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BY TH E ANSI/AIHA Z9.5 SUBCOMMITTEE

A Publication by

American Industrial Hygiene Association

ANSI /AIHA Z9 .5–2012

LaboratoryVentilation

Please note the American Society of Safety Engineers

(ASSE) is now the Secretariat of the Z9 ASC and

holds the copyright to this standard.

American Society of Safety Engineers

www.asse.orgA S

S E

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ANSI/AIHA® Z9.5–201 2

ANSI/AIHA® Z9.5 – 201 2

Laboratory Ventilation

Secretariat


Approved April 26, 201 2

Please note the American Society of Safety Engineers

(ASSE) is now the Secretariat of the Z9 ASC and

holds the copyright to this standard.

American Society of Safety Engineers

www.asse.org

Published by

American Industrial Hygiene Association31 41 Fairview Park Drive, Suite 777, Falls Church, VA 22042www.aiha.org

Copyright © 201 2 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 publ isher.

Printed in the United States of America.

ISBN 978-1 -935082-34-7

Stock Number: LVEA1 2-437

American

National

Standard

Approval of an American National Standard requires verification by ANSI that therequirements for due process, consensus, and other criteria for approval have beenmet by the standard’s developer.

Consensus is establ ished when, in the judgment of the ANSI Board of StandardsReview, substantial agreement has been reached by directly and material ly affectedinterests. Substantial agreement means much more than a simple majority, but notnecessari ly unanimity. Consensus requires that al l views and objections be consid-ered, and that a concerted effort be made toward their resolution.

The use of American National Standards is completely voluntary; their existencedoes not in any respect preclude anyone, whether he or she has approved the stan-dards or not, from manufacturing, marketing, purchasing, or using products, proces-sors, or procedures not conforming to the standards.

The American National Standards Institute does not develop standards and wi l l in nocircumstances give an interpretation of any American National Standard. Moreover,no person shal l have the right or authority to issue an interpretation of an AmericanNational Standard in the name of the American National Standards Institute.Requests for interpretations should be addressed to the secretariat or sponsorwhose name appears on the ti tle page of this standard.

CAUTION NOTICE: This American National Standard may be revised or withdrawnat any time. The procedures of the American National Standards Institute require thataction be taken to reaffirm, revise, or withdraw this standard no later than five yearsfrom the date of approval. Purchasers of American National Standards may receivecurrent information on al l standards by call ing or writing the American NationalStandards Institute.Get more FREE standards from Standard Sharing Group and our chats


Contents

Page

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i i i1 Scope, Application and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 .1 . Scope and Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 .2. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Laboratory Venti lation Management Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1 . General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2. Chemical Hygiene Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3. Responsible Person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.4. The Role of Hazard Assessment in Laboratory Venti lation Management . . . 82.5. Recordkeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2

3 Laboratory Fume Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 23.1 . Design and Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 33.2. Laboratory Fume Hood Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 63.3. Hood Airflow and Monitoring (Design and Performance Specifications) . . . 22

4 Other Containment Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.1 . Gloveboxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.2. Ductless Hoods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.3. Special Purpose Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5 Laboratory Venti lation Systems Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.1 . Laboratory Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.2. Laboratory Airflow Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3. Supply Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465.4. Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

6 Commissioning and Routine Performance Testing . . . . . . . . . . . . . . . . . . . . . . . 656.1 . Performance specifications, tests, and instrumentation . . . . . . . . . . . . . . . . 656.2. Commissioning of Laboratory Venti lation Systems. . . . . . . . . . . . . . . . . . . . 736.3. Commissioning Fume Hoods and Different Types of Systems. . . . . . . . . . . 756.4. Ongoing or Routine Hood and System Tests . . . . . . . . . . . . . . . . . . . . . . . . 81

7 Work Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827.1 . General Requirements and Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827.2. Posting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837.3. Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837.4. Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

8 Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848.1 . Operations During Maintenance Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . 848.2. Housekeeping Before and After Maintenance . . . . . . . . . . . . . . . . . . . . . . . 848.3. Safety for Maintenance Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858.4. Work Permits and Other Communications . . . . . . . . . . . . . . . . . . . . . . . . . . 858.5. Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868.6. Testing and Monitoring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868.7. Monitoring Fans, Motors, and Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888.8. Critical Service Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888.9. Critical Service Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898.1 0. Performance Monitoring Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

9 Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899.1 . Supply Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899.2. Exhaust Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899.3. Fi ltration for Recirculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909.4. Testing and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Appendices

Appendix 1 Definitions, Terms, and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Appendix 2 Referenced Standards and Publications . . . . . . . . . . . . . . . . . . . . . . . . . . 98Appendix 3 Selecting Laboratory Stack Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 01Appendix 4 Audit Form for ANSI/AIHA Z9.5-201 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 08Appendix 5 Sample Table of Contents for Laboratory Venti lation

Management Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 29



Foreword (This foreword is not part of the American National Standard Z9.5–201 2. )

General coverage. This standard describes required and recommended practices for the design and oper-ation of laboratory venti lation systems used for control of exposure to airborne contaminants. I t is intend-ed for use by employers, architects, industrial hygienists, safety engineers, Chemical Hygiene Officers,Environmental Health and Safety Professionals, venti lation system designers, faci l i ties engineers, mainte-nance personnel, and testing and balance personnel. I t is compatible with the ACGIH ® Industrial

Ventilation: A Manual of Recommended Practices, ASHRAE venti lation standards, and other recognizedstandards of good 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 or

examples 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 stack

design. Appendix 4 provides a sample audit document and Appendix 5 presents a sample table of

contents for a Laboratory Ventilation Management Plan.

Flexibi l ity. Requirements should be considered minimum criteria and can be adapted to the needs of theUser establishment. I t is the intent of the standard to al low 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 confl ict, the more stringent applies.

Response and Update. Please contact the standards coordinator at AIHA®, 31 41 Fairview Park Drive,Suite 777, Falls Church, VA 22042, i f you have questions, comments, or suggestions. As with al l ANSIstandards, this is a “work in progress.” Future versions of the standard wil l incorporate suggestions andrecommendations submitted 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 Venti lation Systems. Committee approval of the standarddoes not necessari ly imply that al l committee members voted for i ts approval. At the time i t approved thisstandard the Z9 Committee had the fol lowing members:

Thomas Smith, ChairTheodore Knutson, Vice ChairDavid Hicks, Secretariat RepresentativeAt the time of publ ication, the Secretariat Representative was David Hicks.

Organization Represented . . . . . . . . . . . . . . . . . . . . . . . .Name of Representative

ACGIH® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G. KnutsonASHRAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .T. SmithAmerican Foundry Society . . . . . . . . . . . . . . . . . . . . . . . .R. ScholzASSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P. OsleyGlobal Finishing Solutions . . . . . . . . . . . . . . . . . . . . . . . .G. RaifsniderNational Association of Metal Finishers . . . . . . . . . . . . . .K. HankinsonNIH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F. MemarzadehNIOSH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .M. El l iottOSHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .L. Hathon

i i i

Individual Members

D.J. BurtonS. CrooksL. DiBerardinisC. FigueroaS. GunselE. PomerN. McManusD. O’BrienJ. PriceK. PaulsonM. Rol l insJ. Sheehy

Subcommittee Z9.5 on Laboratory Venti lation, which developed this standard, had the fol lowing members:

Steve Crooks, ChairJames Coogan, Vice Chair

L. DiBerardinisD. Walters (*)D.J. BurtonD. HitchingsT.C. SmithV. NeumanJ.M. PriceG. KnutsonG. SharpS. Hauvil leR.A. (Bob) HenryM. TschidaC.J. McAfeeR.A. DeLucaP. PinkstonK. KretchmanS. LengerichP. Carpenter (Technical Resource)A. Kolesnikov (Observer)

* retired during the standard’s development

iv

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



ANSI/AIHA Z9.5–201 2AMERICAN NATIONAL STANDARD

American National Standard for Laboratory Venti lation

Requirements of the Standard

1 Scope, Application and Purpose

1 .1 Scope and Application

This standard appl ies to the venti lation in most lab-oratories and is written for al l laboratory venti lationstakeholders. An emphasis is placed on those withlegal responsibi l ities and l iabil ity for providing asafe laboratory. However, users/operators, industri-al hygienists, other safety and environmental pro-fessionals wil l also find the standard written fortheir needs.

The standard cannot establish strict l iabil ity in al lcases but does attempt to fix accountabil ity in manyrelationships that exist with its context. Please notethat such relationships are defined throughout thestandard and generally encompass the fol lowing:administration - occupant; employer - employee;management - staff; owner - occupant; owner - tenant;teacher - student; designer - owner, etc.

This standard does not apply to the fol lowing typesof laboratories or hoods except as i t may relate togeneral laboratory venti lation:

• animal facil ities,• biosafety cabinets,• explosives laboratories,• high containment faci l i ties (e.g. , BSL 3, BSL 4,

facil ities operating under “chemical suretyplans,” etc. ) ,

• laminar flow hoods and isolators (e.g. , a cleanbench for product protection, not employeeprotection), and

• radioisotope laboratories.

General laboratory safety practices are not includ-ed except where they may relate to the venti lationsystem’s proper function or effectiveness.

Clarification and Explanation of the Requirements

Laboratories conduct teaching, research, qual itycontrol, and related activities and should satisfyseveral general objectives, in addition to being suit-ed for the intended use they should

• be energy efficient without sacrificing safety,compliance, or space condition requirements,

• be safe places to work,• comply with environmental, health, and safety

regulations, and• meet any necessary criteria for the occupants

and technology involved in terms of control oftemperature, humidity, and air quality.

Appendix 2 offers several references providinginformation, guidel ines or specific requirements for

• laboratory animals – AAALAC,• biosafety cabinets – NSF,• biohazardous materials – ABSA, and CDC, • flammables, pyrophoric and explosives –

NFPA, ISEE, and IMC, • h igh containment facil ities – CDC, ISPE, and

USAMRICD,• laminar flow hoods and isolators – NSF and

CETA,• radioactive materials – NRC, and• special environmental requirements for prod-

uct protection such as contamination controlfrom particulates – CETA and IEST.

This standard does not apply to comfort consider-ations unless they have an effect on contaminantcontrol venti lation.

1

ANSI/AIHA ® Z9.5–201 2

2

1 .2 Purpose

The primary purpose of this standard is toestablish minimum requirements and bestpractices for laboratory venti lation systems toprotect personnel from physical harm andoverexposure to harmful or potential ly harm-ful airborne contaminants generated withinthe laboratory. The standard’s requirementsalso aim to protect property where relevant.

In l ight of significant efforts and initiative toreduce greenhouse gases, the standard alsoconfronts energy considerations, especial lywhere there is a potential to impact workerhealth and safety.

This standard:

• informs the designer of the requirementsand confl icts among various criteria rela-tive to laboratory venti lation,

• informs the user of information neededby designers, and

• sets forth venti lation requirements thatwil l , combined with appropriate workpractices, achieve acceptable concentra-tions of air contaminants.

Thus, this standard provides insight on howinadequate venti lation or other venti lationsystem deficiencies can impact safety andcontainment. However, this standard cannotprovide designers and users with everythingneeded for conducting hazard assessments.Designers and users are thereby cautionedto not misconstrue the purpose of this stan-dard as addressing comprehensive hazardcontrol for particular hazards posed by al loperations that may occur in a laboratoryroom. See Section 2.4.

Persons responsible for laboratory operations and thoseworking within laboratories may not be aware of howventi lation can impact environment, health and safety.On the other hand, venti lation system design profession-als cannot be expected to be ful ly aware of al l the par-ticular hazards posed by every type of operation thatmay occur in a laboratory.




3

2 Laboratory Ventilation

Management Plan

2.1 General Requirements

Management shall establ ish a LaboratoryVenti lation Management Plan (LVMP) toensure proper selection, operation, use, andmaintenance of laboratory venti lation equip-ment.

An LVMP shall be implemented to ensureproper operation of the lab venti lation sys-tems, help protect laboratory personnel work-ing with potential ly hazardous airborne mate-rials, provide satisfactory environmental airquality and maintain efficient operation of thelaboratory venti lation systems.

The LVMP shall provide guidel ines and spec-ifications for

• commissioning to verify proper perfor-mance prior to occupancy and use ofthe laboratory hoods,

• description of training programs forensuring proper use, testing and main-tenance of the laboratory hoods,

• design of laboratory venti lation systems,• maintenance procedures for providing

and documenting rel iable operation,• periodic confirmation that the venti lation

system is used properly,• selection of appropriate laboratory

hoods,• specification of monitors to continuously

verify proper operation of the laboratoryhoods, and

• standard procedures for routine testing.

Laboratory workers and other bu i l d ing occupantsdepend on proper operation of the venti lation systemsto provide safe, comfortable and productive environ-ments for work wi th hazardous materials. The venti la-tion systems comprise numerous sub-systems andindividual components including air handl ing uni ts,exhaust fans, airflow controls, chemical fume hoods,biological safety cabinets and other local exhaustdevices. Ensuring safe and efficient operation of labo-ratory venti lation systems requires careful manage-ment of the systems from design to operation.

An LVMP provides the framework for keeping the sys-tem s operati n g to sati sfy th e pri m ary fu n cti on alrequirements of bui lding personnel .

Management participation in the selection, design,and operation of laboratory venti lation systems is cri t-ical to the overal l success of the effort. The programshould be supported by top management. A sampleTabl e of Con ten ts for a Laboratory Ven ti l ati onManagement Plan is included in Appendix 5.

Management should understand that venti lation equip-ment is not furni ture, but rather i t is part of instal ledcapital equipment. I t must be interfaced to the bu i ldingventi lation system.

An effective LVMP should satisfy several generalobjectives. I t should;

• define the responsibi l i ties of departments andpersonnel responsible for ensuring proper opera-tion of the systems,

• describe how the systems are to be commis-sioned, tested and maintained,

• provide a description of the systems and definethe functional requirements,

• provide specifications for design and operation ofthe laboratory hood systems, and

• resul t in safe, dependable and efficient operationof the laboratory venti lation systems.


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2.1 .1 Exposure Control Devices

Adequate laboratory fume hoods, specialpurpose hoods, or other engineering controlsshall be used when there is a possibi l ity ofemployee overexposure to air contaminantsgenerated by a laboratory activity.

OSHA requires that, employers are responsi-ble for ensuring that exposure controldevices are functioning properly and imple-menting feasible control measures to reduceemployee exposures if the exposures exceedthe PELs (§29 CFR 1 91 0.1 450(e)(3)(i i i )) .Furthermore, i f an employer d iscoversthrough their hazard assessment efforts oremployee feedback, that exposure controldevices are not effectively reducing employ-ee exposures, i t is the employer's responsi-bi l i ty to adjust controls or replace engineer-ing controls as necessary.

The capture and/or containment of theselected exposure control device shall beconsidered adequate if, in combination withprudent practice, laboratory worker exposurelevels are maintained below publ ished or in-house exposure l imits or below those l imitsidentified in applying or using publ ishedexposure l imits.

OSH A speci fical ly states the fol lowingrequirements in regards to employee expo-sure monitoring:

1 91 0.1 450(d) Employee exposure determi-nation

1 91 0.1 450(d)(1 ) Initial monitoring.

There are numerous exposure control devices including:

• biological safety cabinets,

• gloveboxes,

• aboratory fume hoods,

• local exhaust hoods, and

• other venti lated enclosures

Exposure control devices are available in a wide varietyof designs with different capabil ities and l imitations.Selecting the appropriate exposure control device isimportant to ensuring adequate protection for the labora-tory worker.

OSHA does not promulgate specific control device test-ing protocols

The performance of an exposure control device is ulti-mately determined by its abi l i ty to control exposure towithin appl icable standards or other safe l imits.

I f exposure l imits [e.g. , Occupational Safety and HealthAdministration Permissible Exposure Limits (OSH APELs), National Institute for Occupational Safety andHealth Recommended Exposure Limits (OSHA RELs),American Conference of G overnmental I ndustrialHygienists threshold l imit values (ACGI H ® TLVs ® ? ) ,American I ndustrial Hygiene Association WorkplaceEnvironmental Exposure Limi ts (AI H A® ? WEELs ®) ,German MAKs, (maximum admissible concentrations)]or similar l imits used in prescribing and/or assessing safehandling do not exist for chemicals used in the laborato-ry, the employers should establ ish comparable in-houseguidelines. Qualified industrial hygienists and toxicolo-gists working in conjunction may be best suited toaccomplish this need.




5

The employer shall measure the employee'sexposure to any substance regulated by astandard which requires monitoring i f thereis reason to bel ieve that exposure levels forthat substance routinely exceed the actionlevel (or in the absence of an action level, thePEL).

1 91 0.1 450(d)(2) Periodic monitoring.

I f the initial monitoring prescribed by para-graph (d)(1 ) of th is section d isclosesemployee exposure over the action level (orin the absence of an action level, the PEL),the employer shal l immediately comply withthe exposure monitoring provisions of therelevant standard.

1 91 0.1 450(d)(3) Termination of monitoring.

Monitoring may be terminated in accordancewith the relevant standard.

1 91 0. 1 450(d)(4) Employee noti fication ofmonitoring results. The employer shall , with-in 1 5 working days after the receipt of anymonitoring results, notify the employee ofthese results in writing either individual ly orby posting results in an appropriate locationthat is accessible to employees.

Section 8. C. 5 Testing and Veri fication of PrudentPractices in the Laboratory:

Handling and Disposal of Chemicals, 1 995 states the fol-lowing with regards to exposure monitoring for fume hoodusers. “Perhaps the most meaningful method for evaluat-ing hood performance is to measure worker exposurewhile the exposure control device is being used for i tsintended purpose. Where exposure l imits and analyticalmethods exist, personal air-sampling devices can beworn by the user and worker exposure (both excursionpeak and time-weighted average) can be measuredusing standard industrial hygiene techniques. The criteri-on for evaluating the device should be the desired perfor-mance (i .e. , does the device contain chemical at thedesired worker-exposure level?) . A sufficient number ofmeasurements should be made to define a statisticallysignificant maximum exposure based on worst-caseoperating conditions. Direct-reading instruments areavailable for determining the short-term concentrationexcursions that may occur in laboratory hood use.”

Measuring for an “overexposure” to chemicals implies ameans of defining an unsafe l imit and having an analyti-cal means of determining when such l imit is exceeded.Since neither are commonplace or practical, surrogateshave been useful in empirical determinations. However, i fan employee bel ieves that he or she is overexposed tohazardous chemicals despite their use of an exposurecontrol device, he or she should have an internal mecha-nism for resolving their concern (e.g. , informing a super-visor). OSHA requires that any such employee is provid-ed an opportunity to receive an appropriate medicalexamination. Other similar occurrences make i t incum-bent on the employer to protect the employee and ensureadequate control measures (§29 CFR 1 91 0.1 450(g)(1 )(i-i i i ) . In the event an employer remains unresponsive to anemployee’s complaint, the employee would be encour-aged to seek other advice or external intervention (e.g. ,fi l ing a complaint with OSHA.)

In the European Union (EU,) Registration, Evaluation,Authorization and Restriction of Chemicals (REACH) is ineffect and should be consulted as appropriate for hazardevaluation information impacting laboratories operatingwithin the scope of this standard.


6

Chemical “hazard determination” shal l be conduct-ed by chemical manufacturers and importers asrequired by the Occupational Safety and HealthAdministration's (OSHA) Hazard Communicationstandard, specifical ly, 29 CFR 1 91 0.1 200(d). Thisrequires that manufacturers and importers of chem-icals to identify chemical hazards so that employeesand downstream users can be informed about thesehazards.

2.1 .2 Laboratory (Room) Ventilation Rate

The specific room venti lation rate shall be estab-l ished or agreed upon by the owner or his or herdesignee.

2.1 .3 Dilution Ventilation

Dilution venti lation shal l be provided to control thebuildup of fugitive emissions and odors in the labo-ratory. The di lution rate shall be expressed in termsof exhaust flow in negatively pressurized laborato-ries and supply flow in positively pressurized labo-ratories.

Venti lation is a tool for control l ing exposure.Contaminants should be controlled at the source.Potential sources should be identified and expo-sure control devices should be specified asappropriate to control emissions at the source.(See Sections 3 and 4) Al l sources and assump-tions should be clearly defined and documented.

An air exchange rate (air changes per hour) can-not be specified that wi l l meet al l conditions.Furthermore, air changes per hour is not theappropriate concept for designing contaminantcontrol systems.

Excessive airflow with no demonstrable safetybenefit other than meeting an arbitrary air changerate can waste considerable energy.

Control of hazardous chemicals by di lution alone,in the absence of adequate laboratory fumehoods, is seldom effective in protecting laboratoryusers. I t is almost always preferable to capturecontaminants at the source, than attempt to dis-place or di lute them by room venti lation.




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2.2 Chemical Hygiene Plan

The laboratory shal l develop a ChemicalH ygiene Plan according to the OSH ALaboratory Standard (29 CFR 1 91 0.1 450).

The plan shal l address the laboratory opera-tions and procedures that might generate aircontamination in excess of the requirementsof Section 2.1 .2. These operations shall beperformed inside exposure control devicesadequate to attain compliance.

The plan shal l address emergencies and acci-dents, as well as ordinary operation.

2.3 Responsible Person

In each operation using laboratory venti lationsystems, the user shall designate a “responsi-ble person.”

Nevertheless, di lution or displacement may removecontaminants not captured by a specifical ly applieddevice.

The quantity of di lution (or displacement) venti lationrequired is a subject of controversy. Typical di lution ven-ti lation rates can range from 4 to 1 0 air changes perhour depending on heating, cool ing, and comfort needsand the number and size of exposure control devices.

Although some laboratories do not fal l under the OSHAStandard, a Chemical Hygiene Plan or LaboratorySafety Standards (or manual) can establ ish properwork practices.

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

In the event of large accidental releases in the labora-tory room, away from exhausts and control systems,the laboratory owner should specify appropriate evacu-ation protocols. The plan may also include emergencyventi lation modes. (See Section 5.2.3. )

The responsible person may have the fol lowing duties:

• Ensuring that existing conditions and equipmentcomply with appl icable standards and codes,

• Ensuring that testing and monitoring are done onschedule,


8

2.4 The Role of Hazard Assessment in

Laboratory Ventilation Management

2.4.1 General Requirements

Employers shal l ensure the existence of anongoing system for assessing the potential forhazardous chemical exposure.

Employers shal l promote awareness that labo-ratory hoods are not appropriate controldevices for al l potential chemical releases inlaboratory work.

The practical l imits of knowing how each expo-sure control device is being or may be usedshall be considered when specifying designfeatures, performance criteria (commissioningand routine monitoring), or when seeking ener-gy savings. The responsible person as definedin Section 2.3 shall be consulted in making thisjudgment.

Exposure control devices shall be functioningproperly and specific measures shall be takento ensure proper and adequate performance(refer to Section 2.1 .1 ).

• Maintaining adequate records,• Participating in the design (new construction or

renovation) of the lab at the conception/ planningstage (preferably as an IH or EHS professionalwith laboratory venti lation experience),

• Performing visual checks,• Training employees, and• Performing any other related task assigned by the

employer.

At a minimum, the responsible person should coordi-nate the above activities.

Much of this standard addresses a generic approachto exposure control. This is necessary because manyof the chemical hazards in a laboratory are chronic innature and an employee's abi l i ty to sense overexpo-sure is subjective.

The employer may determine that providing standardlaboratory hoods tested to the ANSI/ASHRAE 1 1 0standard and an “as instal led” AI 0.1 rating are bestfor the types of chemical hazards and work beingperformed at the specific workplace. The assumptionthat fol lows is that users are trained to understandlimitations of the hood's control abi l i ty and would notuse it for work that, for example, should be performedin a glovebox. Alternatively, ensuring al l hoods arecapable of meeting an AI 0.1 rating may not be nec-essary, for example, i f the only chemical being han-

dled has an 8-hr time-weighted average (TWA) –

TLV® exposure l imit of 250 ppm.




9

The employer shall establ ish criteria for deter-mining and implementing control measures toreduce employee exposure to hazardouschemicals. Particular attention shall be givento the selection of control measures for chem-icals that are known to be extremely haz-ardous.

The fol lowing briefly describes an approach usedwithin laboratory venti lation management programs inassigning control measures given the abil ity (or inabil-ity) to assess specific day-to-day chemical exposuresituations.

Hazard assessments in general are geared towardidentifying chemicals, their release potential (source),their transmission route (path), and their possibleroutes of entry into the body (receiver). I t is criticalthat assessments be conducted in a competent man-ner such that the source-path-receiver “picture” is notmisconstrued.

Hazard assessments may incorporate results fromtracer gas testing of engineering controls (example:ANSI/ASHRAE 1 1 0 fume hood testing) and transmis-sion routes (example: exhaust reentry into buildingsupply systems).

The first step in the assessment is to identify whatchemical(s) can be released including normallyuncharacterized byproducts. After characterizing theinherent hazard potential (largely based on physicalproperties, toxicity, and routes of entry), the next stepis to ascertain at least qualitatively, the release "pic-ture. " At what points within the "control zone" wil lchemicals be evolved and at what release rate? Wil lthe chemical release have velocity? How has themaximum credible accidental release been accountedfor? Final ly, how many employees are/could beexposed and what means are avai lable for emergencyresponse?

Due to the high cost of venti lation, the choice of hoodand specification of airflow rates should be scrutinizedto ensure adequate protection at minimum flow.


1 0

2.4.2 “Programming” and Control

Objectives for New Construction,

Renovation, or Program Evaluation

The fol lowing items shal l be considered anddecisions made regarding each element's rel-evance fol lowing the hazard assessmentprocess:

• Acceptable exposure concentrations• Adequate workspace,• Air cleaning (exhaust pollution controls),• Air supply diffusers and discharge tem-

perature,• Alarm system (local and central monitor-

ing), • Commissioning (level of formality to be

applied),• Containment (tracer gas containment

"pass" criteria – e.g. , AI 0.5, AI 0.1 , AI0.05, etc. ),

• Decommissioning,• Design sash opening and sash configura-

tion (e.g. , for laboratory fume hoods),• Differential pressure and airflow between

spaces and use of airlocks, etc. ,• Diversity factor in Variable Air Volume

(VAV) controlled laboratory chemicalhood systems,

• Exhaust discharge (stack design) anddilution factors,

• Face velocity for laboratory chemicalhoods,

• Fan selection,• Frequency of routine performance tests,• Hood location,• Manifold or individual systems,• Redundancy and emergency power,• Recirculation of potential ly contaminated

air,• Preventive maintenance, and • Vendor qual ification.

Programming is a term commonly used in the context ofa construction project whereby the needs of a usergroup are developed into the intended del iverables ofthe project. The idea here is that various scientific dis-cipl ines have different needs in terms of venti lation.

Sets of design "templates" exist based on various typesof laboratories. While the characterization of laborato-ries by "organic chemistry, analytical chemistry, biology,etc. , " are generical ly understood by most designers,knowledge of the chemistry and biology and, therefore,potential hazards, are general ly beyond the knowledgebase of most designers.

The overall goal of providing a safe workspace for theend users can be greatly enhanced by the use of a haz-ard assessment and system design team.

Quality of system design and quality of performanceare enhanced by uti l izing the most appropriate skil lsand resources avai lable to an organization. TheLaboratory Venti lation M anagement Plan shoulddescribe specific responsibi l ities for each departmentinvolved in the design, instal lation, operation, and useof venti lation systems (Table 1 provides some guid-ance.)




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Table 1 . Major Responsibilities Recommended for Ensuring an Effective LVMP

Party Responsibility

Employer, Management,Owner, etc.

• Allocate sufficient resources.• Coordinate activities.• Ensure proper personnel training to design, instal l , commission,

maintain and use exposure control devices and venti lation systems.• Implement the plan, do, check, act concepts prescribed in environment,

health and safety management systems.• Provide leadership.• Remove barriers between departments.

Laboratory User

• Indicate and report performance problems.• Provide information on potential ly hazardous materials.• Provide information on procedures, work habits, duration of use,

changes in hazardous operations and materials, etc.• Uti l ize laboratory hoods in accordance with operating requirements and

safety guidel ines.• Work with Environmental Health and Safety to ensure appropriate

safety systems.

Environment Health andSafety

• Assist laboratory users with recognition and evaluation of hazards.• Conduct routine safety audits. • Determine suitable control strategies.• Establish control objectives and safety requirements.• Maintain records of performance.• Provide training for users of laboratories.

Engineering

• Analyze design options in consideration of hazard assessment findings.• Ensure system capabil i ty to provide safe, dependable and efficient

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

Maintenance

• Conduct preventive maintenance and repair.• Ensure proper functioning of systems.• Ensure system dependabil i ty.

Purchasing • Ensure equipment is not purchased without EHS approval.

Space Planning• Ensure safety and engineering issues are considered in any space

al location decisions.

Note to Table 1 : The responsible person could be from any one of the above parties.


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2.5 Recordkeeping

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

Records shall include:

• As-bui lt drawings;• Commissioning report;• Equipment replacement or modifications

Testing and Balance reports;• Inspection and routine test reports;• Periodic performance and operation

reports• Maintenance logs;• Reported problems; • System modifications, and• Written Laboratory Venti lation

Management Plan.

3 Laboratory Fume Hoods

Only permanent records wil l al low a history of the sys-tem to be maintained.

Records should be maintained to establish a perfor-mance history of the system that can be used to opti-mize operation. Records should be kept for at least thelife of the system or unti l the system is altered.

A laboratory fume hood is a box-l ike structure with typ-ical ly one open side, intended for placement on a table,bench, or floor. The bench and the hood may be oneintegral structure. The open side is provided with asash or sashes that move vertically and/or horizontallyto close the opening. Provisions are made for exhaust-ing air from the top or back of the hood and adjustableor fixed internal baffles are usually provided to obtainproper airflow distribution across the open face.

Other terms used for a fume hood include laboratoryhood, laboratory chemical hood, and fume cupboard.

Although not technically correct, the term fume, asused today and historically in the context of definingfume hoods; includes both gases (vapors) andaerosols (i .e. particulates, mists, fumes, smoke, etc. ).

Laboratory fume hoods are often appropriate foraerosol applications. However, because of the internalturbulence, particulates, mists, etc. , can deposit on theinterior surfaces. For certain appl ications, this may pre-clude the use of a fume hood.

Fume hoods have been a major tool in laboratory ven-ti lation. However, a fume hood is not universal ly appl ic-able to al l situations. In many cases, an enclosing hood(e.g. , glovebox, biosafety cabinet, venti lated enclosure)




1 3

3.1 Design and Construction

The design and construction of laboratoryfume hoods shal l conform to the appl icableguidel ines presented in the latest edition ofACGIH ® Industrial Ventilation: A Manual of

Recommended Practice for Design, and themost current codes, guidel ines, and standardsand any other appl icable regulations and rec-ommendations (see Appendix 2).

or a local exhaust hood (snorkel, tight fitting canopyhood, or special ly designed hood) may provide as goodor better control and require less volumetric flow.

I t is the intent of the standard to establish design para-meters and performance criteria without l imiting newand innovative designs.

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

• Airfoi ls or other designs that reduce leakage andairflow eddies at the front edge of the work areashould be provided at the front edge of the bench.Airfoi ls should not interfere with the hood’s abi l ityto meet the criteria of performance testing definedin this standard.

• Airfoi ls, beveled edges or other sidewall designthat reduces leakage and airflow eddies at theside walls should be provided at the side posts.

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

• Cupsinks should be protected by having a verticallip around the sink’s circumference of at least ¼ in.(0.635 cm) or eliminated if not needed.

• Uti l i ties (e.g. , valves and switches) should belocated at readily accessible locations outside thehood. I f additional uti l i ties are required, other thanelectrical, they may be located inside the hoodprovided they have outside cutoffs and can beconnected and operated without potential ly sub-jecting the hood operator to exposure from mate-rials in the hood or other unsafe conditions.

• Work surfaces should be recessed at least ¼ in.(0.635 cm) below the front edge of the bench orsurface; sides and back should be provided with aseamless vertical l ip at least ¼ in. (0.635 cm) highto contain spills. However, excessively deeprecesses can increase the turbulence at the worksurface and induce reverse flow.

ANSI/AIHA Z9.5–2003

1 4

3.1 .1 Sashes

The laboratory fume hood shall be equipped witha safety-viewing sash at the face opening.

Sashes shall not be removed when the hood is inuse.

3.1 .1 .1 Design Opening

The design opening of a laboratory hood is theopen area at the face of the hood, which thedesign team assumed when determining the ven-ti lation requirements of the exhaust system.

Where the design sash opening area is less thanthe maximum sash opening area, the hood shallbe equipped with a mechanical sash stop. Ameans of communicating when openings are inexcess of the design sash opening area shall beprovided.

The Chemical Hygiene Plan shall clearly instructthe hood users to position the sash so that theopening is no greater than the design openingwhile using the hood for protection.

Sash-l imi ting devices (stops) shal l not beremoved without resizing or redesigning theexhaust system if the design opening is less thanfull opening.

Typical sashes avai lable include the fol lowing:

• Combination vertical raising and horizontalsl iding sashes,

• Horizontal sl iding sashes, and • Vertical raising sash or sashes.

Refer to Figure 1 for diagrams of different sash con-figurations.

Sashes should be constructed of transparent shat-terproof material suitable for the intended use. Theforce to open the sash shall be reasonable for thesize and weight of the sash. Typically, a five foothood with a vertical rising sash should requireapproximately five pounds of force to operate thesash. An additional one pound of force may berequired for each additional l inear foot of fume hoodwidth. The sash should remain stationary whenforce is removed unless automatic closing to thedesigned operating sash opening is required.

The responsible person, or the design team, shoulddetermine the design opening of the hood and theposition of the sash-l imiting device based on theneeds of the hood user. Operating the hood with alarger opening than the design opening results in areduced capture velocity (face velocity) and maysignificantly and adversely affect the performanceof the hood. Admin istrative controls, train ing,mechanical sash stops, alarms or other means areimportant for ensuring that the fume hoods andexhaust systems can provide the protection forwhich they were designed. Operating the sash at anincorrect position can jeopardize the protection oth-erwise afforded the hood users and those in theadjacent area.

The Chemical Hygiene Plan should indicate theproper circumstances for overriding the sash stop.




1 5

3.1 .1 .2 Vertical Sashes

Vertical sashes shal l be designed andoperated so as not to be opened more thanthe design opening when hazardous mate-rials are being used within the hood

3.1 .1 .3 Horizontal Sashes

Horizontal sashes shal l be designed so asnot to be opened more than the designopening width when hazardous materialsare being generated in the hood.

3.1 .1 .4 Combination Sashes

I f a combination sash provides horizontal lymoving panels mounted in a frame thatmoves vertically, the above requirements inSections 3.1 .1 .2 to 3.1 .1 .3 shal l apply.

The vertical raising sash can usually be opened for ful l-face opening in the open position. I f this is greater than thedesign opening, control at the ful l open position may becompromised.

The horizontal sash should be designed to al low freemovement of the sash. Accumulation of debris or othermaterials in the sash track can impede movement. Thesash track can be designed to minimize this potential byhanging the sash from overhead. In any event, periodicmaintenance is recommended to ensure proper sash man-agement.

I f three or more sash panels are provided, one panelshould be no more than 1 4 in (35 cm) wide i f i t is to serveas a safety shield narrow enough for a person to reacharound to manipulate equipment.

Caution is advised when using a horizontal panel as ashield in front of the hood operator as high concentrationscan accumulate behind the sash panel and escape alongthe Users’ arms protruding through the opening or escapewhen their arms are withdrawn.

A combination sash has the advantages and disadvan-tages of both types of sashes. The combination verticalraising and horizontal sl iding sash, commonly referred toas a combination sash, is a combination of the verticalsash described in Section 3.1 .1 .2 and horizontal sash inSection 3.1 .1 .3. The combination sash may be raised to ful lvertical sash opening. In the closed vertical position, thehorizontal sl iding panels can be opened to provide accessto the interior hood chamber. Care should be taken indetermining the design opening of a combination sash.Remember to include the area beneath the airfoi l si l l andthrough the bypass if one exists.


1 6

3.1 .1 .5 Automatic Sash Closers

All users shall be trained in good work prac-tices, including the need to close the sashwhen not in use.

All users of VAV systems shal l be trained inthe proper uses of the sash, the energy con-sequences of improper use, and the need toclose the sash when the operation does notrequire i ts use.

Automatic sash positioning systems shall haveobstruction sensing capable of stopping travelduring sash closing operations without break-ing glassware, etc.

3.2 Laboratory Fume Hood Types

3.2.1 Auxiliary Supplied Air Hoods

Auxil iary air hoods have a portion of the totalvolume of exhausted air provided through aplenum located above and outside of the hoodFace.

Auxil iary air hoods shal l meet the require-ments in Section 3.3.

The supply plenum shall be located external lyand above the top of the hood face.

The auxil iary air shall be released outside thehood.

The supply jet shall be distributed so as not toaffect containment adversely.

The auxil iary air shall not disrupt hood con-tainment or increase potential for escape.

Good work practice and energy stewardship (for VAVsystems) requires the user to close the sash when thehood is not in use. A well implemented chemicalhygiene plan and proper administrative actions canensure that the sash is properly positioned. Monitoringof user compliance may be possible with some VAVsystems where the Building Automation System al lowstrending of the sash position and feedback to manage-ment (and subsequently to the user. )

I f the user feels it is his/her responsibility to close thesash and the culture is that they do close the sash, thenan automatic sash closer may not be necessary. On theother hand, if the user does not close the sash and man-agement tolerates this non-compliance, safety could bejeopardized, energy consumption may increase and anautomatic sash closer may be advantageous.

With or without automatic closers, users should under-stand the importance of the closed sash, and integrateproper sash operation into work procedures.

Auxi l iary supplied air hoods are not recommendedunless special energy conditions or design circum-stances exist. The information in this section is providedbecause many auxil iary air hoods are currently in use.The intent is not to discourage innovative design butcurrent experience indicates these requirements arenecessary.

The rationale for using auxi l iary supplied air hoods isthat auxil iary 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, i fnot al l the air from the auxi l iary plenum is captured atthe hood face, the anticipated energy savings is notrealized. With respect to temperature and humidity,workers may experience discomfort i f i t is necessary tospend appreciable time at the hood.

I f auxi l iary air hoods are designed and operated prop-erly, worker protection at the face may be enhanced




1 7

Figure 1 — Diagrams of different sash opening configurations.


1 8

3.2.2 Bypass Hoods

Bypass hoods have a route for air enteringthe hood (the bypass mechanism) whichopens as the sash closes.

Bypass hoods shall meet the requirementsin Section 3.3.

The bypass mechanism shall be designedto minimize potential ejection of l iquid orsolid material outside the hood in the eventof an eruption inside the hood.

because the downward airflow at the breathing zone sup-presses body vortices. However, i f the design and opera-tion are improper, contamination control may be compro-mised. In addition, the air quality and condition inside thehood may be significantly different from the room air andthese conditions may compromise the work conductedinside the hood.

For retrofit projects, auxi l iary air may be installed morecheaply with less disruption than by upgrading the mainair supply system. I f auxil iary air is conditioned to thesame extent as room air, most of the potential energyadvantages are lost whi le the disadvantages remain andthe total system becomes more expensive to install , oper-ate, and maintain.

With a worker (or reasonable proportioned manikin) at thefull open hood face, the hood should capture more than90% of the auxil iary jet airflow when either the auxi l iaryair is at least 20°F (-6.7°C) warmer or cooler than roomair. This does not apply i f the auxil iary air is designed tobe conditioned the same as room air.

Bypass mechanisms should be designed so the bypassopens progressively and proportionally as the sash trav-els to the ful l closed position. The face velocity at the hoodopening should not exceed three times the nominal facevelocity with the sash ful ly open. Excessive velocities,greater than 300 fpm (1 .5 m/s), can disrupt equipment,materials, or operations in the hood possibly creating ahazardous condition.

The hood exhaust volume should remain essential lyunchanged (<5% change) while the sash moves throughits range of opening and closing. This is important to thedesign of the exhaust system.




1 9

3.2.3 Conventional Hoods

Conventional hoods shal l meet the require-ments in Section 3.3.

3.2.4 Floor-Mounted Hoods

Floor-mounted hoods shall meet the require-ments in Section 3.3.

Conventional hoods have the hood exhaust volumeremain nearly unchanged as the sash position variesfrom ful l open to the closed position.

However, as the sash is lowered, the face velocity wi l lincrease. In the ful ly closed position, airflow would bethrough the airfoi l only. With the sash partial ly open, thehood wi l l have very high face velocity.

Floor-mounted hoods are used when the vertical work-ing space of a bench hood is inadequate for the workor apparatus to be contained in the hood.

The base of the hood should provide for the contain-ment of spi l ls by means of a base contiguous with thesidewalls, and a vertical l ip sufficient to contain spil lsinside the hood, often at least 1 in. (2.54 cm) or equiv-alent. The l ip can be replaced by a ramp to al lowwheeled carts to enter the hood. The hood should befurnished with distribution ductwork or interior baffles toprovide uniform face velocity.

Doors and panels on the lower portion should be capa-ble of being opened for the installation of apparatus.

I f the lower doors are kept closed during operation, thehood and exhaust system design and operation may besimilar to a bench top laboratory fume hood and theeffectiveness of the control should be equivalent if all theprovisions of Section 3.3 are implemented. However, inmany floor-mounted hoods, the closed lower sash maycause significant turbulence and the hood may not per-form as well as a bench-top hood.

I f the lower panels are opened during operations, thehood loses much of i ts effectiveness, even if face veloc-ities comply with Section 3.3.

The design and task-specific appl ications of floormounted (walk-in) hoods may make it difficult to complywith the work practices of Section 7 of this standard.


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3.2.5 Perchloric Acid Hoods

Perchloric acid hoods are specifically designedto safely handle certain types of perchloricacid work and shall be used for such work.

Perchloric acid hoods shal l be used for han-dling anhydrous perchloric acid (> 85% con-centration.)

Hence, consideration should be given to preparationand implementation of written standard operating pro-cedures (SOPs) for use of floor-mounted hoods. Forexample, i f manipulations below waist height are nec-essary, special provisions may be necessary such asarmports or small openings strategically located at nec-essary access points.

Small rooms with one wall constituting a supply plenumand the opposite wall constituting an exhaust plenumshould not be called a floor-mounted hood. In suchinstances, workers are intended to be inside the hoodand exposure control provisions are drastically differ-ent. This standard does not apply to such rooms.

Perchloric acid is a strong acid, distinguished by thefact that i t is the only mineral acid that is not constitut-ed as a gas dissolved in water. As a result, the vaporphase above a solution of perchloric acid is devoid ofperchlorate at temperatures below about 1 50°C. I ts oxi-dation power is readily control led by management ofconcentration and temperature, factors conducive to i tsuse both as a process reagent and a catalyst.

Perchloric acid digestions and other procedures per-formed at elevated temperatures should be done inperchloric acid hoods.

Aqueous solutions of perchloric acid – The vapor pres-sure of 72% perchloric acid at 25°C is 6.8 mm Hg. Forcomparison sake, the vapor pressure of 70% nitricacid, a more widely used acid, is 49 mm Hg at 20°C.This simply means that the nitric acid would evaporatefaster. When a bottle of 70% perchloric acid is merelyopened, i t cannot evaporate quantities presenting arisk of making contact with incompatible organic com-pounds.




21

All procedures conducted in a perchloric acidhood shall be reviewed by the responsible personand immediate supervisor.

Al l procedures using a perchloric acid hood shal lbe performed by trained personnel, knowledge-able and informed about the hazards and proper-ties of these substances, provided with appropri-ate protective equipment after suitable emer-gency contingency plans are in place.

The design of a perchloric acid hood shal linclude:

• Al l inside hood surfaces shall use materialsthat wi l l be stable and not react with perchlo-ric acid to form corrosive, flammable, and/orexplosive compounds or byproducts.

• Al l interior hood, duct, fan, and stack sur-faces shall be equipped with water wash-down capabil ities.

• Al l ductwork shall be constructed of materi-als that wil l be stable to and not react withperchloric acid and/or i ts byproducts and wil lhave smooth cleanable seamless joints.

• No part of the system shall be manifolded orjoined to non-perchloric acid exhaust sys-tems.

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

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

Perchloric acid hoods shal l be periodical lywashed down thoroughly with water to remove al lresidues in the hood, duct system, fan, and stack.

The process of di luting 60–70% perchloric acid orhandling di lute aqueous solutions of perchloric acidat room temperature presents l i ttle hazard of accu-mulating pure perchloric acid in hood ducts.

The institutional/corporate responsible person (e.g. ,Safety Officer/Chemical Hygiene Officer) should benotified before procedures requiring a perchloricacid hood are performed.

The complications of wash-down features and cor-rosion resistance of the exhaust fan might beavoided by using an air ejector, with the supplierblower located so it is not exposed to perchloricacid.

The frequency of wash down depends on the pro-cedures inside the hood. Many procedures requiredaily wash down


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3.2.6 Variable Air Volume (VAV) Hoods

VAV hoods shal l meet the requirements inSection 3.3

Variable exhaust flow from a laboratory hoodhas implications for room venti lation which shallbe addressed according to Section 5.

Additional commissioning requirements are nec-essary for these systems (See Section 6).

3.3 Hood Airflow and Monitoring (Design

and Performance Specifications)

3.3.1 Face Velocity

The average face velocity of the hood shal l besufficient to contain the hazardous chemicals forwhich the hood was selected by fol lowing guid-ance in Section 2.4 and as generated under as-used conditions.

An adequate face velocity is necessary but is notthe only criterion to achieve acceptable perfor-mance and shal l not be used as the only perfor-mance indicator.

Hood containment shall be verified as appropri-ate for the hazard being control led (See Section2.1 .1 ).

The VAV hood is a conventional hood equipped witha VAV control system so designed that the exhaustvolume is varied in proportion to the opening of thehood face.

VAV controls appl ied to by-pass hoods have beennoted in many facil ities. These situations appear to bedesign errors as VAV controls appl ied to by-passhoods largely defeats the purpose.

I t is recommended that VAV hoods be equipped withemergency overrides that permit ful l design flow evenwhen the sash is closed.

Face velocity had been used historically as the prima-ry indicator of laboratory hood performance for sever-al decades. However, studies involving large popula-tions of laboratory fume hoods tested using a contain-ment-based test l ike the ANSI/ASHRAE Standard1 1 0, “Method of Testing the Performance ofLaboratory Fume Hoods,” reveal that face velocityalone is an inadequate indicator of hood performance.

In one published study, approximately 1 7% of thehoods tested using the method had "acceptable" facevelocities in the range of 80–1 20 fpm, but "fai led" thetracer gas containment test wi th control levelsexceeding a control level of 0.1 ppm. Some of thesetests were “As Installed” whi le others were “As Used.”

See Section 6 on commissioning and routine perfor-mance testing for additional information.

Exposure assessments involve industrial hygienemeasurement of actual exposure potential to chemi-cals being worked with. This is accomplished throughair sampling in the breathing-zone of hood user.

Design face velocities for laboratory fume hoods in therange of 80 –1 00 fpm (0.40 – 0.50 m/s) wil l provideadequate face velocity for a majority of fume hoods.




23

Containment must be verified quantitatively inthis range and compliance with use restric-tions, etc. enforced.

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

Tracer gas containment testing is a rel iable method forevaluating hood containment and is recommended incommissioning or in further applications as needed.

Most tracer gas containment test methods, includingthe AN SI /ASH RAE 1 1 0 “M ethod of TestingPerformance of Laboratory Fume Hoods” have certainl imitations that must be observed. The ANSI/ASHRAE1 1 0 method is a static test, under controlled conditions,and 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 excel lent containment characteristics mayoperate adequately below 80 fpm (0.40 m/s) whi le oth-ers may require higher face velocities. I t is thereforeinappropriate to prescribe a range of acceptable facevelocities for al l hoods.

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

Room and operator dynamics have significant effect onhood performance at low face velocities. Therefore, i t isimportant to understand the effects of dynamic chal-lenges on hood performance so that standard operat-ing procedures and user restrictions can be estab-l ished. Operating a hood below 60 fpm (0.30 m/s) is notrecommended since containment cannot be rel iablyquantified at low velocities and significant risk of expo-sure may be present.

60–80 fpm (0.30–0.40 m/s): Hoods with excellent con-tainment characteristics operating under relativelyideal environmental conditions (i .e. , room design char-acteristics) and with prudent operating practices canprovide adequate containment in this velocity rangealthough at an increased level of risk. Effective admin-istrative controls should be in place.

80–1 00 fpm (0.40–0.50 m/s): Most hoods can be operat-ed effectively with relatively low risk in this velocity rangealthough containment should still be quantitatively


24

3.3.2 Laboratory Hood Minimum Flow Rate

The flow rate of Constant Volume hoods and theminimum flow rate of Variable Air Volume hoodsshall be sufficient to prevent hazardous concen-

trations of contaminants within the laboratoryfume hood.

In addition to maintaining proper hood facevelocity, laboratory hoods shal l maintain a mini-mum exhaust volume to ensure that contami-nants are properly di luted and exhausted from ahood.

The fol lowing considerations shall be taken intoaccount (as appl icable) when setting the mini-mum hood flow rate for each hood:

• Control of ignition sources within the hood(a),• Design of the hood, the materials used in

the hood and the anticipated maximum gen-eration rates(a),

verified. Proper operator training and enforcement ofadministrative controls are sti l l highly recommended.This is the range recommended for a majority of lab-oratory fume hoods.

1 00–1 20 fpm (0.50–0.60 m/s): This velocity rangehas similar characteristics as 80–1 00 fpm (0.40–0.50m/s) but at significantly higher operating costs.Containment may be sl ightly enhanced in this rangeand hoods that do not contain adequately in the80–1 00 fpm (0.40–0.50 m/s) range may be improvedby operating in this range.

1 20–1 50 fpm (0.60–0.75 m/s): Although most hoodscan operate effectively in this range, performance is notsignificantly better than at the lower ranges of 80–1 00fpm (0.40–0.50 m/s) and 1 00–1 20 fpm (0.50–0.60 m/s).The operating cost penalty imposed by high face veloc-ities in this rage is severe. Consequently, the high facevelocities are not recommended.

>1 50 fpm (>0.75 m/s): Most laboratory experts agreethat velocities above 1 50 fpm (0.75 m/s) at thedesign sash position are excessive at operating sashheight and may cause turbulent flow creating morepotential for leakage.

(a) A specific concern when choosing to minimize

hood flow rates is the potential for fire or explosion

if an ignition source were to exist within a vapor’s

lower and upper flammable or explosive limits.

Scenarios that could generate vapors in suchquanti ties include:

• Flammable l iquids spil l onto the work surface, or• Flammable vapors or gases released by any

other means.

Before selecting the minimum flow rate the usershould calculate the maximum credible concentra-tion that might be reached at locations where an igni-tion source may be present. Assign a minimum flowrate or other control measure capable of maintainingthis concentration at the chosen safety factor per-centage of the LFL for the materials used. Typicallycited percentages range from 1 0% to 25% of the LFL(LEL). This calculation should be made for any newmaterials introduced for which the previous calculation




25

• Potential for increased hood interior corro-sion. (b)

• Effect on exhaust stack discharge velocity (c),• Fume hood density (d),• Need to affect directional airflows (e), and the• Operating range of the hood exhaust equip-

ment and the associated control system. (f)

may not address (e.g. , a flammable material with ahigher generation rate or lower LFL.)

A small body of empirical research and theoreticalcalculations (1 –7) supports a range of values for theminimum flow for spil l conditions and situationsinvolving the use of typical ly used quantities of sol-vents. At least two empirical studies measured con-centrations of contaminants resulting from simulat-ed chemical spi l ls in a hood. Their conclusionsregarding minimum flow rate for the scenarios theystudied, correspond roughly to the high and lowends of the range mentioned below in the brief dis-cussion on energy savings. Additional ly, extensiveexperience in Europe on European hood designsusing European hood testing procedures providesome support for the low end of the range.

Designers may choose to increase minimum hoodflow rates in order to maintain flammable vapor ductconcentrations below code required levels (SeeSection 5.4.1 ).

(b) A secondary concern involves the potential forcorrosion of the hood interior from the use of highlycorrosive operations* that may dictate the use of afume hood minimum flow rate near the higher endof the recommended range.

(c) As stated in the exhaust stack discharge sectionof this standard, exhaust fan systems typical ly havesome minimum design exhaust stack velocity. Theminimum flow rate selected for the hood may affectdesign and operation of the exhaust system.Designers need to coordinate these issues.

(d) In situations where the minimum hood flow dri-ves the airflow rate for the laboratory, the minimumflow affects energy consumption. A higher value forthe minimum flow requires more power to move andcondition the air. Depending on the airflow ratesinvolved, this situation occurs usually when thehood density exceeds values in the range from 2%to 1 0% of the floor space in the room. (For exampleone or more 30x72 inch bench top fume hoods in a750 ft2 (75 m2) lab.) In situations where some otherconsideration sets the flow rate for the room, theminimum hood flow does not affect energy use.


Venti lation system designers shall coordinate theoperating range of the fume hood flow rate withthe operating ranges of the other air supply andexhaust devices in the room.

Where attempting to save energy in typical ly higherhood density installations, minimum fume hood flowrates in the range of 1 50 to 375 hood air changesper hour (ACH) have been used to control vaporconcentrations inside hood interiors.(1 –7)

Minimum hood flow rates might be selected withinthe above range i f the user complies with provisionsin the left hand column. An exception being where awritten hazard assessment indicates otherwise.

(e) Designers may choose to increase minimum hoodflow rate if the ventilation equipment and the airflowcontrol system cannot regulate room air flows at thevalues required to effectively pressurize the room(See Section 5.2.1 ).

(f) The expression “within the operating range”includes accuracy expectations at the minimum hoodair change rate selected to prevent hazardous con-centrations* of contaminants within the hood: +/- 1 0%.

I f a hood is taken completely out of service, the flowmay be reduced further or shut off so long as otherventi lation needs are unaffected.

For the purposes of establishing a value for the internalvolume of the hood used in determining the flow ratecorresponding to the desired value of hood air changesper hour, the internal hood volume is approximated andhereby defined as the total internal hood work surfacearea times the internal height of the hood.

Section References

1 . Sharp, G.P.: “A Review of U.S. and EuropeanEmpirical Research, Theoretical Calcula-tions, and Industry Experience on FumeHood Minimum Flow Rates.” InternationalInstitute of Sustainable Laboratories (I2SL)E-Library, http: //www. i2sl . org/el ibrary/index.html, 2009.

2. Braun, K.O. and K.J. Caplan: “Evapora-tion Rate of Volati le Liquids, Final Report,2nd edition. EPA Contract Number 68-D8-01 1 2”, PACE Laboratories Project890501 .31 5. Washington, D.C. : U.S. Dept.of Commerce, NTIS, December 1 989.

26




27

3.3.3 Flow-Measuring Device for Laboratory

Fume Hoods

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

The flow-measuring device shal l be capable ofindicating that the air flow is in the desired range,and capable of indicating improper flow when theflow is high or low by 20%.

3. Klein, R.C., C. King, and P. Labbie: Solventvapor concentrations following spills in labo-ratory chemical hoods. Chem. Health Safe.11(2):4–8 (2004).4. Harnett, P.B.: Empiri-cal data and modeling of a flammable spil lin a chemical fume hood do not support theneed for fire suppression within the chemi-cal fume hood ductwork. Chem. Health

Safe. 10(4): 1 1 –1 4 (2003).5. Parker, A.J. and P.J. DiNenno: “Evaluation

of Fixed Extinguishing System Effective-ness in Continuously Exhausting ChemicalFume Hoods.” Prepared for Merck & Co. byHughes Associates, September 2001 .

6. Labconco Corp.: Development of the Lab-conco Protector® Xstream ® High Perfor-mance Laboratory Fume Hood. KansasCity, MO: Labconco Corporation, 2009.

7. Venti lation Test according to DIN 1 2 924Part 1 : Fume Cupboard DIN 1 2 924 TA1 500 x 900 – 900, Fume hood Test reportby Waldner Laboreinrichtungen GmbH &Co. for mc6 - Bench Mounted Fume Cup-board: Test Report No.1 59, May 2000.

The purpose of the flow-measuring device is to pro-vide the hood user with continuous informationabout the hood’s airflow. One method is to measurethe total volume flow through the hood. Anothermethod is to measure the face velocity.

One popular method for measuring total volumeflow is the Hood Static Pressure measuring device(See ACGIH’s ® Industrial Ventilation: A Manual of

Recommended Practices for Operation and

Maintenance ), which can be related to flow. Thismethod measures static suction in the exhaust ductclose to the hood throat and, i f there are noadjustable dampers between the hood and themeasuring station, is related to the flow volume.Other methods include various exhaust volume orflow velocity sensors.

The means of alarm or warning chosen should beprovided in a manner both visible and audible to thehood user. The alarm should warn when the flow is20% low, that is, 80% of the set point value.


28

4 Other Containment Devices

4.1 Gloveboxes

4.1 .1 General Description and Use

Gloveboxes shal l not be used for manipulationof hazardous materials with the face or otherpanels open or removed nor with the glovesremoved.

I f the potential combinations of material prop-erties with planned manipulations are so com-plex the hazard cannot be estimated, a glove-box may or may not be suitable. A hazard eval-uation shal l be employed in such complexcases.

Gloveboxes shall be used when the propertiesof the hazardous materials, the planned manip-ulations, or a credible accident would generatehazardous personal exposures i f the workwere done in an ordinary laboratory hood.

4.1 .1 .1 Location

There are no special requirements for locationbeyond those al ready noted for hoods.Gloveboxes shall be located as dictated byworkflow, space requirements and other needswithin the laboratory.

Tissue paper and strings do not qualify as the solemeans of warning.

Some manufacturers may require calibration that ismore frequent.

I f gloves are removed it is not a glovebox but becomesa special enclosure requiring evaluation of effective-ness of containment.

Laboratory-scale gloveboxes, for which this standardapplies, should have a maximum internal chamber vol-ume of 50 ft3 (1 .4 m3) (single-sided access) or 1 00 ft3

(2.8 m3) (double-sided access) respectively (pass-through chambers excluded). Larger gloveboxes mayoccasionally be found in laboratory settings but arebeyond the scope of this standard. For additional guid-ance, see the latest edition of the American GloveboxAssociation Society’s standard for additional adviceGuideline for Gloveboxes (AGS-G001 . )

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

Gloveboxes may be used when the manipulated sub-stances must be handled in a control led (e.g. , inert)atmosphere or when they must be protected from theexternal environment.

Glovebox containment is unaffected by airflow crossdrafts which create challenges for open face hoods.

Since manipulations through glove ports are somewhatdifficult, however, i t is advisable to avoid high trafficareas and to al low ample aisle space.




29

4.1 .2 Design, Construction, and Selection

A hazard assessment as required in Section2.4 shall be done to select the appropriateglovebox.

Positive pressure gloveboxes shal l not be usedwith hazardous materials without a written riskassessment.

Interior cracks, seams, and joints shall be el im-inated or sealed.

4.1 .3 Util ities

Util i ty valves and switches shal l be in confor-mance with applicable codes. When control ofuti l i ties from inside the glovebox is required,additional valves and switches shal l be provid-ed outside the glovebox for emergency shutoff.

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 wil l beapplied. Proper appl ication of ergonomic princi-ples shall be met by referring to the latest edi-tion of, Guideline for Gloveboxes, AGS-G001 .

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

For additional guidance see:

STANDARDS OF PRACTICE FOR THE DESIGN ANDFABRICATION OF GLOVEBAGS(AGS-G002)

STANDARDS OF PRACTICE FOR THE APPLICA-TIONS OF LININGS TO GLOVEBOXES(AGS-G003)

STANDARDS OF PRACTICE FOR THE SPECIFICA-TIONS OF GLOVES FORGLOVEBOXES (AGS-G005)

STANDARDS OF PRACTICE FOR THE DESIGN andFABRICATION OF NUCLEAR APPLICATION GLOVE-BOXES (AGS-G006)

Certain applications require that al l valves be locatedinside of the glovebox containment and al l l ines exteri-or to the box be 1 00% welded.

Frequent use versus infrequent use may dictate theextent to which ergonomics principles wi l l be applied.


30

4.1 .5 Provision for Spills

The design of the glovebox shal l provide forretaining spil led l iquids so the maximum vol-ume of l iquid permitted in the glovebox wil l beretained.

A system for draining the spil led l iquid into asuitable sealed container shall be provided i fthe properties of the spil led l iquid or other cir-cumstances prevent cleanup by workingthrough the gloves.

4.1 .6 Exhaust Ventilation

Containment gloveboxes shal l be providedwith exhaust venti lation to result in a negativepressure inside the box that is capable of con-taining the hazard at acceptable levels.

Gloveboxes shall be exhausted to the outsideunless the provisions described in AN SIStandard Z9.7 and Section 5.3.6.2 of this stan-dard are met.

4.1 .7 Exhaust Air Cleaning

The air or gas exhausted from the gloveboxshall be cleaned and discharged to the atmos-phere in accordance with the general provi-sions of this standard and any pertinent envi-ronmental regulations.

Air-cleaning equipment shal l 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.

I f the air-cleaning device (ACD) is passive (i .e. ,a HEPA fi lter or activated carbon) provisionshall be made for determining the status of theACD, as noted in Section 9.3. I f the ACD isactive (i . e. , a packed-bed wet scrubber) ,instrumentation shall be provided to indicateits status.

The ACD shall be located to permit ready accessfor maintenance. Provision shall be made formaintenance of the ACD without hazard to

See Sections 4.1 .1 1 through 4.1 .1 4 for venti lation rec-ommendations for specific glovebox types.

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

Any ACD should be selected and applied according tothe manufacturer’s specifications, with attention to air-flow rate, and other operating parameters that canaffect performance for the contaminants of interest.

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




31

personnel or the environment and so as not tocontaminate the surrounding areas.

4.1 .8 Exhaust Ducting

Exhaust piping shal l be in accordance with theprinciples described in the latest editions of theACG I H ® I ndustrial Venti lation M anual ,AN SI /AI H A ® Z9. 2, and the ASH RAEHandbook ? Fundamentals. Al l piping within theoccupied premises shal l be under negativepressure when in operation.

Materials shal l 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.

I f audible alarms are not provided, documentedtraining for users in determining safe pressuredifferentials shall be required.

Pressure moni toring devices shal l beadjustable (i .e. , able to be calibrated i f not a pri-mary standard) and subject to periodic calibra-tion at least annually.

4.1 .1 0 Decontamination

A wri tten decom m i ssi on i n g pl an fol l owi n gt h e proced u res ou tl i n ed i n th e l atest ed i -t i o n of AN SI /AI H A ® Z9. 1 1 LaboratoryDecommissioning shall be developed.

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

I f the contaminant is gaseous, the atmospherein the box shall be adequately exchanged toremove the potential ly hazardous gas. This canbe affected by exhausting the box through itsventi lation system, and where necessary pro-viding an air inlet that is fi l tered i f required.

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

Alarms should 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.

Use caution i f gases or vapors may condense ordeposit on surfaces. Decontamination may sti l l berequired.


32

I f the contaminant is l iquid, any l iquid on sur-faces shal l be wiped with suitable adsorbentmaterial or sponges unti l visibly clean anddry. Used wipes shal l be placed in a suitablecontainer before being removed from theglovebox.

I f the contaminant is a powder or dust, al l inter-nal surfaces shall be cleaned and wiped unti lvisibly clean. The exterior surfaces of thegloves also shall be wiped clean.

Precautions to prevent hazards to personneland contamination of the premises shal l bemade i f the ducting is to be opened or disman-tled.

I f there is any uncertainty about the effective-ness of contamination reduction procedures,personnel involved in opening the panels ofthe glovebox shall be provided with appropri-ate PPE or clothing.

4.1 .1 1 High Containment Glovebox

A high containment glovebox shall conform toal l the mandatory requirements ofSections 4.1 .1 through 4.1 .1 1 , and

• Shall be provided with one or more airlockpass-through ports for inserting or remov-ing objects or sealed containers withoutbreaching the physical barrier betweenthe inside and outside of the glovebox;

• Shall maintain negative operating staticpressure within the range of -0.5 to -1 .5in.wg (-1 25 Pa to -374 Pa) such that cont-aminant escape due to “pinhole-type"leaks is minimized.

• Shal l maintain di lution of any flammablevapor–air mixtures to <1 0% of the applic-able lower explosive l imit.

• Shal l prevent transport of contaminantsout of the glovebox.

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

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

Neutralizing reagents should be used, i f available.

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

Nonessential personnel should be excluded from thedecontamination area. The contamination in the gener-al work area should be reduced before use.

For more information see (1 ) EPA 402-R-97-01 6,M ul ti -Agency Radiation Survey and Si te I nvestigationM anual . (2) AN SI /AI H A ® Z9. 1 1 Laboratory

Decommissioning .

Examples include gloveboxes used for control l ingexposures to unknown materials or acutely hazardousand highly volati le materials where any exposure maybe harmful.

Care should be exercised when placing certain haz-ardous l iquids in an evacuated airlock or interior of aglovebox when a decrease in pressure could affect theboil ing point of the l iquid causing it to go to a gaseousstate.

Meeting the above requirements wi l l 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-tional ly opened. The air velocity into the open gloveportor door should be 1 25 ± 25 l inear fpm (0.635 ± 0.1 3m/s).




33

4.1 .1 2 Medium Containment Glovebox

A medium containment glovebox shal l conformto al l the mandatory requirements of Sections4.1 .1 through 4.1 .1 0, is not provided with pass-through airlocks, and shal l be provided withsufficient exhaust venti lation to maintain aninward air velocity of at least 1 00 fpm (0.51m/s) through the open access ports, and cre-ate a negative pressure of at least 0.1 in.wg(25 Pa) when access ports are closed.

4.1 .1 3 Special Case Containment

Glovebox

A special case containment glovebox shall bedesigned for special situations, does not nec-essari ly conform to the provisions of this stan-dard, but has been tested for the intended useand found adequate for that purpose.

4.1 .1 4 Controlled Atmosphere

Containment Glovebox

An isolation and containment glovebox shal lbe a control led atmosphere containmentglovebox required for special atmosphere workwhen either the controlled atmosphere and/orthe contained agents are hazardous.

4.1 .1 4.1 Design and Construction

Design and construction, and materials shal lconform to the requirements for high, medium,or special case containment gloveboxes asnecessary.

I f the control led atmosphere gas is hazardous,the airlocks shall be provided with a purge airexhaust system that, by manipu lation ofvalves, creates a purge flow of room air suffi-cient to provide at least 5 air changes perminute, with good mixing, to the interior spaceof the airlock.

Examples include gloveboxes designed to preventoverexposure to acutely hazardous materials that arenot highly volati le and/or where al lowable exposure lev-els have been establ ished and personnel exposure canbe verified to be below the established al lowable levels.

For example, a positive pressure is maintained in aglovebox used to build desiccant assemblies. The des-iccant requires a very dry environment and the positivepressure pushes moisture away rather than al lowing itto enter. There is also an exhaust fan which creates anegative pressure in the stack from the box.

Examples include appl ications where an inert atmos-phere is necessary to protect the work or when it pro-vides an added measure of safety.

Refer to the AGS-1 998-001 Guidel ine for Gloveboxesfor more details on construction.


34

4.1 .1 4.1 Operation

Operation of an isolation and containment glove-box shall conform to high, medium, or specialcase containment requirements as necessaryand the airlock purge system shal l be operatedfor sufficient time to di lute any hazardous gas inthe airlock to safe concentrations before theouter door is opened.

Care shal l be exercised when placing certainhazardous l iquids in an evacuated airlock or inte-rior of a glovebox when a decrease in pressurecould affect the boil ing point of the l iquid, caus-ing it to go to gaseous state.

4.1 .1 5 Testing and Maintenance

An overall operation and maintenance programshall be documented for each application of theglovebox to provide users with necessary infor-mation on periodic maintenance and testing ofglovebox system components.

4.2 Ductless Hoods

Ductless hoods shall meet the general require-ments of Sections 3.1 and 3.3 as applicable.

A Hazard Evaluation and Analysis shal l be con-ducted as directed in ANSI/AIHA ® Z9.7 andSection 2.1 .1 .4.

Compliance with the general requirements ofSections 2, 3.3, and 5.3.6.2 shall be evaluatedby qualified persons.

Ductless hoods that do not meet the require-ments specified in Sections 9.3 and 9.4 shall beused only for operations that normally would beperformed on an open bench without presentingan exposure hazard.

For the empty airlocks, a purge time of 3 min. at 5 airchanges per minute with good mixing would reducean atmosphere of 1 00% to less than 1 ppm. I f anobject in the airlock has cavities that would trap gas,or i f the gas might be adsorbed in the object, moretime would be required: Such time should be deter-mined by sampling the exhaust stream upstream ofthe ACD.

Components such as air locks, gloves, air cleaningdevices, etc. , require periodic inspection and/or per-formance testing. Some components may alsorequire more detailed operating instructions for usersand specific maintenance procedures for mainte-nance technicians than is normally found for mostlaboratory venti lation systems.

Ductless hoods have l imited application because ofthe wide variety of chemicals used in most laborato-ries. The containment collection efficiency and reten-tion for the air-cleaning system used in the ductlesshood must be evaluated for each hazardous chemical.

As referenced in ANSI/AIHA ® Z9.7, the hazard eval-uation and analysis serve to ensure proper air quali-ty, effective occupant protection, and satisfactory sys-tem performance.

Air-cleaning performance monitoring is typically l imit-ed for many hazardous materials. Chemical-specificdetectors located downstream of adsorption media orpressure drop indicators for particulate fi l ters are nec-essary for systems recirculating treated air from theductless hood back into the laboratory.




35

Ductless hoods shall meet the performancestandards for contaminant removal establ ishedby the owner.

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 l imitations of fi l ters in place, fi l ter change-out schedule, and that the hood recirculates airto the room.

4.2.1 Airborne Particulates

Ductless hoods that uti l ize air-cleaning fi l tra-tion systems for recirculating exhaust air cont-aminated with toxic particulates shall meet therequirements of Section 9.3.1 .

4.2.2 Gases and Vapors

Ductless hoods uti l izing adsorption or other fi l -tration media for the collection or retention ofgases and vapors shal l be specified for a l imit-ed use and shal l meet the requirements ofSection 9.3.2.

Ductless hoods employing fi l ters for removinggases and vapors shall have written documen-tation (records) that the manufacturer hasapproved the specific application of the hoodprior to usage.

Ductless hoods may be appropriate if the contaminantis particulate and provision is made for changing fi l terswithout excessive contamination of the laboratory orpotential exposure to personnel changing the fi l ters.See Sections 9.3 and 9.4.

Adsorption media such as activated charcoal are notefficient for fine particles and are predominately usedfor adsorbing certain gases or vapors. Many gases andvapors of low molecular weight wi l l be stripped from theadsorption media and reenter the room air on contin-ued flow of clean air through the ductless hood. Whenthis happens, the ductless hood only serves to protectthe worker at the hood face and to spread the contam-inant release into the room air during a longer timespan and at a lower concentration. See Section 4.2.2.

Where multiple air contaminants chal lenge the duct-less hood air-cleaning system, the col lection efficiencyand breakthrough properties of the air fi l tering mediaare complicated and are dependent on the nature ofthe specific mixture. Enhanced breakthrough of com-ponents should be especially considered as a part ofthe Hazard Evaluation and Analysis. See Section 4.2.2.

Also the warning properties (i .e. odor, taste) of thechemical being fi l tered must be adequate to provide anearly indication that the fi l tration media are not operat-ing properly.

Each application of the ductless hood must be evaluat-ed prior to use. For each chemical that may be used inthe hood its retention capacity must be known and beappropriate for the intended use.

There is currently no national consensus standard fortesting and performance of gas/vapor adsorbent fi l tersused in ductless hoods. Although widespread experi-ence with i ts use is lacking, there is one standard thatmay be worth considering assuming that i t is made


36

The manufacturer shal l provide a l ist of chemicalsapproved to be used in the hood with their reten-tion capacities.

Proper disposal of unused and used (contaminat-ed) adsorption fi l ters shall be considered as partof the decision to use ductless hood employingsuch.

more widely avai lable.

• Standard AFNOR NF X 1 5-21 1

According to Tronvil le and Rivers, progress towardstandards for gaseous contaminant fi l ters for gener-al-venti lation service has been very slow. Many fac-tors influence the efficiency and service l i fe ofadsorptive and chemisorptive fi l ters for gaseouscontaminants. Standards writers must choose a fewtest contaminants to represent the behavior of fi l terson the hundreds of contaminants that may be ofinterest.

A major problem is to relate the performance of a fi l-ter at the low gaseous contaminant concentrationspresent in real HVAC systems to the performance atthe relatively high test concentrations necessary forreasonable test durations.

ASHRAE is developing a standard comprising threeparts, now at the ‘proposed’ stage:

• For laboratory tests on granular adsorptivemedia

• For laboratory tests on complete fi l ter cel ls• For field tests in installed fi l ters (4, 5 and 6).

ASTM has for many years maintained standards onmany aspects of activated carbon, the most used fi l-ter medium. Standards 7, 8, 9 and 1 0 deal with themass of contaminant a carbon can absorb before itbecomes saturated, and no longer of use.

Paolo Tronvi l le, Richard D. Rivers, International stan-dards: fi l ters for buildings and gas turbines, Fi ltration& Separation, Volume 42, Issue 7, September 2005,Pages 39-43, I SSN 001 5-1 882, DOI :1 0.1 01 6/S001 5-1 882(05)70623-6.

(http: //www.sciencedirect.com/science/article/B6VJM-4H7BN0H-1 3/2/9888f01 240f365fa2efeb29972982d6d)

Other reference standards for performance testinginclude ANSI/ASME N51 0, ANSI/ASHRAE 52.2,and ASHRAE 2001 Handbook – Fundamentals.




37

4.2.3 Handling Contaminated Filters

Contaminated fi l ters shall be unloaded from theair-cleaning system fol lowing safe work practicesto avoid exposing personnel to hazardous condi-tions and to ensure proper containment of the fi l -ters for final disposal. Airflow through the fi l terhousing shall be shut down during fi l ter change-out.

4.2.4 Testing and Maintenance

All of the requirements of Sections 6.3, 6.4, and8.0 for containment and airflow testing and al l ofthe requirements of Sections 9.2 and 9.3.2 for aircleaning performance shall be fol lowed.

4.3 Special Purpose Hoods

Special laboratory chemical hoods shal l bedesigned in accordance with ANSI/AIHA ® Z9.2and the latest edi tion ACG I H ®’s Industrial

Ventilation: A Manual of Recommended Practice.

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 appl icationsmight present opportunities to achieve contamina-tion control with less bench space or less exhaustvolume (such as special mixing stations, sinks,evaporating racks, heat sources, or venti lated worktables).

Additional information on special exhaust systemdesign and operation can be found inSemiconductor Exhaust Ventilation Guidebook byJeff Burton and “Development of a Program forPerformance Evaluation of University SpecialtyLocal Exhaust Systems for Compliance with theOSHA Lab standard” (Hallock et. al . , Appl. Occup.Env. Hyg. 11(3): 1 70–77 (1 995).


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5 Laboratory Ventilation System Design

5.1 Laboratory Design

5.1 .1 Spatial Layout

Laboratory designers shal l consider effects onsafety when establ ishing floor plans and spatiallayout.

5.1 .2 Noise

Venti lation system designers shal l consideracoustical emission when selecting air movingdevices. (fans) Generation of excessive noiseshall be avoided in laboratory venti lation sys-tems.

Fan location and noise treatment shall provide forsound pressure level (SPL) in conformance withlocal ambient noise criteria.

The laboratory venti lation system affects contamina-tion control. Spatial layout, in terms of physical barri-ers, and the flow of personnel and material alsoaffects contamination control . Laboratory designshould address these issues from consistent view.

One useful design concept is a progression ofspaces from ‘clean to dirty’ or ‘ low to high hazard.’This can lead to placement of barriers between officespace and a laboratory corridor, or to an ante-roombetween the corridor and the laboratory.

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 abil ity. Cross currents,drafts, and spurious air currents from these sourcesmay decrease a hood’s containment abi l i ty.

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

Laboratory designers should consider how hoodlocation affects path of egress from the laboratory.

Designers should consider arranging exhaustdevices, and gathering heat producing equipment inways that reduce the energy expense associated withsafe ventilation and effective heating and cooling.

The acoustic character of the venti lation systemshould help create a pleasant working environment.Sound from the venti lation system should not inter-fere with laboratory operations. I t may be used tomask undesirable noise such as vehicular traffic,noisy equipment, or low discourse.

The primary references for design criteria and meth-ods will be found in ASHRAE publications l isted below.

Chapter 7 on Sound and Vibration from the ASHRAE2005 Handbook – Fundamentals




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Chapter 47 on Sound and Vibration Control fromASHRAE 2007 Handbook – HVAC Applications

N oise associated wi th mechanical venti lation andexhaust systems generally originates with fans, duct ordamper vibration, and air noise caused by excessive airvelocity or turbulence. Therefore, the primary designfocus should be on preventing excessive noise genera-tion. Where possible, i t is good practice to locate highstatic pressure fans remote from occupied spaces.

Use good duct design procedures. Avoid abrupt ductturns without turning vanes, change duct dimensionsgradually, and general ly fol low procedures given in thelatest ASHRAE Handbooks chapters on duct design. Thecareful use of vibration isolators, inertia blocks, and suit-able fan speed and outlet velocities is indicated. Variablevolume systems have found wide application in laborato-ries. However i t is important to be aware that variablesound levels may focus unwanted attention on the venti-lation system. Frequently laboratories have large andnumerous fans, and then special care must be taken tocomply with location regulations and good practice withregard to noise contamination of adjoining properties.

NOTE: Such regulations vary but provide for sound pres-sure level (SPL) in the range of 50 dBA and l imit theincrease in SPL above background levels when the ven-ti lation systems are operating.

System design should provide for control of exhaust systemnoise (combination of fan-generated noise and air-generat-ed noise) in the laboratory. Systems should be designed toachieve an acceptable SPL and frequency spectrum [roomcriteria, (RC), or noise criteria (NC)] as described in theASHRAE 2007 Handbook – HVAC Applications. The rec-ommended range for hospital laboratories is 50 – 35; high-er RC ranges might be acceptable for other types of labora-tories. NC curves above 55 might result in unacceptablespeech interference in the laboratory.

Use of porous or flammable sound-absorbing interior l in-ing of exhaust ductwork usually is unacceptable.

Venti lation designers may also consider the soundcaused by operation of venti lation control devices, espe-cial ly when installed in an open ceil ing.


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5.2 Laboratory Airflow Management

5.2.1 Differential Pressure and Airflow

Between Rooms

As a general rule, airflow shal l be fromareas of low hazard to higher hazard unlessthe laboratory is used as a barrier facil i ty,such as a Clean Room, or an isolation orsteri le laboratory, or other special-type lab-oratories. When flow from one area toanother is critical to emission exposurecontrol, airflow monitoring devices shall beinstalled to signal or alarm that there is amalfunction.

Air shal l be al lowed to flow from laboratoryspaces to adjoining spaces only i f

• There are no extremely dangerous andlife-threatening materials used in thelaboratory;

• The concentrations of air contaminantsgenerated by the maximum credibleaccident wil l be lower than the expo-sure l imits required by 2.1 .1 .

‘Space pressurization’ or ‘directional airflow’ betweenspaces is one of many tools available to l imit exposure tolaboratory hazards. Effectively applied, it opposes migrationof air contaminants; it does not eliminate it. Air movesbetween spaces in response to many phenomena, includ-ing thermal effects, movement of people and direct draftsfrom the ventilation system. Effective pressurization over-comes many of those drivers, most of the time. In a labora-tory with ordinary construction, and a properly functioningventilation system, air can move briefly the wrong direction.(Very special techniques for construction and operation caneliminate migration. Such facilities are outside the scope ofthis standard.)

Safety professionals and users should understand pressur-ization as an imperfect secondary barrier, and consider it inthe context of other exposure control measures. This includesconsideration of ordinary work practices, distribution and stor-age of materials, and operation of the primary barriers. I t alsoincludes consideration of emergencies, and accidents.

Pressure within a Lab Room or other space is defined asthe differential pressure between that space and adjacentspace(s). This differential pressure causes air to flow in thedesired direction, which is typically from areas of relativelylow (risk of) contamination and in the direction of increasing(risk of) contamination. The resulting Transfer Air (TA) flowoccurs at all the openings in the room boundary: spacearound the doors, gaps between wall, floor and ceilingmaterials and penetrations for ducts, pipes and wires. Thisdirectional air flow through the envelope reduces the l ikeli-hood of air contaminants moving in the wrong direction. Inmost laboratories a negative pressure (containment) tendsto prevent contaminants from migrating outside the room. Inother appl ications such as Clean Rooms or Steri leLaboratories a positive pressure (barrier) tends to preventcontamination by air from outside the Room.

The flow rate of Transfer Air depends on the differentialpressure and the effective leakage area around the doorsand through envelope. I f the room envelope is tightlysealed, the leakage area is small, and there is very l i ttleTransfer Air flow for a given pressure. I f the room is not sotight, the leakage area is larger, and more Transfer Air flowsfor the same differential pressure.




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Th e desi red d i recti on al ai rfl ow betweenrooms shal l be identified in the design andoperating specifications.

When a door to the laboratory is open, the effective leak-age area is very large. The differential pressure and thedesired containment are lost. Net airflow may continue inthe intended direction as a result of the airflow offset, butthe average velocity is very low. I t is impractical to main-tain a differential pressure across an open door. Air isl ikely to move both directions through the large opening,which is one reason contaminants may migrate, despiteproper ventilation.

The quantity of Transfer Air is also generally equivalent tothe “airflow offset” which is defined as the volumetric dif-ference between Supply Air (SA) to the space andExhaust (or Return) Air (RA) flows driven by the mechan-ical ventilation systems.

For a building with laboratories or other critical spaces itis recommended that an “airflow map” of the building beproduced. This floor plan indicates the Transfer AirVolume through each boundary, or the required relativepressure relationship between across it. I t should alsoshow the Supply Air Volume, the Exhaust (or Return) AirVolume for each space. The flow rates must balance foreach room (TA=SA-EA) and for large common areassuch as corridors. These air volumes are summed to sizefans and other mechanical equipment.

Ventilation system designers use several approaches tocontrol laboratory pressurization. Methods include flowoffset control, direct pressure control and combinationsof those two. ASHRAE (Applications Handbook 2007,Page 1 4–1 2) describes each method in detail and com-pares them, indicating the circumstances that favor eachone. Flow offset control is the most commonly appliedapproach and is i l lustrated in the following example.

A lab designer chooses a value for the offset betweensupply and exhaust. For example, the lab Exhaust Airvolume is 1 000 L/s (21 1 8 CFM) and the Supply AirVolume is 900 L/s (1 906 CFM). This is defined as a “-1 00L/s (-21 2 CFM) offset.” This -1 00 L/s offset draws 1 00 L/sof Transfer Air into the room. I f the flows were reversed(Supply greater than Exhaust) the offset would be+1 00L/s (+21 2 CFM).


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Flow control accuracy is crucial to the performance of apressurization system based on the airflow offset.Designers explicitly specify the accuracy needed for themechanical flows in and out of the room after quantify-ing the effect of inaccuracy on the flow offset and result-ing pressurization.

The leakage of the room envelope is just as important.The quantity of offset air to maintain a desired roompressure depends on the effective leakage area of theroom, through the doors and envelope.

In some projects, delivering an effective pressurizationsystem includes specifying and testing the tightness ofthe room envelope. The construction process mayexplicitly include steps to adjust the observed leakagearea. Rooms that leak too much are far more commonthan rooms that are too tight. Sometimes it is necessaryto seal the envelope more carefully before the room canbe effectively pressurized.

Typically, the leakage area is not known. Designers relyon their experience and published design resources,(ASHRAE Handbook Fundamentals, 2005, Page 27.23)to estimate it. Then during the construction, TAB andCommissioning Phase, air flow and pressure measure-ments confirm the design. I f necessary, the Transfer AirVolume can be adjusted and the sealing of criticalrooms can be corrected to produce the desired RoomPressure Differential.

When rooms are constructed very tightly, the low roomleakage means that small changes in the room offset airvolume cause significant changes in the differentialpressure to the adjacent spaces. Controll ing a very tightroom by volumetric offset requires especially preciseand stable volumetric air flow control. I f the room enve-lope is too tight for volumetric offset, direct pressurecontrol is a practical alternative.

In special cases designers open a hole in the envelopeand fit it with an air balancing device to control the vol-ume of transfer air, and in some cases, a HEPA fi lter toprevent contamination. Such measures only apply tospecial high containment laboratories or barrier facil itiesthat employ rigorous construction methods for the struc-ture, envelope, seals, penetrations and finishes.




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5.2.1 .1 Ante-rooms and Airlocks

When health and safety professionals are con-cerned with containing contaminants duringuse and operation of the doors to the room,designers shall evaluate the application of air-locks and ante-rooms.

An airlock shall consist of a vestibule or smallenclosed area that is immediately adjacent tothe laboratory room and having an airtightdoor at each end for passage. Airlocks shal l beapplied in such a way that one door providesaccess into or out of the laboratory room, andthe other door of the airlock provides passageto or from a corridor (or other non-laboratoryarea). Airlock doors shall be arranged withinterlocking controls so that one door must befully closed before the other door may beopened.

5.2.1 .2 Critical Air Balance

I f the direction of airflow between adjacentspaces is deemed critical, provision shall bemade to local ly indicate and annunciate inade-quate airflow and improper airflow direction.

5.2.2 Diversity

A designer, applying the concept of venti lationload diversity, shal l consider the fol lowingissues:

• Capacity of any existing equipment;

• Expansion considerations;

• Maintenance department’s abi l i ty to perform periodic maintenance

• Minimum and maximum venti lation ratesfor each laboratory;

• Quantity of hoods and researchers;

• Requirements to maintain a minimumexhaust volume for each hood on thesystem;

• Sash management (sash habits of users);

• Thermal loads;

An ante-room (or vestibule) stands between the labo-ratory and the adjacent corridor. This can improve theeffectiveness of the pressurization system, reducingthe l ikelihood that entry and exit by personnel wi l lcause contaminants to move in the wrong direction.

An airlock is distinguished from a more commonvestibule or ante-room by the interlocked, airtightdoors.

Airlocks are uti l ized to prevent undesirable airflow fromone area to another in high hazardous appl ications,which are general ly outside the scope of this standard.

Diversity is a system design concept that can justifysizing components for a total load that is less than thesum of the individual peak demands. A system that isdesigned with fu l l flow capacity for al l hoods isdesigned for 1 00% Usage Factor or 1 00% diversity.

Both existing and new facil ities can benefit from apply-ing diversity to the HVAC design if individual laboratorychemical hoods are used at different times of day.Diversity may al low existing faci l ities to add laboratorychemical hood capacity without adding new mechani-cal equipment. In new construction, diversity al lows thefacil i ty to reduce capital equipment expenditures andspace requirements by downsizing equipment andother infrastructure.


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• Type, size, and operating times of faci l ity;

• Type of laboratory chemical hood controls;

• Type of venti lation system, and

• Use patterns of variable volume hoods.

The fol lowing conditions shall be met in order todesign a system diversity:

• Acceptance of al l 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 al l 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 capabil ities allowed by diversity.

• Restrictions on future expansions or flexi-bi l ity must be identified.

5.2.3 Laboratory Ventilation—Emergency

Modes

A hazard assessment (see Section 2.4) shallbe performed to identify credible emergencyconditions that may occur.

When the type and quantity of chemicals orcompressed gases that are present in a labora-tory room warrant a special, emergency venti-lation mode, the room shall be equipped withprovision(s) to initiate emergency notificationand emergency venti lation.

Emergency situations (see current version ofNFPA 92A) that shall be anticipated and theappropriate venti lation system responses shal linclude:

Lab users can undermine diversity assumptions if theyleave fume hood sashes open. Common approachesfor ensuring diversity include VAV hoods, sash man-agement aids such as building management systemtrending and automated sash closers, and hood usedetection.

Designing with diversity may l imit the number of hoodsin use or l imit the sash openings, thus creating poten-tial for overexposures to personnel, and prevention offuture expansion opportunities. Therefore, diversityshould be applied carefully in al l 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 anygiven faci l i ty. Turnover among laboratory usersmay reduce the future commitment to sash man-agement. The use of bui lding management sys-tems to monitor sash management may help, butthis requires significant commitment by operatingpersonnel to effectively regulate the users.Automatic sash closers—designed to improvesash management habits—may be overriddenand lose their effect on diversity.

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

Each laboratory room should be evaluated withrespect to the potential for hazardous chemical spi l ls,accidental gas release, or a fire occurrence.

I f the type and quantity of chemicals and gas presentcould pose a toxicity or fire hazard if accidentallyspil led, released, or ignited, the room occupantsshould have a means to signal for an appropriateemergency response as well as initiate appropriateemergency venti lation. The means to signal an emer-gency may be a dedicated switch or pull station, or i tmay be a phone. The signal may come from automat-ically monitored Eye Wash Stations of EmergencyShowers. Natural ly, the benefit of such provisions isl imited to incidents that an occupant is present toobserve.




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• CHEMICAL EMERGENCY – A meanssuch as a clearly marked wall switch, post-ed emergency phone number, or otherreadily accessible device shall be providedto enable the room occupants to initiateappropriate emergency response.

For rooms served by VAV venti lation systems,the Chemical Emergency mode of operationshall maximize the room venti lation (air changeper hour) rate. For rooms served by 2-state ven-ti lation systems that uti l ize a reduced venti lationlevel for energy savings, the ChemicalEmergency mode of operation shall apply themaximum venti lation rate.

Operation of the room venti lation system in achemical emergency mode shall not reduce theroom venti lation rate, room negative pressuriza-tion level, or hood exhaust airflow rate.

• FIRE – Any manual or automatic means ofdetecting fire (such as a pul l station orsmoke detector) in a laboratory room shal lalso activate an appropriate fire emergencymode of operation for the room and/orbui lding venti lation system.

The selected fire emergency mode shall oper-ate al l supply and exhaust equipment in theroom in a manner that promotes egress, retardsthe spread of fire and smoke, and complies withapplicable fire safety codes and standards.

The intent of the chemical emergency provision is touti l ize the venti lation system to maximize the di lutionand removal of chemical fumes and vapors, and pre-vent migration of such fumes and vapors to otherbui lding areas. This response is intended to addressa serious chemical spi l l or related incident that hasthe potential for releasing large amounts of haz-ardous fumes or vapors within the room.

In addition to initiating the emergency venti lationmodes, i t is desirable that the emergency situationbe simultaneously indicated to appropriate facil i typersonnel at one or more designated locations.

The intent of the fire emergency venti lation mode isto promote safe egress. This means apply negativepressurization in the room of fire origin in order toretard the spread of smoke and toxic fire gases toother parts of the facil i ty but do not pressurize to theextent that the force needed to open the door isexcessive. (Also refer to the current versions ofNFPA 92A and NFPA 45. )

The common practice of cutting off supply air to afire zone does not apply to some laboratories. Thecombination of a high exhaust rate and no supplycan depressurize a room so far that some occupantswould be unable to open the doors. The initial designof the laboratory venti lation system must includeanalysis of flow rates, pressure levels and forces onthe door to ensure that egress is possible.


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5.3 Supply Air

5.3.1 Supply Air Volume

I f laboratories are to be maintained with a neg-ative pressurization and directional airflow fromthe corridor into the laboratory, supply air vol-ume shal l be less than the exhaust from thelaboratory.

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

To maintain the desired space pressurization,the supply air volume shal l respond to applica-ble dynamic events including:

• changes in desired venti lation rate,• flow changes in VAV exhaust devices,• temperature control demands, and• temporary deficit of exhaust system capac-

ity.

Note: There are other fai lures and abnormal events(e.g. drop out of supply fans due to freeze statalarms) that can cause excessive space pressure dif-ferences. Each of these scenarios should be identi-fied and addressed in the design of the supply air,exhaust air, and smoke management system so thatsafe laboratory and building egress is maintainedunder al l conditions.

Depending on the chemicals used, the risk of firemay be heightened upon a spi l l or gas release. Suchsituations may justify initiating a fire alarm and sum-moning the local fire department to respond even if afire has not started.

In general, return air is not used in laboratories withhazardous chemicals or biological hazards. The differ-ence between the air supplied by the venti lation sys-tem and that exhausted is the Transfer Air described inSection 5.2.1 . I t serves to resist the escape of airbornehazardous materials from the laboratory room.

Energy recovery systems should be evaluated toreduce the energy needed to condition a large outsideair intake.

The venti lation rate selected for a laboratory dependson the fol lowing concerns:

• control of the thermal and psychrometric environ-ment (ASHRAE Laboratory Design Guide,)

• di lution and displacement of contaminants notcaptured by exposure control devices,

• effective operation of exposure control devices,such as laboratory hoods (See Sections 3 and4,) and

• space pressurization (See Section 5.2.1 . )

Typical ly, the air flow rate is selected to satisfy the con-cern requiring the greatest flow. This rationale appliesfrom room to room during the design process, andmay apply from moment to moment in an active venti-lation control system.




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The laboratory venti lation system shal l bedesigned to remove and di lute air contaminants inaccordance wi th the Laboratory Venti lationManagement Plan.

The venti lation rate must also satisfy the generalcodes and standards that apply to the occupancyclass.

From a practical point of view, the venti lationdesigner may restrict the range of air flow ratesbased on the capabil i ty of the venti lation equip-ment and associated control system.

Current information about the costs of venti lationindicates that i t costs approximately $3 to $9 percfm-year. This cost includes the energy required tomove and condition the supply and exhaust air.The costs can vary based on geography anddepend on the cost of energy for given area.Minimizing airflow reduces energy use and operat-ing costs.

The quanti ty of d i lution (or d isplacement) venti la-ti on req u i red i s a su bj ect of con troversy.N umerous studies make i t clear that the air flowrate is just one factor affecting contaminant lev-els in the room. Frequently, other factors havebeen shown to make a bigger d i fference thansome changes in the air flow rate. These factorsinclude the mechanical arrangement of the sup-ply and exhaust devices, thermal effects, occu-pant movement and the motion and location ofdoors.

(Manning, et al . 2000, ASHRAE Transactions, DA-00-1 4-3: Analysis of Air Supply Type and ExhaustLocation in Laboratory Animal Research Faci l i tiesUsing CFD

Klein, et al . 2009, JCHAS, Laboratory air qualityand room venti lation rates

Smith and Yancey-Smith , 2009, J CH AS,Specification of Airflow Rates in Laboratories)

These studies do not show that the flow rate doesnot matter. On the contrary, they have shown thatthe flow rate certainly does affect contaminant lev-els, but that there is no air change rate that isalways appropriate.

Usually a laboratory venti lation system surpassesthe codes and standards that apply to the bui ldingin general. For example, the OA venti lation per per-son usually exceeds the requirements of ASHRAEStandard 62.1 .


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5.3.2 Supply Air Distribution

Supply air distribution shal l be designed tokeep air jet velocities less than half, preferablyless than one-third of the capture velocity orthe face velocity of the laboratory chemicalhoods at their face opening.

5.3.3 Supply Air Quality

Supply systems shal l meet the technicalrequirements of the laboratory work and therequirements of the current version ofANSI/ASHRAE Standard 62.1 .

For most laboratory chemical hoods, this requirementwil l mean 50 fpm (0.25 m/s) or less terminal throwvelocity at 6 ft (1 .8 m) above the floor. For laboratorieswith very small volumes of hood exhaust this may beachieved by correct selection and placement of con-ventional aspirating supply diffusers. For rooms withgreater supply air requirements, either perforated cei l-ings or special large-capacity radial diffusers may benecessary. These special laboratory diffusers systemsare preferable from a safety viewpoint to auxil iary airhoods because the venti lation air can also be used tosweep gases and vapors from the room into the labo-ratory chemical hoods. The large capacity radial dif-fusers are avai lable from several manufacturersdesigned specifical ly for laboratory use. These dif-fusers have capacities of up to 1 00 cfm (47.2 L/s) persquare foot of diffuser and come in 1 ft ? 1 ft (0.3 m ? 0.3m), 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 nonaspiratingdesign and omnidirectional radial flow patterns.

Supply air diffusers where practical should be locatedclose to the personnel corridor and entry door to thelaboratory and far from the major exhaust devices. Thislocation promotes unidirectional flow, sweeping conta-minants into the exhaust devices and helping furtherprotect the corridor from airborne hazardous materials.The ideal arrangement locates hoods and exhaustdevices away from entry doors and exit corridors andlocates supply air diffusers close to entry doors andexit corridors.

Additional design information can be obtained usingComputational Fluid Dynamics (see Memarzadeh,1 996).

The outside air should be drawn from the least conta-minated location available. Wind studies are often usedto select relative placement of air intakes and exhaust




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5.4 Exhaust

5.4.1 Exhaust System Classification

Designers shal l review existing regulations andcode requirements for the project location.

I n cases where Section 51 0 of theI nternational M echanical Code appl ies,designers shall consult the current version ofIMC 51 0.

5.4.2 Exhaust System Ductwork

5.4.2.1 Design

Laboratory exhaust system ductwork shal lcomply with the appropriate sections of currentversions of the Sheet M etal and AirConditioning Contractors’ National Association(SMACNA) standards.

Systems and ductwork shal l be designed tomaintain negative pressure within al l portionsof the ductwork inside the building when thesystem is in operation.

International Mechanical Code (IMC) – Section 51 0 –Hazardous Exhaust Systems:

M any bui lding codes based on the I M C defineHazardous Exhaust Systems in a way that sometimesincludes laboratory exhaust systems. In the past, thedesignation has been an obstacle to HVAC designers.Since 2006, revisions to the IMC make that designa-tion less of a burden. In particular, the code more read-i ly permits manifolding, and usually el iminates theneed for fire suppression.

Most states have adopted this section into their statemechanical code. Section 51 0.2 of this code providesa definition based decision process to determinewhether Section 51 0 appl ies to their design. Theexceptions in Section 51 0.4 serve to more readi ly per-mit manifolding of laboratory exhaust, when appropri-ate. The exception in Section 51 0.7 addresses anexemption for laboratory ducts from requirements forautomatic suppression.

The laboratory definition and exception language forlaboratories are changes that were first publ ished inthe 2004 Supplement to the International Codes andthe 2006 I nternational M echanical Code. Thesechanges were made to support safety and efficiency ingeneral, and to permit manifolding where appropriate.

I t is permissible to locate exhaust fans in a normallyunoccupied enclosed space such as a roof penthousewhen the fan discharge ductwork is well sealed and theenclosed space is adequately venti lated.


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Exhaust ductwork shal l be designed in accor-dance with the current versions of ANSI/AIHA ®

Z9. 2, the ASH RAE H andbook –Fundamentals, and NFPA 45.

Branch ducts shall enter a main duct so thatthe branch duct centerl ine is on a plane thatincludes the centerl ine of the main duct. Forhorizontal main ducts, branch ducts shal l notenter a main duct on a plane below the hori-zontal traverse centerl ine of the main duct.Horizontal runs of branch ducts shal l be kept ata minimum.

Longitudinal sections of a duct shall be a con-tinuous seamless tube or of a continuouslywelded formed sheet. Longitudinal seams thatare formed mechanically shall be uti l ized onlyfor l ight duty systems with no condensation oraccretion inside the duct. Spiral ducts may beone gauge l ighter than the required gauge oflongitudinal seam duct, except the spiral ductgauge shal l always meet the abrasive wearresistance requirements.

Traverse joints shal l be continuously welded orflanged with welded or Van Stone flanges.(When nonmetall ic materials are used, jointsshall be cemented in accordance with themanufacturer’s procedures.) I f the duct is coat-ed with a corrosion-resistant material , thecoating shall extend from the inside of the ductto cover the entire face of the flange. Flangefaces shall be gasketed or beaded with mater-ial suitable for service.

I f condensation within the duct is l ikely, al l hor-izontal duct runs shall be sloped downward atleast 1 in. per 1 0 ft in the direction of the airflowto a suitable drain or sump.

When nonmetal l ic materials are used, joints cementedin accordance with the manufacturer’s procedures maybe considered equivalent to welding.

Exhaust duct sizes should be selected to ensure suffi-ciently high airflow velocity to retard condensation ofl iquids or the adherence of sol ids within the exhaustsystem.




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

Al l duct connections to the exhaust fan shall beconsistent with good venti lation design prac-tice. As an alternative, the duct connectionsmay be made by means of inlet and outletboxes. I f circumstances such as space l imita-tions prevent the implementation of the preced-ing requirements, then applicable speed andpower corrections shall be made by applyingthe “System Effect Factor" (see AMCA 201 -90).

Where optimum duct connections cannot bemade due to space or other l imitations, suitablealternative means shall be substituted to com-pensate for the space l imitations.

I f adequate duct connections cannot be provid-ed at the fan, the fan shal l be equipped withinlet and outlet boxes furnished by the fan man-ufacturer. The manufacturer shall furnish per-formance curves for the fan with the inlet andoutlet box(es) as part of the fan.

I f neither adequate connections nor inlet/outletboxes are present, the fan speed and powerrequirements represented in the fan rating tableshal l be corrected by the “System EffectFactor.”

In some cases, accumulation of sol id material withinthe duct system may be prevented by providing waterspray nozzles in the duct at frequent intervals andsloping the duct down to an appropriate receptor (e.g. ,a wet dust col lector).

This temperature l imit applies in case of ignition of aspi l l of flammable l iquid that in turn requires an esti-mate of the maximum credible accident that wouldgenerate heat.

I f variable air volume (VAV) laboratory chemical hoodsare used, satisfying this criterion might require a heatsensor arrangement to signal the VAV controls systemto increase the exhaust airflow. An alternative solutionwould be to provide a higher temperature exhaust sys-tem design or a high-temperature combustion fluedesign for the portions of the exhaust system in whichtemperatures might exceed 400°F (204°C) in conjunc-tion with the current version of NFPA 86.

For good inlet and outlet duct design refer to the AirMovement and Control Association’s Fan ApplicationManual Part 1 , the ACGIH ® Laboratory Venti lationManual, and the ASHRAE Handbook – Fundamentals.

An adequate outlet duct connection has the samerequirements as an air inlet duct except i t need be only3 diameters in length and no vortex breaker is neces-sary.

Transition fi ttings at the inlet and outlet should have a1 5° or less included angle in any plane.


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5.4.2.2 Materials

Exhaust system materials shal l be in accordancewith the current version of ACGIH’s IndustrialVentilation: A Manual of Recommended Practice,the ASHRAE Handbook – Fundamentals, andNFPA 45.

Exhaust system materials shal l be resistant tocorrosion by the agents to which they areexposed. Exhaust system materials shall be non-combustible i f perchloric acid or similar oxidizingagents that pose a fire or explosive hazard areused.

5.4.3 Manifolds

5.4.3.1 Combined Exhaust Systems

Computation of this factor requires data on the fan’s“blast area” and must typical ly be obtained from themanufacturer.

Solid metal ductwork has good fire characteristics butin some cases has inferior corrosion resistance forsome chemicals. Solid plastic ductwork generally hasgood corrosion resistance but may not be acceptableto the local fire authority. An economical material thatcan be used when appropriate and if proper care isused in installation and maintenance is a metal ductwith a protective coating. However, because of thethin coatings generally used, pinhole defects in thecoating may be relatively common, which wouldeventually lead to a very small amount of leakage.Any mechanical damage or scratching of the coatingin installation or maintenance would have to beimmediately and properly repaired or the bare metalrevealed in the scratch wil l be eaten away. Owner’srepresentatives must spend more time and moneyduring installation to make sure contractor coats allexposed metal during initial installation and similarcare must be exercised whenever the coated exhaustduct is modified during renovations.

Two or more exhaust systems may be combined intoa single manifold and stack, i f the conditions of5.4.3.2 are met.

Manifold exhaust systems frequently have significantadvantages over individual (single-hood/single-fan)systems and are encouraged.

Exhaust systems may combine al l lab exhaust, ormay segregate general room exhaust from fumehood exhaust. This decision can affect options forheat recovery and air cleaning.




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Manifold and individual systems have the fol lowing

characteristics:

Manifold Systems:

Advantages:

• Contaminant concentrations from individual hoodsare di luted by the air from al l the other hoods onthe manifold before being released into the atmos-phere.

• Energy recovery is financially feasible.• Fan maintenance costs are reduced.• Fewer stacks to locate in ideal location (5.4.5, 5.4.6,

Appendix 3).• First costs are lower.• H igh mass of discharge makes it less susceptible to

wind.• Operating costs are lower.• Opportunity to instal l redundant fans is increased

and may only require one additional fan (i .e. , costto provide redundancy is reduced.)

• Opportunity to instal l emergency power is increasedwhile the cost is reduced.

• Opportunity to uti l ize diversity is increased.• Opportunity to efficiently uti l ize VAV controls is

increased.• Opportunity to provide additional capacity for future

expansion is increased.• Shaft space for ductwork is reduced.• The number of roof penetrations and potential leaks

are reduced.

Disadvantages:

• Changing the appl ication of a single hood (i .e. , froma standard laboratory chemical hood to radioiso-tope hood or perchloric acid hood) is difficult.

• Controls for system static pressure, capacity con-trol, etc. , are more complex than individual sys-tems.

• Fan fai lure affects al l hoods on the system andredundancy is required.

• May be difficult to apply in existing buildings.• The abi l i ty to provide treatment (i .e. , scrubbing, fi l -

tering, etc. ) for an individual exhaust sourcerequires an in-l ine scrubber and additional static


54

pressure for the entire manifold or in the specifichood branch.

Individual Systems:

Advantages:

• Changing the appl ication of a single hood (i .e. , froma standard laboratory chemical hood to radioiso-tope hood or perchloric acid hood) is easily accom-plished.

• Fan fai lure affects only a single hood.• Less complex system.• The abil i ty to provide treatment (i .e. , scrubbing, fi l-

tering, etc. ) for an individual exhaust source is eas-i ly accomplished.

Disadvantages:

• Applying diversity is difficult.• Energy recovery is not financially feasible.• First costs are higher.• Impossible to locate al l stacks in ideal location

(5.4.5, 5.4.6, Appendix 3).• Low mass of discharge makes it more susceptible

to wind• Operating costs are higher.• Providing redundancy is difficult due to space l imi-

tations and is more expensive.• Providing emergency power is difficult and more

expensive.• Providing future capacity for expansion requires

additional ductwork, equipment, and uti l i ties.• Maintenance costs are higher.• Requires a larger number of roof penetrations and

roof leak potential is increased.• Shaft space requirements are higher.• There is no di lution of the source effluent before

releasing it to the atmosphere.




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Large Systems:

Large and/or diverse systems that have several typesof hoods often benefit from a hybrid approach where amanifold is designed to handle a majority of the hoodsand individual exhaust systems are installed for thosethat cannot or should not be manifolded such as per-chloric acid or radioisotope hoods.

Adverse Chemical Reaction Potential:

Contrary to popular bel ief, the probabil ity of two ormore reagents from different sources combining in themanifold to produce an explosion is extremely small butshould be evaluated for special cases involving largequantities of materials.

Consider the minimum manifold with two hoods con-nected to a single fan: Reagent A is spi l led in Hood A,covering the entire work surface and producing maxi-mum evaporation and duct concentration whi leReagent B is similarly spil led in Hood B. Reactivechemistry experts attempting to devise worst-casebinary reaction assure us that although these twochemicals, when mixed in l iquid or solid form, wil l cer-tainly explode, when mixed in concentrations less than1 0,000 ppm (1 %) in air, i t is unl ikely that an explosivereaction can be in i tiated or sustained (Hitchings,unpublished data). The last statement notwithstanding,assuming that a reaction can be initiated, the resultwould be only a sl ight adiabatic temperature increasein the duct.

The abil ity of chemicals from different sources to formtoxic products is similarly l imited by low concentrationsthat become lower and lower the closer they get to thefan in manifold systems.


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5.4.3.2 Manifold Requirements

Laboratory chemical hood ducts may be com-bined into a common manifold with the fol low-ing exceptions and l imitations:

Each control branch shall have a flow-regulat-ing device to buffer the fluctuations in pressureinherent in manifolds.

Perchloric acid hoods shal l not be manifoldedwith nonperchloric acid hoods unless a scrub-ber is installed between the hood and the man-ifold.

Where there is a potential for ductwork conta-mination from hood operations as determinedfrom the Hazard Assessment of Section 2.4,radioisotope hoods shall not be manifoldedwith nonradioisotope hoods unless an appro-priate air-cleaning system is provided betweenthe hood and the manifold: HEPA fi l ter and/orcarbon bed fi l ters for gases.

Flow regulating devices that are pressure-independentdevices also al low changes to be made in the systemwithout the need to rebalance the entire system.

Manifolding of perchloric acid hoods is discouragedbecause nonvertical ductwork is implied by connectingone or more hoods together and nonvertical ducts aredifficult to wash down properly using duct-mountedspray heads.

Install ing in-l ine fi l tration is impractical in most situa-tions because it increases the overall static pressurefor the entire system unless a booster fan is instal ledwith the HEPA fi lters, which increases a leak potential.Manifolding of radioisotope hoods is discouraged dueto the potential contamination of the entire exhaustsystem in the event of HEPA fi l tration fai lure and thepossibi l i ty of pressurizing the exhaust manifold with thebooster fan.

HEPA fi lters only cover radioactive dust, not radioac-

tive gases.

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.




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5.4.3.3 Compatibil ity of Sources

Exhaust streams that contain concentrationsof flammable or explosive vapors at concentra-tions above the Lower Explosion Limit (LEL) aswell as those that might form explosive com-pounds (i .e. , perchloric acid hood exhaust)shal l not be connected to a central izedexhaust system. Exhaust streams comprisedof radioactive materials shall be adequately fi l-tered to ensure removal of radioactive materi-al before being connected to a central izedexhaust system. Biological exhaust hoodsshall be adequately fi l tered to remove al l haz-ardous biological substances prior to connec-tion to a central ized exhaust system.

5.4.3.4 Exhaust System Reliability

Unless al l individual exhausts connected to thecentral ized exhaust system can be completelystopped without creating a hazardous situa-tion, provision shal l be made for continuousmaintenance of adequate negative static pres-sure (suction) in al l parts of the system.

As an alternative, i f the hood is completelyturned off, the hood shall be emptied anddecontaminated and provisions shall be imple-mented to prevent the hood from back-draft-ing.

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

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

• Multiple operating fans so the loss of a single fandoes not result in loss of total system negativestatic 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 al lexhaust fans and the associated control system.

Before considering complete shutdown of the hood, thefol lowing considerations should be investigated:

• Notification to occupants • Room air balance, and • Use of other chemicals in the space

Under these conditions, the exhaust volume is inde-pendent of the sash position.

Note this requires careful planning for a system withless than 1 00% diversi ty (See Section 5. 1 . 2) .

I f the maximum exhaust volume of the variable air vol-ume hoods in one room exceeds 1 0% of the room airsupply volume, and if the laboratory is designed for


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5.4.3.5 Biological Safety Cabinets

Biological safety cabinets manifolded withchemical laboratory chemical hoods shall haveeither:

1 ) A thimble connection (also known as acanopy connection), or

2) An air flow control device and an inter-lock/alarm for these devices shall be installedbetween the cabinet outlet and the exhaustmanifold.

Where Hazard Evaluation and Analysis deter-mines that the instal lation calls for direct con-nection (hard ducted) of the biological safetycabinet (e.g. , Class I I–Type B) to an exhaustmanifold system to al low work with toxic chem-icals or radionucl ides, interlocks and alarmsshall be provided to prevent the biologicalsafety cabinet from operating i ts normal start-ing mode or to immediately warn the operatorin the event of an exhaust system fai lure(CDC-NIH, 1 999).

controlled 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.

Thimbles al low 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 fi l ters.

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

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

For direct (hard ducting) of Class I I 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 I I–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 fai lure. Thimble connections can be improperlydesigned 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 fai lure. Interlocks, i f activated during an exhaustsystem fai lure involving radioactive materials, couldcause worker or product exposure. A non-manifoldeddedicated exhaust system connection directly ventedto the atmosphere may be needed for work with thesetypes of hazardous materials.




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5.4.3.6 Static Pressure

The static pressure in the exhaust system shal lbe lower than the surrounding areas through-out the entire length, with the exception notedin Section 5.3.1 .1 .

5.4.3.7 Fire Dampers

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

5.4.3.8 Fire Suppression

Fire sprinklers shal l not be installed in labora-tory chemical hood exhaust manifolds.

Constant volume control devices maintain a constantexhaust rate from al l types of biological safety cabinetsregardless of changes in exhaust system static pres-sure.

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.

The accidental activation of a fire damper wil l 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 a lab-oratory chemical hood wil l shut off airflow from thathood making i t impossible to remove the combustionproducts from the hood and forcing the hood tobecome positively pressurized. This condition makes itl ikely that the fire wi l l escape the fire-resistant hood intothe laboratory.

With the exhaust flow from one or more hoods shut off,the laboratory may become positively pressurized withrespect to the corridor, encouraging the spread of thecombustion products, and perhaps the fire, from thelaboratory to adjoining spaces.

Studies of actual exhaust systems have demonstratedthat the spray cone produced by sprinkler heads canactual ly act as a damper and reduce or prevent airflowin the duct past the sprinkler head (Hitchings andDeluga, personal communication). Like a fire damper,this may produce a lack of flow at one or more labora-tory chemical hoods at the moment when it is neededmost.


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5.4.3.9 Continuous Operation

Exhaust systems shal l operate continuously toprovide adequate venti lation for any hood atany time i t is in use and to prevent backflow ofair into the laboratory when the fol lowing con-ditions are present:

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

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

• There are powered devices connected tothe manifold. Powered devices include,but are not l imited to: biological safetycabinets, in-l ine scrubbers, motorizeddampers, and booster fans.

5.4.3.1 0 Constant Suction, Redundancy

and Emergency Power

Manifolds shal l be maintained under negativepressure at al l times and be provided with atleast two exhaust fans for redundant capacity.

Emergency power shall be connected to oneor more of the exhaust fans where exhaustsystem function must be maintained evenunder power outage situations.

5.4.4 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 thenecessary amount of exhaust airflow in con-junction with the size, amount, and configura-tion of the connecting ductwork. In addition,each fan’s rotational speed and motor horse-power shal l be sufficient to maintain both therequired exhaust airflow and stack exit velocityand the necessary negative static pressure(suction) in al l parts of the exhaust system.

I f flammable gas, vapor, or combustible dust ispresent in concentrations above 20% of theLower Flammable Limit, fan construction shal l

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

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




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be as recommended by the current version ofAM CA’s 99-0401 , Classi fications for SparkResistant Construction.

Laboratory exhaust fans shal l 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 maintained ata negative static pressure with respect to therest of the facil ity, and provides direct fan dis-charge into the exhaust stack(s).

Al l laboratory exhaust fans shall include provi-sions to al low periodic shutdown for inspectionand maintenance. Such provisions include:

• Isolation dampers on the inlet side of al l cen-tralized exhaust system fans that have indi-vidual discharge arrangements or their ownindividual exhaust stacks.

• Isolation dampers on both the inlet and outletsides of al l central ized exhaust system fansthat discharge into a common exhaust stackor plenum.

• Ready access to al l fans, motors, belts, dri-ves, isolation dampers, associated controlequipment, and the connecting ductwork.

• Sufficient space to al low removal andreplacement of a fan, i ts motor, and al l otherassociated exhaust system components andequipment without affecting other mechani-cal equipment or the need to alter the build-ing structure.

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

Under most operating conditions, centrifugal fanswil l leak small amounts of system gases at the fanshaft. Also, fan discharge ducts typical ly are underpositive pressure and any air leaks would dischargeinto the room. Locating laboratory exhaust fans asrequired helps ensure that any leakage wil l beeffectively removed and wil l not migrate within thebui lding.

I t is permissible to locate exhaust fans in a normal-ly unoccupied enclosed space such as a roof pent-house when the fan discharge ductwork is wel lsealed and the enclosed space is adequately venti-lated.

The requirements for inspection access and ser-viceabil ity are intended to ensure that laboratoryexhaust systems can be kept and maintained inproper operating condition. I f 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.


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5.4.5 Discharge of Contaminated Air

The discharge of potential ly contaminated air that con-tains a concentration more than the al lowable breath-ing air concentration shall be

• direct to the atmosphere unless the air is treatedto the degree necessary for recirculation (seeSection 9.3),

• discharged in a manner and location to avoidreentry into the laboratory bui lding or adjacentbuildings at concentrations above 20% of al low-able concentrations inside the laboratory for rou-tine emissions or 1 00% of al lowable concentra-tions for emergency emissions under wind condi-tions up to the 1 %-wind speed for the site, and

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

5.4.6 Exhaust Stack Discharge

The exhaust stack discharge shal l be in accordancewith the current version of ASHRAE Handbook –HVAC Applications, and the chapter or section dealingwith Building Air Intake and Exhaust Design.

In any event the discharge shal l be a minimum of 1 0 ft(3 m) above adjacent roof l ines and air intakes and ina vertical up direction.

The in-stack concentrations of contaminantsallowed under such regulations typical ly rangefrom 1 00 to 1 000 times higher than safe breath-ing concentrations.

The 1 % wind speed is the value exceeded atthe site only 1 % of time, according to historicalweather records.

Necessary measures must be taken to protectthe laboratory bui lding and adjacent buildingsfrom toxic materials reentry.

The 1 0 ft (3 m) height above the adjacent roofl ine cal led for by this standard is primarilyintended to protect maintenance workers fromdirect exposure from the top of the stack. How-ever, this minimum 1 0 ft (3 m) height may beinsufficient to guarantee that harmful contami-nants won’t enter the outside air intake of thebuilding or of nearby buildings.

After initial installation, the exhaust stack isunchanged for the l i fetime of the hood. I t isuncertain that the l i fetime hood usage can beaccurately projected. In most cases, consistentdiscipl ine in safe hood procedures cannot beassured. Accordingly, i t is prudent to use con-servative gu idel ines in the location andarrangement of the hood discharge.

The basic chal lenge in locating the hood dis-charge is to avoid re-entrainment of effluentinto any building air intake or opening and tominimize exposure of the public. The selectionof stack height is dependent on the buildinggeometry and airflow pattern around the build-




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Exhaust stack discharge velocity shal l be atleast 3000 fpm (1 5.2 m/s) is required unless itcan be demonstrated that a specific designmeets the di lution criteria necessary to reducethe concentration of hazardous materials in theexhaust to safe levels (See Section 2.1 ) at al lpotential receptors.

Aesthetic condi tions concerning externalappearance shall not supersede the require-ments of Sections 5.4.5 and 5.4.6.

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

The air intake or exhaust gri l les shal l not belocated within the architectural screen or maskunless it is demonstrated to be acceptable.

ing and is as variable as meteorological conditions.

An excellent resource is Chapter 44 of the ASHRAE2007 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 (1 2.7 m/s) preventsdownward flow of condensed moisture within theexhaust stack. I t is good practice to make the terminalvelocity at least 3000 fpm (1 5.2 m/s) to encourageplume rise and di lution.

These factors affect the di lution 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 confl ict, the requirements of Section5.3.4 take priority. Some solutions that may be usedare:

• 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 44of the ASHRAE 2007 Handbook – HVACApplications. The limitations of the technique utilizedshould be understood and evidence should be pro-vided that the results are conservative or accuratefor the case being modeled. When physical model-ing is used, procedures discussed in the EPAGuideline for Modeling of Atmospheric Diffusion(Office of Air Quality Planning and Standards, EPA-600/8-81 -009, April 1 981 ) should be employed.

• Treatment of the discharge gas may permit alower and esthetical ly acceptable stack. The tech-nology of gas-treating equipment is outside thescope of this standard except as described in


64

5.4.7 Recirculation of Room Exhaust Air

Non-laboratory air or air from bui lding areasadjacent to the laboratory is permitted as part ofthe supply air to the laboratory i f i ts qual ity isadequate.

5.4.7.1 General Room Exhaust

Air exhausted from the general laboratoryspace (as distinguished from laboratory chemi-cal hoods) shall not be recirculated to otherareas unless one of the fol lowing sets of criteriais met:

1 ) Criteria A

• The concentration of air contaminants gen-erated by maximum credible accident wi l lbe lower than short-term exposure l imitsrequired by 2.1 .1 ;

• There are no extremely dangerous or l i fe-threatening materials used in the laborato-ry; and

• The system serving the laboratory chemi-cal hoods is provided with installed redun-dancy, emergency power, and other rel ia-bi l ity features as necessary, or

2) Criteria B

• Provision of 1 00% outside air, whenevercontinuous monitoring indicates an alarmcondition;

• Recirculated air is treated to reduce conta-minant concentrations to those specified in2.1 .1 ; and

Section 9.2.• Appendix 3 is provided to assist the designer in

understanding stack height determination andevaluation methods.

In many laboratory settings, the laboratory is pur-posely kept at a sl ight negative differential pressurewith respect to adjacent building spaces. In this situa-tion, air flows from the adjacent spaces into the labo-ratory through bui lding cracks and doorways, at leastwhen open. This may be highly desirable; i f not, thisflow can be reduced, but not completely el iminated, byuse of double-door anterooms, with correspondingconsumption of interior space and some hindrance totraffic.

Some laboratories have no general exhaust, so thereis no flow to consider recirculating.

Devices that are intended to provide heating and/orcooling by recirculating the air within a laboratoryspace (i .e. , fan coi l units) are exempt from thisrequirement




65

• Recirculated air is monitored continuouslyfor contaminant concentrations or provid-ed with a secondary backup air-cleaningdevice that also serves as a monitor (viaa HEPA fi lter in a series with a less effi-cient fi l ter, for particulate contaminationonly). Refer to Section 9.3.1 .

5.4.7.2 Hood Exhaust

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

Hood exhaust air meeting the same criteria asnoted in Section 5.4.7.1 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.

6 Commissioning and Routine

Performance Testing

6.1 Performance specifications, tests,

and instrumentation

6.1 .1 Specifying Laboratory Fume Hood

Performance

Test specifications used for selecting a hood,in commissioning or in routine testing, shal lrefer to the appl icable ANSI/ASHRAE 1 1 0defined performance tests or to a test standardrecognized to be equivalent.

Specification and procurement of laboratoryfume hoods shal l be based on “AsManufactured” ANSI /ASHRAE 1 1 0 definedperformance tests conducted on a representa-tive hood (or prototype hood) that demonstrate

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.

Refer to the current version of NFPA 45 for i ts positionon recirculation of laboratory chemical hood air whenusing flammables.

Some “single purpose” laboratories might find i t practi-cal to recirculate laboratory chemical hood air; therequirements are similar to those in Section 5.3.7.1 cri-teria B. See Section 4.2 for more information.

ANSI/ASHRAE 1 1 0 defines three different test scenar-ios, “As Manufactured, As Installed and As Used.”

”As Manufactured” tests, usually performed at the hoodmanufacturer’s facil ity, are conducted to determinewhether the hood is adequately designed to provide


66

adequate hood containment.

The performance tests to be witnessed, referencedor otherwise shall include

• airflow visualization tests,• auxi l iary air velocity tests (if applicable, )• cross drafts velocity tests,• exhaust flow measurements,• face velocity tests,• hood static pressure measurement, and • tracer gas containment tests

The tests shall be conducted under constant vol-ume conditions where exhaust and air supply floware stable and exhibit no more than 5% variationfrom set-point.

the required level of performance. In addition, thetests are conducted to determine appropriateoperating specifications. I t is only necessary toperform these tests on one hood for each uniquehood design or mode.

Credible catalog data on the fundamental perfor-mance and capabil ities of a hood as i t comes fromthe manufacturer are useful. The designer can thenspecify the unit with confidence that it wil l performas per the manufacturer’s catalog data. I t is recom-mended that the manufacturers’ tests be conductedor witnessed by the laboratory owner and designprofessional, and/or independent third party.

The containment tests should be conducted overthe range of possible operating configurationsafforded by the hood design (i .e. , sash position, baf-fle configurations, etc.) and at different target facevelocities or exhaust flow rates to determine opera-tional boundary conditions and hood l imitations.

Proper containment of a laboratory fume hood isaffected by a number of factors including design ofthe hood, design of the laboratory, and design andoperation of the venti lation systems. Controlledtests enable el imination of one variable: design ofthe hood. Therefore, performance problemsencountered after instal lation can be attributed toother factors.

Where possible, containment tests should be con-ducted according to methods described in themost recent ANSI/ASHRAE 1 1 0 standard equal toor more challenging than the standardized test.

ANSI/ASHRAE 1 1 0 does not specify a face veloc-ity. The standard yields a performance rating in theform of AM yy, AI yy, or AU yy where, AM means“as manufactured,” AI means “as instal led,” and AUmeans “as used.” The symbol yy represents theaverage 5-minute concentration of tracer gas mea-sured in the breathing zone of a mannequin usedto simulate a hood user.

The ANSI/ASHRAE 1 1 0 standard recommends agas generation rate of 4 L/m. However, other gen-eration rates (i .e. , 1 L/m or 8 L/m) can be specifiedby the design professional or responsible person




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6.1 .2 Performance Tests

The fol lowing performance tests shal l be con-ducted as indicated and as prescribed in thecommissioning plan, laboratory venti lationmanagement plan, or as d i rected by theresponsible person.

6.1 .2.1 Airflow Visualization Tests

Airflow visual ization tests shall be conductedas described in the ANSI/ASHRAE 1 1 0–1 995,Method of Testing Performance of LaboratoryFume Hoods.

The tests shall consist of small-volume genera-tion and large-volume generation smoke toidentify areas of reverse flow, stagnation zones,vortex regions, escape, and clearance.

Visible escape beyond the plane of the sashwhen generated 6 in. (1 5.2 cm) into the hoodshall constitute a fai lure during the perfor-mance test.

(2.3) when deemed appropriate.

Testing at different operating configurations wil l help toidentify operational l imitations or worst-case operatingconditions. This information helps the design profes-sional in their work and can then be relayed to thehood users to ensure proper work practices that mini-mize potential for exposure.

Smoke tests are valuable because they indicate thedirection of airflow through the opening and within thehood enclosure when the smoke plume is visible.Smoke particles are rapidly di luted to the extent wherethey may not be visible even though significant con-centrations may exist in the invisible plume. Smoketests should be used only as an indication of flowdirection and absence of visible smoke should not beinterpreted as an absence of smoke. Users of smokeshould note that smoke tubes and candles can becaustic and detrimental to the user, test equipment,and apparatus in the hood.

Attempts to improve airflow patterns should be attempt-ed by adjusting the baffles and slot widths, redirectingroom air currents, or changing the opening configura-tion by moving the sash panels. Closure of the sashesresulting in an opening smaller than the design openingmay represent a “restricted use” condition.

Often the most devastating area for reverse flow isbehind the airfoi l si l l on bench-top-mounted hoods. Animproperly designed airfoi l or lack of an airfoi l wi l lcause reverse flow along the work surface within 6 in.(1 5.2 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.


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6.1 .2.2 Auxiliary Air Velocity Tests

For auxi l iary air hoods, the face velocity shal l bemeasured with the auxil iary air turned off unlessroom pressurization would change significantly toaffect exhaust flow. Where exhaust flow would beaffected by turning off the auxil iary airflow, auxi l-iary air must be redirected from the hood openingso as not to interfere with flow into the hood whi leconducting the face velocity traverse.

The velocity of the auxil iary air exiting the auxi l iaryair plenum shal l be measured to determine themagnitude and distribution of air supplied abovethe hood opening.

The average auxi l iary air velocity shall be deter-mined from the average of grid velocities mea-sured across the plenum outlet.

Hood face velocity is usually defined as air speed ina direction normal to the plane of the hood faceopening. For auxi l iary air hoods in standard opera-tion, the directional component of the air velocity isnot normal to the hood face plane. Accurate deter-mination of the flow direction and derivation of thehorizontal and vertical components of the velocityvector require very sophisticated instrumentationbecause of the low air speeds involved. Hence,measuring the hood’s face velocity with the auxi l-iary air shut off is an acceptable measure of hoodexhaust volume, i f turning off the auxil iary air doesnot upset the room air balance enough to reducesignificantly the volume extracted by the hoodexhaust system.

Face velocity measurements should be determinedwith the supply air off or with special devicesdesigned to el iminate the effect of the auxil iary airat the hood face. For example, supply air from theauxil iary air plenum can be temporari ly redirectedaway from the sash opening by use of a portablebaffle, hand held or otherwise placed beneath thesupply air discharge without blocking off the supplyair flow.

NOTE: The 90% capture efficiency should be test-ed by material balance by introducing a tracer gasinto the auxil iary airstream and sampling the hoodexhaust. Flow volume and sampling should be inaccordance with EPA methods 1 , 2, and 1 7 (40CFR 60, Appendix A) or by other methods mutual-ly agreed on by al l parties.

The auxi l iary air supply plenum located above thetop of the hood face and external to the hoodshould be designed to distribute air across thewidth of the hood opening so as not to affect con-tainment.

Excessive auxil iary air velocity can interfere orovercome air flowing into the hood opening andcause escape from the hood.

The downflow veloci ties should be measuredapproximately 6 in. (1 5.2 cm) above the bottomedge of the sash positioned at the design openingheight.




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6.1 .2.3 Cross-Draft Velocity Tests

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

Over a period of 1 0–30 sec. , cross-draft veloc-ities shall be recorded approximately 1 readingper second using a thermal anemometer withan accuracy of +5% at 50 fpm (0.25 m/s) orbetter.

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 such mag-nitude and direction as to negatively affectcontainment.

6.1 .2.4 Exhaust Flow Measurements

The volumetric flow exhausted from a labora-tory fume hood shall be determined by mea-suring the flow in the exhaust duct using indus-try-approved methods.

More test locations may be required or can be usefulfor determining cross-draft velocities past the hoodopening. Vertical and horizontal components of cross-draft velocities 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 properroom air 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. Ideal ly, cross-draft velocities should be lessthan 30%.

I f the supply tracks the exhaust, measure the crossdrafts at the maximum conditions.

See the current version of ACG I H ®’s Industrial

Ventilation: A Manual for Recommended Practice, orANSI/ASHRAE 41 .2–1 987 (RA 92), for measuring flow.

The hood exhaust flow should be adjusted to achievethe target average face velocity at the design openingand to achieve the specified flow with the sash closed.

Typical ly, exhaust flow can be predicted from the areaof the opening multipl ied by the design face velocity.However, infi ltration of air into the hood through open-ings other than the face may require approximately5–1 0% more exhaust flow than calculated. The exhaustflow and variance from the calculated flow should bedetermined to enable proper specification of flows fordesign of the venti lation systems.

Failure to determine the total exhaust flow required toachieve the desired average face velocity may result inunder sizing of the exhaust system or improper speci-fication of supply volume to achieve required lab pres-surization or differential airflow.


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6.1 .2.5 Face Velocity Tests

Once adequate performance has been estab-l ished for a particular hood at a given bench-mark face veloci ty using the methodsdescribed herein, that benchmark face veloci-ty shal l be used as a periodic check for contin-ued performance as long as no substantivechanges have occurred to the hood or otheraspects that affect hood performance.

Face velocity measurements shal l be madewith the sash in the Design Sash Position. TheDesign Sash Position is the maximum openingor configuration al lowed by user standards,SOPs, or the Chemical H ygiene Plan,whichever is appl icable, and used in thedesign of the exhaust system to which thehood is connected.

The sash position at which benchmark facevelocity is measured shall be recorded with theface velocity measurement and reproducedeach time measurements are taken.

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.

Calculation of exhaust flow from face velocity mea-surements multipl ied by hood face area is not a mea-surement of exhaust flow and due to the reasons stat-ed above, true exhaust flow can vary significantly fromthe calculated exhaust flow. In addition, the accuracy offace velocity measurements can affect the accuracy ofthe average face velocity used to calculate exhaustflow. Face velocities measured at the plane of the sashopening using hot-wire anemometers or pressure gridassemblies can be subject to significant error due toturbulence at the opening and direction of airflow overthe probes where average face velocities could varyfrom actual by 5–20%.

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

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.

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

This magnitude of decrease may impair performance.

An increase in individual hood average face velocitynot exceeding 20% of the benchmark face velocity wi l lprobably not significantly alter hood performance andis acceptable with no corrective action. I t should benoted, however, that there is an unnecessary increasein operating cost wi th increased face veloci ties.I ncreases exceeding 20% and the accompanying




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The average face velocity shal l be determinedby the method described in the current versionof AN SI /ASH RAE 1 1 0 Method of TestingPerformance of Laboratory Fume Hoods.

Face velocity measurements shal l be made bydividing the hood opening into equal area gridswith sides measuring no more than 1 2 in. (30.5cm). The tip of the probe shal l be positioned inthe plane of the sash opening and fixed (nothandheld) at the approximate center of eachgrid. Grid measurements around the perimeter

increase in supply flow rates may degrade performancedue to increased impingement and cross-draft veloci-ties. In addition, an increase in face velocity at the mea-sured hood may indicate a decrease in face velocity atother hoods in the exhaust systems.

In constant volume systems, the face velocity wi l lincrease 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 increases asvolume 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.

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 , for information about analysis offace velocity data and recommended criteria.

The accuracy of face velocity measurements can beaffected by numerous factors including instrumentaccuracy, measurement technique, hood aerodynam-ics, room air conditions (cross drafts), and exhaust flowstabil ity. Average face velocities and grid velocities canbe significantly affected by turbulence (temporal varia-tion) and direction through the opening (spatial 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.


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of the hood opening shall be made at a distanceof approximately 6 in. (1 5.2 cm) from the top,bottom, and sides of the opening enclosure.

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

Each grid velocity shall be the average of atleast 1 0 measurements made over at least 1 0seconds.

The plane of the sash shall be defined as theexterior surface of the outer most glass panel.

6.1 .2.6 Hood Static Pressure Measurements

The hood static pressure shall be measuredabove the outlet collar of the hood at the flowsrequired to achieve the design average facevelocity.

6.1 .2.7 Tracer Gas Containment Tests

The tracer gas containment tests shall be con-ducted as described in the ANSI/ASHRAE1 1 0–1 995, 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 shal l be no greater than 0.05 ppm for"as manufactured” tests and 0.1 0 ppm for “asinstalled” (AM 0.05, AI 0.1 ).

Escape more than the control levels statedabove shal l be acceptable at the discretion ofthe design professional in agreement with theresponsible person (2.4.2). The “as used” 0.1 0ppm level or more is at the discretion of theresponsible person (2.3).

Multiple readings at each grid point wil l 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.

Manufacturers have been defining the sash plane some-what subjectively, thus making it difficult for users to com-pare face velocity data and AM containment test results.This definition from ANSI/ASHRAE 1 1 0 aims to lessenthe subjectivity in AM as well as AI and AU testing.

For test method, refer to current version ofANSI/ASHRAE 41 .3. Hood static pressure is a mea-sure of the resistance imposed on the exhaust systemby the hood. Determination of hood static pressure isrequired to ensure proper system design. Typical hoodstatic pressures range from 0.1 to 0.75 in.wg (25 to 1 87Pa) at face velocities between 80 to 1 20 fpm (0.41 to0.61 m/s). However, the hood static pressure wil ldepend on the hood design and exhaust flow.

Tracer gas tests enable the abi l ity to quantify the poten-tial for escape from a laboratory fume 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-l ishing 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 l ive operator, who mayincrease potential for escape due to operator size,movements near the hood opening, or improper hooduse.




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6.1 .3 Test Instrumentation

All test instrumentation uti l ized for the testsprescribed throughout this section shall be ingood working order and shal l have been facto-ry cal ibrated within 1 year of the date of use.(See 8. 6. 1 , Ai r Veloci ty, Ai r Pressure,Temperature and Humidity Instruments)

6.2 Commissioning of Laboratory

Ventilation Systems

6.2.1 Commissioning Process

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

6.2.2 Commissioning Authority

The commissioning process shal l be overseenby a responsible person or commissioningauthority.

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 fume hood. I t 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).

Commissioning tests are conducted to ensure that lab-oratory venti lation systems operate according todesign specifications and are capable of meeting con-trol objectives under resulting operating conditions. Theextent of the commissioning process depends on thecomplexity of the systems along with the anticipatedrisk associated with work to be conducted in the labo-ratory.

The commissioning authority should be someone whorepresents the interests of the system owner andshould be knowledgeable in the design and operationof laboratory venti lation 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, instal lation, and use of the new


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6.2.3 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 shal l address operationof the entire venti lation system where thehoods, laboratories, and associated exhaustand air supply venti lation systems are consid-ered subsystems.

The plan shall include written procedures toverify or val idate proper operation of al l systemcomponents and include:

• Laboratory Fume Hood Specification andPerformance Tests

• Preoccupancy Hood and Venti lationSystem Commissioning Tests

• Preoccupancy Laboratory CommissioningTests

or renovated systems should assist the commissioningauthority. A commissioning team might include:

• Chemical Hygiene Officer• Commissioning Consultant;• Health and Safety Personnel;• Hood Performance Tester;• HVAC Controls Expert;• HVAC Design Engineers;• Laboratory Managers;• Maintenance Engineers, and• Principal Researchers or Hood Users; TAB

(Testing, Adjusting and Air Balance) Leader.

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 wi l l 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 sl iding sash at a heightof 28 in. (71 .1 cm) must have an average face velocitybetween 80–1 20 fpm (0.41 to 0.61 m/s) and providecontainment below a control level of AU 0.1 ppm asdetermined by methods described in theAN SI /ASH RAE 1 1 0–1 995, M ethod of TestingPerformance of Laboratory Fume Hoods.

A laboratory fume hood system includes al l associatedsubsystems such as the hoods, ducts, dampers, auto-mated controls, fi l tration, fan, motor, and exhauststacks. In laboratories, the air supply system is consid-ered part of the hood system when operation can affecthood performance.




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6.2.4 Commissioning Documentation

Preliminary and final commissioning docu-ments shal l be issued to the appropriateparty(s) by the Commissioning Authority.

The documents shall include:

• Commissioning Test Data;• Copy of Test and Balance Report;• Design Flow Specifications;• Laboratory and System Drawings for Final

System Design;• List of Venti lation System Deficiencies

uncovered and the details of how (and if)they were satisfactori ly resolved.

Operational deficiencies and other problemsuncovered by the commissioning process shal lbe communicated to the responsible party(i .e. , instal ler, subcontractor, etc. ) for promptcorrection.

6.3 Commissioning Fume Hoods and

Different Types of Systems

6.3.1 Laboratory Fume Hoods

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

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

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

The documents should detail the status of the venti la-tion systems relative to maintaining a safe faci l ity envi-ronment.

The document should clearly indicate, based upon theventi lation system functionality, which laboratory roomsand equipment (i . e. , chemical laboratory hoods,biosafety cabinets, etc. ) are ready for safe use, anyareas or equipment that are not safe for use or occu-pancy, and other safety-related venti lation systemdetai ls.

U nreasonable delays or unsatisfactory fol low-upshould be communicated to the owner as well as anycontractors in the tier to which this subcontractor isresponsible.

See the current edition of the ACGIH ®– Industrial

Ventilation: A Manual of Recommended Practice. I f aflowmeter is used, care should be taken to ensure thatthe element has not been compromised by chemicalaction or deposition of sol ids.


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I f 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-pl ied by the open area in the plane of thevelocity measurements to obtain the flowrate.

I f the flowrate is more than 1 0% different fromdesign, corrective action shall be taken

6.3.2 Single Hood CAV Systems

Commissioning tests on single hood, constantair volume (CAV) systems shal l 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.

Exhaust duct measurements shal l consist ofexhaust flow measurement and hood staticpressure measurement.

Hood performance tests shal l consist of testsdescribed in Section 6.1 .2.

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

6.3.3 Multiple Hood CAV Systems

Commissioning of multiple hood, constant airvolume systems shal l include:

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

and balance of branch exhaust flow andstatic pressures (exhaust flow and staticpressure for each branch shall be record-ed after final balancing is complete);

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

Ensuring proper operation of a laboratory fume hoodrequires proper design, instal lation, and operation of al lcomponents of the exhaust systems and many timesthe air supply systems as well .

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

The exhaust flow should be measured in the exhaustduct according the methods described in the currentversion of ANSI/ASHRAE 41 .2 or as described above.

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 control lers areadjusted unti l flow through each hood is in accordancewith design specifications.

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




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• Hood Performance tests as describedabove in Sections 6.1 .2; and

• Hood and System Monitor Calibration

6.3.4 VAV Laboratory Fume Hood Systems

VAV hood systems shall be commissionedprior to use by laboratory personnel to ensurethat al l system components function properlyand the system operates as designed under al lanticipated 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 Venti lation System

Tests; and• Verification of System Diversity.

6.3.4.1 VAV Sensor Calibration

VAV sensors shal l be capable of accuratemeasurement and control within 1 0% of actualat the design maximum and minimum flowconditions.

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

Performance of laboratory fume hoods connected tovariable air volume systems (VAV) can be affected bynumerous factors associated with proper design, cali-bration, and tuning of the control systems. I t is impera-tive that al l components of the VAV system be in prop-er operating condition to ensure proper hood perfor-mance.

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 instal l ing theVAV controls or through the Testing, Adjustment andAir Balance process (TAB).

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 fume hood systems such as sash positionsensors and room differential pressure sensors, toname a few. The accuracy of the sensors depends onproper methods to measure the physical parametersand abil ity to adjust calibration. Sensors that reportinaccurate information wil l not only be misleading whenmonitoring system operation but may result in unsafehood and laboratory conditions.

Part of the process of instal l ing VAV controls and bal-ancing system airflows should involve cal ibration ofsensors and documentation of i t.

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


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6.3.4.2 VAV Hood Performance Tests

I n addi tion 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 Stabil i ty tests.

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

VAV Response and Stabil i ty 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.

VAV Stabi l ity shall be sufficient to prevent flowvariations in excess of 1 0% from design ateach sash configuration or operating mode.

6.3.4.3 VAV Ventilation System Tests

The VAV hood controls shall provide stablecontrol of flow in the exhaust and supply ductsand variation of flow must not exceed 1 0%from design at each sash configuration oroperating mode.

6.3.4.4 Verification of System Diversity

System diversity shal l be verified prior to useof laboratory fume hoods. The tests shall bedesigned to verify that users wi l l be alertedwhen system capacity is exceeded and unsafeconditions may exist.

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 (1 0% 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 fol lowing the sash movement.

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




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6.3.5 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 andtotal exhaust.

All venti lation system alarm and monitoringprovisions associated with occupant safetyshall be verified for proper functionality.

6.3.5.1 CAV Laboratory Room Tests

These tests shal l ensure that the venti lationsystem design airflow is being maintainedwithin the al lowable tolerance in:

• Al l hood exhausts;• Al l other bench-top and equipment

exhaust provisions that may be present;• The room general exhaust i f present;• The room supply; and• Room air cross currents at the hood face

opening.

I f a specific room differential pressure (dP) hasbeen specified, the dP shall be measured toensure that i t is within i ts al lowable range.

I f a room differential airflow is specified, actualroom differential airflow shall be determined toensure that is within al lowable maximum andminimum l imits and in the proper direction.

I f the room has more than one venti lation con-trol mode (i .e. , occupied/unoccupied, etc. ) ,each individual mode shal l be enabled andapplicable parameters (i .e. , room supply, roomtotal exhaust, etc. ) shall be performed for eachseparate mode.

The laboratory commissioning tests are used to ensureproper air supply and exhaust for each laboratory orzone.

TAB data once verified can be substituted whereappropriate.

This includes local monitoring provisions for such itemsas hood airflow or room differential pressure as well asremote and central monitoring provisions for suchparameters.


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Room ambient condi tions (temperature,humidity, air currents, etc. ) shal l also be mea-sured to ensure they are being maintainedunder the conditions specified.

6.3.5.2 VAV Laboratory Room Tests

These tests shall ensure proper performanceof the VAV venti lation system and i ts associat-ed controls such that:

• The room general exhaust provides thespecified range of airflow.

• The room supply provides the specifiedrange of airflow.

• Room air cross currents at the laboratoryhood face opening are within l imits.

I f a specified room dP has been specified, thedP shal l be measured to ensure that i t is beingcontrol led within i ts al lowable range with al ldoors closed and at minimum and maximumroom exhaust airflow.

I f a room differential airflow is specified, actualroom differential airflow shall be determined toensure that i t is within al lowable maximum andminimum l imits and direction at minimum andmaximum room exhaust airflow.

I f the room has more than one venti lation con-trol mode (i . e. , occupied/unoccupied, etc. )conditions shal l be evaluated for each mode.

Room ambient condi tions (temperature,humidity, air currents, etc. ) shal l also be mea-sured to ensure they are being maintainedunder the conditions specified.

The VAV systems shall be capable of main-tain ing the offset flow required betweenexhaust and supply to achieve the desiredarea pressurization within the desired timespecified.

For most operations, 1 0 seconds wi l l be an acceptabletime to achieve the desired area pressurization but aHazard Evaluation should be conducted to determinethe acceptable time.




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6.4 Ongoing or Routine Hood and

System 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 1 0% belowthe designated average face velocity shall belabeled as out of service or restricted use andcorrective actions shall be taken to increaseflow.

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

ANSI/ASHRAE 1 1 0–1 995 may be used in the labora-tory as an accepted test with specific values for thecontrol levels (and the release rate i f you depart fromthe standard). I t also may be used for routine periodictesting, but i t 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:

• Al l other room exhaust provisions are within speci-fications;

• Room differential pressure is within specifications(if appl icable);

• Room differential airflow is within specifications (ifapplicable).

Periodic tests concerning face velocity or hood exhaustvolume are val id indications of hood operation provid-ed no changes have been made in that hood structure,supply air distribution, or other factors l isted 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.


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7 Work Practices and Training


The user shal l establ ish work practices thatreduce emissions and employee exposures.

The user shall not modify the interior or exteri-or components of the hood wi thout theapproval of the Chemical Hygiene Officer,Responsible Person, or other appropriateauthority in the organization.

The fol lowing l ist concerns only those workpractices that relate directly to hood perfor-mance and appl ies only when hazardousmaterials are to be used in the hood.

• The user shal l not lean into the hood sothat his/her head is inside the plane ofthe hood, as defined by the sash, withoutadequate respiratory and personal pro-tection.

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

• Al l work shall be conducted at least 6 in.(1 5.24 cm) behind the plane of the sash(hood face).

• The horizontal sash or panels shal l not beremoved.

• The hood shall not be operated withoutthe back baffles in place.

• Flammable l iquids shal l not be stored per-manently in the hood or the cabinet underthe hood unless that cabinet meets therequirements the current editions ofNFPA 30 and NFPA 45 for flammable l iq-uid storage.

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

Many work practices affect the overall safety andhealth in the laboratory.

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

When large equipment must be placed in a laboratorychemical hood, placing the equipment on a stand toal low air to flow under the stand can reduce the signif-icance of any airflow disturbance.

Marking the work surface with a tape or other means,to indicate the 6 in. (1 5.24 cm) l ine, wil l assist the userin identifying the l imits of usable space.

In some cases, whi le the hood is empty, the sash couldbe 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 materialsunder the hood. Individual pol icies are often site spe-cific; hence, the Chemical Hygiene Officer shouldalways be consulted.

In some laboratory design, the normal sash position isnot ful l open. When the sash is raised above the designlevel, the hood could lose adequate control.




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• The sash or panels shall be closed to themaximum position possible while sti l lal lowing comfortable working conditions.

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

• The hood user shal l not operate with thesashes opened beyond the design open-ing.

• Pedestrian traffic shall be restricted nearoperating hoods.

• Rapid movement within the hood shal l bediscouraged.

• The hood shall not be operated unlessverified i t is working.

7.2 Posting

Each hood shal l be posted with a notice givingthe date of the last periodic field test. I f thehood fai led the performance test, i t shall betaken out of service unti l repaired, or postedwith a restricted use notice.

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

7.3 Operating Conditions

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

7.4 Training

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

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.

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 1 00% diversity and an emergencyphone number.

A hood that is more than 1 0% 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 al l materials are removed from theinterior and only i f the hood does not provide generalexhaust venti lation to the space.


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8 Preventive Maintenance

Inspection and maintenance shal l fol low aPreventive Maintenance (PM) Program devel-oped by the user.

Preventive maintenance shal l be performedon a regularly scheduled basis.

8.1 Operations During Maintenance

Shutdown

Operations served by equipment being shutdown for inspection or maintenance shal l besafely discontinued and secured during suchmaintenance.

Lock-out/tag-out procedures shal l be imple-mented.

Laboratory workers shal l be noti fied inadvance of inspection and maintenance oper-ations.

8.2 Housekeeping Before and After

Maintenance

All toxic or otherwise dangerous materials onor in the vicinity of the subject equipment shal lbe removed or cleaned up before mainte-nance. Any hazardous materials and anyother debris shall be cleaned up before oper-ations resume.

PM programs should be “preventive” in nature.

The written PM Program should identify potential haz-ards and problems associated with laboratory opera-tions and designate appropriate PM procedures to min-imize such hazards and problems. This could include,for example, routine inspection of fan belts to ensurethat hood exhaust venti lation fans are turning at thedesigned speeds, that hoods are being cleaned to min-imize bui ldup of hazardous chemicals in the hoods, evi-dence of tampering with performance equipment orblast gates, and so forth.

The written program should identify standard operatingprocedures to be fol lowed during PM activities.

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

“Secured” condition wil l vary from case to case. I t mightconsist of ceasing operation, or requiring removal fromthe premises of al l flammable and highly toxic materi-als.

Al l venti lation equipment should be de-energized andlabeled as such with appropriate signage before start-ing any repair work.

I f possible, equipment to be removed should be decon-taminated. I f the maintenance activities involve contactwith potential ly contaminated parts of the system,these parts should be evaluated first by appropriatemethods.




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8.3 Safety for Maintenance Personnel

Maintenance personnel shall be trained andrequired to use appropriate PPE (such as res-pirators, goggles or faceshields, gloves, andprotective clothing) during parts of the workinvolving potential hazard.

A procedure shal l be establ ished to notify hoodusers before any maintenance is to be per-formed so work in the hood can be halted dur-ing maintenance.

8.4 Work Permits and Other

Communications

A written work permit system or other equallyeffective means of communication shal l beestablished whenever any PM or unscheduledmaintenance;

• could affect the safety of maintenancepersonnel, hood users or others

• could jeopardize the integrity of the exper-iments/procedures/etc. , underway in theaffected hood(s.)

Such system(s) shall be designed to suit thecircumstances and address the fol lowing:

• a means to communicate when systemsare returned to normal operations,

• oversight by the responsible person asdefined in this standard,

• signed or otherwise endorsed and com-municated by the person(s) to do thework, his/her supervisor, and communi-cated to any and al l hood users and oth-ers affected by the work,

• the nature of the work and the health andsafety precautions, and

Allowable variance from design conditions,or conditions determined otherwise satis-factory, shall be:

• For air velocity, +1 0%;• For venti lation air pressure or differential

pressure, +20%; For pneumatic controlsystem air pressure, <5%; and

• For electronic control system, +2% of ful l-scale values.

There may be situations in the United States whereOSH A’s hazardous energy control standard (29CFR1 91 0.1 47) conceivably be applied to the situationsbeing addressed in this section.


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• the date(s), time(s) and affected loca-tion(s) of the work.

Records shall be maintained in accordancewith the organizations records retention pol icy.

8.5 Records

Records shall be maintained for al l inspectionsand maintenance. I f testing involves quantita-tive values (such as hood throat suction) theobserved values shall be recorded. Inspectionforms designed for the several categories oftesting shall be provided and shal l include thenormal values for the parameters tested.

8.6 Testing and Monitoring Instruments

8.6.1 Air Velocity, Air Pressure, Temperature

and Humidity Measurements

Pressure instrumentation and measurementshall be in compliance with ANSI/ASHRAE41 . 3–1 989. Temperature instruments andmeasurement techniques shall be in compliancewith ANSI/ASHRAE 41 .1 –1 986 (RA 01 ). Al l

Records should be kept for at least 1 year or unti l thenext required test is performed.

Instruments of a “primary standard” nature (i .e. , stan-dard pitot tubes, flow tube manometers, draft gauges,etc. ) – i f used with fluids for which they are designedand tested for leaks – require no further cal ibration.

Performance measurement equipment can be used todetermine many different system changes requiringattention (e. g. , exhaust fi l tration loading, damperchanges, fan operation, etc. ) and provides real-timeindication of system performance.

Pressure indicating manometers can lose indicatingfluids due to leaks or evaporation. These devicesshould be checked on a regular basis. Fluids should berefi l led and the device re-leveled as needed.

Velocity

Below 1 00 fpm (0.51 m/s)

1 00 fpm (0.51 m/s)and higher

Accuracy

5 fpm (0.025 m/s)

5% of signal

Pressure

0.1 in.wg (25 Pa)

Between 0.1 in. wg(25 Pa) and 0.5 in.wg (1 25 Pa)

0.5 in.wg (1 25 Pa)and higher

Accuracy

0% of signal

Interpolate l inearly

5% of signal




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instruments using electrical , electronic, ormechanical components shall be calibrated nolonger than 1 2 months before use or after anypossible damage (including impacts with noapparent damage) since the last cal ibration.The accuracy of a scale used for a given para-meter shal l meet the fol lowing requirements:

Pitot-static tube measurements shall be inaccordance with ANSI/ASHRAE’s Method ofTest Measurement of Flow of Gas, 41 .7–1 984(RA 00). Incl ined manometers shall be select-ed so that the nominal value of the measuredparameter is at least 5% of ful l scale. U-tubemanometers shall not be used for pressuresless than 0.5 in.wg (1 25 Pa). Pitot tubes otherthan standard shall be cal ibrated.

Temperature measurement instrumentationshall have an accuracy of +0.5°F or +1 °C overthe entire measurement range.

Humidity measurement instrumentation shallhave an accuracy of +3.0% relative humidityover the 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 test-ing shall include the sensing element, zero drift,and actuation of signals, alarms, or controls.

Continuous air monitors shall be calibrated permanufacturer’s speci fications or more fre-quently i f experience dictates.

8.6.3 Tolerance of Test Results

Allowable variance from design conditions, orconditions determined otherwise satisfactory,shall be:

• For air velocity, +1 0%;• For venti lation air pressure or differential

pressure, +20%; For pneumatic controlsystem air pressure, <5%; and

• For electronic control system, +2% of ful l-scale values.


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8.6.4 Other Test Instruments

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

8.7 Monitoring Fans, Motors, and Drives

8.7.1 Visual Inspection

Fans, blowers, drive mechanisms, and stacksystems shal l be visually checked at leastsemi-annually.

8.7.2 V-belt Drives

V-belt drives on non-redundant fans servingexposure control devices without performancemonitoring equipment shall be stopped andinspected monthly for belt tension, signs of beltwear, sheave wear, checking, or excessiveamperage pull on the motor.

Belt guard shall be reinstalled after any removal.

8.7.3 Lubrication

Blowers, drives, and other necessary compo-nents shall be lubricated at intervals and withlubricants recommended by the manufacturer.

8.8 Critical Service Spares

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

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

Inspections should focus on key problematic issueswith the fans, blowers, and drive apparatus looking forabnormal noise, vibration, bearing noise, excessivetemperature, high amperage of motors, and signs suchas lubricant leaks, etc.

Stack inspection should include the fol lowing:

• Ensuring that any tags, labels, etc. , used to asso-ciate the stack and hood device(s) are legible,

• Support structure such as guide wires, • That conditions surrounding the discharge haven’t

changed resulting in re-entrainment of exhaust, and• The stack discharge velocity is sti l l in accordance

with design.

This wil l probably require removing the belt guard.

The use of performance monitoring equipment (SeeSection 8.1 0) al lows for maintenance as requiredrather than on any time-based interval.

Lead time for parts should be considered such thatperiodic inspection schedules are not affected.Maintenance supplies and spares should be plannedconsidering factors such as:

• Availabil ity of spares or replacements,• Economic cost of faci l ity being out of service, and• Potential health or safety risk of breakdown.




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8.9 Critical Service Instrumentation

All critical service instrumentation shal l havecontingency plans in place.

8.1 0 Performance Monitoring Equipment

All hoods and exposure control devices shal lbe equipped with a flow indicator, flow alarm,or face velocity alarm indicator as applicable toalert users to improper exhaust flow. Whenthese devices are marked and labeled so thehood operator can easi ly interpret the equip-ment reading and know when to shut down ahood and request maintenance.

9 Air Cleaning

9.1 Supply Air Cleaning

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 wil l meet the perfor-mance criteria necessary for regulatory com-pliance. See the current version of ASHRAEHandbook—Fundamentals.

For critical equipment of 1 00 horsepower (74.6 kW) orlarger, consideration should be given to providing tem-perature and vibration sensors to give early warning ofproblems.

Key instrumentation should include at least one spareperformance monitoring device.

Performance monitoring equipment al lows the hooduser to check and monitor the rel iabi l i ty of the hoodsystem compared to normal. The performance equip-ment should be on an annual pm. The performanceequipment should be calibrated and relabeled so thehood operator can readily understand the findings.

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 1 999 Handbook –HVAC Applications.

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 l imitedfor many hazardous materials. Chemical speci ficdetectors located downstream of adsorption media,pressure drop indicators for particulate fi l ters, and/orperiodic stack sampling for contaminant emissions maybe required to monitor for regulatory compliance.


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9.3 Filtration for Recirculation

Air-cleaning systems for recirculating generalexhaust or hood exhaust from laboratoriesshall meet the design and installation require-ments in the current version of ANSI/AIHA ®

Z9.7.

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

Filter installations shall be tested for leaks andhave al l leaks repaired or the fi l ter replacedbefore use.

The flow rate through the fi l ters shall be main-tained at design specifications not to exceed1 00% of the rated flow capacity of the fi l ters.

9.3.1 Particulates

Air-cleaning fi l tration systems for recirculatingexhaust air contaminated with toxic particu-lates shal l be fi l tered through a particulate fi l -tration system specified fol lowing the standardperformance and design cri teria of theASHRAE Systems and Equipment to meet theobjectives described in General Requirementswithin the Laboratory Venti lation Managementsection of this standard.

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

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

• Gases and vapors that can be removed efficientlyby adsorption media.

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

See the I nsti tute of Environmental SciencesRecommended Practice for Laminar Flow Clean AirDevices.

The fi l ter assembly should be provided with a damperand control that:

• Indicate the static pressure differential separatelyacross the primary and secondary fi l ters and thepressure differential across both fi l ters and thedamper;

• Actuate a damper motor (or al low manual activa-tion) to open the damper from an initial partial lyclosed position when fi l ters are clean to a ful l-open position when fi l ters are ful ly loaded; and

• Actuate a signal or alarm when the pressure dropacross either the primary or secondary fi l terreaches 0.01 in.wg (2.5 Pa) more than the rated-loaded pressure drop.




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9.3.2 Gases and Vapors

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

A rel iable and adequately sensitive monitoringsystem shall be uti l ized 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®, shal l be sufficient, based uponsystem capacity design to al low a work opera-tion shut down or parallel fi l ter switch-over,thus proving a fresh fi l ter.

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

Also see the ASH RAE 2001 H andbook

Fundamentals for additional information on the theoryand need for appl ication of air cleaning equipment forthe emission control of hazardous materials from workoperations.

The intent of this section is to specify the need to havea method for detecting fi l ter 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 avai l-able in a number of configurations as fi l ter housings.Media may be sprayed onto another fi l tration media asa thin coat or be packed into thin panels less than 2 in.(5.1 cm) in depth. Also, deep- bed fi l ters, typically cyl in-drical in shape and up to several feet in diameter andlength, are uti l ized 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 shal low beds used in panels or insmaller cyl indrical cartridges. Saturation of the activeadsorption sites occurs progressively through the layerof carbon and depends on the burden of adsorbate,which typical ly is variable. Therefore, breakthrough ofcontaminant on the downstream side of the carbonlayer is difficult to predict.

Other gas and vapor fi l tration systems use absorbentssuch as potassium permanganate that are impregnat-ed onto the media that transform, oxidize, or otherwisetreat the specific air contaminant to remove the haz-ardous material from the air stream.

A particulate fi l ter should be located upstream of theadsorption fi l ter to serve as a pre fi l ter to prevent par-ticulate loading on the adsorption fi l ter.


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9.3.3 Handling Contaminated Filters

When required, contaminated fi lters shall beunloaded from the air-cleaning system followingsafe work practices to avoid exposing personnelto hazardous conditions, to avoid contaminationof downstream ductwork and to ensure propercontainment of the fi lters for final disposal.

Airflow through the fi l ter housing shal l be shutdown during fi l ter change-out.

9.4 Testing and Monitoring

9.4.1 Recirculation – Particulate Filter

Systems

Recirculation air fi l ters shall be inspected andtested as per Section 9.3.1 before initial useand then at least once per year.

Inspections and testing shall be done after anysystem maintenance or modification that disturbsthe filter housing, filter seals, and/or filter media.

9.4.2 Recirculation – Adsorption and

Absorption Filter Systems

Recirculation systems that uti l ize activatedcarbon adsorption or chemical absorption fi l-ters shal l be tested as per Section 9.3.2 atintervals no longer than 1 month initial ly andthen based on experience with the particularinstallation and a schedule shal l be prepared.

9.4.3 Air Pollution Control Equipment

Air pollution control equipment shall be inspect-ed visually at intervals no longer than 1 weekand, if necessary, at shorter intervals. Specifictests and repairs shall be in accordance withthe manufacturer’s recommendations or incompliance with applicable regulations.

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

Care should be taken during fi lter replacement to mini-mize the release of hazardous materials from the fi lters.The most common and recommended practice employsthe use of bag-in/bag-out systems. Another approachinvolving the careful introduction of encapsulantsupstream of the fi lter just prior to shut down and fi l terchanges has been described in various documents. Anexample is CAG-005–2007 Servicing Hazardous DrugCompounding Primary Engineering Controls.

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

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




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APPENDIX 1 Definitions, Terms, and Units

There are many terms and definitions associatedwith laboratory venti lation that have special mean-ing. The fol lowing are definitions of terms or unitsused in this document:

A2.1 adjacent roof l ine: For the purposes ofdetermining the laboratory chemical hood stackheight, the adjacent roof wil l be within 6 feet hori-zontally of the nearest outer point of the exhaustfan stack. This criterion is intended to protect main-tenance workers from direct exposure to theirbreathing zone, hands, feet, and other parts of theirbody. Parts of the building that are within 6 feet hor-izontally of the exhaust fan stack are exempted if i twould be impossible for a person to stand or cl ingto the surface in question.

A2.2 air changes per hour (ACH): A commonmeans for expressing a volumetric airflow througha room. Each ACH for a room is intended to repre-sent an amount of air equal to the gross volume ofthe air passing through the room each hour. AnACH rate for a room can be converted to volumet-ric airflow by multiplying the ACH number times thegross volume of the room. For instance, for an ACHof 1 0, a room with a gross volume of 2400 cubicfeet has a volumetric airflow of 400 cfm (1 0 ? 2400÷ 60). The air change rate depends on exhaust flowfor a negatively pressurized room and on supplyflow for a positively pressurized room. This termdoes not reflect actual mixing factors and thereforedoes not indicate the effective air exchange rate inthe room. See the ACGIH® publication, IndustrialVenti lation Manual for further information on mixingfactors.

A2.3 air lock: An intermediate chamberbetween two dissimilar spaces with airtight doorsor openings to each of the spaces. The doors areinterlocked to ensure that there is always at leastone of them closed.

A2.4 auxiliary air hood: A laboratory chemicalhood with an external supply air plenum at the topof the laboratory chemical hood. The auxil iary airplenum provides a makeup airstream comprised ofunconditioned or only minimally conditioned out-side air to substantial ly reduce the amount of con-

ditioned room air exhausted by the laboratoryhood.

A2.5 bypass hood (constant air volume

bypass 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 ful ly open, the sashblocks off this bypass area and al l 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 uti l izedwith a constant air volume venti lation system, thebypass area keeps the laboratory hood face veloc-ity relatively constant and from increasing to anobjectionably high value as the sash is lowered.

A2.6 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.

A2.7 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.

A2.8 constant air volume (CAV) ventilation

system: A venti lation system designed to maintaina constant quantity of airflow within i ts 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 bui lding loading. Although relativelysimple, a constant volume venti lation system typi-cally requires the maximum ongoing energy usagesince the system always operates at maximumcapacity.

A2.9 design sash position: The maximumopen area of the hood face that achieves thedesired face velocity during any work inside thehood that produces airborne contaminants.

A2.1 0 dilution venti lation: Venti lation airflowthat di lutes contaminant concentrations by mixingwith contaminated air, as distinguished from cap-turing the contaminated air.

A2.1 1 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 uti l izefans specifically designed to discharge directlyupward, the discharge velocity normally refers tothe air velocity as i t 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 i tself. 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.

A2.1 2 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 1 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 venti lation system. The overal lintention of applying a diversity factor when design-ing a VAV venti lation system is to achieve a lowerl ife cycle cost (e.g. , lower system first cost and/orlower system energy costs).

A2.1 3 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 fi l ters as an integral part

of the laboratory hood and discharges the exhaustdirectly into the room. Ductless laboratory hoodsare of l imited size and capacity in comparison toconventional ducted laboratory hoods.

A2.1 4 exhaust air: Air that is removed from anenclosed space and discharged to atmosphere.

A2.1 5 face velocity: The air velocity at the planeof and perpendicular to the opening of a laborato-ry chemical hood.

A2.1 6 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 al low i t, 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.

A2.1 7 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.

A2.1 8 hazardous chemical – Encompasses 1 )regulatory definitions such as found in 29 CFR1 91 0.1 450 (which appears to almost mistakenlyrefer exclusively to health hazards) and 29 CFR1 91 0.1 200 (which refers to both health and physi-cal hazards), and 2) other accepted definitionssuch as offered by OSHA on its safety and healthtopics web page http: //www.osha.gov/SLTC/haz-ardoustoxicsubstances/index.html.

A2.1 9 HEPA: High Efficiency Particulate Air (fi l -ter) for air fi l ters 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.

A2.20 laboratory: I t 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 faci l i ty in


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95

which the amounts of chemicals handled are small[perhaps 22 or 44 lbs (1 0 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 faci l i ty, i t is suggested that theparties involved in the activity agree whether thefaci l i ty is to be considered a laboratory. TheOccupational Safety and Health Administration, in29 CFR 1 91 0. 1 450 (subpart 2, paragraph1 91 .1 450) [4], provides a definition of “laboratory”for regulatory purposes.

A2.21 laboratory fume hood: a box-l ike struc-ture with typically one open side, intended forplacement on a table, bench, or floor. The benchand the hood may be one integral structure. Theopen side is provided with a sash or sashes thatmove vertically and/or horizontally to close theopening. Provisions are made for exhausting airfrom the top or back of the hood and adjustable orfixed internal baffles are usually provided to obtainproper airflow distribution across the open face

A2.22 makeup air (replacement air): Any com-bination of transfer air and air provided by a venti-lation system to replace air being exhausted from alaboratory hood, canopy hood, room, or space.

A2.23 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 i ts exhaust system must be constructed ofall inorganic materials and be equipped with awater washdown system that is regularly used toremove al l 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.

A2.24 recirculation: Air removed or exhaustedfrom a bui lding area and ducted back to an air-han-dling system where i t is mixed with outside fresh

air. This air mixture is then conditioned and uti l izedfor venti lation. Since air removed from a space ismore often close to the temperature and humidityof the bui lding interior than outside air, the recircu-lation process enables achieving a greater reduc-tion in heating and cooling energy than i f 1 00%outside air was uti l ized (also see return air) .

A2.25 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.

A2.26 replacement air: See makeup air.

A2.27 responsible person: An individual whohas the responsibi l i ty and authority for the designand implementation of the venti lation managementplan. This person may be the Chemical HygieneOfficer or work in conjunction with the ChemicalHygiene Officer.

A2.28 return air: Air being returned from a spaceto the venti lation fan that supplies air to a space.

A2.29 room air balance: A general term describ-ing the requirement that a laboratory room havethe proper relationship with respect to the totalexhaust airflow from the room and the supplymakeup airflow. The relationship of these airflowsalso establishes the pressure differential betweenthe laboratory room and adjacent rooms andspaces.

A2.30 room ventilation: The volumetric airflowthrough a room expressed in terms of cfm or L/sec.

A2.31 special purpose hood: An exhaustedhood, not otherwise classified for a special pur-pose such as but not l imited to capturing emis-sions from equipment such as atomic absorptiongas chromatographs; l iquid pouring, mixing, orweighing stations; and heat sources. These hoodsmight not meet the design description of varioustypes of laboratory chemical hoods discussedhere. They may be exterior hoods, receivinghoods, or enclosing hoods, as described in the lat-est ACGI H I ndustrial Venti lation: A Manual ofRecommended Practice.


96

A2.32 – transfer air – air that moves betweenspaces in a bui lding, driven by the venti lation sys-tem.

A2.33 variable air volume—two-position venti-

lation system: A constant air volume venti lationsystem (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 facil i ty is nor-mally occupied such as during regular work hours.The lower level of airflow is uti l ized during unoccu-pied times (e.g. , nighttime, hol idays, etc. ) whenventi lation needs and internal loads require lessairflow.

A2.34 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.

A2.35 variable air volume (VAV) ventilation

system: A type of HVAC system specifical lydesigned 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).

A2.36 velocity: Magnitude and direction of airmotion. As used in this standard, i f the direction isomitted i t is implied to be perpendicular to theplane of the airflow cross section. I f the direction isimportant, i t wi l l be stated.

A2.37 volumetric airflow rate: The rate of air-flow expressed in terms of volume (cubic feet orl i ters) per uni t of time. These are commonlyexpressed as cubic feet per minute (cfm) in USCSunits or l i ters per second (l/s) in SI units. (Also seeroom venti lation. )

A2.38 Walk-in hood: See floor-mounted hood.

A2.39 units and abbreviations:

AAALAC – Association for Assessment andAccreditation of Laboratory Animal Care

ABSA – American Biological Safety Association

ACD – air-cleaning device

AMCA – Air Movement Control Association

ACGIH® – American Conference of GovernmentalIndustrial Hygienists

AGS – American Glovebox Society

AIHA® – American Industrial Hygiene Association

USAMRICD – United States Army Medical Research Institute of Chemical Defense

ASME – American Society of MechanicalEngineers

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

AI – as installed

AM – as manufactured

AU – As used

CAV – constant air volume

CETA – Control led Environment Testing Association

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)




97

IEST – Institute of Environmental Sciences and Technology

ISEE – International Society of Explosives Engineers

ISPE – International Society for Pharmaceutical Engineering

JIC – joint industry codes (hydraulic equipment)

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 Occupational Safety and Health

NSF – National Sanitation Foundation

PEL – Permissible Exposure Limit

PPE – personal protective equipment

RC – room criteria curves

REL – Recommended Exposure Levels

SEFA – Scientific Equipment and Furniture Association

SMACNA – Sheet Metal and Air Conditioning Contractors National Association

SPL – sound pressure level

TA – Transfer Air

TAB – testing, adjusting and air balancing

TLV® – Threshold Limit Value

TWA – time weighted average

VAV – variable air volume

WEEL® – Workplace Environmental Exposure Levels

APPENDIX 2. Referenced Standards and

Publications

The fol lowing standards and associated publ ica-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 current edi-tions of these documents.

ACGIH®: Industrial Ventilation: A Manual of

Recommended Practice, 27th edition. Cincinnati,OH : American Conference of G overnmentalIndustrial Hygienists, 2001 .

ACGIH®: Threshold Limit Values (TLV®) For

Chemical Substances and Physical Agents .Cincinnati , OH : American Conference ofGovernmental Industrial Hygienists, 201 2.

AGS-G001 –2007: Guideline for Gloveboxes, 3rd

edition. Santa Rosa, CA: American GloveboxSociety, 2007.

AMCA 99–201 0: Standards Handbook. Arl ingtonHeights, IL: Air Movement and Control Association,1 986.

AMCA 200-95 (RA 2007): Fan Application Manual,

Part I, Fans and Systems: AMCA Classification for

Spark Resistant Construction . Arl ington Heights,IL: Air Movement and Control Association, 2007.

ANSI/AIHA® Z9.2–2001 : Fundamentals Governing

the Design and Operation of Local Exhaust

Systems. Fairfax, VA: American Industrial HygieneAssociation, 2001 .

ANSI/AIHA® Z9.7–1 998: Recirculation of Air from

Industrial Process Exhaust Systems. Fairfax, VA:American Industrial Hygiene Association, 1 998.

ANSI/AIHA® Z9.1 1 –2008: LaboratoryDecommissioning. Fairfax, VA: AIHA®, 2008.

ANSI/ASHRAE 41 .1 –1 986 (RA 01 ): Standard

Method for Temperature Measurement. Atlanta,GA: American Society of Heating, Refrigeratingand Air Conditioning Engineers, 1 991 .

ANSI/ASHRAE 41 .2–1 987 (RA 92): Standard

Methods for Laboratory Air Flow Measurement.Atlanta, G A: American Society of H eating,Refrigerating and Air Conditioning Engineers,1 992.

ANSI/ASHRAE 41 .3–1 989: Standard Method for

Pressure Measurement. Atlanta, GA: AmericanSociety of H eating, Refrigerating and AirConditioning Engineers, 1 989.

ANSI/ASHRAE 41 .7–1 984 (RA 00): Method of

Test Measurement of Flow of Gas. Atlanta, GA:American Society of Heating, Refrigerating and AirConditioning Engineers, 2000.

ANSI/ASHRAE 52.1 –1 992: Gravimetric and Dust-

Spot Testing Procedure for Testing Air-Cleaning

Devices Used in General Ventilation for Removing

Particulate Matter. Atlanta, GA: American Societyof Heating, Refrigerating and Air ConditioningEngineers, 1 992.

ANSI/ASHRAE 52.2–2007: Method of Testing

General Ventilation Air-Cleaning Devices for

Removal Efficiency by Particle Size. Atlanta, GA:American Society of Heating, Refrigerating and AirConditioning Engineers, 2007.

ANSI/ASHRAE 62.1 –201 0: Ventilation for

Acceptable Indoor Air Quality. Atlanta, G A:American Society of Heating, Refrigerating and AirConditioning Engineers, 201 0.

ANSI/ASHRAE 1 1 0–1 995: Method of Testing

Performance of Laboratory Fume Hoods. Atlanta,GA: American Society of Heating, Refrigeratingand Air Conditioning Engineers, 1 995.

ASHRAE 2009 Handbook – Fundamentals

(Inch-Pound edition). Atlanta, GA: AmericanSociety of H eating, Refrigerating, and Air-Conditioning Engineers, Inc. , 2009.


98




99

ASHRAE 201 1 Handbook – HVAC Applications

(Inch-Pound edition). Atlanta, GA: AmericanSociety of H eating, Refrigerating, and Air-Conditioning Engineers, Inc. , 201 1 .

Braun, K.O. and K.J. Caplan: “Evaporation Rateof Volati le Liquids, Final Report, 2nd edition.EPA Contract N umber 68-D8-01 1 2”, PACELaboratories Project 890501 . 31 5. Washington,D.C. : U.S. Dept. of Commerce, NTIS, December1 989.

Controlled Environment Testing Association.

CAG -005-2007, Servicing H azardous DrugCompounding Primary Engineering Controls,Controlled Environment Testing Association, 1 500Sunday Drive, Suite 1 02, Raleigh, NC 27607,http: //www.cetainternational.org/reference/CAG005-v1 5.pdf

CDC-NIH: Biosafety in M icrobiological andBiomedical Laboratories, Appendix A, CDC-NIH,5th edition, Atlanta, GA: Centers for DiseaseControl and Prevention, 2009.

EPA-600/8-81 -009: G uidel ine for Model ing ofAtmospheric Di ffusion. Office of Air Qual i tyPlanning and Standards, Apri l 1 981 .

Harnett, P.B.: Empirical data and modeling of aflammable spil l in a chemical fume hood do notsupport the need for fire suppression within thechemical fume hood ductwork. Chem. Health Safe.

10(4): 1 1 –1 4 (2003).

“Hazard Communication,” Code of Federal

Regulations. Title 29, Part 1 91 0.1 200, 1 988.

HVAC Duct Construction Standards: Metal andFlexible, M erri field, VA: Sheet M etal and AirConditioning Contractors’ National Association,2005.

IMC-201 2: International Mechanical Code. FallsChurch, VA: International Code Council , 201 2.

Insti tute of Environmental Sciences and

Technology (IEST) , Laminar Flow Clean AirDevices, IEST-RP-CC-002-86 Arl ington Heights,IL, http: //www. iest.org

Ivany, R., M. First, and L.J. DiBerardinis: A NewQuanti tative M ethod for I n-Place Testing ofLaboratory H oods. Am. Ind. Hyg. Assoc. J.

50(5):275–80 (1 989).

Klein, R.C., C. King, and P. Labbie: Solvent vaporconcentrations fol lowing spil ls in laboratory chemi-cal hoods. Chem. Health Safe. 11(2):4–8 (2004).

Klein, R.C., et al.: Laboratory air qual ity and roomventi lation rates. J. Chem. Health Safety

16(5):36–42 (2009).

Kolesnikov, A., R. Ryan, and D.B. Walters: Use ofComputational Fluid Dynamics to Optimize Airflowand Energy Conservation in Laboratory Hoods andVented Enclosures. Washington, D.C. : EPA Labsfor the 21 st Century, January 2002.

Kolesnikov, A., J. McNally, R. Ryan, and D.B.

Walters: CFD-Driven Design of a Low AirFlow,

Rapid Recovery System to Maximize Safety and

Optimize Energy Efficiency. Durham, NC: EPALabs for the 21 st Century, October 2002.

Labconco Corp.: Development of the LabconcoProtector® Xstream® H igh PerformanceLaboratory Fume H ood. Kansas Ci ty, MO:Labconco Corporation, 2009.

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

Manning, A., et al.: Analysis of Air Supply Typeand Exhaust Location in Laboratory AnimalResearch Faci l i ties U sing CFD. ASHRAE

Transactions DA-00-1 4-3 (2000).

Memarzadeh, F.: Methodology for Optimization of

Laboratory Hood Containment, Volumes I and I I .Bethesda, MD: National Institutes of Health, 1 996.

NFPA 30–2008: Flammable and Combustible

Liquids Code. Quincy, MA: National Fire ProtectionAssociation, 2000.

NFPA 45–201 1 : Standard on Fire Protection for

Laboratories Using Chemicals . Qu incy, MA:National Fire Protection Association, 201 1 .


1 00

NFPA 86–2007: Standards for Ovens and

Furnaces. Quincy, MA: National Fire ProtectionAssociation, 2007.

NFPA 92A–2009: Recommended Practice for

Smoke Control Systems. Quincy, MA: National FireProtection Association, 2009.

NSF 49–2004: Class II (Laminar Flow) Biohazard

Cabinetry. Ann Arbor, MI : National SanitationFoundation, International, 2004.

“Occupational Exposure to Hazardous

Chemicals in Laboratories,” Code of FederalRegulations Title 29, Part 1 91 0.1 450, 1 988.

Parker, A.J. and P.J. DiNenno: “Evaluation ofFixed Extinguish ing System Effectiveness inContinuously Exhausting Chemical Fume Hoods.”Prepared for Merck & Co. by Hughes Associates,September 2001 .

Petersen, R.L., B.C. Cochran, and J. LeCompte:

“Specifying Exhaust Systems that Avoid FumeReentry and Adverse Health Effects.” SymposiumPaper at ASHRAE Summer Meeting, Honolulu, HI ,June 23-26, 2002. To be publ ished in 2002ASHRAE Transactions.

Ratcliff, M.A. and E. Sandru: Dilution Calculationsfor Determining Laboratory Exhaust Stack Heights.ASHRAE Transactions 105(1):Ch-99-7-2 (1 999).

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

Sharp, G.P.: “A Review of U.S. and EuropeanEmpirical Research, Theoretical Calculations, andIndustry Experience on Fume Hood Minimum FlowRates.” I nternational I nsti tute of Sustainable

Laboratories (I2SL) E-Library, http://www.i2sl.org/elibrary/ index.html, 2009.

Smith, T.C. and S.M. Crooks: Implementing aLaboratory Venti lation M anagement Program.Chem. Health Safety 3 : 1 2 (1 996).

Smith, T.C. and S. Yancey-Smith: Specification ofAirflow Rates in Laboratories. J. Chem. HealthSafety 16(5):27–35 (2009).

Tronville, P. and R.D. Rivers: International stan-dards: fi l ters for bu i ld ings and gas turbines,Fi l tration & Separation, Volume 42, I ssue 7,September 2005, Pages 39-43, ISSN 001 5-1 882,DOI : 1 0.1 01 6/S001 5-1 882(05)70623-6.

“Test Methods,” Code of Federal Regulations

Title 40, Part 60, Appendix A, 1 989.

UMC–201 2: Uniform Mechanical Code. Whittier,CA: International Conference of Building Officialsand Los Angeles, CA: International Association ofPlumbing and Mechanical Officials, 201 2.

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-97-01 6), 2001 .

Venti lation Test according to DIN 1 2 924 Part 1 :Fume Cupboard DIN 1 2 924 TA 1 500 x 900 – 900,Fume hood Test report by WaldnerLaboreinrichtungen GmbH & Co. for mc6 - BenchMounted Fume Cupboard: Test Report No.1 59,May 2000.




1 01

APPENDIX 3. Selecting Laboratory Stack

Designs

Necessary measures must be taken to protect thelaboratory building and adjacent buildings from re-ingestion of toxic laboratory chemical hood exhaustback into a building air supply system. The 1 0 ft(3.05 m) minimum stack height cal led for in thebody of this standard is primari ly intended to pro-tect maintenance workers from direct contamina-tion from the top of the stack. However, the mini-mum height of 1 0 ft is not enough by itself to guar-antee that harmful contaminants would not be re-ingested. Similarly, a minimum 3000 fpm (1 5.3 m/s)exit velocity is specified in the body of this stan-dard, but this exit velocity does not guarantee thatre-ingestion wil l 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 bui lding and associatedzones of turbulent airflow. The geometric method isful ly described here and is accompanied by anexample. The second analysis method, brieflydescribed, predicts exhaust di lution at downwindlocations. The di lution equations are not presentedhere but can be obtained from the ASHRAEHandbook HVAC Applications. A di lution criterionis presented in this appendix to judge the adequa-cy of the predicted di lutions in minimizing re-inges-tion. The third analysis method described is windtunnel or water flume modeling.

General Guidelines

Laboratory chemical hood exhaust stacks shouldhave vertical, unobstructed exhaust openings. TheBuilding Air Intake and Exhaust Design chapter of theASHRAE Handbook – HVAC Applications describesappropriate rain protection devices. Goosenecks,flapper dampers, and rain caps are unacceptable asthey deflect the exhaust sideways or downward, mak-ing it much more likely that re-ingestion will occur.

The stack must reach high enough to ensure thatthe exhaust plume is sufficiently di luted when it

reaches sensi tive areas such as bui lding airintakes, entrances, operable windows, and outdoorplazas. The appropriate stack height is a function ofthe plume height for the exhaust system beingdesigned and the subsequent dispersion, or con-centration levels at the aforementioned sensitivelocations. The dispersion model ing process(numerical or physical modeling) is discussed in alater section. The plume rise should be calculatedusing the equations that compute plume rise ver-sus downwind distance. I f two exhaust systemsgive the same plume height at the same downwinddistance, the dispersion and resulting concentra-tion levels wil l be identical. I t should be noted thatby adding 5 to 1 0 ft to the stack height anddecreasing the exit velocity, the same plume rise(and di lution) can be achieved which can lead tothe fan energy savings.

For a given exhaust flow rate, reducing the exitdiameter with an exhaust nozzle is recommendedto increase the exit velocity and rise or throw of theexhaust over the bui lding. However, exit velocitiesmuch larger than 3000–4000 fpm (1 5.3 to 20.4m/s) may result in high noise and vibration. Toosmall of a nozzle, or one with too rapid a decreasein area, could result in excessive pressure loss inthe exhaust and the resulting combination ofreduced flow due to fan system effect and reduceddilution and safety.

Combining exhausts into a common stack, eitherby manifolding exhausts or with very close group-ing of stacks, wil l 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 general ly give greaterbenefit than instal l ing an exhaust nozzle on a stackserving a single laboratory chemical hood.

Manifolding of exhausts can also provide someinternal dilution of fume hood exhausts when themajority of chemical emissions are from an upsetcondition or large release from a single laboratorychemical hood. Such upset or large release condi-tions are the primary cause of odor complaints andpotential health effects. However, this internal di lu-tion is partially offset by the decreased atmospheric

dilution due to the larger plume size. Nevertheless,manifolding of exhausts is sti l l beneficial and rec-ommended.

Variable exhaust flow rates, used to reduce ener-gy costs, can periodically result in low exit veloci-ties. Minimum exit velocities below 1 500 fpm (7.65m/s) are discouraged because for such low exitvelocities, high winds can cause the exhaust totravel down the side of the stack instead of risingvertical ly. A dispersion modeling assessment candefine the minimum exhaust velocity and volumeflow needed to avoid fume reentry. I f this assess-ment shows a higher exhaust velocity and/or vol-ume flow is needed, there are other methods toachieve the desired dispersion:

• Variable flow geometry

• Induction of outdoor air

• Staging of multiple fans on a common inletplenum

• Use of a control system and on-site weatherstation so that low velocities can be set duringlow wind and high velocities during high winds.

Adding outdoor air to the exhaust is the most com-mon approach because i t provides the largerplume rise and some internal di lution.

Air intake placement is as important as stackdesign. Intakes on the side of the building or atgrade wi l l usually provide greater protection fromrooftop exhausts. Intakes on the roof may work i fplaced a sufficient distance from the exhausts.When only a single tal l stack is present, an intakelocation near the base of the stack may be a goodlocation. The advantage of this location is dimin-ished i f 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 i t is the dif-ference in roof heights that is particularly importantwhen analyzing the adjacent building effect.

First Stack Design Method—The Geometric

Method

The ASHRAE Handbook—HVAC Applications

describes the geometric method. This simplifiedmethod is intended to be conservative, but thereare l imi ts on i ts appl icabi l i ty. The ASH RAEHandbook also describes those l imits.

The geometric method is designed for isolated rec-tangular buildings that do not have tal ler buildings,dense tal ler trees, or tal ler hi l ls 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 asfol lows:

1 ) Calculate the length of the recirculation zone (R)downwind of the building for each of the four basicapproach wind directions. For a given direction, R =(Bsmall

0.67) (B large0.33), where Bsmall is the smaller of

the building height and width, and B large is the larg-er of the two. As used here, the recirculation zoneheight is the height of the emitting building.

Table A2 presents recirculation zone length for var-ious building dimensions.

2) Calculate the plume rise (throw) due to exhaustmomentum and add i t to the stack height, to obtainthe effective stack height.

is the final plume rise, where

is the momentum flux, ft4/s2 (m4/s2)

is the jet entrainment coefficient

is the well-known logarithmic wind profi le equation,


1 02

0. 9[FmUH/U*]1 /2

hf =UHßj

Fm = Ve{ }

1 UHßj = +

3 Ve

d2

4

UH / U* = 2. 5ln (H/z0)




1 03

Ve = stack exit velocity, fpm (m/s)

d = stack diameter, ft (m)

UH = wind speed at stack top, fpm (m/s)

H = stack height above ground level, ft (m)

U* = friction velocity, ft (m)

zo = surface roughness length, ft (m)

Table A1 describes various zo values for a range ofsites. For example i f zo equals 0.5 m and H = 1 1 m,substituting into the logarithmic wind profi le equa-tion gives UH/U* = 8.3.

Table A1 : Terrain Factors

The 1 %-wind speed is a high wind speed exceed-ed only 1 % of the time. These wind speeds areavailable for numerous locations in the ASHRAEH andbook—Fundamentals , Chapter Climatic

Design Information .

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 should clearthe emitting building, including penthouses, andthe recirculation zone downwind of the building.The bottom of the plume extends downward at a5:1 slope (5 units horizontal and 1 unit downward)from the effective stack height (physical height plusadded plume rise). This should be done for al l four

of the basic approach wind directions. Table A3shows flowrates required to meet the geometricmethod, given a 1 0 ft (3.5 m) stack height and a3000 fpm (1 5.3 m/s) exit velocity (as per this stan-dard), a 1 %-wind speed of 1 5 mph (24 k/h), andvarious horizontal distances to clear. The horizon-tal distance is the distance between the stack andthe downwind building edge plus the recirculationzone length.

The same method can be used to determine atal ler stack that also complies.

Example Calculation for the First Stack Design

Method—The Geometric Method

A laboratory building is 1 00 ft (30.5 m) wide, 200 ft(61 m) long, and 60 ft (1 8.3 m) high. A manifoldedlaboratory exhaust with a flowrate of 1 0,000 cfm(4.7 m3/s) is located in the center of the roof. Forwind approaching the 1 00 ft (30.5 m) wide side,Bsmall is 60 ft (1 8.3 m) and B large is 1 00 ft (30.5 m).The length of the recirculation zone is R =(600. 67)(1 00 0.33) = 71 ft (21 .7 m). The horizontaldistance that must be cleared by the plume equals1 00 ft (30.5 m) from the center to the edge of thebuilding plus 71 ft (21 .7 m) for the recirculationzone, or 1 71 ft (52.2 m). The required effective stackheight to clear the building and recirculation zone is1 71 /5 (using the 5:1 slope) = 34.2 ft (1 0.4 m).

The added stack height due to momentum is cal-culated next. The stack diameter is 2.06 ft (.63 m)based on a 3000 fpm (1 5.3 m/s) exit velocity and a1 0,000 cfm (4.7 m3/s) flow rate. Using a 1 5 mph(24 k/h), 1 320 fpm (6.7 m/s) 1 %-wind speed, theadded stack height = 3 °F 2.06 °F 3000/1 320 = 1 4ft (4.3 m). Given a physical stack height of 1 0 ft(3.05 m) based on the minimum required to meetthis standard, the effective stack height is 1 4 + 1 0ft = 24 ft (7.32 m).

The required effective height computed above is34.2 ft (1 0.4 m), which is not met with a 1 0 ft (3.05m) physical stack height. The designer canincrease the physical height to 20 ft (6.1 m). As analternative, the designer can increase the momen-tum of the air by introducing outside air to the sys-tem. I f the physical stack height remains at 1 0 ft(3.05 m), the diameter would need to increase to

Terrain zo, ft (m)

Flat, water, desert 0.03 (0.01 )

Flat, airport, grassland 0.1 6 (0.05)

Suburban 2.0 (0.6)

Urban 6.0 (2.0)

3.5 ft (1 .1 m), increasing flow rate to about 30,000cfm (1 4.1 m3/s). Also, increasing to 30,000 cfm(1 4.1 m3/s) wi l l increase in-stack di lution by a fac-tor of 3:1 . This in-stack di lution, whether achievedby manifolding exhausts in the building or byadding roof air, can be very valuable to achievingsafe results. The other wind direction (aimedtoward the long side of the bui lding) should bechecked, but for this example this wind direction isthe worst case.

High volume flow in i tself is not a guarantee of ade-quate di lution. For a given source spil l rate in ki lo-grams/second, a higher exhaust volume flow Qeincreases the in-stack di lution, but somewhatreduces the atmospheric di lution because theatmosphere is now presented with a larger volumeof gas to disperse.

Tables A2 and A3 assist in estimating a stackheight that ensures that the plume avoids recircu-lation zones and the edge of the building.


1 04

Table A1 Length of Downstream Recirculation Zone (feet and meters)

Each story is 1 5 ft (4.6 m) high

Bldg.Dimensions

1 Story 2 Stories 3 Stories 4 Stories 5 Stories 6 Stories 7 Stories

Height inFeet (meters)

1 5 ft (4.6 m)

30 ft (9.1 m)

45 ft (1 3.7 m)

60 ft (1 8.3 m)

75 ft (22.9 m)

90 ft (27.4 m)

1 05 ft (32.0 m)

Length orWidth

50 ft (1 5.2 m)

22.3ft (6.8 m)

35.5 ft (1 0.8 m)

46.6 ft(1 4.2 m)

53.1 ft(1 6.2 m)

57.2 ft(1 7.4 m)

60.7 ft(1 8.5 m)

63.9 ft(1 9.5 m)

75 ft(22.9 m)

25.5 ft(7.8 m)

40.6 ft(1 2.4 m)

53.3 ft(1 6.2 m)

64.6 ft(1 9.7 m)

75.0 ft(22.9 m)

79.7 ft(24.3 m)

83.3 ft(25.4 m)

1 00 ft(30.5 m)

28.1 ft(8.6 m)

44.6 ft (1 3.6 m)

58.6 ft(1 7.9 m)

71 .0 ft(21 .6 m)

82.5 ft(25.1 m)

93.2 ft(28.4 m)

1 01 .6 ft(31 .0 m)

1 50 ft(45.7 m)

29.8 ft(9.1 m)

51 .0 ft(1 5.5 m)

67.0 ft(20.4 m)

81 .2 ft(24.7 m)

94.3 ft(28.7 m)

1 06.5 ft(32.5 m)

1 1 8.1 ft(36.0 m)

200 ft(61 .0 m)

29.8 ft(9.1 m)

56.1 ft(1 7.1 m)

73.6 ft(22.4 m)

89.3 ft(27.2 m)

1 03.7 ft(31 .6 m)

1 1 7.1 ft(35.7 m)

1 29.9 ft(39.6 m)

250 ft(76.2 m)

29.8 ft(9.1 m)

59.6 ft(1 8.2 m)

79.2 ft(24.1 m)

96.1 ft(29.3 m)

1 1 1 .6 ft(34.0 m)

1 26.1 ft(38.4 m)

1 39.8 ft(42.6 m)

300 ft(91 .4 m)

29.8 ft(9.1 m)

59.6 ft(1 8.2 m)

84.2 ft(25.7 m)

1 02.0 ft(31 .1 m)

1 1 8.5 ft(36.1 m)

1 33.9 ft(40.8 m)

1 48.5 ft(45.3 m)

500 ft(1 52.4 m)

29.8 ft(9.1 m)

59.6 ft(1 8.2 m)

89.4 ft(27.2 m)

1 1 9.2 ft(36.3 m)

1 40.3 ft(42.8 m)

1 58.5 ft(48.3 m)

1 75.7 ft(53.6 m)

1 000 ft(304.8 m)

29.8 ft(9.1 m)

59.6 ft(1 8.2 m)

89.4 ft(27.2 m)

1 1 9.2 ft(36.3 m)

1 49.0 ft(45.4 m)

1 78.8 ft(54.5 m)

208.5 ft(63.6 m)

Formula for figure is:

Length of downstream recirculation zone is Bsmall(0.67) °F B large

(0.33) where Bsmall is the smaller of

height and width or length and B large is the larger of the two (from ASHRAE, 1 997).

Where B large is > 8 Bsmall , use Blarge = 8 Bsmall




1 05

Second Stack Design Method—The Numerical

Method

A more detai led analysis that accounts for di lutionwithin the plume can be used if the required stackheights or flowrates are too large from the geomet-ric method. Minimum di lution can be predictedusing equations from the ASHRAE Handbook—HVAC Applications . The equations are not dis-cussed in detail here. These equations apply onlyto intakes below stack top. The stack height used inthese equations 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.

The numerical methods are continually evolving.Designers are advised to consult current sourcesfor specific calculations. The discussion here i l lus-trates issues; i t does not teach a design procedure.

For the example case discussed above [1 0 ft (3.05m) stack, diameter = 2.06 ft (0.628 m), exit velocity= 3000 fpm (1 5.24 m/s), flowrate = 1 0,000 cfm (4.7m3/s), receptor at end of wake recirculation zone1 71 ft (52.2 m) away], the predicted minimum di lu-tion from the ASHRAE Handbook is 455:1 . I f thediameter is increased to 3.5 ft (1 .07 m) associatedwith a larger flow rate of 30,000 cfm (1 4.1 m3/s),

the minimum di lution decreases to 264:1 .

At first glance, the smaller flowrate stack that yieldsthe larger dilution would seem to be preferred.H owever, the larger 30, 000 cfm (1 4. 1 m 3/s) ,flowrate provides an internal di lution of 3:1 com-pared to the original 1 0,000 cfm (4.7 m3/s). Whencomparing the two cases, the larger flowrate casehas a total di lution of 3 °F 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 spil l rate tomeet the 0.05 ppm at the receptor location would be1 1 .2 L/m of toxic vapor. The original design with d =2.06 ft (0.63 m) has a higher dilution Dcrit of 455 butthe reduced volume flow only allows a spil l volumerate of 6.4 L/m. In effect, the factor of 3 volume flowincrease in the stack with the fan allows about a fac-tor of 1 .75 increase in al lowable spil l rate.

In conceptual terms, exit velocity and volume flowrate are "equal partners" in plume rise and theresulting increase in safety through greater di lution.However, in practical terms, exit velocities can onlybe increased by doubling or tripl ing whi le manifold-ing or adding roof air to the stack can easily resultin a 1 0-fold increase in di lution.

Di lution in the context of dispersion of laboratoryexhaust is a deceptively difficult concept becauseone must account for both the di lution within the

Table A2 Volume Necessary to Achieve Throw Off Edge of Building and

Recirculation Zone, cfm and L/s

Assume stack is 1 0 ft (3.0 m) high and fan exit velocity is 3000 fpm (1 5.2 m/s) with 1 5 mph(24.1 km/h) wind speed

Distance to Edge of

Building and Recirc. Zone

Feet to throw

horizontally

Meters to throw

horizontally

Flow needed,

cfm

Flow needed,

L/s

75 22.9 1 ,267 598.0

1 00 30.5 5,068 2392.0

1 50 45.7 20,272 9567.3

200 61 .0 45,61 2 21 526.5

250 76.2 81 ,088 38269.3

300 91 .4 1 26,699 59795.3


1 06

exhaust system, De, which is present at the stackand the di lution 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 di lution or a nor-malized concentration value. A normalized di lutionvalue can be obtained by multiplying D by the ratioof the actual volume flow rate and a standardizedvolume flowrate [i .e. , 1 000 cfm (4.7 m3/s) °F (Qact /Qstd)]. The result is a di lution 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 al l of the values arereferenced to the same 1 000 cfm (0.47 m3/s) vol-ume flowrate.

A normalized concentration value is obtained byapplying the definitions of concentration and di lu-tion provided in the ASHRAE Handbook—HVAC

Applications , [C/m = 1 / (D * Q)]. The result is a nor-malized concentration value that is the ratio of theconcentration present at the downwind locationand the mass emission rate of the emitted chemi-cal, expressed in units of µg/m 3 per g/s. This valueis completely independent of the volume flowratethrough the exhaust stack, and thus can be used toreadi ly compare the effectiveness of exhauststacks with various volume flowrates. Anotheradvantage of this method is that i f the emissionrate of a chemical is known, you can simply multi-ply the emission rate by the C/m value to obtain apol lutant concentration. This concentration canthen be compared directly with establ ished healthand odor l imits.

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 di lution crite-rion can be difficult since the types and quantitiesof laboratory chemicals can vary significantly fromlaboratory to laboratory. As a starting place, i t is

suggested 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 1 1 0 test per-formed by a manufacturer, and the ANSI/ASHRAE1 1 0 rating should be AM 0.05 or lower. This ratingtranslates to the worker being exposed to 0.05 ppmor lower of tracer gas whi le 4 l i ters per minute (4L/min.) of tracer gas are being emitted from withinthe laboratory chemical hood. The same 4 L/min. oftracer gas are being emitted from the laboratorychemical hood exhaust stack. The recommendeddesign criterion is that the 0.05 ppm concentrationalso be the maximum concentration at the airintake. (The time constant for exposure concentra-tions mentioned in this standard is measuring overa 1 0-minute span of time.)

The detailed calculations are not presented here,but i t can be confirmed that the 4 L/min. emissionrate and an al lowable air intake concentration of0.05 ppm corresponds to a normalized concentra-tion design criterion of 750 µg/m 3 per g/s or a2800:1 di lution for a 1 000 cfm (0.47 m3/s) flowrateexhaust, 280:1 for a 1 0,000 cfm (4.7 m3/s) flowrate, and a 93:1 di lution for a 30,000 cfm exhaust.These suggested design criteria is somewhat morelenient than the smaller criteria suggested in theASHRAE Handbook—HVAC Applications , ChapterLaboratories, which has recommended that airintake concentrations should be less than 3 ppmdue to an evaporating l iquid spi l l in a fume hoodand exhausted at a rate of 7.5 L/s. The ASHRAEcriteria translate to a normalized concentrationdesign criterion of 400 µg/m 3 per g/s or a 5000:1dilution for a 1 000 cfm flowrate exhaust. For faci l i-ties with intense chemical uti l ization, design criteriaspecific for that faci l i ty can be developed using thechemical inventory.

In the stack examples above, the 1 0,000 cfm (4.7m3/s) case had a predicted di lution of 455:1 , whichmeets the 280:1 criterion for a 1 0,000 cfm (4.7m3/s) flowrate. The 30,000 cfm (1 4.1 m3/s) casehad a predicted di lution of 264:1 , which also meetsthe 93:1 criterion for this flowrate, by a larger mar-gin than the 1 0,000 cfm (4.7 m3/s) stack.




1 07

Graphical Solution Referenced for the Second

Stack Design Method Using the Halitsky Criteria

Two graphical solutions can be consulted that showa solution to the di lution calculations. The first isRatcliff and Sandru (ASHRAE Transactions , 1 05,part 1 , paper Ch-99-7-1 , 1 999) and the second isPetersen, Cochran, and LeCompte (to be pub-l ished in 2002 ASHRAE Transactions ). The solu-tions in both papers are for a Halitsky Criteria spi l l ,0.028 ppm, rather than the criterion derived fromthe ANSI/ASHRAE 1 1 0 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 (23.5 L/s)and an exit velocity of 3000 fpm (1 5.24 m/s) wouldrequire an offset distance of 1 20 ft (36.6 m) to thenearest receptor site using the 0.028 ppm expo-sure l imit at the receptor. These graphs werederived from Chapter 43 of ASH RAE 1 999Handbook—Applications Manual equations for crit-ical wind speeds and di lutions. Zero-height stacksare quite common because stacks that end belowparapet walls, below the height of adjacent pent-houses, or that end below adjacent screen walls orscreens wil l act as a zero-height stack. Receptorsites would include operable doors and windows,and any location where pedestrian access wasallowed as well as to outside air intakes.

Third Stack Design Method—Physical Modeling

Using the Wind Tunnel or Water Flume

I f the stack heights determined from the first twomethods described above are undesirable or i f 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 more

accurate, and typically less conservative, predic-tions than the numerical or geometric methods.Physical modeling is the safest method to choosestack heights in new bui ldings or in bui ldings beingretrofitted.

Wind-tunnel model ing is often the preferredmethod for predicting maximum concentrations forstack designs and locations of interest when ener-gy and equipment optimization is desired. I t is therecommended approach because it gives the mostaccurate estimates of concentration levels in com-plex building environments. A wind-tunnel model-ing study is l ike a ful l-scale field study, except i t isconducted before a project is bui lt. Typically, ascale model of the bui lding under evaluation, alongwith the surrounding buildings and terrain within a1 000-ft radius, is placed in an atmospheric bound-ary layer wind tunnel. A tracer gas is released fromthe exhaust sources of interest, and concentrationlevels of this gas are then measured at receptorlocations (i .e. , air intakes, operable windows, etc. )of interest and converted to ful l-scale concentrationvalues. Next, these values are compared againstthe appropriate health or odor design criteria out-l ined in Section 5.3.4 to evaluate the acceptabil i tyof the exhaust design. ASHRAE (2009) and Snyder(1 981 ) provide more information on scale-modelsimulation and testing methods.

Dilution criteria are sti l l necessary to evaluate theresults of physical modeling. The design criteriadiscussed above provide initial guidance. A morecomplete evaluation of appropriate design criteriashould be conducted when the chemical usage isexpected to exceed minimal levels. In addition, thedesign criteria should take into account the 20%factor outl ined in Section 5.3.4.


1 08

APPENDIX 4. Audit Form for ANSI/AIHA®

Z9.5–201 2


Audit i tem numbers refer to Standard paragraphs.Compliance with the Standard should only beclaimed when al l applicable provisions or elementsof the Standard are met. Note: Mark (X) al l thosethat genuinely apply.

2 Lab Ventilation Management Plan


( ) 2. 1 Management has established a LaboratoryVenti lation Management Plan (LVMP) to ensureproper selection, operation, use, and maintenanceof laboratory venti lation equipment.

( ) The LVMP has been implemented to ensure proper operation of the lab venti lation sys-tems, help protect laboratory personnel workingwith potential ly hazardous airborne materials, pro-vide satisfactory environmental air qual ity andmaintain efficient operation of the laboratory venti-lation systems.

( ) 2. 1 .1 Adequate laboratory chemical hoods,special purpose hoods, or other engineering con-trols are used when there is a possibi l i ty ofemployee overexposure to air contaminants gen-erated by a laboratory activity.

( ) Laboratory worker chemical exposures aremaintained below applicable published or in-house exposure l imits.

( ) Chemical “hazard determinations” are con-ducted by chemical manufacturers and importersas required by the Occupational Safety andHealth Administration's (OSHA) HazardCommunication standard, specifically, 29 CFR1 91 0.1 200(d).

( ) 2. 1 .2 The specific room venti lation rate isestabl ished or agreed upon by the owner or theirdesignee.

( ) 2.1 .3 Di lution venti lation is provided to controlthe bui ldup of fugitive emissions and odors in thelaboratory.

2.2 Chemical Hygiene Plan

( ) 2.2 The laboratory develops a ChemicalHygiene Plan according to the OSHA LaboratoryStandard (29 CFR 1 91 0.1 450).

( ) The plan addresses the laboratory operationsand procedures that might generate air contami-nation in excess of the requirements of Section2.1 .1 .

( ) These operations are performed inside a hoodadequate to attain compliance.

2.3 Responsible Person

( ) 2.3 In each operation using laboratory venti la-tion systems, the user designates a “responsibleperson.”

2.4 Roll of Hazard Assessments

( ) 2.4.1 Employers ensure an ongoing system forassessing the potential for hazardous chemicalexposure.

( ) Employers promote awareness that laboratoryhoods are not appropriate control devices for al lpotential chemical releases in laboratory work.

( ) The practical l imits of knowing how each venti-lation control is being used in the laboratory areconsidered when specifying design features andperformance criteria.

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

( ) The employer establishes criteria for determin-ing and implementing control measures to reduceemployee exposures to hazardous chemicals; par-ticular attention is given to the selection of controlmeasures for chemicals that are known to beextremely hazardous.




1 09

( ) Laboratory chemical hoods are functioningproperly and specific measures are taken toensure proper and adequate performance.

( ) 2.4.2 The fol lowing i tems are considered anddecisions made regarding each element's rele-vance 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 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 pol lution controls);( ) Exhaust discharge (stack design) and di lution

factors;( ) Recirculation of potential ly 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 Fume Hoods

3.1 Design and Construction

( ) 3.1 The design and construction of laboratorychemical hoods conform to the appl icable guide-l ines presented in the latest edition of ACGIH®Industrial Venti lation: A Manual of RecommendedPractice, and the most current codes, guidelinesand standards, and any other appl icable regula-tions and recommendations.

( ) 3.1 .1 The laboratory chemical hood is

equipped with a safety viewing sash at the faceopening.

( ) Sashes are not removed when the hood is inuse.

( ) 3.1 .1 .1 Where the design sash opening areais less than the maximum sash opening area, thehood is equipped with a mechanical sash stop.

( ) A means of communicating when openingsare in excess of the design sash opening area isprovided.

( ) The Chemical Hygiene Plan clearly instructsthe hood users to position the sash so that theopening is no greater than the design openingwhile using the hood for protection.

( ) 3.1 .1 .2 Vertical sashes are designed and oper-ated so as not to be opened more than the designopening when hazardous materials are beingused within the hood.

( ) 3.1 .1 .3Horizontal sashes arfe designed so asnot to be opened more than the design openingwidth when hazardous materials are being gener-ated in the hood.

( ) 3.1 .1 .4 I f a combination sash provides hori-zontally moving panels mounted in a frame thatmoves vertically, the above requirements are met.

( ) 3.1 .1 .5 Al l users are trained in good workpractices, including the need to close the sashwhen not in use.

( ) Al l users of VAV systems shal l be trained inthe proper uses of the sash, the energy conse-quences of improper use, and the need to closethe sash when the operation does not require i tsuse.

( ) Automatic sash positioning systems haveobstruction sensing capable of stopping travelduring sash closing operations without breakingglassware, etc.

( ) Automatic sash positioning al lows manualoverride of positioning with forces of no more than


1 1 0

1 0 lbs (45 N) mechanical both when powered andduring fault modes during power fai lures.

3.2 Hood Types

( ) 3.2.1 Auxil iary air hoods meet the require-ments in Section 3.3.

In addition:

( ) The supply plenum is located externally andabove the top of the hood face;

( ) The supply jet is distributed uniformly acrossthe hood width;

( ) The auxi l iary air does not disrupt hood con-tainment or increase potential for escape.

( ) 3.2.2 Bypass hoods have a route for air enter-ing the hood (the bypass mechanism) opens asthe sash closes.

( ) The bypass mechanism shall be designed tominimize potential ejection of l iquid or sol id mater-ial outside the hood in the event of an eruptioninside the hood.

( ) 3.2.3 Conventional hoods meet the require-ments in Section 3.3.

( ) 3.2. .4 Floor-mounted hoods meet the require-ments in Section 3.3.

( ) 3.2.5 Perchloric acid hoods are specificallydesigned to safely handle certain types of per-chloric acid work and are actually used for suchwork.

( ) Perchloric acid hoods are used for handlinganhydrous perchloric acid (> 85% concentration. )

( ) Al l procedures conducted in a perchloric acidhood are reviewed by an immediate supervisor.

( ) Al l procedures using a perchloric acid hoodare performed by trained personnel, knowledge-able and informed about the hazards and proper-ties of these substances, and are provided withappropriate protective equipment after suitable

emergency contingency plans are in place.

In addition:

( ) Al l inside hood surfaces use materials that wil lbe stable and not react with perchloric acid to formcorrosive, flammable, and/or explosive compoundsor byproducts;

( ) Al l interior hood, duct, fan, and stack surfacesare equipped with water washdown capabil ities;

( ) Al l ductwork is constructed of materials that wil lbe stable to and not react with perchloric acidand/or i ts byproducts and wil l have smooth weldedseams;

( ) No part of the system is manifolded or joined tononperchloric acid exhaust systems;

( ) No organic materials, including gaskets areused in the hood construction unless they areknown not to react with perchloric acid and/or i tsbyproducts;

( ) Perchloric acid hoods are prominently labeled“Perchloric Acid H ood, Organic ChemicalsProhibited.”

( ) 3.2.6 VAV hoods meet the requirements inSection 3.3.

( ) Variable exhaust flow from a laboratory hoodhas implications for room venti lation which areaddressed according to Section 5.

3.3 Hood Airflow and Monitoring

( ) 3.3.1 The average face velocity of the hood issufficient to capture and contain the hazardouschemicals for which the hood was selected, andfol lows guidance in Section 2.4 and as generatedunder as-used conditions.

( ) An adequate face velocity is is not the only cri-terion to achieve acceptable performance and isnot used as the only performance indicator.

( ) Hood containment is verified as appropriatefor the hazard being controlled (e.g. , visual meth-




1 1 1

ods such as smoke, face velocity testing, expo-sure assessments, tracer gas containment testing,etc. )

( ) 3.3.2 The flow rate of Constant Volume hoodsand the minimum flow rate of Variable Air Volumehoods is sufficient to prevent hazardous concen-trations of contaminants within the laboratoryfume hood.

( ) In addition to maintaining proper hood facevelocity, laboratory hoods maintain a minimumexhaust volume to ensure that contaminants areproperly di luted and exhausted from a hood.

( ) The fol lowing considerations are taken intoaccount (as applicable) when setting the minimumhood flow rate: hood interior corrosion, need toaffect directional airflows, fume hood density,hood design, hood materials, generation or emis-sion rates, exhaust parameters.

( ) The hood flow rate is set within the operatingrange of the hood exhaust equipment and theassociated control system.

( ) Venti lation system designers coordinate theoperating range of the fume hood flow rate withthe operating ranges of the other air supply andexhaust devices in the room.

3.3.3 Flow Measuring Devices

( ) Al l hoods are equipped with a flow indicator,flow alarm, or face velocity alarm indicator to alertusers to improper exhaust flow.

( ) The flow-measuring device is capable of indi-cating that the air flow is in the desired range, andcapable of indicating alarms when the flow is highor low by 20%.

( ) The device is cal ibrated at least annually andwhenever damaged.

4 Other Containment Devices

4.1 Gloveboxes

( ) 4.1 .1 Gloveboxes are not used for manipula-tion of hazardous materials with the face or

other panels open or removed.

( ) 4.1 .2 Materials: Interior cracks, seams, andjoints are el iminated or sealed.

( ) 4.1 .3 Uti l i ty valves and switches are in confor-mance with appl icable codes.

( ) When control of uti l i ties from inside the glove-box is required, additional valves and switches areprovided outside the glovebox for emergencyshutoff.

( ) 4.1 .4 Proper appl ication of ergonomic princi-ples is met by referring to Chapter 5.1 0,“Guidelines for Gloveboxes,” AGS-G001 –1 998.

( ) 4.1 .5 The design of the glovebox provides forretaining spil led l iquids so the maximum volumeof l iquid permitted in the glovebox wi l l be retained.

( ) 4.1 .6 Containment gloveboxes are providedwith exhaust venti lation to result in a negativepressure inside the box that is capable of contain-ing the hazard to acceptable levels.

( ) 4.1 .7 The air or gas exhausted from the glove-box is cleaned, and discharged to the atmospherein accordance with the general provisions of thisstandard and pertinent environmental regulations.

( ) Air-cleaning equipment is sized for the maxi-mum airflow anticipated when hazardous agentsare exposed in the glovebox and the gloveboxopenings are open to the extent permitted underthat condition.

( ) I f the air-cleaning device (ACD) is passive,provision is made for determining the status of theACD, as noted in Section 9.3. I f the ACD is active,instrumentation is provided to indicate i ts status.

( ) The ACD is located to permit ready access formaintenance.

( ) Provision is made for maintenance of the ACDwithout hazard to personnel or the environment


1 1 2

and so not to contaminate the surrounding areas.

( ) 4.1 .8 Exhaust piping is in accordance with theprinciples described in ACGIH ® Industrial

Ventilation: A Manual of Recommended Practices,ANSI/AIHA ® Z9.2, and the ASHRAE 1 997Handbook − Fundamentals.

( ) Al l piping within the occupied premises isunder negative pressure when in operation.

( ) Materials are resistant to corrosion by theagents to be used.

( ) 4.1 .9 A glovebox pressure monitoring devicewith a means to locally indicate adequate pres-sure relationships to the user is provided on al lgloveboxes.

( ) I f audible alarms are not provided, document-ed training for users in determining safe pressuredifferentials is required.

( ) Pressure monitoring devices are adjustableand subject to periodic calibration.

( ) 4.1 .1 0 A written decommissioning plan fol low-ing the procedures outl ined in the latest edition ofANSI/AIHA ® Standard Z9.1 1 LaboratoryDecommissioning is developed.

( ) Before the access panel(s) of the glovebox areopened or re moved, the interior contamination isreduced to a safe level.

( ) I f the contaminant is gaseous, the atmospherein the box is adequately exchanged to remove thepotential ly hazardous gas.

( ) I f the contaminant is l iquid, any l iquid on sur-faces is wiped with suitable adsorbent material orsponges unti l visibly clean and dry.

( ) Used wipes are placed in a suitable containerbefore being removed from the glovebox.

( ) I f the contaminant is a powder or dust, al linternal surfaces are cleaned and wiped unti l visi-

bly clean and the exterior surfaces of the glovesalso are wiped clean.

( ) Precautions to prevent personnel hazard andcontamination of the premises are made if theducting is to be opened or dismantled.

( ) When there is any uncertainty about the effec-tiveness of the contamination reduction proce-dures, personnel involved in opening the panels ofthe glovebox are provided with appropriatePersonal Protective Equipment or clothing.

( ) 4.1 .1 1 A high containment glovebox conformsto al l the mandatory requirements of 4.1 .1 through4.1 .1 0, and

( ) I s provided with one or more air-lock pass-through ports for inserting or removing objects orsealed containers without breaching the physicalbarrier between the inside and outside of theglovebox.

( ) Maintains negative operating static pressurewithin the range of -0.5 to -1 .5 in. wg (–1 24 to–373.5 Pa) such that contaminant escape due to“pinhole-type" leaks is minimized.

( ) Maintains di lution of any flammable vapor-airmixtures to <1 0% of the appl icable lower explo-sive l imit.

( ) Prevents transport of contaminants out of theglovebox.

( ) 4.1 .1 2 A medium containment glovebox con-forms to al l the mandatory requirements ofSections 4.1 .1 through 4.1 .1 0, and is not providedwith pass-through airlocks, and is provided withsufficient exhaust venti lation to maintain an inwardair velocity of at least 1 00 fpm (0.51 m/s) throughthe open access ports, and creates a negativepressure of at least 0.1 in. w g (2.49 Pa) whenaccess ports are closed.

( ) 4.1 .1 3 Special case containment gloveboxesare tested for the intended use and foundadequate for that purpose.




1 1 3

( ) 4.1 .1 4 An isolation and containment gloveboxis used to control special atmosphere work wheneither the controlled atmosphere and/or the con-tained agents are hazardous.

( ) Design and construction and materials conformsto the requirements for high, medium, or specialcase containment gloveboxes as necessary.

( ) I f the controlled atmosphere gas is hazardous,the airlocks are 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.

( ) Operation of an isolation and containmentglovebox conform to high, medium, or specialcase containment requirements as necessary andthe airlock purge system is operated for sufficienttime to di lute any hazardous gas in the airlock tosafe concentrations before the outer door isopened.

( ) Care is exercised when placing certain haz-ardous l iquids in an evacuated airlock or interiorof a glovebox when a decrease in pressure couldaffect the boi l ing point of the l iquid, causing i t togo to gaseous state.

4.1 .1 5 An overall operation and maintenance pro-gram is documented for each application of theglovebox to provide users with necessary informa-tion on periodic maintenance and testing of glove-box system components.

4.2. Ductless Hoods

( ) Ductless hoods meet the general require-ments of Sections 3.1 and 3.3 as applicable.

( ) A Hazard Evaluation and Analysis is conduct-ed as directed in ANSI/AIHA ® Z9.7 and Section2.1 .1 of this Standard.

( ) Compliance with the general requirements ofSections 2, 3.3 and 5.3.6.2, are evaluated byqualified persons.

( ) Ductless hoods that do not meet the require-ments specified in Sections 9.3 and

9.4 are used only for operations that normallywould be performed on an open bench without pre-senting an exposure hazard.

( ) Ductless hoods have signage prominentlyposted on them to inform operators and mainte-nance personnel about the al lowable chemicalsused in the hood, type and l imitations of fi l ters inplace, fi l ter changeout schedule, and that thehood recirculates air to the room.

( ) 4.2.1 Ductless hoods uti l izing air-cleaning fi l-tration systems for recirculating exhaust air conta-minated with toxic particulates must meet therequirements of Section 9.3.1 .

( ) 4.2.2 Ductless hoods uti l izing adsorption orother fi l tration media for the col lection or retentionof gases and vapors are specified for a l imiteduse and meet the requirements of Section 9.3.2.

( ) Ductless hoods employing fi l ters for removinggases and vapors have written documentation(records) that the manufacturer has approved thespecific application of the hood prior to usage.

( ) The manufacturer provides a l ist of chemicalsapproved to be used in the hood with their reten-tion capacities.

( ) Proper disposal of unused and used (contami-nated) adsorption fi l ters is considered as part ofthe decision to use ductless hood employingsuch.

( ) 4.2.3 Contaminated fi l ters are unloaded fromthe air-cleaning system fol lowing safe work prac-tices to avoid exposing personnel to hazardousconditions and to ensure proper containment ofthe fi l ters for final disposal.

( ) Airflow through the fi l ter housing is shut downduring fi l ter change-out.

( ) 4.2.4 Al l of the requirements of sections 6.3,


1 1 4

6.4, 6.5.3.1 and 8.0 for containment and airflowtesting and al l of the requirements of sections 9.2and 9.3.2 for air cleaning performance shal l befol lowed.

4.3 Special Purpose Hoods

( ) 4.3 Special laboratory chemical hoods aredesigned in accordance with ANSI/AIHA® Z9.2and ACGIH ® Industrial Ventilation: A Manual of

Recommended Practices.

5 Laboratory Ventilation System Design

5.1 Lab Design

( ) 5.1 .1 Laboratory designers consider effects onsafety when establishing floor plans and spatiallayout.

( ) Laboratory chemical hoods are located sotheir performance is not adversely affected bycross drafts.

( ) Windows in laboratories with hoods shall beful ly closed whi le hoods are in use (emergencyconditions excepted).

( ) 5.1 .2 Generation of excessive noise is avoidedin laboratory venti lation systems.

( ) Fan location and noise treatment provide forSPL in conformance wi th local ambient noisecriteria.

( ) 5.1 .4 When the type and quantity of chemicalsor compressed gases that are present in a labora-tory room could pose a significant toxic or firehazard, the room is equipped with provision(s) toinitiate emergency notification and initiate theoperation of the venti lation system in a mode con-sistent with accepted safety practices.

( ) A hazard assessment is performed to identifythe credible emergency conditions that may occur.

( ) For rooms served by VAV venti lation systems,the chemical emergency mode of operation maxi-

mizes the room venti lation (air changes per hour)rate and, i f appropriate, increases negative roompressurization.

( ) For rooms served by CAV venti lation systemsthat uti l ize a reduced venti lation level for energysavings, the chemical emergency mode of opera-tion ensures that the room venti lation and nega-tive pressurization are at the maximum rate.

( ) Operation of the room venti lation system in achemical emergency mode does not reduce theroom venti lation rate, room negative pressuriza-tion level, or hood exhaust airflow rate.

5.2 Lab Airflow Management

5.2.1 . ( ) As a general rule, airflow is from areas oflow hazard to higher hazard and exceptions aredocumented.

( ) When flow from one area to another is criticalto emission exposure control, airflow-monitoringdevices are installed to signal or alarm a malfunc-tion.

( ) Air is al lowed to flow from laboratory spaces toadjoining spaces only i f:

( ) There are no extremely dangerous and l i fe-threatening materials used in the laboratory;

( ) The concentrations of air contaminants gener-ated by the maximum credible accident wil l belower than the exposure l imits required by 2.1 .1 .

( ) The desired directional airflow between roomsis identified in the design and operating specifica-tions.

( ) 5.2.1 .1 Airlocks are uti l ized to prevent undesir-able airflow from one area to another in high haz-ardous appl ications, or to minimize volume of sup-ply air required by Section 5.1 .1 .

( ) Airlocks are applied in such a way that onedoor provides access into or out of the laboratoryroom, and the other door of the airlock providespassage to or from a corridor (or other non-labo-ratory area).




1 1 5

( ) Airlock doors are arranged with interlockingcontrols so that one door must be ful ly closedbefore the other door may be opened.

( ) 5.2.1 .2 I f the direction of airflow between adja-cent spaces is deemed critical, provision is madeto local ly indicate and annunciate inadequate air-flow and improper airflow direction.

( ) 5.2.2 The fol lowing issues are evaluated inorder to design for diversity:( ) Use patterns of hoods;( ) Type, size, and operating times of facil i ty;( ) Quantity of hoods and researchers;( ) Sash management (sash habits of users);( ) Requirements to maintain a minimum exhaustvolume for each hood on the system;( ) Type of venti lation system;( ) Type of laboratory chemical hood controls;( ) Minimum and maximum venti lation rates for

each laboratory;( ) Capacity of any existing equipment;( ) Expansion considerations;( ) Thermal loads; and( ) Abil ity to perform periodic maintenance.( ) The fol lowing conditions are met in order to

design a system diversity:( ) Acceptance of al l 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 al l laboratoryusers to make them aware of any l imitationsimposed on their freedom to use the hoods at anytime.

( ) An airflow alarm system is installed to warnusers when the system is operating beyond capa-bil ities al lowed by diversity.

( ) Restrictions on future expansions or flexibi l ityare identified.

5.2.3 Lab Ventilation – Emergency Modes

( ) A hazard assessment (see Section 2.4) is per-formed to identify credible emergency conditionsthat may occur.

( ) When the type and quantity of chemicals orcompressed gases that are present in a laborato-ry room could pose a significant toxic or fire haz-ard, the room is equipped with provision(s) to initi-ate emergency notification and initiate the opera-tion of the venti lation system in a mode consistentwith accepted safety practices.

( ) Emergency situations (see current version ofNFPA 92A) that are anticipated and the appropri-ate venti lation system responses are provided, asfollows:

( ) For a CHEMICAL EMERGENCY – A meanssuch as a clearly marked wall switch, , or otherreadily accessible device is provided to enable theroom occupants to initiate appropriate emergencynotification and simultaneously activate the venti-lation system’s chemical emergency mode ofoperation if one exists.

( ) For rooms served by VAV venti lation systems,the Chemical Emergency mode of operation maxi-mizes the room venti lation (air change per hour)rate.

( ) For rooms served by 2-state venti lation sys-tems that uti l ize a reduced venti lation level forenergy savings, the Chemical Emergency modeof operation applies the maximum venti lation rate.

( ) Operation of the room venti lation system in achemical emergency mode does not reduce theroom venti lation rate, room negative pressuriza-tion level, or hood exhaust airflow rate.

( ) For FIRE – Any manual or automatic means ofdetecting fire (such as a pul l station or smokedetector) in a laboratory room also activates anappropriate fire emergency mode of operation forthe room and/or building venti lation system.

( ) The selected fire emergency mode operatesall supply and exhaust equipment in the room in amanner that promotes egress, retards the spreadof fire and smoke, and complies with applicablefire safety codes and standards.

5.3 Supply Air


1 1 6

5.3.1 Supply Air Volume

( ) I f laboratories are to be maintained with anegative pressurization and directional airflowfrom the corridor into the laboratory, supply airvolumes are less than the exhaust flowrate fromthe laboratory.

( ) When laboratories are to be maintained with apositive pressurization and directional airflow, sup-ply air volume is more than the exhaust from thelaboratory.

( ) To maintain the desired space pressurization,the supply air volume responds to appl icabledynamic events including:

• changes in desired venti lation rate,

• flow changes in VAV exhaust devices,

• temperature control demands, and

• temporary deficit of exhaust system capacity.

( ) The laboratory ventilation system is designed toremove and dilute air contaminants in accordancewith the Laboratory Ventilation Management Plan.

( ) The venti lation rate also satisfies the generalcodes and standards that apply to the occupancyclass.

5.3.2 Supply Air Distribution and Quality

( ) Supply air distribution is designed to keep airjet velocities less than half, preferably less thanone-fourth of the capture velocity or the facevelocity of the laboratory chemical hoods at theirface opening.

( ) Supply systems meet the technical require-ments of the laboratory work and the require-ments of the latest version of ANSI/ASHRAEStandard 62.1 .

5.4 Exhaust System Classification

5.4.1 ( ) Designers reviews existing regulationsand code requirements for the project location.

( ) In cases where Section 51 0 of theInternational Mechanical Code applies, designersconsult the most current version of IMC 51 0.

5.4.2 Exhaust System Ductwork

( ) Laboratory exhaust system ductwork complieswith the appropriate sections of current versionsof the Sheet Metal and Air ConditioningContractors’ National Association (SMACNA)standards.

( ) Systems and ductwork are designed to main-tain negative pressure within al l portions of theductwork inside the building when the system is inoperation.

( ) Exhaust ductwork is designed in accordancewith the current versions of ANSI/AIHA ® Z9.2, theASHRAE Handbook – Fundamentals, and NFPA45.

( ) Branch ducts enter a main duct so that thebranch duct centerl ine is on a plane that includesthe centerl ine of the main duct.

( ) For horizontal main ducts, branch ducts do notenter a main duct on a plane below the horizontaltraverse centerl ine of the main duct. Horizontalruns of branch ducts shall be kept at a minimum.

( ) Longitudinal sections of a duct are a continu-ous seamless tube or of a continuously weldedformed sheet.

( ) Longitudinal seams that are formed mechani-cally are uti l ized only for l ight duty systems withno condensation or accretion inside the duct.

( ) Spiral ducts can be one gauge l ighter than therequired gauge of longitudinal seam duct i f thespiral duct gauge always meets the abrasive wearresistance requirements.

( ) Traverse joints are continuously welded orflanged with welded or Van Stone flanges.

( ) When nonmetal l ic materials are used, jointsare cemented in accordance with the manufactur-




1 1 7

er’s procedures.

( ) I f the duct is coated with a corrosion-resistantmaterial , the coating extends from the inside ofthe duct to cover the entire face of the flange.

( ) Flange faces are gasketed or beaded withmaterial suitable for service.

( ) I f condensation within the duct is l ikely, al l hor-izontal duct runs are sloped downward at least 1in. per 1 0 ft in the direction of the airflow to a suit-able drain or sump.

( ) Exhaust airflow volume are sufficient to keepthe temperature in the duct below 400°F (204°C)under al l foreseeable circumstances.

( ) Al l duct connections to the exhaust fan areconsistent with good venti lation design practice.As an alternative, the duct connections may bemade by means of inlet and outlet boxes.

( ) I f circumstances such as space l imitationsprevent the implementation of the precedingrequirements, then appl icable speed and powercorrections are made by applying the “SystemEffect Factor" (see AMCA 201 -90).

( ) Where optimum duct connections cannot bemade due to space or other l imitations, suitablealternative means are substituted to compensatefor the space l imitations.

( ) I f adequate duct connections cannot be pro-vided at the fan, the fan is equipped with inlet andoutlet boxes furnished by the fan manufacturer.

( ) The manufacturer furnishes performancecurves for the fan with the inlet and outlet box(es)as part of the fan.

( ) I f neither adequate connections nor inlet/outletboxes are present, the fan speed and powerrequirements represented in the fan rating tableare corrected by the “System Effect Factor.”

( ) Exhaust system materials chosen in accordancewith the current version of ACGIH’s ® Industrial

Ventilation: A Manual of Recommended Practice,the ASH RAE H andbook—Fundamentals, and

NFPA 45.

( ) Exhaust system materials are resistant to cor-rosion by the agents to which they are exposed.

( ) Exhaust system materials are noncombustibleif perchloric acid or similar oxidizing agents thatpose a fire or explosive hazard are used.

5.4.3 Manifolds

( ) Laboratory chemical hood ducts are combinedinto a common manifold with the fol lowing excep-tions and l imitations:

( ) Each control branch has a flow-regulatingdevice to buffer the fluctuations in pressure inher-ent in manifolds.

( ) Perchloric acid hoods are not manifolded withnonperchloric acid hoods unless a scrubber isinstalled between the hood and the manifold.

( ) Where there is a potential for ductwork conta-mination from hood operations as determinedfrom the Hazard Assessment of Section 2.4,radioisotope hoods are not manifolded with nonra-dioisotope hoods unless an appropriate air-clean-ing system is provided between the hood and themanifold: HEPA fi lter and/or carbon bed fi l ters forgases.

( ) Exhaust streams that contain concentrationsof flammable or explosive vapors at concentra-tions above the Lower Explosion Limit (LEL) aswell as those that might form explosive com-pounds (i .e. , perchloric acid hood exhaust) are notconnected to a centralized exhaust system.

( ) Exhaust streams comprised of radioactivematerials are adequately fi l tered to ensureremoval of radioactive material before being con-nected to a central ized exhaust system.

( ) Biological exhaust hoods are adequately fi l-tered to remove al l hazardous biological sub-stances prior to connection to a centralizedexhaust system.

( ) Unless al l individual exhausts connected tothe central ized exhaust system can be completely


1 1 8

stopped without creating a hazardous situation,provision is made for continuous maintenance ofadequate negative static pressure (suction) in al lparts of the system.

( ) As an alternative, i f the hood is completelyturned off, the hood is emptied and decontaminat-ed and provisions are implemented to prevent thehood from back-drafting.

( ) A VAV hood is provided with an emergencyswitch that al lows the hood exhaust volume toreturn to the maximum.

( ) Biological safety cabinets manifolded withchemical laboratory chemical hoods have either:(1 ) A thimble connection or (2) An air flow controldevice and an interlock/alarm for these devicesinstalled between the cabinet outlet and theexhaust manifold.

( ) Where Hazard Evaluation and Analysis deter-mines that the installation cal ls for direct connec-tion (hard ducted) of the biological safety cabinet(e.g. , Class I I–Type B) to an exhaust manifoldsystem to al low work with toxic chemicals orradionuclides, interlocks and alarms are providedto prevent the biological safety cabinet from oper-ating i ts normal starting mode or to immediatelywarn the operator in the event of an exhaust sys-tem fai lure (CDC-NIH, 1 999).

( ) The static pressure in the exhaust system islower than the surrounding areas throughout theentire length, with the exception noted in Section5.3.1 .1 .

( ) Fire dampers are not installed in exhaust sys-tem ductwork (NFPA 45).

( ) Fire sprinklers are not installed in laboratorychemical hood exhaust manifolds.

( ) Exhaust systems operate continuously to pro-vide adequate venti lation for any hood at any timeit is in use and to prevent backflow of air into thelaboratory when the fol lowing conditions are pre-sent: Chemicals are present in any hood (openedor unopened), exhaust system operation isrequired to maintain minimum venti lation ratesand room pressure control, there are powered

devices connected to the manifold, and powereddevices include, but are not l imited to: biologicalsafety cabinets, in-l ine scrubbers, motorizeddampers, and booster fans.

( ) Manifolds are maintained under negative pres-sure at al l times and be provided with at least twoexhaust fans for redundant capacity.

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

5.4.4 Fans

( ) Each fan serving a laboratory exhaust systemor to exhaust an individual piece of laboratoryequipment (e.g. , a laboratory chemical hood,biosafety cabinet, chemical storage, etc. ) is ade-quately sized to provide the necessary amount ofexhaust airflow in conjunction with the size,amount, and configuration of the connecting duct-work.

( ) In addition, each fan’s rotational speed andmotor horsepower are sufficient to maintain boththe required exhaust airflow and stack exit veloci-ty and the necessary negative static pressure(suction) in al l parts of the exhaust system.

( ) I f flammable gas, vapor, or combustible dust ispresent in concentrations above 20% of theLower Flammable Limit, fan construction is asrecommended by the most current version ofAMCA’s 99-0401 , Classifications for SparkResistant Construction.

( ) Laboratory exhaust fans are located as fol lows

• Physically outside of the laboratory buildingand preferably on the highest level roof of thebui lding served. (This is the preferred locationsince it generally minimizes risk of personnelcoming into contact with the exhaust airflow.)

• In roof penthouse or a roof mechanical equip-ment room that is always maintained at anegative static pressure with respect to therest of the faci l i ty, and provides direct fan dis-charge into the exhaust stack(s).




1 1 9

( ) Al l laboratory exhaust fans include provisionsto al low periodic shutdown for inspection andmaintenance. Such provisions include:

• Isolation dampers on the inlet side of al l 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 al l central ized exhaust system fansthat discharge into a common exhaust stackor plenum.

• Ready access to al l fans, motors, belts, dri-ves, isolation dampers, associated controlequipment, and the connecting ductwork.

• Sufficient space to al low removal and replace-ment of a fan, i ts motor, and al l other associ-ated exhaust system components and equip-ment without affecting other mechanicalequipment or the need to alter the bui ldingstructure.

5.4.5. Discharge of Contaminated Air

( ) The discharge of potential ly contaminated airthat contains a concentration more than the al low-able breathing air concentration is:

• direct to the atmosphere unless the air istreated to the degree necessary for recircula-tion (see Section 9.3),

• discharged in a manner and location to avoidreentry into the laboratory bui lding or adjacentbuildings at concentrations above 20% ofallowable concentrations inside the laboratoryfor routine emissions or 1 00% of al lowableconcentrations for emergency emissionsunder wind conditions up to the 1 %-windspeed for the site, and in compliance withapplicable federal, state, or local regulationswith respect to air emissions

5.4.6 Exhaust Stack Discharge

( ) The exhaust stack discharge is in accordancewith the current version of ASHRAE Handbook –HVAC Applications, and the chapter or sectiondealing with Building Air Intake and Exhaust

Design.

( ) In any event the discharge is a minimum of 1 0ft (3 m) above adjacent roof l ines and air intakesand in a vertical up direction.

( ) Exhaust stack discharge velocity is at least3000 fpm (1 5.2 m/s) (unless it can be demonstrat-ed that a specific design meets the di lution criterianecessary to reduce the concentration of haz-ardous materials in the exhaust to safe levels (seeSection 2.1 ) at al l potential receptors. )

( ) Esthetic conditions concerning externalappearance do not supersede the requirements ofSections 5.4.5 and 5.4.6.

( ) Any architectural structure that protrudes to aheight close to the stack-top elevation (i .e. , archi-tectural structure to mask unwanted appearanceof stack, penthouses, mechanical equipment,nearby bui ldings, trees or other structures) is eval-uated for i ts effects on re-entrainment.

( ) The air intake or exhaust gri l ls are not locatedwithin the architectural screen or mask unless it isdemonstrated to be acceptable.

5.4.7 Recirculation

( ) Air exhausted from the general laboratoryspace (as distinguished from laboratory chemicalhoods) is not recirculated to other areas unlessone of the fol lowing sets of criteria is met:

3) Criteria A

• The concentration of air contaminants gener-ated by maximum credible accident wil l belower than short-term exposure l imits requiredby 2.1 .1 ;

• There are no extremely dangerous or l i fe-threatening materials used in the laboratory;and

• The system serving the laboratory chemicalhoods is provided with instal led redundancy,emergency power, and other rel iabil ity fea-tures as necessary, or


1 20

4) Criteria B

• Provision of 1 00% outside air, whenever con-tinuous monitoring indicates an alarm condi-tion;

• Recirculated air is treated to reduce contami-nant concentrations to those specified in2.1 .1 ; and recirculated air is monitored contin-uously for contaminant concentrations or pro-vided with a secondary backup air-cleaningdevice that also serves as a monitor (via aHEPA fi l ter in a series with a less efficient fi l -ter, for particulate contamination only; refer toSection 9.3.1 ) and exhaust air from laboratoryhoods shall not be recirculated to other areas.

( ) Hood exhaust meeting the same criteria asnoted in Section 5.4.7.1 is only recirculated to thesame work area where the hood operators havecontrol of the hood work practices and can moni-tor the status of air cleaning.

6. Commissioning and Routine Performance

Testing

6.1 Specifying Laboratory Fume Hood

Performance

( ) Test specifications used for selecting a hood,in commissioning or in routine testing, refer to theapplicable ANSI/ASHRAE 1 1 0 defined perfor-mance tests. or to a test standard recognized tobe equivalent.

( ) Specification and procurement of laboratoryfume hoods are based on “As Manufactured”ANSI/ASHRAE 1 1 0 defined performance testsconducted on a representative hood (or prototypehood) that demonstrate adequate hood contain-ment.

( ) The performance tests to be witnessed, refer-enced or otherwise include:

• airflow visualization tests,

• auxil iary air velocity tests (i f appl icable, )

• cross drafts velocity tests,

• exhaust flow measurements,

• face velocity tests,

• hood static pressure measurement, and

• tracer gas containment tests

( ) The tests are conducted under constant vol-ume conditions where exhaust and air supply floware stable and exhibit no more than 5% variationfrom set-point.

6.1 .1 Performance Tests

( ) The fol lowing performance tests are conduct-ed as indicated and as prescribed in the commis-sioning plan, laboratory venti lation managementplan, or as directed by the responsible person.

6.1 .1 .1 Airflow Visualization Tests

( ) Airflow visualization tests are conducted asdescribed in the ANSI/ASHRAE 1 1 0–1 995,Method of Testing Performance of LaboratoryFume Hoods.

( ) The tests consist of small-volume generationand large-volume generation smoke to identifyareas of reverse flow, stagnation zones, vortexregions, escape, and clearance.

( ) Visible escape beyond the plane of the sashwhen generated 6 in. (1 5.2 cm) into the hood con-stitutes a fai lure during the performance test.

6.1 .1 .2 Auxiliary Air Velocity Tests

( ) For auxi l iary air hoods, the face velocity ismeasured with the auxil iary air turned off unlessroom pressurization would change significantly toaffect exhaust flow. Where exhaust flow would beaffected by turning off the auxil iary airflow, auxil-iary air is redirected from the hood opening so asnot to interfere with flow into the hood while con-ducting the face velocity traverse.

( ) The velocity of the auxi l iary air exiting the aux-i l iary air plenum is measured to determine themagnitude and distribution of air supplied abovethe hood opening.

( ) The average auxil iary air velocity is deter-mined from the average of grid velocities mea-




1 21

sured across the plenum outlet.

6.1 .1 .3 Cross-Draft Velocity Tests

( ) Cross-draft velocity measurements are madewith the sashes open and the velocity probe posi-tioned at several locations near the hood openingto detect potential ly interfering room air currents(cross drafts). Record measurement locations.

( ) Over a period of 1 0–30 sec. , cross-draft veloc-ities are recorded approximately 1 reading persecond using a thermal anemometer with anaccuracy of +5% at 50 fpm (0.25 m/s) or better.

( ) The average and maximum cross-draft veloci-ties at each location are recorded and not be suf-ficient to cause escape from the hood.

( ) Cross draft velocities are not of such magnitudeand direction as to negatively affect containment.

6.1 .1 .4 Exhaust Flow Measurement

( ) The volumetric flow exhausted from a labora-tory fume hood is determined by measuring theflow in the exhaust duct using industry-approvedmethods.

6.1 .1 .5 Face Velocity Tests

( ) Once adequate performance has been estab-l ished for a particular hood at a given benchmarkface velocity using the methods described above,that benchmark face velocity is used as a periodiccheck for continued performance as long as nosubstantive changes have occurred to the hood orother aspects that affect hood performance.

( ) Face velocity measurements are made withthe sash in the Design Sash Position. The DesignSash Position is the maximum opening or configu-ration al lowed by user standards, SOPs, or theChemical Hygiene Plan, whichever is applicable,and used in the design of the exhaust system towhich the hood is connected.

( ) The sash position at which benchmark facevelocity is measured is recorded with the facevelocity measurement and reproduced each time

measurements are taken.

( ) A decrease in the average face velocity below90% of the benchmark velocity is corrected priorto continued hood use.

( ) The average face velocity is determined by themethod described in the current version ofANSI/ASHRAE 1 1 0 Method of TestingPerformance of Laboratory Fume Hoods.

( ) Face velocity measurements are made bydividing the hood opening into equal area gridswith sides measuring no more than 1 2 in. (30.5cm).

( ) The tip of the probe is positioned in the planeof the sash opening and fixed (not handheld) atthe approximate center of each grid.

( ) Grid measurements around the perimeter ofthe hood opening are made at a distance ofapproximately 6 in. (1 5.2 cm) from the top, bot-tom, and sides of the opening enclosure.

( ) The average face velocity is the average of thegrid velocity measurements.

( ) Each grid velocity is the average of at least 1 0measurements made over at least 1 0 seconds.

( ) The plane of the sash is defined as the exteri-or surface of the outer most glass panel.

6.1 .1 .6 Hood Static Pressure Measurement

( ) The hood static pressure is measured abovethe outlet collar of the hood at the flows requiredto achieve the design average face velocity.

6.1 .1 .7 Tracer Gas Containment Tests

( ) Ttracer gas containment tests are conducted asdescribed in the ANSI/ASHRAE 1 1 0–1 995, Methodof Testing Performance of Laboratory Fume Hoods

or by a test recognized to be equivalent.

( ) A control level for 5-minute average tests at


1 22

each location conducted at a generation rate of 6L/m is no greater than 0.05 ppm for "as manufac-tured” tests and 0.1 0 ppm for “as installed” (AM0.05, AI 0.1 ).

( ) Escape of emissions more than the controllevels stated above are acceptable at the discre-tion of the design professional in agreement withthe responsible person (2.4.2).

( ) The “as used” 0.1 0 ppm level or more is at thediscretion of the responsible person (2.3).

( ) Face velocity increases exceeding 20% of thebenchmark are corrected prior to continued use.

6.1 .2 Test Instrumentation

( ) Al l test instrumentation uti l ized for the testsprescribed throughout this section are in goodworking order and have been factory calibratedwithin 1 year of the date of use. (See 8.6.1 AirVelocity, Air Pressure, Temperature and HumidityInstruments)

6.2 Commissioning of Laboratory Ventilation

Systems

6.2.1 Commissioning Process

( ) Al l newly instal led, renovated, or moved hoodsare commissioned to ensure proper operationprior to use by laboratory personnel.

6.2.2 Commissioning Authority

( ) The commissioning process is overseen by aresponsible person or commissioning authority.

6.2.3 Commissioning Plan

( ) A written commissioning plan accompaniesdesign documents and is approved by the com-missioning authority in advance of constructionactivities.

( ) The commissioning plan is available to al lpotential suppliers and contractors prior to bid

along with the other project documents.

( ) A commissioning plan addresses operation ofthe entire ventilation system where the hoods, lab-oratories, and associated exhaust and air supplyventi lation systems are considered subsystems.

( ) The plan includes written procedures to verifyor val idate proper operation of al l system compo-nents and include:

• Laboratory Fume Hood Specification andPerformance Tests

• Preoccupancy Hood and Venti lation SystemCommissioning Tests

• Preoccupancy Laboratory CommissioningTests

6.2.4 Commissioning Documentation

( ) Preliminary and final commissioning docu-ments are issued to the appropriate party(s) bythe Commissioning Authority.

The documents include:

• Commissioning Test Data;

• Copy of Test and Balance Report;

• Design Flow Specifications;

• Laboratory and System Drawings for FinalSystem Design;

• List of Venti lation System Deficiencies uncov-ered and the details of how (and if) they weresatisfactori ly resolved.

( ) Operational deficiencies and other problemsuncovered by the commissioning process arecommunicated to the responsible party (i .e. ,installer, subcontractor, etc. ) for prompt correction.

6.3 Commissioning Fume Hoods and Different

Types of Systems

6.3.1 Laboratory Fume Hoods

( ) I f practical, the exhaust flowrate from hoods




1 23

are tested by measuring the flow in the duct bythe hood throat suction method or by flow meter.

( ) I f flow measurement in the duct is not practi-cal, velocity at the hood face or opening are mea-sured at a sufficient number of points to obtain areal istic average velocity, and multipl ied by theopen area in the plane of the velocity measure-ments to obtain the flowrate.

( ) I f the flowrate is more than 1 0% different fromdesign, corrective actions are taken.

6.3.2 Single Hood CAV Systems

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

• Fan Performance Tests;

• Exhaust Duct Measurements;

• Hood Performance Tests; and

• Hood Monitor Cal ibration.

( ) Fan Performance Tests include measurementof fan speed, fan static pressure, motor speed,and amp draw.

( ) Exhaust duct measurements consist ofexhaust flow measurement and hood static pres-sure measurement.

( ) Hood performance tests consist of testsdescribed in Section 6.1 .2.

( ) The hood monitor is calibrated and adjustedafter hood performance has been determined assatisfactory.

( ) Safe operating points are clearly identified forthe hood user.

6.3.3 Multiple Hood CAV Systems

( ) Commissioning of multiple hood, constant airvolume systems include:

• Fan Performance Tests;

• Verification of proper test, adjustment, andbalance of branch exhaust flow and staticpressures (exhaust flow and static pressurefor each branch shal l be recorded after finalbalancing is complete);

• Hood Performance tests as described abovein Sections 6.1 .2; and

• Hood and System Monitor Calibration.

6.3.4 VAV Laboratory Fume Hood Systems

( ) VAV hood systems are commissioned prior touse by laboratory personnel to ensure that al l sys-tem components function properly and the systemoperates as designed under al l anticipated operat-ing modes (defined under the VAV section).

( ) The commissioning procedures for VAV sys-tems include:

• Verification of VAV Sensor Calibration;

• VAV Hood Performance Tests;

• VAV Laboratory and Venti lation System Tests,and

• Verification of System Diversity.

6.3.4.1 VAV Sensor Calibration

( ) VAV sensors are capable of accurate mea-surement and control within 1 0% of actual at thedesign maximum and minimum flow conditions.

6.3.4.2 VAV Hood Performance Tests

( ) In addition to hood performance testsdescribed for evaluation of CAV hood systems,commissioning tests on VAV hood systemsinclude measurement of flow or face velocities atdifferent sash configurations and VAV Responseand Stabi l ity tests.

( ) Flow or face velocity measurements are con-ducted at a minimum of two separate sash config-urations.

( ) VAV Response and Stabil ity tests include con-tinuous measurements and recording of flow whileopening and closing the sashes for each hood


1 24

(cal ibrated flow sensors or measurement of slotvelocity within the hood can be used as an indica-tor of flow).

( ) VAV Response is sufficient to increase ordecrease flow within 90% of the target flow orface velocity in a manner that does not increasepotential for escape.

6.3.4.3 VAV Ventilation System Tests

( ) The VAV hood controls provide stable controlof flow in the exhaust and supply ducts and varia-tion of flow do not exceed 1 0% from design ateach sash configuration or operating mode.

6.3.4.4 Verification of System Diversity

( ) System diversity is verified prior to use of lab-oratory fume hoods.

( ) The tests are designed to verify that users wil lbe alerted when system capacity is exceeded andunsafe conditions may exist.

( ) VAV Stabil ity is sufficient to prevent flow varia-tions in excess of 1 0% from design at each sashconfiguration or operating mode.

6.3.5 Laboratory Airflow Verification Tests

( ) Tests to verify and commission the laboratoryconsist of:

• Air supply measurements;

• General room exhaust flow measurement (ifapplicable);

• Room differential pressure measurement; and

• Calculation of the difference between totalarea (laboratory, zone, etc. ) supply and totalexhaust.

( ) Al l venti lation system alarm and monitoring pro-visions associated with occupant safety are verifiedfor proper functional ity.

6.3.5.1 CAV Laboratory Room Tests

( ) These tests ensure that the venti lation systemdesign airflow is being maintained within the al low-able tolerance in:

• All hood exhausts;

• All other bench-top and equipment exhaustprovisions that may be present;

• The room general exhaust i f present;

• The room supply; and

• Room air cross currents at the hood faceopening.

( ) I f a specific room differential pressure (dP)has been specified, the dP is measured to ensurethat i t is within i ts al lowable range.

( ) I f a room differential airflow is specified, actualroom differential airflow is determined to ensurethat is within al lowable maximum and minimumlimits and in the proper direction.

( ) I f the room has more than one venti lation con-trol mode (i .e. , occupied/unoccupied, etc. ), eachindividual mode is enabled and applicable para-meters (i .e. , room supply, room total exhaust, etc. )are performed for each separate mode.

( ) Room ambient conditions (temperature,humidity, air currents, etc. ) are also measured toensure they are being maintained under the con-ditions specified

6.3.5.2 VAV Laboratory Room Tests

( ) These tests ensure proper performance of theVAV venti lation system and i ts associated controlssuch that:

• The room general exhaust provides the speci-fied range of airflow.

• The room supply provides the specified rangeof airflow.

• Room air cross currents at the laboratoryhood face opening are within l imits.

( ) I f a specified room dP has been specified, thedP is measured to ensure that i t is being con-trol led within i ts al lowable range with al l doors




1 25

closed and at minimum and maximum roomexhaust airflow.

( ) I f a room differential airflow is specified, actualroom differential airflow is determined to ensurethat i t is within al lowable maximum and minimumlimits and direction at minimum and maximumroom exhaust airflow.

( ) I f the room has more than one venti lation con-trol mode (i .e. , occupied/unoccupied, etc. ) condi-tions are evaluated for each mode.

( ) Room ambient conditions (temperature,humidity, air currents, etc. ) are measured toensure they are being maintained under the con-ditions specified.

( ) VAV systems are capable of maintaining theoffset flow required between exhaust and supplyto achieve the desired area pressurization withinthe desired time specified.

6.4 Ongoing or Routine Hood and System

Tests

( ) Routine performance tests are conducted atleast annually or whenever a significant changehas been made to the operational characteristicsof the hood system.

( ) A hood that is found to be operating with anaverage face velocity more than 1 0% below thedesignated average face velocity is labeled as outof service or restricted use and corrective actionsare taken to increase flow.

( ) Each hood is posted with a notice giving thedate of the routine performance test, and themeasured average face velocity.

( ) I f i t is taken out of service, i t is posted with arestricted use or outof-service notice.

( ) The restricted use notice states the requisiteprecautions concerning the type of materials per-mitted or prohibited for use in the hood.

7 Work Practices

( ) Hood users are trained in the proper operationand use of hood.

( ) The user establishes work practices thatreduce emissions and employee exposures.

( ) The user does not modify the interior or exteri-or components of the hood without the approvalof the Chemical Hygiene Officer, ResponsiblePerson, or other appropriate authority in the orga-nization.

( ) The fol lowing work practices are fol lowedwhen hazardous materials are used in the hood:

( ) The user does not lean into the hood so thathis/her head is inside the plane of the hood, asdefined by the sash, without adequate respiratoryand personal protection.

( ) Equipment and materials are not placed in thehood so that they block the slots or otherwiseinterfere with the smooth flow of air into the hood.

( ) Al l work is conducted at least 6 inches behindthe plane of the sash (hood face).

( ) The horizontal sash or panels are notremoved.

( ) The hood is not operated without the back baf-fles in place.

( ) Flammable l iquids are not stored permanentlyin the hood or the cabinet under the hood unlessthat cabinet meets the requirements of NFPA 30and NFPA 45 for flammable l iquid storage.

( ) The sash or panels are closed to the maxi-mum position possible while sti l l al lowing comfort-able working conditions.

( ) Hood users are trained to close the sash orpanels when the hood is not in use.

( ) The hood user does not operate with thesashes opened beyond the design opening.


1 26

( ) Pedestrian traffic is restricted near operatinghoods.

( ) Rapid movement within the hood is discouraged

( ) The hood is not operated unless it is verifiedthat i t is working.

( ) Rapid movement of the sash or panels is dis-couraged.

( ) 7.1 Each hood is posted with a notice givingthe date of the last periodic field test.

( ) I f the hood fai led the performance test, i t istaken out of service unti l repaired, or a restricteduse notice is posted on the hood.

( ) The notice states the partial ly closed sashposition necessary for safe/normal operation andany other precaution concerning the type of workand materials permitted or prohibited.

( ) 7.2 Hoods are in operation whenever haz-ardous volati le materials are being used or storedinside.

8 Preventive Maintenance

( ) Inspection and maintenance fol low a writtenI&M Program developed by the user.

( ) Preventative maintenance is performed on aregularly scheduled basis.

( ) 8.1 Operations served by equipment being shutdown for inspection or maintenance are safely dis-continued and secured during such maintenance.

( ) Laboratory workers are notified in advance ofinspection and maintenance operations.

( ) 8.2 All toxic or otherwise dangerous materialson or in the vicinity of the subject equipment isremoved or cleaned up before maintenance.

( ) Any hazardous materials and any other debrisare cleaned up before operations resume.

( ) 8.3 Maintenance personnel are trained andrequired to use appropriate PPE during workinvolving potential hazards.

( ) 8.4 A written work permit system is estab-l ished whenever the integrity of a potential ly cont-aminated venti lation system is to be breached.

( ) Such work permits are designed to suit the cir-cumstances, and at least address the fol lowingfactors:

( ) The permit system is overseen by a ResponsiblePerson, as defined in this standard, and is signedby the person(s) to do the work, their supervisor,and any other supervisors affected by the work;

( ) The nature of the work, and the health andsafety precautions, aredescribed;

( ) The time and place of the work are described;

( ) The same persons who signed the permit (ortheir counterparts on a different shift) sign offwhen the work is complete;

( ) Completed work permits are fi led by an appro-priate management function and retained for aminimum of 3 years or as specified by individualorganizational policy.

( ) 8.5 Records are maintained for al l inspectionsand maintenance.

( ) I f testing involves quantitative values, theobserved values are recorded.

( ) Inspection forms designed for the several cat-egories of testing are provided and include thenormal values for the parameters tested.

( ) 8.6.1 Pressure instrumentation and measure-ment are in compliance with ANSI/ASHRAE 41 .3.Temperature instruments and measurement tech-niques are in compliance with ANSI/ASHRAE 41 .1 .

( ) Al l instruments using electrical, electronic, ormechanical components are




1 27

calibrated no longer than 1 2 months before use orafter any possible damage (including impacts withno apparent damage) since the last calibration.

( ) The accuracy of a scale used for a given para-meter meets the fol lowing requirements:

( ) Velocity − fpm Accuracy( ) Below 1 00 (5 m/s) 5 fpm (0.25 m/s)( ) 1 00 (5 m/s) and higher 5% of signal( ) Pressure − in. wg Accuracy( ) 0.1 in. wg (25 Pa) 1 0% of signal( ) 0.5 in. wg (1 25 Pa) and higher 5% of signal( ) Between 25 and 1 25 Pa, interpolate l inearly.( ) Pitot-static tube measurements are in

accordance with ANSI/ASHRAE 41 .7– 1 984 (RA 91 ).

( ) Incl ined manometers are selected so that thenominal value of the measured parameter is atleast 5% of ful l scale. U-tube manometers shouldnot be used for pressures less than 0.5 in. wg.

( ) Pitot tubes other than standard are cal ibrated.

( ) 8.6.2 Air contaminant monitors are tested atleast monthly or more often, i f experience or man-ufacturer¹ s recommendation indicates.

( ) Such testing includes the sensing element, zerodrift, and actuation of signals, alarms, and controls.

( ) Continuous air monitors are calibrated permanufacturer¹ s specifications or more frequently i fexperience dictates.

( ) 8.6.3 Other instruments (such as voltmetersand tachometers) are checked for function andaccuracy against a “known source” before useand fol low manufacturer’s

recommendation, when provided, for periodic cali-bration.

( ) 8.7.1 Fans, blowers, and drive mechanismsare visual ly inspected weekly.

( ) 8.7.2 V-belt drives are stopped and inspectedmonthly for belt tension and signs of belt wear orchecking.

( ) 8.7.3 Blowers, drives, and other criticalmachine elements are lubricated at intervals andwith lubricants recommended by the manufacturer.

( ) 8.8 Venti lation system management planaddresses the need to provide critical serviceissues and keep spare parts on hand.

( ) 8.9 All critical service instrumentation has con-tingency plans in place.

9 Air Cleaning

( ) 9.2 Air-cleaning systems for laboratoryexhaust systems, where required, are designed orspecified by a Responsible Person to ensure thatair-cleaning systems wil l meet the performancecriteria necessary for regulatory compliance.

( ) 9.3 Air-cleaning systems for recirculating gen-eral exhaust or hood exhaust from laboratoriesmeet the design and installation requirements ofANSI/AIHA ® Z9.7.

( ) Recirculation of process air is returned to thesame room where the process is isolated andcontrol of the process is supervised.

( ) 9.3.1 Air-cleaning fi l tration systems for recircu-lating exhaust air contaminated with toxic particu-lates are fi l tered through a two-stage particulatefi l tration system specified as fol lowing the stan-dard performance and design criteria of theASHRAE systems and equipment to meet theobjectives of 2.4.1 .

( ) Fi lter instal lations are tested for leaks andhave al l leaks repaired or the fi l ter

replaced before use.

( ) The flowrate through the fi l ters is maintainedat design specifications and does not exceed1 00% of the rated flow capacity of the fi l ters.

( ) 9.3.2 Adsorption or other fi l tration media usedfor the col lection or retention of gases and vaporsare specified for a l imited use.

( ) Specific hazardous materials to be collected,


1 28

airflow rate, temperature, and other relevant phys-ical properties of the system are incorporated intothe selection of fi l tration media.

( ) A rel iable and adequately sensitive monitoringsystem is uti l ized to indicate adsorbent break-through. The sensitivity of the monitoring systemis a predetermined fraction of the TLV® or appro-priate health standard of the contaminant beingadsorbed but is not more than 25% of the TLV®.

( ) The breakthrough time of the contaminant,before the effluent reaches no more then 50% ofthe TLV®, is sufficient, based upon system capacitydesign to al low a work operation shut down orparallel fi lter switch-over, thus proving a fresh fi l ter.

( ) For toxic gases and vapors, the fi l tration sys-tem is designed and sized to ensure adequatecollection and retention for a worst case scenariowhen in the event of a spil l or other major release.

( ) Adequate warning is provided for personnel tostop work or enact other emergency procedures.

( ) 9.3.3 When required, contaminated fi l ters are

unloaded from the air-cleaning system fol lowingsafe work practices to avoid exposing personnelto hazardous conditions and to ensure propercontainment of the fi l ters for final disposal.

( ) Airflow through the fi l ter housing is shut downduring fi l ter change-out.

( ) 9.4.1 Recirculation air fi l ters are inspected andtested as per Section 9.3.1 except that provisionsare mandatory.

( ) 9.4.2 Activated carbon beds or panels aretested as per Section. 9.3.2 at intervals no longerthan 1 month initial ly and then, based on experi-ence with the particular instal lation, a schedule isprepared.

( ) 9.4.3 Air pollution control equipment is inspect-ed visually at intervals no longer than 1 week and,if necessary, at shorter intervals.

( ) Specific tests and repairs are in accordance withthe manufacturer’srecommendations or are in com-pliance with applicable regulations.Get more FREE standards from Standard Sharing Group and our chats



1 29

APPENDIX 5 Sample Table of Contents for

Laboratory Ventilation Management Plan

Foreword

Purpose

Scope

PART A – Standards and Procedures

Section I Facility Organization

• Roles and Responsibi l i ties

Section II – Characterizing Hazardous Procedures

• Categorizing Laboratory Hazards andProcedures

• Effluent Characteristics

• Hazard Information Summary

Section I II – Selection and Performance

of Hoods

• Laboratory Hoods

° Chemical Fume Hoods

° Biological Safety Cabinets

° Venti lation Balance Enclosures

° Laminar Flow Fume Hoods

° Snorkels

° Canopies

° Venti lation Enclosures

° Gloveboxes

• Minimum Design and Operating Specifications

Section IV – System Design and Operation

• Systems Safety

• Laboratory Design Minimum Specifications

• Laboratory Venti lation Systems MinimumSpecifications

Section V – Operational Tests and

Maintenance

• Recommended Performance Criteria

• Installation and Commissioning Procedures

• Routine Test Procedures

• Maintenance Management Procedures

Section VI – Proper Work Practices

• Personnel Training Programs

• Verifying and Maintaining Work Practices

PART B – Laboratory Hood Systems

Information

Design DrawingsBasis of DesignOperating SpecificationsTAB and Commissioning ReportsTest and Maintenance Data


1 30



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American National Standard for

ANSI/AIHA Z9.5–2012


BY THE ANSI /AIHA Z9.5 SUBCOMMITTEE

Every laboratory wil l beneft from this outl ine of laboratory

venti lation requ irements and practices. Chapters include

performance tests, air cleaning, preventive maintenance,

and work practices. Five appendices covering defnitions,

terms and units are included. Those involved in laboratory

management, including chemical hygiene offcers, campus

and institutional health and safety staff, industrial hygienists,

and environmental health and safety staff wi l l beneft from

th is standard.

STOCK NUMBER: LVEA12 -437

A Publication by


ANSI /AIHA STANDARDS



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