoke Control Systems. Quincy, MA: National FireProtection Association, 2000.

NSF 49-1992: Class II (Laminar Flow) BiohazardCabinetry. Ann Arbor, MI: National SanitationFoundation, International, 1992.

“Occupational Exposure to Hazardous Chemicalsin Laboratories,” Code of Federal Regulations Title29, Part 1910.1450, 1988.

Petersen, R.L., Cochran, B.C., LeCompte, J.:“Specifying Exhaust Systems that Avoid FumeReentry and Adverse Health Effects.” SymposiumPaper at ASHRAE Summer Meeting, Honolulu, HI,June 23-26, 2002. To be published in 2002ASHRAE Transactions.

Ratcliff and Sandru: “Dilution Calculations fordetermining Laboratory Exhaust Stack Heights,”(ASHRAE Transactions, 105, part 1, paper Ch-99-7-2, 1999).

SEFA-1-2002: Scientific Equipment and FurnitureAssociation, 2001.

SMACNA. HVAC Duct Construction Standards:Metal and Flexible, Merrifield, VA: Sheet Metal andAir Conditioning Contractors’ National Association,1995.

Smith, T.C. and Crooks, S.M: “Implementing aLaboratory Ventilation Management Program.”Chemical Health Safety 3 (1996): 12.

“Test Methods,” Code of Federal Regulations Title40, Part 60, Appendix A, 1989.

UMC-1997: Uniform Mechanical Code. Whittier,CA: International Conference of Building Officialsand Los Angeles, CA: International Association ofPlumbing and Mechanical Officials, 1997.

U.S. Nuclear Regulatory Commission, U.S.Department of Energy, U.S. EnvironmentalProtection Agency, and U.S. Department ofDefense: Multi-Agency Radiation Survey and SiteInvestigation Manual (MARSSIM) (EPA 402-R-97-016), 1997.

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APPENDIX 3 Selecting Laboratory Stack Designs

Necessary measures must be taken to protect thelaboratory building and adjacent buildings fromreingestion of toxic laboratory chemical hoodexhaust back into a building air supply system. The10 ft (3.0 m) minimum stack height called for in thebody of this standard is primarily intended to pro-tect maintenance workers from direct contamina-tion from the top of the stack. However, the mini-mum height of 10 ft (3.0 m) is not enough by itselfto guarantee that harmful contaminants would notbe reingested. Similarly, a minimum 3000 fpm (15.2m/s) exit velocity is specified in the body of thisstandard, but this exit velocity does not guaranteethat reingestion will not occur.

This appendix describes general stack designguidelines and three analysis methods for deter-mining an adequate stack design. The first analysismethod is termed the “Geometric” method, whichensures that the lower edge of an exhaust plumestays above the emitting building and associatedzones of turbulent airflow. The geometric method isfully described here and is accompanied by anexample. The second analysis method, brieflydescribed, predicts exhaust dilution at downwindlocations. The dilution equations are not presentedhere but can be obtained from Chapter 43 of theASHRAE 1999 Handbook – HVAC Applications. Adilution criterion is presented in this appendix tojudge the adequacy of the predicted dilutions inminimizing

reingestion. The third analysis method described iswind tunnel or water flume modeling.

General Guidelines

Laboratory chemical hood exhaust stacks shouldhave vertical, unobstructed exhaust openings.Chapter 43 of the ASHRAE 1999 Handbook –HVAC Applications describes appropriate rain pro-tection devices. Goosenecks, flapper dampers, andrain caps are unacceptable as they deflect theexhaust sideways or downward, making it muchmore likely that reingestion will occur.

For a given exhaust flow rate, reducing the exitdiameter with an exhaust nozzle is recommendedto increase the exit velocity and rise or throw ofthe exhaust over the building. However, exit veloc-ities much larger than 3000–4000 fpm (15.24 to20.32 m/s) may result in high noise and vibration.Too small of a nozzle, or one with too rapid adecrease in area, could result in excessive pres-sure loss in the exhaust and the resulting combi-nation of reduced flow due to fan system effectand reduced dilution and safety.

Combining exhausts into a common stack, eitherby manifolding exhausts or with very close group-ing of stacks, will enhance the rise of the exhaustplume. Close grouping of stacks can be used forspecialty exhausts that cannot be manifoldedbecause of their chemical nature. Manifolding orcombining exhausts can generally give greaterbenefit than installing an exhaust nozzle on a stackserving a single laboratory chemical hood.

Manifolding of exhausts can also provide someinternal dilution of laboratory chemical hoodexhausts when the majority of chemical emissionsare from an upset condition or large release from asingle laboratory chemical hood. Such upset orlarge release conditions are the primary cause ofodor complaints and potential health effects.However, this internal dilution is partially offset bythe decreased atmospheric dilution due to the larg-er plume size. Nevertheless, manifolding ofexhausts is still beneficial and recommended.

Variable exhaust flow rates, used to reduce energycosts, can periodically result in low exit velocities.Minimum exit velocities below 1500 fpm (7.62 m/s)are discouraged because for such low exit veloci-ties, high winds can cause the exhaust to traveldown the side of the stack instead of rising verti-cally. Makeup air or variable nozzles are recom-mended to maintain high exit velocities. Addingmakeup air is preferred because it provides thelarger plume rise and some internal dilution.

Air intake placement is as important as stackdesign. Intakes on the side of the building or atgrade will usually provide greater protection fromrooftop exhausts. Intakes on the roof may work ifplaced a sufficient distance from the exhausts.

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When only a single tall stack is present, an intakelocation near the base of the stack may be a goodlocation. The advantage of this location is dimin-ished if there are sources of toxic or odorousexhausts at other locations on the roof. Nearbyintakes elevated above a laboratory exhaust stackshould be avoided.

Rooftop obstacles, such as parapets or architec-tural fences, and penthouses on the same roof asthe hazardous exhaust stack can also act as adja-cent buildings causing wind flow disturbances thatreduce the rise of the exhaust. Note that it is the dif-ference in roof heights that is particularly importantwhen analyzing the adjacent building effect.

First Stack Design Method—The Geometric Method

Chapter 43 of the ASHRAE 1999 Handbook –HVAC Applications describes the geometricmethod. This is a conservative simplified methodmost appropriate for use by laboratory buildingventilation designers.

The geometric method is designed for isolated rec-tangular buildings that do not have taller buildings,dense taller trees, or taller hills close to the labora-tory building. Also air intakes on the emitting build-ing should be no higher than the top of the physicalexhaust stack opening. Provided these conditionsare met, the geometric method can be applied asfollows:

1) Calculate the length of the recirculation zone(R) downwind of the building for each of the fourbasic approach wind directions. For a givendirection, R = (Bsmall

0.67) (Blarge0.33), where Bsmall is

the smaller of the building height and width, andBlarge is the larger of the two. As used here, therecirculation zone height is the height of theemitting building.

Table A1 presents recirculation zone length forvarious building dimensions.

2) Calculate the added plume rise (throw) due toexhaust momentum and add it to the stackheight, to obtain the effective stack height. Theadded plume rise due to momentum (h-added)

equals 3 × (stack diameter) × (stack exit veloci-ty/1%-wind speed). The 1%-wind speed is ahigh wind speed exceeded only 1% of the time.These wind speeds are available for numerouslocations in the ASHRAE 1997 Handbook –Fundamentals, Chapter 26.

3) The effective height of the stack is the physicalstack height plus the added plume rise due tomomentum.

4) The geometric method, as stated here, specifiesthat the bottom of an exhaust plume shouldclear the emitting building, including penthous-es, and the recirculation zone downwind of thebuilding.The bottom of the plume extends down-ward at a 5:1 slope (5 units horizontal and 1 unitdownward) from the effective stack height(physical height plus added plume rise). Thisshould be done for all four of the basicapproach wind directions. Table A2 showsflowrates required to meet the geometricmethod, given a 10 ft (3.0 m) stack height and a3000 fpm (15.2 m/s) exit velocity (as per thisstandard), a 1%-wind speed of 15 mph (24 km/h), and various horizontal distances to clear.The horizontal distance is the distance betweenthe stack and the downwind building edge plusthe recirculation zone length.

The same method can be used to determine ataller stack that also complies.

Example Calculation for the First Stack DesignMethod—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 manifold-ed laboratory exhaust with a flowrate of 10,000 cfm(4719 L/s) is located in the center of the roof. Forwind 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 horizon-tal distance that must be cleared by the plumeequals 100 ft (30.5 m) from the center to the edgeof the building plus 71 ft (21.6 m) for the recirculationzone, or 171 ft (52.1 m). The required effective stackheight to clear the building and recirculation zone is171/5 (using the 5:1 slope) = 34.2 ft (10.4 m).

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The added stack height due to momentum is cal-culated next. The stack diameter is 2.06 ft (0.63 m)based on a 3000 fpm (15.2 m/s) exit velocity and a10,000 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 thisstandard, the effective stack height is 14 + 10 ft = 24 ft (7.32 m).

The required effective height computed above is34.2 ft (10.4 m), which is not met with a 10 ft (3.0 m)physical stack height.The designer can increase thephysical height to 20 ft (6.1 m). As an alternative, thedesigner can increase the momentum of the air byintroducing outside air to the system. If the physicalstack height remains at 10 ft (3.0 m), the diameterwould need to increase to 3.5 ft (1.1 m), increasingflow rate to about 30,000 cfm (14158 L/s). Also,

increasing to 30,000 cfm (14158 L/s) will increasein-stack dilution by a factor of 3:1. This in-stack dilu-tion, whether achieved by manifolding exhausts inthe building or by adding roof air, can be very valu-able to achieving safe results. The other wind direc-tion (aimed toward the long side of the building)should be checked, but for this example this winddirection is the worst case.

High volume flow in itself is not a guarantee of ade-quate dilution. For a given source spill rate in kilo-grams/second, a higher exhaust volume flow Qeincreases the in-stack dilution, but somewhatreduces the atmospheric dilution because theatmosphere is now presented with a larger volumeof gas to disperse.

The following Tables A1 and A2 allow for rapid esti-mates of required dilution to be made wherenumerical calculation is not possible at the time.

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Table A1 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 inFeet (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)

Length orWidth50 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)



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

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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 ofBuilding and Recirc.Zone

Feet to throw horizontally

Meters to throwhorizontally

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 dilutionwithin the plume can be used if the required stackheights or flowrates are too large from the geomet-ric method. Minimum dilution can be predictedusing equations from Chapter 43 of the ASHRAE1999 Handbook – HVAC Applications. The equa-tions are not discussed in detail here. The equationnumbers of most interest are equations 25 to 30 inChapter 43. These equations apply only to intakesbelow stack top. The stack height used in theseequations is the physical stack height only.“Effective stack height,” including the effect ofplume rise, should not be used. The EPA screeningdispersion model, SCREEN3, can also be used incertain situations to supplement the ASHRAEHandbook 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 recirculationzone 171 ft (52.1 m) away], the predicted minimumdilution from Chapter 43 is 455:1. If the diameter isincreased to 3.5 ft (1.07 m) associated with a largerflow rate of 30,000 cfm (14152.4 L/s), the minimumdilution decreases to 264:1.

At first glance, the smaller flowrate stack that yieldsthe 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 com-pared to the original 10,000 cfm (4719 L/s). Whencomparing the two cases, the larger flowrate casehas a total dilution of 3 × 264 = 792:1, which is bet-ter than the lower flowrate case and would providelower chemical concentrations at an air intake for agiven chemical release rate. Allowable spill rate tomeet the 0.05 ppm at the receptor location wouldbe 11.2 L/m of toxic vapor. The original design withd = 2.06 ft (0.63 m) has a higher dilution Dcrit of 455but the reduced volume flow only allows a spill



volume rate of 6.4 L/m. In effect, the factor of 3 vol-ume flow increase in the stack with the fan allowsabout a factor of 1.75 increase in allowable spillrate.

In conceptual terms, exit velocity and volume flowrate are “equal partners” in plume rise and theresulting increase in safety through greater dilution.However, in practical terms, exit velocities can onlybe increased by doubling or tripling while manifold-ing or adding roof air to the stack can easily resultin a 10-fold increase in dilution.

Dilution in the context of dispersion of laboratoryexhaust is a deceptively difficult concept becauseone must account for both the dilution within theexhaust system, De, which is present at the stackand the dilution from the stack to a downwind loca-tion, D. The concept can be simplified by normaliz-ing D by the volume flow rate through the exhauststack, Q. By normalizing D, only the dispersion,which occurs between the exhaust stack and thedownwind location, needs to be considered.

The normalized value can be presented in one oftwo ways, either as a normalized dilution or a nor-malized concentration value. A normalized dilutionvalue can be obtained by multiplying D by the ratioof the actual volume flow rate and a standardizedvolume flowrate [i.e., 1000 cfm (472 L/s) × (Qact /Qstd)]. The result is a dilution value that is indepen-dent of the actual volume flowrate through theexhaust stack, making it possible to compare theeffectiveness of various exhaust stacks with differ-ent volume flowrates, because all of the values arereferenced to the same 1000 cfm (0.47 m3/s) vol-ume flowrate.

A normalized concentration value is obtained byapplying the definitions of concentration and dilu-tion provided in the ASHRAE 1999 Handbook –HVAC Applications, Chapter 43 [C/m = 1/ (D × Q)].The result is a normalized concentration value thatis the ratio of the concentration present at thedownwind location and the mass emission rate ofthe emitted chemical, expressed in units of µg/m3

per g/s.This value is completely independent of thevolume flowrate through the exhaust stack, andthus can be used to readily compare the effective-ness of exhaust stacks with various volume

flowrates. Another advantage of this method is thatif the emission rate of a chemical is known, you cansimply multiply the emission rate by the C/m valueto obtain a pollutant concentration. This concentra-tion can then be compared directly with establishedhealth and odor limits.

Design Criteria

When designing stacks with the numerical method,it is necessary to have a design criterion for select-ing a stack design. Development of a dilution crite-rion can be difficult since the types and quantitiesof laboratory chemicals can vary significantly fromlaboratory to laboratory. As a starting place, it issuggested here to have the stack provide protec-tion similar to what a laboratory chemical hoodwould provide a worker standing at the hood. Asdescribed in this standard, a laboratory chemicalhood should have an ANSI/ASHRAE 110 test per-formed by a manufacturer, and the ANSI/ASHRAE110 rating should be AM 0.05 or lower. This ratingtranslates to the worker being exposed to 0.05 ppmor lower of tracer gas while 4 L/min of tracer gasare being emitted from within the laboratory chem-ical hood.The same 4 L/min of tracer gas are beingemitted from the laboratory chemical hood exhauststack. The recommended design criterion is thatthe 0.05 ppm concentration also be the maximumconcentration at the air intake. (The time constantfor exposure concentrations mentioned in this stan-dard 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. emissionrate and an allowable air intake concentration of0.05 ppm corresponds to a normalized concentra-tion design criterion of 750 µg/m3 per g/s or a 2800:1dilution for a 1000 cfm (472 L/s) flowrate exhaust,280:1 for a 10,000 cfm (4719 L/s) flow rate, and a93:1 dilution for a 30,000 cfm (14158 L/s) exhaust.These suggested design criteria is somewhat morelenient than the smaller criteria suggested in theASHRAE 1999 Handbook – HVAC Applications,Chapter 13, which recommend that air intake con-centrations should be less than 3 ppm due to anevaporating liquid spill in a laboratory chemicalhood and exhausted at a rate of 7.5 L/s. TheASHRAE criteria translate to a normalized concen-tration design criterion of 400 µg/m3 per g/s or a

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5000:1 dilution for a 1000 cfm (472 L/s) flowrateexhaust. For facilities with intense chemical utiliza-tion, design criteria specific for that facility can bedeveloped 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 alsomeets the 93:1 criterion for this flowrate, by a larg-er 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 showa solution to the dilution calculations. The first isRatcliff and Sandru (ASHRAE Transactions, 105,part 1, paper Ch-99-7-2, 1999) and the second isPetersen, Cochran, and LeCompte (to be pub-lished in 2002 ASHRAE Transactions). The solu-tions in both papers are for a Halitsky Criteria spill,0.028 ppm, rather than the criterion derived fromthe ANSI/ASHRAE 110 test specification. Quite abit of expertise is required to interpret the graphs.As an example, in the second paper, one point cal-culated and shown on the graph is that a zeroheight stack with a flow of 50,000 cfm (23597 L/s)and an exit velocity of 3000 fpm (15.2 m/s) wouldrequire an offset distance of 120 ft (36.6 m) to thenearest receptor site using the 0.028 ppm expo-sure limit at the receptor. These graphs werederived from Chapter 43 of ASHRAE 1999Handbook – Applications equations for critical windspeeds and dilutions. Zero-height stacks are quite

common because stacks that end below parapetwalls, below the height of adjacent penthouses, orthat end below adjacent screen walls or screenswill act as a zero-height stack. Receptor siteswould include operable doors and windows, andany location where pedestrian access was allowedas 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 twomethods described above are undesirable or if thegeometry or topography of the building site makessimple analysis methods unreliable, a scale modelof the building and surroundings should be physi-cally modeled in an atmospheric wind tunnel orwater flume. Physical modeling provides moreaccurate, and typically less conservative, predic-tions than the numerical or geometric methods.Physical modeling is the safest method to choosestack heights in new buildings or in buildings beingretrofitted. It more accurately accounts for complexbuilding geometries, taller nearby buildings, hills,architectural screens, and several stacks placedclosely together. Physical modeling should followthe guidelines given in the ASHRAE 2001Handbook – Fundamentals, Chapter 16. Dilutioncriteria are still necessary to evaluate the results ofphysical modeling. The design criteria discussedabove provide initial guidance. A more completeevaluation of appropriate design criteria should beconducted when the chemical usage is expected toexceed minimal levels. In addition, the design crite-ria should take into account the 20% factor outlinedin Section 5.3.4.

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APPENDIX 4 Audit Form for ANSI/AIHA Z9.5-2003

Laboratory Ventilation

Audit item numbers refer to Standard paragraphs. Compliance with the Standard should only be claimedwhen 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 controlsare used when there is a possibility of employee overexposure to air contaminants gener-ated by a laboratory activity.

( ) Laboratory worker chemical exposures are maintained below applicable in-house expo-sure limits.

( ) 2.1.2 The specific room ventilation rate is established or agreed upon by the owner or theirdesignee.

( ) 2.1.3 The general ventilation system is designed to replace exhausted air and provide the tem-perature, humidity, and air quality required for the laboratory procedures without creatingdrafts at exhaust hoods.

( ) 2.1.4 Dilution ventilation is provided to control the buildup of fugitive emissions and odors in thelaboratory.

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

( ) The plan addresses the laboratory operations and procedures that might generate air con-tamination 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 “responsibleperson.”

( ) 2.4.1 Employers ensure an ongoing system for assessing the potential for hazardous chemicalexposure.

( ) Employers promote awareness that laboratory hoods are not appropriate control devicesfor all potential chemical releases in laboratory work.

( ) The practical limits of knowing how each ventilation control is being used in the laboratoryare 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 toensure proper and adequate performance.

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( ) The employer establishes criteria for determining and implementing control measures toreduce employee exposures to hazardous chemicals; particular attention is given to theselection 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 rele-vance following the hazard assessment process:

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

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

3 Laboratory Chemical Hoods

( ) 3.1 The design and construction of laboratory chemical hoods conform to the applicable guide-lines presented in the latest edition of ACGIH Industrial Ventilation: A Manual ofRecommended Practice, and the most current codes, guidelines and standards, and anyother 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 open-ing.

( ) 3.1.1.1 Vertical sashes are designed so as not to be opened more than the design opening whenhazardous materials are present within the hood.

( ) Where the design sash opening area is less than the maximum sash opening area, thehood is equipped with a mechanical sash stop or alarm to indicate openings in excess ofthe design opening area.

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( ) 3.1.1.2 Horizontal sashes are designed so as not to be opened more than the design openingwidth 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.

( ) If a combination sash provides horizontally moving panels mounted in a frame that movesvertically, the above requirements are met.

( ) 3.1.1.4 The adverse consequences of the sash closing when the hood operator is not present toobserve is considered before automatic sash closing devices are installed on a laboratorychemical 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 travelduring sash closing operations without breaking glassware, etc.

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

( ) 3.2.1 Bypass hoods with either vertical or horizontal moving sashes meet the requirements ofSection 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:

( ) 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.

( ) 3.2.4 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 acidto form corrosive, flammable, and/or explosive compounds or byproducts;

( ) All interior hood, duct, fan, and stack surfaces are equipped with water wash-down capa-bilities;

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( ) All ductwork is constructed of materials that will be stable to and not react with perchloricacid 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 areknown 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 Sections3.2.1 and 3.3.

( ) 3.2.6 A variable air volume hood meets all mandatory requirements of Sections 3.2.1 and 3.3and is designed so the exhaust volume is varied in proportion to the opening of the hoodface.

( ) 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 haz-ardous chemicals generated under as-used conditions.

( ) The mechanism that controls the exhaust fan speed or damper position to regulate thehood exhaust volume is designed to ensure a minimum exhaust volume of 50 cfm/ft ofhood width, for a 24 in. (61 cm) deep hood (or 25 cfm/ft2 of hood work surface for differentdepth 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 bench-mark face velocity using the methods described above, that benchmark face velocity isused as a periodic check for continued performance as long as no substantive changeshave 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 facevelocity measurement and reproduced each time measurements are taken.

( ) Decreases in the average face velocity below 90% of the benchmark velocity are correct-ed prior to continued hood use.

( ) Face velocity increases exceeding 20% of the benchmark are corrected.

( ) 3.3.3 All hoods are equipped with a flow-measuring device or a face velocity alarm indicator orboth.

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

( ) The device is calibrated at least annually and whenever damaged.

( ) 3.3.4 Lab chemical hoods are located so their performance is not adversely effected by crossdrafts.

( ) Windows in laboratories with hoods are fully closed while hoods are in use (emergencyconditions excepted).

4 Other Containment Devices

( ) 4.1.1 Gloveboxes are not used for manipulation of hazardous materials with the face or otherpanels 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 switch-es are provided outside the glovebox for emergency shutoff.

( ) 4.1.4 Proper application of ergonomic principles is met by referring to Chapter 5.10, “Guidelinesfor Gloveboxes,” AGS-G001-1998.

( ) 4.1.5 The design of the glovebox provides for retaining spilled liquids so the maximum volume ofliquid permitted in the glovebox will be retained.

( ) 4.1.6 Containment gloveboxes are provided with exhaust ventilation to result in a negative pres-sure 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 atmospherein accordance with the general provisions of this standard and pertinent environmental reg-ulations.

( ) Air-cleaning equipment is sized for the maximum airflow anticipated when hazardousagents are exposed in the glovebox and the glovebox openings are open to the extent per-mitted under that condition.

( ) If the air-cleaning device (ACD) is passive, provision is made for determining the status ofthe ACD, as noted in Section 9.3. If the ACD is active, instrumentation is provided to indi-cate 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 environ-ment and so not to contaminate the surrounding areas.

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( ) 4.1.8 Exhaust piping is in accordance with the principles described in ACGIH IndustrialVentilation: A Manual of Recommended Practice, ANSI/AIHA Z9.2, and the ASHRAE 2001Handbook – 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 pressurerelationships to the user is provided on all gloveboxes.

( ) If audible alarms are not provided, documented training for users in determining safe pres-sure 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 contami-nation is reduced to a safe level.

( ) If the contaminant is gaseous, the atmosphere in the box is adequately exchanged toremove the potentially hazardous gas.

( ) If the contaminant is liquid, any liquid on surfaces is wiped with suitable adsorbent mater-ial 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 vis-ibly clean and the exterior surfaces of the gloves also are wiped clean.

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

( ) When there is any uncertainty about the effectiveness of the contamination reduction pro-cedures, personnel involved in opening the panels of the glovebox are provided with appro-priate PPE or clothing.

( ) 4.1.11 A high containment glovebox conforms to all the mandatory requirements of 4.1.1 through4.1.11, and

( ) Is provided with one or more air-lock pass-through ports for inserting or removing objectsor sealed containers without breaching the physical barrier between the inside and outsideof the glovebox.

( ) Maintains negative operating static pressure within the range of –0.5 to –1.5 in. wg (–125to –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 lowerexplosive limit.

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( ) Prevents transport of contaminants out of the glovebox.

( ) 4.1.12 A medium containment glovebox conforms to all the mandatory requirements of Sections4.1.1 through 4.1.10, and is not provided with pass-through airlocks, and is provided withsufficient exhaust ventilation to maintain an inward air velocity of at least 100 fpm (0.51m/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 adequatefor that purpose.

( ) 4.1.14 An isolation and containment glovebox is used to control special atmosphere work wheneither 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, orspecial case containment gloveboxes as necessary.

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

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

( ) Care is exercised when placing certain hazardous liquids in an evacuated airlock or interi-or of a glovebox when a decrease in pressure could affect the boiling point of the liquid,causing it to go to gaseous state.

( ) 4.2 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 Section2.1.1 of this Standard.

( ) Compliance with the general requirements of Sections 2, 3.3 and 5.3.6.2, are evaluated byqualified persons.

( ) Ductless hoods that do not meet the requirements specified in Sections 9.3 and 9.4 areused only for operations that normally would be performed on an open bench without pre-senting an exposure hazard.

( ) Ductless hoods have signage prominently posted on them to inform operators and main-tenance personnel about the allowable chemicals used in the hood, type and limitations offilters 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 contam-inated with toxic particulates must meet the requirements of Section 9.3.1.

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( ) 4.2.2 Ductless hoods utilizing adsorption or other filtration media for the collection or retention ofgases and vapors are specified for a limited use.

( ) 4.2.3 Contaminated filters are unloaded from the air-cleaning system following safe work prac-tices to avoid exposing personnel to hazardous conditions and to ensure proper contain-ment of the filters for final disposal.

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

( ) 4.3 Special laboratory chemical hoods are designed in accordance with ANSI/AIHA Z9.2 andACGIH Industrial Ventilation: A Manual of Recommended Practice.

5 Laboratory Ventilation System Design

( ) 5.1.1 As a general rule, airflow is from areas of low hazard to higher hazard and exceptions aredocumented.

( ) When flow from one area to another is critical to emission exposure control, airflow-moni-toring 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 willbe lower than the exposure limits required by 2.1.1.

( ) The desired directional airflow between rooms is identified in the design and operatingspecifications.

( ) 5.1.1.1 Airlocks are utilized to prevent undesirable airflow from one area to another in high haz-ardous 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 labora-tory room, and the other door of the airlock provides passage to or from a corridor (or othernonlaboratory area).

( ) Airlock doors are arranged with interlocking controls so that one door must be fully closedbefore the other door may be opened.

( ) 5.1.1.2 If the direction of airflow between adjacent spaces is deemed critical, provision is made tolocally 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);

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( ) 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 locationand 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 labo-ratory room could pose a significant toxic or fire hazard, the room is equipped with provi-sion(s) to initiate emergency notification and initiate the operation of the ventilation systemin a mode consistent with accepted safety practices.

( ) A hazard assessment is performed to identify the credible emergency conditions that mayoccur.

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

( ) For rooms served by CAV ventilation systems that utilize a reduced ventilation level forenergy savings, the chemical emergency mode of operation ensures that the room venti-lation and negative pressurization are at the maximum rate.

( ) Operation of the room ventilation system in a chemical emergency mode does not reducethe 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 airflowfrom the corridor into the laboratory, supply air volume is less than the exhaust from thelaboratory.

( ) When laboratories are to be maintained with a positive pressurization and directional air-flow, 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 one-third of the capture velocity or the face velocity of the laboratory chemical hoods at theirface opening.

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( ) 5.2.3 Supply systems meet the technical requirements of the laboratory work and the require-ments of the latest version of ANSI/ASHRAE 62.

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

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

( ) Exhaust ductwork is designed in accordance with ANSI/AIHA Z9.2 and Chapter 34 of theASHRAE 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 thatincludes the centerline of the main duct.

( ) For horizontal main ducts, branch ducts do not enter a main duct on a plane below the hor-izontal 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 weld-ed formed sheet.

( ) Longitudinal seams that are formed mechanically are utilized only for light duty systemswith 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 insideof 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 atleast 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 IndustrialVentilation: A Manual of Recommended Practice, Chapter 34 of the ASHRAE 2001Handbook – Fundamentals, and Chapter 6-5 of NFPA 45.

( ) Exhaust system materials are resistant to corrosion by the agents to which they areexposed.

( ) Exhaust system materials are noncombustible if perchloric acid or similar oxidizing agentsthat pose a fire or explosive hazard are used.

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( ) 5.3.2.2 Laboratory chemical hood ducts combined into a common manifold adhere to the follow-ing exceptions and limitations:

( ) Perchloric acid hoods are not manifolded with nonperchloric acid hoods unless a scrubberis installed between the hood and the manifold.

( ) Where there is a potential contamination from hood operations as determined from theHazard Evaluation and Analysis of Section 2.4, radioisotope hoods are not manifolded withnonradioisotope hoods unless in-line HEPA filtration and/or other necessary air- cleaningsystems are provided between the hood and the manifold.

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

( ) Exhaust streams comprised of radioactive materials are adequately filtered to ensureremoval of radioactive material before being connected to a centralized exhaust system.

( ) Biological exhaust hoods are adequately filtered to remove all hazardous biological sub-stances prior to connection to a centralized exhaust system.

( ) 5.3.2.4 Provision is made for continuous maintenance of adequate negative static pressure in allparts of the system, as necessary, or the hood is emptied and decontaminated and provi-sions are implemented to prevent the hood from back-drafting.

( ) The VAV hood is provided with an emergency switch that allows the hood exhaust volumeto return to the maximum.

( ) 5.3.2.5 Class II-Type A and Type B3 biological safety cabinets manifolded with chemical laborato-ry chemical hoods have either:

( ) A thimble connection; or

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

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

( ) 5.3.2.6 The static pressure in the exhaust system is lower than the surrounding areas throughoutthe 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 andthe discharge ductwork passes directly from the fan to the outside without passing throughanother room or space.

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( ) There are no flexible connections on the discharge side of the fan and all ductwork in thedischarge 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” asdefined 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 anytime it is in use and to prevent backflow of air into the laboratory when the following condi-tions are present:

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

( ) Exhaust system operation is required to maintain minimum ventilation rates and room pres-sure control.

( ) There are powered devices connected to the manifold. Powered devices include, but arenot 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 atleast two exhaust fans for redundant capacity.

( ) Emergency power is connected to one or more of the exhaust fans where exhaust systemfunction 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 indi-vidual piece of laboratory equipment is adequately sized to provide the necessary amountof exhaust airflow in conjunction with the size, amount, and configuration of the connectingductwork.

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

( ) If flammable gas, vapor, or combustible dust is present in concentrations above 20% of theLower Flammable Limit, fan construction is as recommended by AMCA’s Classification forSpark Resistant Construction.

( ) Laboratory exhaust fans are located as follows:

( ) Physically outside of the laboratory building and preferably on the highest levelroof of the building served.

( ) In a roof penthouse or a roof mechanical equipment room that is always main-tained at a negative static pressure with respect to the rest of the facility, and providesdirect fan discharge into the exhaust stack(s).

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( ) All laboratory exhaust fans include provisions to allow periodic shutdown for inspection andmaintenance. Such provisions include:

( ) Ready access to all fans, motors, belts, drives, isolation dampers, associated con-trol equipment, and the connecting ductwork.

( ) Isolation dampers on the inlet side of all centralized exhaust system fans that haveindividual discharge arrangements or their own individual exhaust stacks.

( ) Isolation dampers on both the inlet and outlet sides of all centralized exhaust sys-tem fans that discharge into a common exhaust stack or plenum.

( ) Sufficient space to allow removal and replacement of a fan, its motor, and all otherassociated exhaust system components and equipment without affecting other mechanicalequipment or the need to alter the building structure.

( ) 5.3.4 The discharge of potentially contaminated air to a concentration more than the allowablebreathing 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 emis-sions;

( ) Discharged in a manner and location to avoid reentry into the laboratory building or adja-cent buildings at concentrations above 20% of allowable concentrations inside the labora-tory for routine emissions or 100% of allowable concentrations for emerging emissionsunder 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 1999Handbook – HVAC Applications.

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

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

( ) Esthetic conditions concerning external appearance do not supersede the requirements ofSections 5.3.4 and 5.3.5.

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

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

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( ) 5.3.6 Nonlaboratory air or air from building areas adjacent to the laboratory is used as part ofthe 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) isnot recirculated to other areas unless one of the following sets of criteria is met:

1) Criteria A

• 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.

2) Criteria B

• Recirculated air is treated to reduce contaminant concentrations to those specified in2.1.1.

• Recirculated air is monitored continuously for contaminant concentrations or provided witha secondary backup air-cleaning device that also serves as a monitor (via a HEPA filter ina 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.

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

6 Commissioning Tests

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

( ) 6.2 All newly installed, renovated, or moved hoods are commissioned to ensure proper oper-ation prior to use by laboratory personnel.

( ) 6.2.1 The commissioning process is overseen by a responsible person or commissioning authori-ty.

( ) 6.2.2 A written commissioning plan accompanies design documents and is approved by thecommissioning authority in advance of construction activities.

( ) The commissioning plan is available to all potential suppliers and contractors prior to bidalong with the other project documents.

( ) The commissioning plan addresses operation of the entire ventilation system where thehoods, laboratories, and associated exhaust and air supply ventilation systems are con-sidered subsystems.

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

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

( ) 6.2.3 Preliminary and final commissioning documents are issued to the appropriate party(s) bythe 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 arecommunicated to the responsible party (i.e., installer, subcontractor, etc.) for prompt cor-rection.

( ) 6.3 Specification and procurement of laboratory chemical hoods are based on performancetests conducted on the hood (or prototype hood) that demonstrate adequate hood con-tainment.

( ) 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 supplyflow 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 measur-ing 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 flowsrequired to achieve the design average face velocity.

( ) 6.3.3 The average face velocity is determined by the method described in the ANSI/ASHRAE110, Method of Testing Performance of Laboratory Fume Hoods.

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( ) Face velocity measurements are made by dividing the hood opening into equal area gridswith sides measuring no more than 12 in. ( 30.5 cm). The tip of the probe is positioned inthe plane of the sash opening and fixed at the approximate center of each grid, and gridmeasurements around the perimeter of the hood opening are made at a distance ofapproximately 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 unlessroom pressurization would change significantly to affect exhaust flow.

( ) Where exhaust flow would be affected by turning off the auxiliary airflow, auxiliary air isredirected from the hood opening.

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

( ) The average auxiliary air velocity is determined from the average of grid velocities mea-sured across the plenum outlet.

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

( ) Over a period of 10 – 30 sec., cross-draft velocities are recorded approximately at 1 read-ing 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 notsufficient to cause escape from the hood.

( ) Cross-draft velocities are not of such magnitude and direction as to negatively affect con-tainment.

( ) 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 iden-tify 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 hoodconstitute 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 beequivalent.

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

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

( ) 6.4 Routine performances tests are conducted at least annually or whenever a significantchange 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% belowthe designated average face velocity is labeled as out of service or restricted use and cor-rective actions are taken to increase flow.

( ) Each hood is posted with a notice giving the date of the routine performance test, and themeasured 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 materialspermitted 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, motorspeed, and amp draw.

( ) Exhaust duct measurements consist of exhaust flow measurement and hood static pres-sure 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 determinedas 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 sys-tems include:

( ) Fan Performance Tests;( ) Verification of proper test, adjustment, and balance of branch exhaust flow and static pres-

sures (exhaust flow and static pressure for each branch are recorded after final balancingis complete);

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( ) Hood Performance Tests as described above in Sections 6.3.1 through 6.3.6 ; and( ) Hood and System Monitor Calibration.

( ) 6.5.3 VAV hood systems are commissioned prior to use by laboratory personnel to ensure thatall system components function properly and the system operates as designed under allanticipated 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 thedesign maximum and minimum flow conditions.

( ) 6.5.3.2 In addition to hood performance tests described for evaluation of CAV hood systems, com-missioning tests on VAV hood systems include measurement of flow or face velocities atdifferent sash configurations and VAV Response and Stability tests.

( ) Flow or face velocity measurements are conducted at a minimum of two separate sashconfigurations.

( ) VAV Response and Stability tests include continuous measurements and recording of flowwhile opening and closing the sashes for each hood (calibrated flow sensors or measure-ment 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 orface 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 eachsash configuration or operating mode.

( ) 6.5.3.3 The VAV hood controls provide stable control of flow in the exhaust and supply ducts andvariation of flow does not exceed 10% from design at each sash configuration or operatingmode.

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

( ) The tests are designed to verify that users will be alerted when system capacity is exceed-ed and unsafe conditions may exist.

( ) 6.5.4 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.

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( ) All ventilation system alarm and monitoring provisions related to occupant safety are veri-fied for proper functionality.

( ) 6.5.4.1 CAV laboratory room tests ensure that the ventilation system design airflow is being main-tained 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 itsallowable range.

( ) If a room differential airflow is specified, actual room differential airflow is determined toensure 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 totalexhaust, etc.) are performed for each separate mode.

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

( ) 6.5.4.2 VAV laboratory room tests ensure proper performance of theVAV ventilation system and itsassociated 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 beingcontrolled within its allowable range with all doors closed and at minimum and maximumroom exhaust airflow.

( ) If a room differential airflow is specified, actual room differential airflow is determined toensure that it is within allowable maximum and minimum limits and direction at minimumand 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 toensure they are being maintained under the conditions specified.

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

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( ) 6.6 If practical, the exhaust flowrate from hoods is tested by measuring the flow in the duct bythe 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 mea-sured at a sufficient number of points to obtain a realistic average velocity, and multiplied bythe 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.

7 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 theapproval of the Chemical Hygiene Officer, Responsible Person, or other appropriate author-ity 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 thehood, 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 orotherwise 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 thehood unless that cabinet meets the requirements of NFPA 30 and NFPA 45 for flammableliquid storage.

( ) The sash or panels are closed to the maximum position possible while still allow-ing 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.

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

( ) If the hood failed the performance test, it is taken out of service until repaired, or a restrict-ed use notice is posted on the hood.

( ) The notice states the partially closed sash position necessary for safe/normal operationand any other precaution concerning the type of work and materials permitted or prohibit-ed.

( ) 7.2 Hoods are in operation whenever hazardous volatile materials are being used or storedinside.

8 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 Operations served by equipment being shut down for inspection or maintenance are safe-ly discontinued and secured during such maintenance.

( ) Laboratory workers are notified in advance of inspection and maintenance operations.

( ) 8.2 All toxic or otherwise dangerous materials on or in the vicinity of the subject equipment isremoved 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 workinvolving potential hazards.

( ) 8.4 A written work permit system is established whenever the integrity of a potentially conta-minated ventilation system is to be breached.

( ) Such work permits are designed to suit the circumstances, and at least address the fol-lowing factors:

( ) The permit system is overseen by a Responsible Person, as defined in this stan-dard, and is signed by the person(s) to do the work, their supervisor, and any other super-visors 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 differentshift) sign off when the work is complete;

( ) Completed work permits are filed by an appropriate management function andretained for a minimum of 3 years or as specified by individual organizational policy.

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( ) 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 includethe normal values for the parameters tested.

( ) 8.6.1 Pressure instrumentation and measurement are in compliance with ANSI/ASHRAE41.3(1989. Temperature instruments and measurement techniques are in compliance withANSI/ASHRAE 41.1(1986(RA 01).

( ) All instruments using electrical, electronic, or mechanical components are calibrated nolonger than 12 months before use or after any possible damage (including impacts with noapparent damage) since the last calibration.

( ) The accuracy of a scale used for a given parameter meets the following requirements:

Velocity-fpm AccuracyBelow 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 Accuracy0.1 in.wg (25 Pa) 10% of signal0.5 in.wg (125 Pa) and higher 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 isat least 5% of full scale. U-tube manometers should not be used for pressures less than0.5 in. wg (125 Pa).

( ) Pitot tubes other than standard are calibrated.

( ) 8.6.2 Air contaminant monitors are tested at least monthly or more often, if experience or man-ufacturer¹s recommendation indicates.

( ) Such testing includes the sensing element, zero drift, and actuation of signals, alarms, andcontrols.

( ) Continuous air monitors are calibrated per manufacturer¹s specifications or more fre-quently if experience dictates.

( ) 8.6.3 Other instruments (such as voltmeters and tachometers) are checked for function andaccuracy 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.

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( ) 8.7.2 V-belt drives are stopped and inspected monthly for belt tension and signs of belt wear orchecking.

( ) 8.7.3 Blowers, drives, and other critical machine elements are lubricated at intervals and withlubricants recommended by the manufacturer.

( ) 8.8 Ventilation system management plan addresses the need to provide critical service issuesand 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 orspecified by a Responsible Person to ensure that air-cleaning systems will meet the per-formance criteria necessary for regulatory compliance.

( ) 9.3 Air-cleaning systems for recirculating general exhaust or hood exhaust from laboratoriesmeet 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 andcontrol of the process is supervised.

( ) 9.3.1 Air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particu-lates are filtered through a two-stage particulate filtration system specified as following thestandard performance and design criteria of the ASHRAE systems and equipment to meetthe objectives of 2.4.1.

( ) Filter installations are tested for leaks and have all leaks repaired or the filter replacedbefore use.

( ) The flowrate through the filters is maintained at design specifications and does not exceed100% 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 vaporsare specified for a limited use.

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

( ) A reliable and adequately sensitive monitoring system is utilized to indicate adsorbentbreakthrough. The sensitivity of the monitoring system is a predetermined fraction of theTLV® or appropriate health standard of the contaminant being adsorbed but is not morethan 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 shutdown or parallel filter switch-over, thus proving a fresh filter.

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( ) For toxic gases and vapors, the filtration system is designed and sized to ensure adequatecollection and retention for a worst case scenario when in the event of a spill or other majorrelease.

( ) Adequate warning is provided for personnel to stop work or enact other emergency proce-dures.

( ) 9.3.3 When required, contaminated filters are unloaded from the air-cleaning system followingsafe work practices to avoid exposing personnel to hazardous conditions and to ensureproper 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 provisionsare mandatory.

( ) 9.4.2 Activated carbon beds or panels are tested as per Section. 9.3.2 at intervals no longer than1 month initially and then, based on experience with the particular installation, a scheduleis 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 orare in compliance with applicable regulations.

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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

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American Industrial Hygiene Association2700 Prosperity Ave., Suite 250

Fairfax, VA 22031(703) 849-8888

[email protected]

Stock Number: LVEA03-437

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Documents

ANSI-AIHA Z9-5-2003