ANSI/AIHA Z9.5–2012
Laboratory
Ventilation
A Publication by
American Industrial Hygiene Association
BY THE
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ANSI/AIHA Z9.5 SUBCOMMITTEE
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ANSI/AIHA® Z9.5–2012
ANSI/AIHA® Z9.5 – 2012
Laboratory Ventilation
Secretariat
American Industrial Hygiene Association
Approved April 26, 2012
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American
National
Standard
Approval of an American National Standard requires verification by ANSI that the
requirements for due process, consensus, and other criteria for approval have been
met by the standard’s developer.
Consensus is established when, in the judgment of the ANSI Board of Standards
Review, substantial agreement has been reached by directly and materially affected
interests. Substantial agreement means much more than a simple majority, but not
necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution.
The use of American National Standards is completely voluntary; their existence
does not in any respect preclude anyone, whether he or she has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processors, or procedures not conforming to the standards.
The American National Standards Institute does not develop standards and will in no
circumstances give an interpretation of any American National Standard. Moreover,
no person shall have the right or authority to issue an interpretation of an American
National Standard in the name of the American National Standards Institute.
Requests for interpretations should be addressed to the secretariat or sponsor
whose name appears on the title page of this standard.
CAUTION NOTICE: This American National Standard may be revised or withdrawn
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action be taken to reaffirm, revise, or withdraw this standard no later than five years
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Published by
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Copyright © 2012 by the American Industrial Hygiene Association
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ISBN 978-1-935082-34-7
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Contents
Page
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
1
Scope, Application and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1. Scope and Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2
Laboratory Ventilation Management Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Chemical Hygiene Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3. Responsible Person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. The Role of Hazard Assessment in Laboratory Ventilation Management . . . 8
2.5. Recordkeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3
Laboratory Fume Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Design and Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Laboratory Fume Hood Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3. Hood Airflow and Monitoring (Design and Performance Specifications) . . . 22
4
Other Containment Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1. Gloveboxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2. Ductless Hoods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3. Special Purpose Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5
Laboratory Ventilation Systems Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.1. Laboratory Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.2. Laboratory Airflow Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3. Supply Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.4. Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
6
Commissioning and Routine Performance Testing . . . . . . . . . . . . . . . . . . . . . . . 65
6.1. Performance specifications, tests, and instrumentation . . . . . . . . . . . . . . . . 65
6.2. Commissioning of Laboratory Ventilation Systems. . . . . . . . . . . . . . . . . . . . 73
6.3. Commissioning Fume Hoods and Different Types of Systems. . . . . . . . . . . 75
6.4. Ongoing or Routine Hood and System Tests . . . . . . . . . . . . . . . . . . . . . . . . 81
7
Work Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.1. General Requirements and Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.2. Posting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.3. Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.4. Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
8
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
8.1. Operations During Maintenance Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . 84
8.2. Housekeeping Before and After Maintenance . . . . . . . . . . . . . . . . . . . . . . . 84
8.3. Safety for Maintenance Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.4. Work Permits and Other Communications . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.5. Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
8.6. Testing and Monitoring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
8.7. Monitoring Fans, Motors, and Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.8. Critical Service Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.9. Critical Service Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
8.10. Performance Monitoring Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9
Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9.1. Supply Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9.2. Exhaust Air Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9.3. Filtration for Recirculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
9.4. Testing and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
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Appendices
Appendix 1 Definitions, Terms, and Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Appendix 2 Referenced Standards and Publications . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Appendix 3 Selecting Laboratory Stack Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Appendix 4 Audit Form for ANSI/AIHA Z9.5-2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Appendix 5 Sample Table of Contents for Laboratory Ventilation
Management Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
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Foreword (This foreword is not part of the American National Standard Z9.5–2012.)
General coverage. This standard describes required and recommended practices for the design and operation of laboratory ventilation systems used for control of exposure to airborne contaminants. It is intended for use by employers, architects, industrial hygienists, safety engineers, Chemical Hygiene Officers,
Environmental Health and Safety Professionals, ventilation system designers, facilities engineers, maintenance personnel, and testing and balance personnel. It is compatible with the ACGIH® Industrial
Ventilation: A Manual of Recommended Practices, ASHRAE ventilation standards, and other recognized
standards of good practice.
HOW TO READ THIS STANDARD. The standard is presented in a two-column format. The left column represents the requirements of the standard as expressed by the use of “shall.” The right column provides description and explanation of the requirements and suggested good practices or
examples as expressed by the use of “should.” Appendices 1 and 2 provide supplementary information on definitions and references. Appendix 3 provides more detailed information on stack
design. Appendix 4 provides a sample audit document and Appendix 5 presents a sample table of
contents for a Laboratory Ventilation Management Plan.
Flexibility. Requirements should be considered minimum criteria and can be adapted to the needs of the
User establishment. It is the intent of the standard to allow and encourage innovation provided the main
objective of the standard, “control of exposure to airborne contaminants,” is met. Demonstrably equal or
better approaches are acceptable. When standard provisions are in conflict, the more stringent applies.
Response and Update. Please contact the standards coordinator at AIHA®, 3141 Fairview Park Drive,
Suite 777, Falls Church, VA 22042, if you have questions, comments, or suggestions. As with all ANSI
standards, this is a “work in progress.” Future versions of the standard will incorporate suggestions and
recommendations submitted by its Users and others.
This standard was processed and approved for submittal to ANSI by the Z9 Accredited Standards
Committee on Health and Safety Standards for Ventilation Systems. Committee approval of the standard
does not necessarily imply that all committee members voted for its approval. At the time it approved this
standard the Z9 Committee had the following members:
Thomas Smith, Chair
Theodore Knutson, Vice Chair
David Hicks, Secretariat Representative
At the time of publication, the Secretariat Representative was David Hicks.
Organization Represented . . . . . . . . . . . . . . . . . . . . . . . .Name of Representative
ACGIH® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G. Knutson
ASHRAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .T. Smith
American Foundry Society . . . . . . . . . . . . . . . . . . . . . . . .R. Scholz
ASSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P. Osley
Global Finishing Solutions . . . . . . . . . . . . . . . . . . . . . . . .G. Raifsnider
National Association of Metal Finishers . . . . . . . . . . . . . .K. Hankinson
NIH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F. Memarzadeh
NIOSH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .M. Elliott
OSHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .L. Hathon
iii
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Individual Members
D.J. Burton
S. Crooks
L. DiBerardinis
C. Figueroa
S. Gunsel
E. Pomer
N. McManus
D. O’Brien
J. Price
K. Paulson
M. Rollins
J. Sheehy
Subcommittee Z9.5 on Laboratory Ventilation, which developed this standard, had the following members:
Steve Crooks, Chair
James Coogan, Vice Chair
L. DiBerardinis
D. Walters (*)
D.J. Burton
D. Hitchings
T.C. Smith
V. Neuman
J.M. Price
G. Knutson
G. Sharp
S. Hauville
R.A. (Bob) Henry
M. Tschida
C.J. McAfee
R.A. DeLuca
P. Pinkston
K. Kretchman
S. Lengerich
P. Carpenter (Technical Resource)
A. Kolesnikov (Observer)
* retired during the standard’s development
* Contributing member of Z9.5 subcommittee but not a voting member of the full Z9 Committee at the time of standard approval.
iv
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AMERICAN NATIONAL STANDARD
ANSI/AIHA Z9.5–2012
American National Standard
for Laboratory Ventilation
Requirements of the Standard
1
Scope, Application and Purpose
1.1
Scope and Application
This standard applies to the ventilation in most laboratories and is written for all laboratory ventilation
stakeholders. An emphasis is placed on those with
legal responsibilities and liability for providing a
safe laboratory. However, users/operators, industrial hygienists, other safety and environmental professionals will also find the standard written for
their needs.
The standard cannot establish strict liability in all
cases but does attempt to fix accountability in many
relationships that exist with its context. Please note
that such relationships are defined throughout the
standard and generally encompass the following:
administration - occupant; employer - employee;
management - staff; owner - occupant; owner - tenant;
teacher - student; designer - owner, etc.
This standard does not apply to the following types
of laboratories or hoods except as it may relate to
general laboratory ventilation:
•
•
•
•
animal facilities,
biosafety cabinets,
explosives laboratories,
high containment facilities (e.g., BSL 3, BSL 4,
facilities operating under “chemical surety
plans,” etc.),
• laminar flow hoods and isolators (e.g., a clean
bench for product protection, not employee
protection), and
• radioisotope laboratories.
General laboratory safety practices are not included except where they may relate to the ventilation
system’s proper function or effectiveness.
Clarification and Explanation of the Requirements
Laboratories conduct teaching, research, quality
control, and related activities and should satisfy
several general objectives, in addition to being suited 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 of
temperature, humidity, and air quality.
Appendix 2 offers several references providing
information, guidelines or specific requirements for
•
•
•
•
laboratory animals – AAALAC,
biosafety cabinets – NSF,
biohazardous materials – ABSA, and CDC,
flammables, pyrophoric and explosives –
NFPA, ISEE, and IMC,
• high containment facilities – CDC, ISPE, and
USAMRICD,
• laminar flow hoods and isolators – NSF and
CETA,
• radioactive materials – NRC, and
• special environmental requirements for product protection such as contamination control
from particulates – CETA and IEST.
This standard does not apply to comfort considerations unless they have an effect on contaminant
control ventilation.
1
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ANSI/AIHA® Z9.5–2012
1.2
Purpose
The primary purpose of this standard is to
establish minimum requirements and best
practices for laboratory ventilation systems to
protect personnel from physical harm and
overexposure to harmful or potentially harmful airborne contaminants generated within
the laboratory. The standard’s requirements
also aim to protect property where relevant.
In light of significant efforts and initiative to
reduce greenhouse gases, the standard also
confronts energy considerations, especially
where there is a potential to impact worker
health and safety.
This standard:
• informs the designer of the requirements
and conflicts among various criteria relative to laboratory ventilation,
• informs the user of information needed
by designers, and
• sets forth ventilation requirements that
will, combined with appropriate work
practices, achieve acceptable concentrations of air contaminants.
Thus, this standard provides insight on how
inadequate ventilation or other ventilation
system deficiencies can impact safety and
containment. However, this standard cannot
provide designers and users with everything
needed for conducting hazard assessments.
Designers and users are thereby cautioned
to not misconstrue the purpose of this standard as addressing comprehensive hazard
control for particular hazards posed by all
operations that may occur in a laboratory
room. See Section 2.4.
Persons responsible for laboratory operations and those
working within laboratories may not be aware of how
ventilation can impact environment, health and safety.
On the other hand, ventilation system design professionals cannot be expected to be fully aware of all the particular hazards posed by every type of operation that
may occur in a laboratory.
2
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ANSI/AIHA® Z9.5–2012
2
Laboratory Ventilation
Management Plan
2.1
General Requirements
Management shall establish a Laboratory
Ventilation Management Plan (LVMP) to
ensure proper selection, operation, use, and
maintenance of laboratory ventilation equipment.
An LVMP shall be implemented to ensure
proper operation of the lab ventilation systems, help protect laboratory personnel working with potentially hazardous airborne materials, provide satisfactory environmental air
quality and maintain efficient operation of the
laboratory ventilation systems.
The LVMP shall provide guidelines and specifications for
• commissioning to verify proper performance prior to occupancy and use of
the laboratory hoods,
• description of training programs for
ensuring proper use, testing and maintenance of the laboratory hoods,
• design of laboratory ventilation systems,
• maintenance procedures for providing
and documenting reliable operation,
• periodic confirmation that the ventilation
system is used properly,
• selection of appropriate laboratory
hoods,
• specification of monitors to continuously
verify proper operation of the laboratory
hoods, and
• standard procedures for routine testing.
Laboratory workers and other building occupants
depend on proper operation of the ventilation systems
to provide safe, comfortable and productive environments for work with hazardous materials. The ventilation systems comprise numerous sub-systems and
individual components including air handling units,
exhaust fans, airflow controls, chemical fume hoods,
biological safety cabinets and other local exhaust
devices. Ensuring safe and efficient operation of laboratory ventilation systems requires careful management of the systems from design to operation.
An LVMP provides the framework for keeping the systems operating to satisfy the primary functional
requirements of building personnel.
Management participation in the selection, design,
and operation of laboratory ventilation systems is critical to the overall success of the effort. The program
should be supported by top management. A sample
Table of Contents for a Laboratory Ventilation
Management Plan is included in Appendix 5.
Management should understand that ventilation equipment is not furniture, but rather it is part of installed
capital equipment. It must be interfaced to the building
ventilation system.
An effective LVMP should satisfy several general
objectives. It should;
• define the responsibilities of departments and
personnel responsible for ensuring proper operation of the systems,
• describe how the systems are to be commissioned, tested and maintained,
• provide a description of the systems and define
the functional requirements,
• provide specifications for design and operation of
the laboratory hood systems, and
• result in safe, dependable and efficient operation
of the laboratory ventilation systems.
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ANSI/AIHA® Z9.5–2012
2.1.1 Exposure Control Devices
Adequate laboratory fume hoods, special
purpose hoods, or other engineering controls
shall be used when there is a possibility of
employee overexposure to air contaminants
generated by a laboratory activity.
There are numerous exposure control devices including:
•
•
•
•
•
biological safety cabinets,
gloveboxes,
aboratory fume hoods,
local exhaust hoods, and
other ventilated enclosures
Exposure control devices are available in a wide variety
of designs with different capabilities and limitations.
Selecting the appropriate exposure control device is
important to ensuring adequate protection for the laboratory worker.
OSHA requires that, employers are responsible for ensuring that exposure control
devices are functioning properly and implementing feasible control measures to reduce
employee exposures if the exposures exceed
the PELs (§29 CFR 1910.1450(e)(3)(iii)).
Furthermore, if an employer discovers
through their hazard assessment efforts or
employee feedback, that exposure control
devices are not effectively reducing employee exposures, it is the employer's responsibility to adjust controls or replace engineering controls as necessary.
OSHA does not promulgate specific control device testing protocols
The capture and/or containment of the
selected exposure control device shall be
considered adequate if, in combination with
prudent practice, laboratory worker exposure
levels are maintained below published or inhouse exposure limits or below those limits
identified in applying or using published
exposure limits.
If exposure limits [e.g., Occupational Safety and Health
Administration Permissible Exposure Limits (OSHA
PELs), National Institute for Occupational Safety and
Health Recommended Exposure Limits (OSHA RELs),
American Conference of Governmental Industrial
Hygienists threshold limit values (ACGIH® TLVs® ),
American Industrial Hygiene Association Workplace
Environmental Exposure Limits (AIHA® WEELs®),
German MAKs, (maximum admissible concentrations)]
or similar limits used in prescribing and/or assessing safe
handling do not exist for chemicals used in the laboratory, the employers should establish comparable in-house
guidelines. Qualified industrial hygienists and toxicologists working in conjunction may be best suited to
accomplish this need.
OSHA specifically states the following
requirements in regards to employee exposure monitoring:
1910.1450(d) Employee exposure determination
The performance of an exposure control device is ultimately determined by its ability to control exposure to
within applicable standards or other safe limits.
1910.1450(d)(1) Initial monitoring.
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ANSI/AIHA® Z9.5–2012
The employer shall measure the employee's
exposure to any substance regulated by a
standard which requires monitoring if there
is reason to believe that exposure levels for
that substance routinely exceed the action
level (or in the absence of an action level, the
PEL).
1910.1450(d)(2) Periodic monitoring.
If the initial monitoring prescribed by paragraph (d)(1) of this section discloses
employee exposure over the action level (or
in the absence of an action level, the PEL),
the employer shall immediately comply with
the exposure monitoring provisions of the
relevant standard.
1910.1450(d)(3) Termination of monitoring.
Monitoring may be terminated in accordance
with the relevant standard.
1910.1450(d)(4) Employee notification of
monitoring results. The employer shall, within 15 working days after the receipt of any
monitoring results, notify the employee of
these results in writing either individually or
by posting results in an appropriate location
that is accessible to employees.
Section 8.C.5 Testing and Verification of Prudent
Practices in the Laboratory:
Handling and Disposal of Chemicals, 1995 states the following with regards to exposure monitoring for fume hood
users. “Perhaps the most meaningful method for evaluating hood performance is to measure worker exposure
while the exposure control device is being used for its
intended purpose. Where exposure limits and analytical
methods exist, personal air-sampling devices can be
worn by the user and worker exposure (both excursion
peak and time-weighted average) can be measured
using standard industrial hygiene techniques. The criterion for evaluating the device should be the desired performance (i.e., does the device contain chemical at the
desired worker-exposure level?). A sufficient number of
measurements should be made to define a statistically
significant maximum exposure based on worst-case
operating conditions. Direct-reading instruments are
available for determining the short-term concentration
excursions that may occur in laboratory hood use.”
Measuring for an “overexposure” to chemicals implies a
means of defining an unsafe limit and having an analytical means of determining when such limit is exceeded.
Since neither are commonplace or practical, surrogates
have been useful in empirical determinations. However, if
an employee believes that he or she is overexposed to
hazardous chemicals despite their use of an exposure
control device, he or she should have an internal mechanism for resolving their concern (e.g., informing a supervisor). OSHA requires that any such employee is provided an opportunity to receive an appropriate medical
examination. Other similar occurrences make it incumbent on the employer to protect the employee and ensure
adequate control measures (§29 CFR 1910.1450(g)(1)(iiii). In the event an employer remains unresponsive to an
employee’s complaint, the employee would be encouraged to seek other advice or external intervention (e.g.,
filing a complaint with OSHA.)
In the European Union (EU,) Registration, Evaluation,
Authorization and Restriction of Chemicals (REACH) is in
effect and should be consulted as appropriate for hazard
evaluation information impacting laboratories operating
within the scope of this standard.
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ANSI/AIHA® Z9.5–2012
Chemical “hazard determination” shall be conducted by chemical manufacturers and importers as
required by the Occupational Safety and Health
Administration's (OSHA) Hazard Communication
standard, specifically, 29 CFR 1910.1200(d). This
requires that manufacturers and importers of chemicals to identify chemical hazards so that employees
and downstream users can be informed about these
hazards.
2.1.2
Laboratory (Room) Ventilation Rate
The specific room ventilation rate shall be established or agreed upon by the owner or his or her
designee.
Ventilation is a tool for controlling exposure.
Contaminants should be controlled at the source.
Potential sources should be identified and exposure control devices should be specified as
appropriate to control emissions at the source.
(See Sections 3 and 4) All sources and assumptions should be clearly defined and documented.
An air exchange rate (air changes per hour) cannot be specified that will meet all conditions.
Furthermore, air changes per hour is not the
appropriate concept for designing contaminant
control systems.
Excessive airflow with no demonstrable safety
benefit other than meeting an arbitrary air change
rate can waste considerable energy.
2.1.3
Dilution Ventilation
Dilution ventilation shall be provided to control the
buildup of fugitive emissions and odors in the laboratory. The dilution rate shall be expressed in terms
of exhaust flow in negatively pressurized laboratories and supply flow in positively pressurized laboratories.
Control of hazardous chemicals by dilution alone,
in the absence of adequate laboratory fume
hoods, is seldom effective in protecting laboratory
users. It is almost always preferable to capture
contaminants at the source, than attempt to displace or dilute them by room ventilation.
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Nevertheless, dilution or displacement may remove
contaminants not captured by a specifically applied
device.
The quantity of dilution (or displacement) ventilation
required is a subject of controversy. Typical dilution ventilation rates can range from 4 to 10 air changes per
hour depending on heating, cooling, and comfort needs
and the number and size of exposure control devices.
2.2
Chemical Hygiene Plan
The laboratory shall develop a Chemical
Hygiene Plan according to the OSHA
Laboratory Standard (29 CFR 1910.1450).
Although some laboratories do not fall under the OSHA
Standard, a Chemical Hygiene Plan or Laboratory
Safety Standards (or manual) can establish proper
work practices.
Persons participating in writing the plan should be
knowledgeable in industrial hygiene, laboratory procedures and chemicals, the design of the ventilation systems, and the system’s maintenance needs. The plan
should be disseminated and become the basis for
employee training.
The plan shall address the laboratory operations and procedures that might generate air
contamination in excess of the requirements
of Section 2.1.2. These operations shall be
performed inside exposure control devices
adequate to attain compliance.
In the event of large accidental releases in the laboratory room, away from exhausts and control systems,
the laboratory owner should specify appropriate evacuation protocols. The plan may also include emergency
ventilation modes. (See Section 5.2.3.)
The plan shall address emergencies and accidents, as well as ordinary operation.
2.3
Responsible Person
In each operation using laboratory ventilation
systems, the user shall designate a “responsible person.”
The responsible person may have the following duties:
• Ensuring that existing conditions and equipment
comply with applicable standards and codes,
• Ensuring that testing and monitoring are done on
schedule,
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• Maintaining adequate records,
• Participating in the design (new construction or
renovation) of the lab at the conception/ planning
stage (preferably as an IH or EHS professional
with laboratory ventilation experience),
• Performing visual checks,
• Training employees, and
• Performing any other related task assigned by the
employer.
At a minimum, the responsible person should coordinate the above activities.
2.4
The Role of Hazard Assessment in
Laboratory Ventilation Management
2.4.1
General Requirements
Employers shall ensure the existence of an
ongoing system for assessing the potential for
hazardous chemical exposure.
Much of this standard addresses a generic approach
to exposure control. This is necessary because many
of the chemical hazards in a laboratory are chronic in
nature and an employee's ability to sense overexposure is subjective.
Employers shall promote awareness that laboratory hoods are not appropriate control
devices for all potential chemical releases in
laboratory work.
The practical limits of knowing how each exposure control device is being or may be used
shall be considered when specifying design
features, performance criteria (commissioning
and routine monitoring), or when seeking energy savings. The responsible person as defined
in Section 2.3 shall be consulted in making this
judgment.
Exposure control devices shall be functioning
properly and specific measures shall be taken
to ensure proper and adequate performance
(refer to Section 2.1.1).
The employer may determine that providing standard
laboratory hoods tested to the ANSI/ASHRAE 110
standard and an “as installed” AI 0.1 rating are best
for the types of chemical hazards and work being
performed at the specific workplace. The assumption
that follows is that users are trained to understand
limitations of the hood's control ability and would not
use it for work that, for example, should be performed
in a glovebox. Alternatively, ensuring all hoods are
capable of meeting an AI 0.1 rating may not be necessary, for example, if the only chemical being handled has an 8-hr time-weighted average (TWA) –
TLV® exposure limit of 250 ppm.
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The following briefly describes an approach used
within laboratory ventilation management programs in
assigning control measures given the ability (or inability) to assess specific day-to-day chemical exposure
situations.
Hazard assessments in general are geared toward
identifying chemicals, their release potential (source),
their transmission route (path), and their possible
routes of entry into the body (receiver). It is critical
that assessments be conducted in a competent manner such that the source-path-receiver “picture” is not
misconstrued.
The employer shall establish criteria for determining and implementing control measures to
reduce employee exposure to hazardous
chemicals. Particular attention shall be given
to the selection of control measures for chemicals that are known to be extremely hazardous.
Hazard assessments may incorporate results from
tracer gas testing of engineering controls (example:
ANSI/ASHRAE 110 fume hood testing) and transmission routes (example: exhaust reentry into building
supply systems).
The first step in the assessment is to identify what
chemical(s) can be released including normally
uncharacterized byproducts. After characterizing the
inherent hazard potential (largely based on physical
properties, toxicity, and routes of entry), the next step
is to ascertain at least qualitatively, the release "picture." At what points within the "control zone" will
chemicals be evolved and at what release rate? Will
the chemical release have velocity? How has the
maximum credible accidental release been accounted
for? Finally, how many employees are/could be
exposed and what means are available for emergency
response?
Due to the high cost of ventilation, the choice of hood
and specification of airflow rates should be scrutinized
to ensure adequate protection at minimum flow.
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2.4.2
“Programming” and Control
Objectives for New Construction,
Renovation, or Program Evaluation
The following items shall be considered and
decisions made regarding each element's relevance following the hazard assessment
process:
•
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Acceptable exposure concentrations
Adequate workspace,
Air cleaning (exhaust pollution controls),
Air supply diffusers and discharge temperature,
Alarm system (local and central monitoring),
Commissioning (level of formality to be
applied),
Containment (tracer gas containment
"pass" criteria – e.g., AI 0.5, AI 0.1, AI
0.05, etc.),
Decommissioning,
Design sash opening and sash configuration (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 chemical
hood systems,
Exhaust discharge (stack design) and
dilution factors,
Face velocity for laboratory chemical
hoods,
Fan selection,
Frequency of routine performance tests,
Hood location,
Manifold or individual systems,
Redundancy and emergency power,
Recirculation of potentially contaminated
air,
Preventive maintenance, and
Vendor qualification.
Programming is a term commonly used in the context of
a construction project whereby the needs of a user
group are developed into the intended deliverables of
the project. The idea here is that various scientific disciplines have different needs in terms of ventilation.
Sets of design "templates" exist based on various types
of laboratories. While the characterization of laboratories by "organic chemistry, analytical chemistry, biology,
etc.," are generically understood by most designers,
knowledge of the chemistry and biology and, therefore,
potential hazards, are generally beyond the knowledge
base of most designers.
The overall goal of providing a safe workspace for the
end users can be greatly enhanced by the use of a hazard assessment and system design team.
Quality of system design and quality of performance
are enhanced by utilizing the most appropriate skills
and resources available to an organization. The
Laboratory Ventilation Management Plan should
describe specific responsibilities for each department
involved in the design, installation, operation, and use
of ventilation systems (Table 1 provides some guidance.)
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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, install, commission,
maintain and use exposure control devices and ventilation 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 potentially hazardous materials.
• Provide information on procedures, work habits, duration of use,
changes in hazardous operations and materials, etc.
• Utilize laboratory hoods in accordance with operating requirements and
safety guidelines.
• Work with Environmental Health and Safety to ensure appropriate
safety systems.
Environment Health and
Safety
Engineering
Maintenance
Purchasing
Space Planning
•
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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.
• Analyze design options in consideration of hazard assessment findings.
• Ensure system capability to provide safe, dependable and efficient
operation.
• Ensure proper design, installation, and commissioning of systems.
• Maintain up-to-date system documentation.
• Conduct preventive maintenance and repair.
• Ensure proper functioning of systems.
• Ensure system dependability.
• Ensure equipment is not purchased without EHS approval.
• Ensure safety and engineering issues are considered in any space
allocation 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 maintained for each laboratory ventilation system.
Only permanent records will allow a history of the system to be maintained.
Records shall include:
Records should be maintained to establish a performance history of the system that can be used to optimize operation. Records should be kept for at least the
life of the system or until the system is altered.
• As-built 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 Ventilation
Management Plan.
3
Laboratory Fume Hoods
A laboratory fume hood is a box-like structure with typically one open side, intended for placement on a table,
bench, or floor. The bench and the hood may be one
integral structure. The open side is provided with a
sash or sashes that move vertically and/or horizontally
to close the opening. Provisions are made for exhausting air from the top or back of the hood and adjustable
or fixed internal baffles are usually provided to obtain
proper airflow distribution across the open face.
Other terms used for a fume hood include laboratory
hood, laboratory chemical hood, and fume cupboard.
Although not technically correct, the term fume, as
used today and historically in the context of defining
fume hoods; includes both gases (vapors) and
aerosols (i.e. particulates, mists, fumes, smoke, etc.).
Laboratory fume hoods are often appropriate for
aerosol applications. However, because of the internal
turbulence, particulates, mists, etc., can deposit on the
interior surfaces. For certain applications, this may preclude the use of a fume hood.
Fume hoods have been a major tool in laboratory ventilation. However, a fume hood is not universally applicable to all situations. In many cases, an enclosing hood
(e.g., glovebox, biosafety cabinet, ventilated enclosure)
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or a local exhaust hood (snorkel, tight fitting canopy
hood, or specially designed hood) may provide as good
or better control and require less volumetric flow.
3.1
Design and Construction
The design and construction of laboratory
fume hoods shall conform to the applicable
guidelines presented in the latest edition of
ACGIH® Industrial Ventilation: A Manual of
Recommended Practice for Design, and the
most current codes, guidelines, and standards
and any other applicable regulations and recommendations (see Appendix 2).
It is the intent of the standard to establish design parameters and performance criteria without limiting new
and innovative designs.
Although construction varies among models and manufacturers, the following are recognized as good design
features:
• Airfoils or other designs that reduce leakage and
airflow eddies at the front edge of the work area
should be provided at the front edge of the bench.
Airfoils should not interfere with the hood’s ability
to meet the criteria of performance testing defined
in this standard.
• Airfoils, beveled edges or other sidewall design
that reduces leakage and airflow eddies at the
side walls should be provided at the side posts.
• Baffle design should provide for the capture of
materials generated within the hood and distribute
flow through the opening to minimize potential for
escape.
• Cupsinks should be protected by having a vertical
lip around the sink’s circumference of at least ¼ in.
(0.635 cm) or eliminated if not needed.
• Utilities (e.g., valves and switches) should be
located at readily accessible locations outside the
hood. If additional utilities are required, other than
electrical, they may be located inside the hood
provided they have outside cutoffs and can be
connected and operated without potentially subjecting the hood operator to exposure from materials in the hood or other unsafe conditions.
• Work surfaces should be recessed at least ¼ in.
(0.635 cm) below the front edge of the bench or
surface; sides and back should be provided with a
seamless vertical lip at least ¼ in. (0.635 cm) high
to contain spills. However, excessively deep
recesses can increase the turbulence at the work
surface and induce reverse flow.
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3.1.1
Sashes
The laboratory fume hood shall be equipped with
a safety-viewing sash at the face opening.
Typical sashes available include the following:
• Combination vertical raising and horizontal
sliding sashes,
• Horizontal sliding sashes, and
• Vertical raising sash or sashes.
Refer to Figure 1 for diagrams of different sash configurations.
Sashes shall not be removed when the hood is in
use.
Sashes should be constructed of transparent shatterproof material suitable for the intended use. The
force to open the sash shall be reasonable for the
size and weight of the sash. Typically, a five foot
hood with a vertical rising sash should require
approximately five pounds of force to operate the
sash. An additional one pound of force may be
required for each additional linear foot of fume hood
width. The sash should remain stationary when
force is removed unless automatic closing to the
designed operating sash opening is required.
3.1.1.1 Design Opening
The design opening of a laboratory hood is the
open area at the face of the hood, which the
design team assumed when determining the ventilation requirements of the exhaust system.
Where the design sash opening area is less than
the maximum sash opening area, the hood shall
be equipped with a mechanical sash stop. A
means of communicating when openings are in
excess of the design sash opening area shall be
provided.
The Chemical Hygiene Plan shall clearly instruct
the hood users to position the sash so that the
opening is no greater than the design opening
while using the hood for protection.
Sash-limiting devices (stops) shall not be
removed without resizing or redesigning the
exhaust system if the design opening is less than
full opening.
The responsible person, or the design team, should
determine the design opening of the hood and the
position of the sash-limiting device based on the
needs of the hood user. Operating the hood with a
larger opening than the design opening results in a
reduced capture velocity (face velocity) and may
significantly and adversely affect the performance
of the hood. Administrative controls, training,
mechanical sash stops, alarms or other means are
important for ensuring that the fume hoods and
exhaust systems can provide the protection for
which they were designed. Operating the sash at an
incorrect position can jeopardize the protection otherwise afforded the hood users and those in the
adjacent area.
The Chemical Hygiene Plan should indicate the
proper circumstances for overriding the sash stop.
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3.1.1.2 Vertical Sashes
Vertical sashes shall be designed and
operated so as not to be opened more than
the design opening when hazardous materials are being used within the hood
The vertical raising sash can usually be opened for fullface opening in the open position. If this is greater than the
design opening, control at the full open position may be
compromised.
3.1.1.3 Horizontal Sashes
Horizontal sashes shall be designed so as
not to be opened more than the design
opening width when hazardous materials
are being generated in the hood.
The horizontal sash should be designed to allow free
movement of the sash. Accumulation of debris or other
materials in the sash track can impede movement. The
sash track can be designed to minimize this potential by
hanging the sash from overhead. In any event, periodic
maintenance is recommended to ensure proper sash management.
If three or more sash panels are provided, one panel
should be no more than 14 in (35 cm) wide if it is to serve
as a safety shield narrow enough for a person to reach
around to manipulate equipment.
Caution is advised when using a horizontal panel as a
shield in front of the hood operator as high concentrations
can accumulate behind the sash panel and escape along
the Users’ arms protruding through the opening or escape
when their arms are withdrawn.
3.1.1.4 Combination Sashes
If a combination sash provides horizontally
moving panels mounted in a frame that
moves vertically, the above requirements in
Sections 3.1.1.2 to 3.1.1.3 shall apply.
A combination sash has the advantages and disadvantages of both types of sashes. The combination vertical
raising and horizontal sliding sash, commonly referred to
as a combination sash, is a combination of the vertical
sash described in Section 3.1.1.2 and horizontal sash in
Section 3.1.1.3. The combination sash may be raised to full
vertical sash opening. In the closed vertical position, the
horizontal sliding panels can be opened to provide access
to the interior hood chamber. Care should be taken in
determining the design opening of a combination sash.
Remember to include the area beneath the airfoil sill and
through the bypass if one exists.
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3.1.1.5 Automatic Sash Closers
All users shall be trained in good work practices, including the need to close the sash
when not in use.
All users of VAV systems shall be trained in
the proper uses of the sash, the energy consequences of improper use, and the need to
close the sash when the operation does not
require its use.
Automatic sash positioning systems shall have
obstruction sensing capable of stopping travel
during sash closing operations without breaking glassware, etc.
3.2
Laboratory Fume Hood Types
3.2.1
Auxiliary Supplied Air Hoods
Auxiliary air hoods have a portion of the total
volume of exhausted air provided through a
plenum located above and outside of the hood
Face.
Auxiliary air hoods shall meet the requirements in Section 3.3.
The supply plenum shall be located externally
and above the top of the hood face.
The auxiliary air shall be released outside the
hood.
The supply jet shall be distributed so as not to
affect containment adversely.
The auxiliary air shall not disrupt hood containment or increase potential for escape.
Good work practice and energy stewardship (for VAV
systems) requires the user to close the sash when the
hood is not in use. A well implemented chemical
hygiene plan and proper administrative actions can
ensure that the sash is properly positioned. Monitoring
of user compliance may be possible with some VAV
systems where the Building Automation System allows
trending of the sash position and feedback to management (and subsequently to the user.)
If the user feels it is his/her responsibility to close the
sash and the culture is that they do close the sash, then
an automatic sash closer may not be necessary. On the
other hand, if the user does not close the sash and management tolerates this non-compliance, safety could be
jeopardized, energy consumption may increase and an
automatic sash closer may be advantageous.
With or without automatic closers, users should understand the importance of the closed sash, and integrate
proper sash operation into work procedures.
Auxiliary supplied air hoods are not recommended
unless special energy conditions or design circumstances exist. The information in this section is provided
because many auxiliary air hoods are currently in use.
The intent is not to discourage innovative design but
current experience indicates these requirements are
necessary.
The rationale for using auxiliary supplied air hoods is
that auxiliary air need not be conditioned as much (i.e.,
temperature, humidity) as room supply air, and that
energy cost savings may offset the increased cost of
installation, operation, and maintenance. However, if
not all the air from the auxiliary plenum is captured at
the hood face, the anticipated energy savings is not
realized. With respect to temperature and humidity,
workers may experience discomfort if it is necessary to
spend appreciable time at the hood.
If auxiliary air hoods are designed and operated properly, worker protection at the face may be enhanced
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Figure 1 — Diagrams of different sash opening configurations.
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because the downward airflow at the breathing zone suppresses body vortices. However, if the design and operation are improper, contamination control may be compromised. In addition, the air quality and condition inside the
hood may be significantly different from the room air and
these conditions may compromise the work conducted
inside the hood.
For retrofit projects, auxiliary air may be installed more
cheaply with less disruption than by upgrading the main
air supply system. If auxiliary air is conditioned to the
same extent as room air, most of the potential energy
advantages are lost while the disadvantages remain and
the total system becomes more expensive to install, operate, and maintain.
With a worker (or reasonable proportioned manikin) at the
full open hood face, the hood should capture more than
90% of the auxiliary jet airflow when either the auxiliary
air is at least 20°F (-6.7°C) warmer or cooler than room
air. This does not apply if the auxiliary air is designed to
be conditioned the same as room air.
3.2.2
Bypass Hoods
Bypass hoods have a route for air entering
the hood (the bypass mechanism) which
opens as the sash closes.
Bypass hoods shall meet the requirements
in Section 3.3.
The bypass mechanism shall be designed
to minimize potential ejection of liquid or
solid material outside the hood in the event
of an eruption inside the hood.
Bypass mechanisms should be designed so the bypass
opens progressively and proportionally as the sash travels to the full closed position. The face velocity at the hood
opening should not exceed three times the nominal face
velocity with the sash fully open. Excessive velocities,
greater than 300 fpm (1.5 m/s), can disrupt equipment,
materials, or operations in the hood possibly creating a
hazardous condition.
The hood exhaust volume should remain essentially
unchanged (<5% change) while the sash moves through
its range of opening and closing. This is important to the
design of the exhaust system.
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3.2.3 Conventional Hoods
Conventional hoods shall meet the requirements in Section 3.3.
Conventional hoods have the hood exhaust volume
remain nearly unchanged as the sash position varies
from full open to the closed position.
However, as the sash is lowered, the face velocity will
increase. In the fully closed position, airflow would be
through the airfoil only. With the sash partially open, the
hood will have very high face velocity.
3.2.4
Floor-Mounted Hoods
Floor-mounted hoods shall meet the requirements in Section 3.3.
Floor-mounted hoods are used when the vertical working space of a bench hood is inadequate for the work
or apparatus to be contained in the hood.
The base of the hood should provide for the containment of spills by means of a base contiguous with the
sidewalls, and a vertical lip sufficient to contain spills
inside the hood, often at least 1 in. (2.54 cm) or equivalent. The lip can be replaced by a ramp to allow
wheeled carts to enter the hood. The hood should be
furnished with distribution ductwork or interior baffles to
provide uniform face velocity.
Doors and panels on the lower portion should be capable of being opened for the installation of apparatus.
If the lower doors are kept closed during operation, the
hood and exhaust system design and operation may be
similar to a bench top laboratory fume hood and the
effectiveness of the control should be equivalent if all the
provisions of Section 3.3 are implemented. However, in
many floor-mounted hoods, the closed lower sash may
cause significant turbulence and the hood may not perform as well as a bench-top hood.
If the lower panels are opened during operations, the
hood loses much of its effectiveness, even if face velocities comply with Section 3.3.
The design and task-specific applications of floor
mounted (walk-in) hoods may make it difficult to comply
with the work practices of Section 7 of this standard.
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Hence, consideration should be given to preparation
and implementation of written standard operating procedures (SOPs) for use of floor-mounted hoods. For
example, if manipulations below waist height are necessary, special provisions may be necessary such as
armports or small openings strategically located at necessary access points.
Small rooms with one wall constituting a supply plenum
and the opposite wall constituting an exhaust plenum
should not be called a floor-mounted hood. In such
instances, workers are intended to be inside the hood
and exposure control provisions are drastically different. This standard does not apply to such rooms.
3.2.5
Perchloric Acid Hoods
Perchloric acid hoods are specifically designed
to safely handle certain types of perchloric
acid work and shall be used for such work.
Perchloric acid hoods shall be used for handling anhydrous perchloric acid (> 85% concentration.)
Perchloric acid is a strong acid, distinguished by the
fact that it is the only mineral acid that is not constituted as a gas dissolved in water. As a result, the vapor
phase above a solution of perchloric acid is devoid of
perchlorate at temperatures below about 150°C. Its oxidation power is readily controlled by management of
concentration and temperature, factors conducive to its
use both as a process reagent and a catalyst.
Perchloric acid digestions and other procedures performed at elevated temperatures should be done in
perchloric acid hoods.
Aqueous solutions of perchloric acid – The vapor pressure of 72% perchloric acid at 25°C is 6.8 mm Hg. For
comparison sake, the vapor pressure of 70% nitric
acid, a more widely used acid, is 49 mm Hg at 20°C.
This simply means that the nitric acid would evaporate
faster. When a bottle of 70% perchloric acid is merely
opened, it cannot evaporate quantities presenting a
risk of making contact with incompatible organic compounds.
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All procedures conducted in a perchloric acid
hood shall be reviewed by the responsible person
and immediate supervisor.
All procedures using a perchloric acid hood shall
be performed by trained personnel, knowledgeable and informed about the hazards and properties of these substances, provided with appropriate protective equipment after suitable emergency contingency plans are in place.
The process of diluting 60–70% perchloric acid or
handling dilute aqueous solutions of perchloric acid
at room temperature presents little hazard of accumulating pure perchloric acid in hood ducts.
The institutional/corporate responsible person (e.g.,
Safety Officer/Chemical Hygiene Officer) should be
notified before procedures requiring a perchloric
acid hood are performed.
The design of a perchloric acid hood shall
include:
• All inside hood surfaces shall use materials
that will be stable and not react with perchloric acid to form corrosive, flammable, and/or
explosive compounds or byproducts.
• All interior hood, duct, fan, and stack surfaces shall be equipped with water washdown capabilities.
• All ductwork shall be constructed of materials that will be stable to and not react with
perchloric acid and/or its byproducts and will
have smooth cleanable seamless joints.
• No part of the system shall be manifolded or
joined to non-perchloric acid exhaust systems.
• No organic materials, including gaskets, shall
be used in the hood construction unless they
are known not to react with perchloric acid
and/or its byproducts.
• Perchloric acid hoods shall be prominently
labeled “Perchloric Acid Hood, Organic
Chemicals Prohibited.”
Perchloric acid hoods shall be periodically
washed down thoroughly with water to remove all
residues in the hood, duct system, fan, and stack.
The complications of wash-down features and corrosion resistance of the exhaust fan might be
avoided by using an air ejector, with the supplier
blower located so it is not exposed to perchloric
acid.
The frequency of wash down depends on the procedures inside the hood. Many procedures require
daily wash down
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3.2.6
Variable Air Volume (VAV) Hoods
VAV hoods shall meet the requirements in
Section 3.3
Variable exhaust flow from a laboratory hood
has implications for room ventilation which shall
be addressed according to Section 5.
Additional commissioning requirements are necessary for these systems (See Section 6).
The VAV hood is a conventional hood equipped with
a VAV control system so designed that the exhaust
volume is varied in proportion to the opening of the
hood face.
VAV controls applied to by-pass hoods have been
noted in many facilities. These situations appear to be
design errors as VAV controls applied to by-pass
hoods largely defeats the purpose.
It is recommended that VAV hoods be equipped with
emergency overrides that permit full design flow even
when the sash is closed.
3.3
Hood Airflow and Monitoring (Design
and Performance Specifications)
3.3.1
Face Velocity
The average face velocity of the hood shall be
sufficient to contain the hazardous chemicals for
which the hood was selected by following guidance in Section 2.4 and as generated under asused conditions.
An adequate face velocity is necessary but is not
the only criterion to achieve acceptable performance and shall not be used as the only performance indicator.
Hood containment shall be verified as appropriate for the hazard being controlled (See Section
2.1.1).
Face velocity had been used historically as the primary indicator of laboratory hood performance for several decades. However, studies involving large populations of laboratory fume hoods tested using a containment-based test like the ANSI/ASHRAE Standard
110, “Method of Testing the Performance of
Laboratory Fume Hoods,” reveal that face velocity
alone is an inadequate indicator of hood performance.
In one published study, approximately 17% of the
hoods tested using the method had "acceptable" face
velocities in the range of 80–120 fpm, but "failed" the
tracer gas containment test with control levels
exceeding a control level of 0.1 ppm. Some of these
tests were “As Installed” while others were “As Used.”
See Section 6 on commissioning and routine performance testing for additional information.
Exposure assessments involve industrial hygiene
measurement of actual exposure potential to chemicals being worked with. This is accomplished through
air sampling in the breathing-zone of hood user.
Design face velocities for laboratory fume hoods in the
range of 80 –100 fpm (0.40 – 0.50 m/s) will provide
adequate face velocity for a majority of fume hoods.
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Factors including the design of the hood, the laboratory layout, and cross-drafts created by supply air and
traffic all influence hood performance as much as or
more than the face velocity.
Tracer gas containment testing is a reliable method for
evaluating hood containment and is recommended in
commissioning or in further applications as needed.
Most tracer gas containment test methods, including
the ANSI/ASHRAE 110 “Method of Testing
Performance of Laboratory Fume Hoods” have certain
limitations that must be observed. The ANSI/ASHRAE
110 method is a static test, under controlled conditions,
and at low face velocities [<60 fpm (0.30 m/s)] may not
adequately reflect containment under dynamic (realworld) conditions as room and operator dynamics have
significant effect on containment at these low face
velocities.
Hoods with excellent containment characteristics may
operate adequately below 80 fpm (0.40 m/s) while others may require higher face velocities. It is therefore
inappropriate to prescribe a range of acceptable face
velocities for all hoods.
Face velocity can be divided into ranges with differing
characteristics as shown below:
Containment must be verified quantitatively in
this range and compliance with use restrictions, etc. enforced.
Room and operator dynamics have significant effect on
hood performance at low face velocities. Therefore, it is
important to understand the effects of dynamic challenges on hood performance so that standard operating procedures and user restrictions can be established. Operating a hood below 60 fpm (0.30 m/s) is not
recommended since containment cannot be reliably
quantified at low velocities and significant risk of exposure may be present.
60–80 fpm (0.30–0.40 m/s): Hoods with excellent containment characteristics operating under relatively
ideal environmental conditions (i.e., room design characteristics) and with prudent operating practices can
provide adequate containment in this velocity range
although at an increased level of risk. Effective administrative controls should be in place.
80–100 fpm (0.40–0.50 m/s): Most hoods can be operated effectively with relatively low risk in this velocity range
although containment should still be quantitatively
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verified. Proper operator training and enforcement of
administrative controls are still highly recommended.
This is the range recommended for a majority of laboratory fume hoods.
100–120 fpm (0.50–0.60 m/s): This velocity range
has similar characteristics as 80–100 fpm (0.40–0.50
m/s) but at significantly higher operating costs.
Containment may be slightly enhanced in this range
and hoods that do not contain adequately in the
80–100 fpm (0.40–0.50 m/s) range may be improved
by operating in this range.
120–150 fpm (0.60–0.75 m/s): Although most hoods
can operate effectively in this range, performance is not
significantly better than at the lower ranges of 80–100
fpm (0.40–0.50 m/s) and 100–120 fpm (0.50–0.60 m/s).
The operating cost penalty imposed by high face velocities in this rage is severe. Consequently, the high face
velocities are not recommended.
>150 fpm (>0.75 m/s): Most laboratory experts agree
that velocities above 150 fpm (0.75 m/s) at the
design sash position are excessive at operating sash
height and may cause turbulent flow creating more
potential for leakage.
3.3.2
Laboratory Hood Minimum Flow Rate
The flow rate of Constant Volume hoods and the
minimum flow rate of Variable Air Volume hoods
shall be sufficient to prevent hazardous concentrations of contaminants within the laboratory
fume hood.
In addition to maintaining proper hood face
velocity, laboratory hoods shall maintain a minimum exhaust volume to ensure that contaminants are properly diluted and exhausted from a
hood.
The following considerations shall be taken into
account (as applicable) when setting the minimum 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 generation rates(a),
(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 such
quantities include:
• Flammable liquids spill onto the work surface, or
• Flammable vapors or gases released by any
other means.
Before selecting the minimum flow rate the user
should calculate the maximum credible concentration that might be reached at locations where an ignition source may be present. Assign a minimum flow
rate or other control measure capable of maintaining
this concentration at the chosen safety factor percentage of the LFL for the materials used. Typically
cited percentages range from 10% to 25% of the LFL
(LEL). This calculation should be made for any new
materials introduced for which the previous calculation
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• Potential for increased hood interior corrosion. (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 equipment and the associated control system. (f)
may not address (e.g., a flammable material with a
higher generation rate or lower LFL.)
A small body of empirical research and theoretical
calculations(1–7) supports a range of values for the
minimum flow for spill conditions and situations
involving the use of typically used quantities of solvents. At least two empirical studies measured concentrations of contaminants resulting from simulated chemical spills in a hood. Their conclusions
regarding minimum flow rate for the scenarios they
studied, correspond roughly to the high and low
ends of the range mentioned below in the brief discussion on energy savings. Additionally, extensive
experience in Europe on European hood designs
using European hood testing procedures provide
some support for the low end of the range.
Designers may choose to increase minimum hood
flow rates in order to maintain flammable vapor duct
concentrations below code required levels (See
Section 5.4.1).
(b) A secondary concern involves the potential for
corrosion of the hood interior from the use of highly
corrosive operations* that may dictate the use of a
fume hood minimum flow rate near the higher end
of the recommended range.
(c) As stated in the exhaust stack discharge section
of this standard, exhaust fan systems typically have
some minimum design exhaust stack velocity. The
minimum flow rate selected for the hood may affect
design and operation of the exhaust system.
Designers need to coordinate these issues.
(d) In situations where the minimum hood flow drives the airflow rate for the laboratory, the minimum
flow affects energy consumption. A higher value for
the minimum flow requires more power to move and
condition the air. Depending on the airflow rates
involved, this situation occurs usually when the
hood density exceeds values in the range from 2%
to 10% of the floor space in the room. (For example
one or more 30x72 inch bench top fume hoods in a
750 ft2 (75 m2) lab.) In situations where some other
consideration sets the flow rate for the room, the
minimum hood flow does not affect energy use.
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Where attempting to save energy in typically higher
hood density installations, minimum fume hood flow
rates in the range of 150 to 375 hood air changes
per hour (ACH) have been used to control vapor
concentrations inside hood interiors.(1–7)
Minimum hood flow rates might be selected within
the above range if the user complies with provisions
in the left hand column. An exception being where a
written hazard assessment indicates otherwise.
(e) Designers may choose to increase minimum hood
flow rate if the ventilation equipment and the airflow
control system cannot regulate room air flows at the
values required to effectively pressurize the room
(See Section 5.2.1).
(f) The expression “within the operating range”
includes accuracy expectations at the minimum hood
air change rate selected to prevent hazardous concentrations* of contaminants within the hood: +/- 10%.
--------------------------------------------------Ventilation system designers shall coordinate the
operating range of the fume hood flow rate with
the operating ranges of the other air supply and
exhaust devices in the room.
If a hood is taken completely out of service, the flow
may be reduced further or shut off so long as other
ventilation needs are unaffected.
For the purposes of establishing a value for the internal
volume of the hood used in determining the flow rate
corresponding to the desired value of hood air changes
per hour, the internal hood volume is approximated and
hereby defined as the total internal hood work surface
area times the internal height of the hood.
Section References
1. Sharp, G.P.: “A Review of U.S. and European
Empirical Research, Theoretical Calculations, and Industry Experience on Fume
Hood Minimum Flow Rates.” International
Institute of Sustainable Laboratories (I2SL)
E-Library,
http://www.i2sl.org/elibrary/
index.html, 2009.
2. Braun, K.O. and K.J. Caplan: “Evaporation Rate of Volatile Liquids, Final Report,
2nd edition. EPA Contract Number 68-D80112”, PACE Laboratories Project
890501.315. Washington, D.C.: U.S. Dept.
of Commerce, NTIS, December 1989.
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3. Klein, R.C., C. King, and P. Labbie: Solvent
vapor concentrations following spills in laboratory chemical hoods. Chem. Health Safe.
11(2):4–8 (2004).4. Harnett, P.B.: Empirical data and modeling of a flammable spill
in a chemical fume hood do not support the
need for fire suppression within the chemical fume hood ductwork. Chem. Health
Safe. 10(4):11–14 (2003).
5. Parker, A.J. and P.J. DiNenno: “Evaluation
of Fixed Extinguishing System Effectiveness in Continuously Exhausting Chemical
Fume Hoods.” Prepared for Merck & Co. by
Hughes Associates, September 2001.
6. Labconco Corp.: Development of the Labconco Protector® Xstream® High Performance Laboratory Fume Hood. Kansas
City, MO: Labconco Corporation, 2009.
7. Ventilation Test according to DIN 12 924
Part 1: Fume Cupboard DIN 12 924 TA
1500 x 900 – 900, Fume hood Test report
by Waldner Laboreinrichtungen GmbH &
Co. for mc6 - Bench Mounted Fume Cupboard: Test Report No.159, May 2000.
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 alert
users to improper exhaust flow.
The purpose of the flow-measuring device is to provide the hood user with continuous information
about the hood’s airflow. One method is to measure
the total volume flow through the hood. Another
method is to measure the face velocity.
One popular method for measuring total volume
flow is the Hood Static Pressure measuring device
(See ACGIH’s® Industrial Ventilation: A Manual of
Recommended Practices for Operation and
Maintenance), which can be related to flow. This
method measures static suction in the exhaust duct
close to the hood throat and, if there are no
adjustable dampers between the hood and the
measuring station, is related to the flow volume.
Other methods include various exhaust volume or
flow velocity sensors.
The flow-measuring device shall be capable of
indicating that the air flow is in the desired range,
and capable of indicating improper flow when the
flow is high or low by 20%.
The means of alarm or warning chosen should be
provided in a manner both visible and audible to the
hood user. The alarm should warn when the flow is
20% low, that is, 80% of the set point value.
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Tissue paper and strings do not qualify as the sole
means of warning.
Some manufacturers may require calibration that is
more frequent.
4
Other Containment Devices
4.1
Gloveboxes
4.1.1
General Description and Use
Gloveboxes shall not be used for manipulation
of hazardous materials with the face or other
panels open or removed nor with the gloves
removed.
If the potential combinations of material properties with planned manipulations are so complex the hazard cannot be estimated, a glovebox may or may not be suitable. A hazard evaluation shall be employed in such complex
cases.
Gloveboxes shall be used when the properties
of the hazardous materials, the planned manipulations, or a credible accident would generate
hazardous personal exposures if the work
were done in an ordinary laboratory hood.
If gloves are removed it is not a glovebox but becomes
a special enclosure requiring evaluation of effectiveness of containment.
Laboratory-scale gloveboxes, for which this standard
applies, should have a maximum internal chamber volume of 50 ft3 (1.4 m3) (single-sided access) or 100 ft3
(2.8 m3) (double-sided access) respectively (passthrough chambers excluded). Larger gloveboxes may
occasionally be found in laboratory settings but are
beyond the scope of this standard. For additional guidance, see the latest edition of the American Glovebox
Association Society’s standard for additional advice
Guideline for Gloveboxes (AGS-G001.)
Gloveboxes may be used for any laboratory manipulations that can be conducted under the restraints
imposed by working with gloves through armholes.
Gloveboxes may be used when the manipulated substances must be handled in a controlled (e.g., inert)
atmosphere or when they must be protected from the
external environment.
4.1.1.1 Location
There are no special requirements for location
beyond those already noted for hoods.
Gloveboxes shall be located as dictated by
workflow, space requirements and other needs
within the laboratory.
Glovebox containment is unaffected by airflow cross
drafts which create challenges for open face hoods.
Since manipulations through glove ports are somewhat
difficult, however, it is advisable to avoid high traffic
areas and to allow ample aisle space.
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4.1.2
Design, Construction, and Selection
A hazard assessment as required in Section
2.4 shall be done to select the appropriate
glovebox.
Positive pressure gloveboxes shall not be used
with hazardous materials without a written risk
assessment.
Depending upon the nature of the hazard controlled, a
glovebox may be constructed of material with favorable
characteristics such as fire rating, radiation shielding,
nonporous and/or impervious surfaces, corrosionresistance for the intended use, and easily cleaned.
Interior corners should be covered.
For additional guidance see:
Interior cracks, seams, and joints shall be eliminated or sealed.
STANDARDS OF PRACTICE FOR THE DESIGN AND
FABRICATION OF GLOVEBAGS(AGS-G002)
STANDARDS OF PRACTICE FOR THE APPLICATIONS OF LININGS TO GLOVEBOXES(AGS-G003)
STANDARDS OF PRACTICE FOR THE SPECIFICATIONS OF GLOVES FORGLOVEBOXES (AGS-G005)
STANDARDS OF PRACTICE FOR THE DESIGN and
FABRICATION OF NUCLEAR APPLICATION GLOVEBOXES (AGS-G006)
4.1.3
Utilities
Utility valves and switches shall be in conformance with applicable codes. When control of
utilities from inside the glovebox is required,
additional valves and switches shall be provided outside the glovebox for emergency shutoff.
4.1.4
Certain applications require that all valves be located
inside of the glovebox containment and all lines exterior to the box be 100% welded.
Ergonomic Design
Ergonomics shall be a significant consideration
in the design, construction, and/or selection of
gloveboxes. Frequency of use shall dictate the
extent to which ergonomic principles will be
applied. Proper application of ergonomic principles shall be met by referring to the latest edition of, Guideline for Gloveboxes, AGS-G001.
Frequent use versus infrequent use may dictate the
extent to which ergonomics principles will be applied.
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4.1.5
Provision for Spills
The design of the glovebox shall provide for
retaining spilled liquids so the maximum volume of liquid permitted in the glovebox will be
retained.
A system for draining the spilled liquid into a
suitable sealed container shall be provided if
the properties of the spilled liquid or other circumstances prevent cleanup by working
through the gloves.
4.1.6
Exhaust Ventilation
Containment gloveboxes shall be provided
with exhaust ventilation to result in a negative
pressure inside the box that is capable of containing the hazard at acceptable levels.
See Sections 4.1.11 through 4.1.14 for ventilation recommendations for specific glovebox types.
Gloveboxes shall be exhausted to the outside
unless the provisions described in ANSI
Standard Z9.7 and Section 5.3.6.2 of this standard are met.
4.1.7
Exhaust Air Cleaning
The air or gas exhausted from the glovebox
shall be cleaned and discharged to the atmosphere in accordance with the general provisions of this standard and any pertinent environmental regulations.
Air-cleaning equipment shall be sized for the
maximum airflow anticipated when hazardous
agents are exposed in the glovebox and the
glovebox openings are open to the extent permitted under that condition.
If the air-cleaning device (ACD) is passive (i.e.,
a HEPA filter or activated carbon) provision
shall be made for determining the status of the
ACD, as noted in Section 9.3. If the ACD is
active (i.e., a packed-bed wet scrubber),
instrumentation shall be provided to indicate
its status.
If the glovebox is sealed tightly when closed, a pressure relief valve might be required to prevent excessive
negative pressure in the glovebox, depending on the
choice of air-cleaning equipment and exhaust blower.
Any ACD should be selected and applied according to
the manufacturer’s specifications, with attention to airflow rate, and other operating parameters that can
affect performance for the contaminants of interest.
The ACD should be located as close as is practical to
the glovebox to minimize the length of contaminated
piping or the need for maintaining high transport velocity.
The ACD shall be located to permit ready access
for maintenance. Provision shall be made for
maintenance of the ACD without hazard to
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personnel or the environment and so as not to
contaminate the surrounding areas.
4.1.8
Exhaust Ducting
Exhaust piping shall be in accordance with the
principles described in the latest editions of the
ACGIH® Industrial Ventilation Manual,
ANSI/AIHA® Z9.2, and the ASHRAE
Handbook Fundamentals. All piping within the
occupied premises shall be under negative
pressure when in operation.
Materials shall be resistant to corrosion by the
agents to be used.
4.1.9
Monitoring and Alarms
A glovebox pressure monitoring device with a
means to locally indicate adequate pressure
relationships to the user shall be provided on
all gloveboxes.
Ergonomics principles indicate that the total number
and types of alarms should be minimized.
If audible alarms are not provided, documented
training for users in determining safe pressure
differentials shall be required.
Alarms should be clearly distinguished from each
other.
Pressure monitoring devices shall be
adjustable (i.e., able to be calibrated if not a primary standard) and subject to periodic calibration at least annually.
4.1.10 Decontamination
A written decommissioning plan following
the procedures outlined in the latest edition of ANSI/AIHA® Z9.11 Laboratory
Decommissioning shall be developed.
Before the access panel(s) of the glovebox are
opened or removed, the interior contamination
shall have been reduced to a safe level.
If the contaminant is gaseous, the atmosphere
in the box shall be adequately exchanged to
remove the potentially hazardous gas. This can
be affected by exhausting the box through its
ventilation system, and where necessary providing an air inlet that is filtered if required.
Safe level is relative to the contaminant involved.
Analytical techniques for determining surface contamination (mass/unit area, counts per minute/unit area)
are helping to provide increasingly sensitive but not
always specific risk information. Correlating surface
contamination with exposure potential remains more of
an art than a science.
Use caution if gases or vapors may condense or
deposit on surfaces. Decontamination may still be
required.
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If the contaminant is liquid, any liquid on surfaces shall be wiped with suitable adsorbent
material or sponges until visibly clean and
dry. Used wipes shall be placed in a suitable
container before being removed from the
glovebox.
Many liquids and some solids have vapor pressures
that might cause hazardous concentrations of vapor. A
combination of the contamination reduction procedures
discussed above might be necessary.
If the contaminant is a powder or dust, all internal surfaces shall be cleaned and wiped until
visibly clean. The exterior surfaces of the
gloves also shall be wiped clean.
Certain direct-reading instruments (e.g., combustible
gas indicators) may lend themselves to such an
assessment.
Neutralizing reagents should be used, if available.
Precautions to prevent hazards to personnel
and contamination of the premises shall be
made if the ducting is to be opened or dismantled.
If there is any uncertainty about the effectiveness of contamination reduction procedures,
personnel involved in opening the panels of
the glovebox shall be provided with appropriate PPE or clothing.
The exhaust piping from the glovebox to the ACD may
be contaminated, especially if a hazardous particulate
is involved.
Nonessential personnel should be excluded from the
decontamination area. The contamination in the general work area should be reduced before use.
For more information see (1) EPA 402-R-97-016,
Multi-Agency Radiation Survey and Site Investigation
Manual. (2) ANSI/AIHA® Z9.11 Laboratory
Decommissioning.
4.1.11 High Containment Glovebox
A high containment glovebox shall conform to
all the mandatory requirements of
Sections 4.1.1 through 4.1.11, and
• Shall be provided with one or more airlock
pass-through ports for inserting or removing objects or sealed containers without
breaching the physical barrier between
the inside and outside of the glovebox;
• Shall maintain negative operating static
pressure within the range of -0.5 to -1.5
in.wg (-125 Pa to -374 Pa) such that contaminant escape due to “pinhole-type"
leaks is minimized.
• Shall maintain dilution of any flammable
vapor–air mixtures to <10% of the applicable lower explosive limit.
• Shall prevent transport of contaminants
out of the glovebox.
Examples include gloveboxes used for controlling
exposures to unknown materials or acutely hazardous
and highly volatile materials where any exposure may
be harmful.
Care should be exercised when placing certain hazardous liquids in an evacuated airlock or interior of a
glovebox when a decrease in pressure could affect the
boiling point of the liquid causing it to go to a gaseous
state.
Meeting the above requirements will depend on
whether the glovebox is continuous flow or is sealed.
The minimum exhaust flow rate is usually based on a
glove being breached or an access door being intentionally opened. The air velocity into the open gloveport
or door should be 125 ± 25 linear fpm (0.635 ± 0.13
m/s).
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4.1.12 Medium Containment Glovebox
A medium containment glovebox shall conform
to all the mandatory requirements of Sections
4.1.1 through 4.1.10, is not provided with passthrough airlocks, and shall be provided with
sufficient exhaust ventilation to maintain an
inward air velocity of at least 100 fpm (0.51
m/s) through the open access ports, and create a negative pressure of at least 0.1 in.wg
(25 Pa) when access ports are closed.
Examples include gloveboxes designed to prevent
overexposure to acutely hazardous materials that are
not highly volatile and/or where allowable exposure levels have been established and personnel exposure can
be verified to be below the established allowable levels.
4.1.13 Special Case Containment
Glovebox
A special case containment glovebox shall be
designed for special situations, does not necessarily conform to the provisions of this standard, but has been tested for the intended use
and found adequate for that purpose.
For example, a positive pressure is maintained in a
glovebox used to build desiccant assemblies. The desiccant requires a very dry environment and the positive
pressure pushes moisture away rather than allowing it
to enter. There is also an exhaust fan which creates a
negative pressure in the stack from the box.
4.1.14 Controlled Atmosphere
Containment Glovebox
An isolation and containment glovebox shall
be a controlled atmosphere containment
glovebox required for special atmosphere work
when either the controlled atmosphere and/or
the contained agents are hazardous.
Examples include applications where an inert atmosphere is necessary to protect the work or when it provides an added measure of safety.
4.1.14.1 Design and Construction
Design and construction, and materials shall
conform to the requirements for high, medium,
or special case containment gloveboxes as
necessary.
Refer to the AGS-1998-001Guideline for Gloveboxes
for more details on construction.
If the controlled atmosphere gas is hazardous,
the airlocks shall be provided with a purge air
exhaust system that, by manipulation of
valves, creates a purge flow of room air sufficient to provide at least 5 air changes per
minute, with good mixing, to the interior space
of the airlock.
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4.1.14.1 Operation
Operation of an isolation and containment glovebox shall conform to high, medium, or special
case containment requirements as necessary
and the airlock purge system shall be operated
for sufficient time to dilute any hazardous gas in
the airlock to safe concentrations before the
outer door is opened.
For the empty airlocks, a purge time of 3 min. at 5 air
changes per minute with good mixing would reduce
an atmosphere of 100% to less than 1 ppm. If an
object in the airlock has cavities that would trap gas,
or if the gas might be adsorbed in the object, more
time would be required: Such time should be determined by sampling the exhaust stream upstream of
the ACD.
Care shall be exercised when placing certain
hazardous liquids in an evacuated airlock or interior of a glovebox when a decrease in pressure
could affect the boiling point of the liquid, causing it to go to gaseous state.
4.1.15 Testing and Maintenance
An overall operation and maintenance program
shall be documented for each application of the
glovebox to provide users with necessary information on periodic maintenance and testing of
glovebox system components.
4.2
Components such as air locks, gloves, air cleaning
devices, etc., require periodic inspection and/or performance testing. Some components may also
require more detailed operating instructions for users
and specific maintenance procedures for maintenance technicians than is normally found for most
laboratory ventilation systems.
Ductless Hoods
Ductless hoods shall meet the general requirements of Sections 3.1 and 3.3 as applicable.
A Hazard Evaluation and Analysis shall be conducted as directed in ANSI/AIHA® Z9.7 and
Section 2.1.1.4.
Compliance with the general requirements of
Sections 2, 3.3, and 5.3.6.2 shall be evaluated
by qualified persons.
Ductless hoods that do not meet the requirements specified in Sections 9.3 and 9.4 shall be
used only for operations that normally would be
performed on an open bench without presenting
an exposure hazard.
Ductless hoods have limited application because of
the wide variety of chemicals used in most laboratories. The containment collection efficiency and retention for the air-cleaning system used in the ductless
hood must be evaluated for each hazardous chemical.
As referenced in ANSI/AIHA® Z9.7, the hazard evaluation and analysis serve to ensure proper air quality, effective occupant protection, and satisfactory system performance.
Air-cleaning performance monitoring is typically limited for many hazardous materials. Chemical-specific
detectors located downstream of adsorption media or
pressure drop indicators for particulate filters are necessary for systems recirculating treated air from the
ductless hood back into the laboratory.
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Ductless hoods shall meet the performance
standards for contaminant removal established
by the owner.
Ductless hoods may be appropriate if the contaminant
is particulate and provision is made for changing filters
without excessive contamination of the laboratory or
potential exposure to personnel changing the filters.
See Sections 9.3 and 9.4.
Ductless hoods shall have signage prominently posted on the ductless hood to inform operators and maintenance personnel on the
allowable chemicals used in the hood, type
and limitations of filters in place, filter changeout schedule, and that the hood recirculates air
to the room.
Adsorption media such as activated charcoal are not
efficient for fine particles and are predominately used
for adsorbing certain gases or vapors. Many gases and
vapors of low molecular weight will be stripped from the
adsorption media and reenter the room air on continued flow of clean air through the ductless hood. When
this happens, the ductless hood only serves to protect
the worker at the hood face and to spread the contaminant release into the room air during a longer time
span and at a lower concentration. See Section 4.2.2.
Where multiple air contaminants challenge the ductless hood air-cleaning system, the collection efficiency
and breakthrough properties of the air filtering media
are complicated and are dependent on the nature of
the specific mixture. Enhanced breakthrough of components should be especially considered as a part of
the Hazard Evaluation and Analysis. See Section 4.2.2.
Also the warning properties (i.e. odor, taste) of the
chemical being filtered must be adequate to provide an
early indication that the filtration media are not operating properly.
4.2.1
Airborne Particulates
Ductless hoods that utilize air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates shall meet the
requirements of Section 9.3.1.
4.2.2
Gases and Vapors
Ductless hoods utilizing adsorption or other filtration media for the collection or retention of
gases and vapors shall be specified for a limited use and shall meet the requirements of
Section 9.3.2.
Each application of the ductless hood must be evaluated prior to use. For each chemical that may be used in
the hood its retention capacity must be known and be
appropriate for the intended use.
Ductless hoods employing filters for removing
gases and vapors shall have written documentation (records) that the manufacturer has
approved the specific application of the hood
prior to usage.
There is currently no national consensus standard for
testing and performance of gas/vapor adsorbent filters
used in ductless hoods. Although widespread experience with its use is lacking, there is one standard that
may be worth considering assuming that it is made
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more widely available.
• Standard AFNOR NF X 15-211
The manufacturer shall provide a list of chemicals
approved to be used in the hood with their retention capacities.
Proper disposal of unused and used (contaminated) adsorption filters shall be considered as part
of the decision to use ductless hood employing
such.
According to Tronville and Rivers, progress toward
standards for gaseous contaminant filters for general-ventilation service has been very slow. Many factors influence the efficiency and service life of
adsorptive and chemisorptive filters for gaseous
contaminants. Standards writers must choose a few
test contaminants to represent the behavior of filters
on the hundreds of contaminants that may be of
interest.
A major problem is to relate the performance of a filter at the low gaseous contaminant concentrations
present in real HVAC systems to the performance at
the relatively high test concentrations necessary for
reasonable test durations.
ASHRAE is developing a standard comprising three
parts, now at the ‘proposed’ stage:
• For laboratory tests on granular adsorptive
media
• For laboratory tests on complete filter cells
• For field tests in installed filters (4, 5 and 6).
ASTM has for many years maintained standards on
many aspects of activated carbon, the most used filter medium. Standards 7, 8, 9 and 10 deal with the
mass of contaminant a carbon can absorb before it
becomes saturated, and no longer of use.
Paolo Tronville, Richard D. Rivers, International standards: filters for buildings and gas turbines, Filtration
& Separation, Volume 42, Issue 7, September 2005,
Pages
39-43,
ISSN
0015-1882,
DOI:
10.1016/S0015-1882(05)70623-6.
(http://www.sciencedirect.com/science/article/
B6VJM-4H7BN0H-13/2/9888f01240f365fa2
efeb29972982d6d)
Other reference standards for performance testing
include ANSI/ASME N510, ANSI/ASHRAE 52.2,
and ASHRAE 2001 Handbook – Fundamentals.
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4.2.3
Handling Contaminated Filters
Contaminated filters shall be unloaded from the
air-cleaning system following safe work practices
to avoid exposing personnel to hazardous conditions and to ensure proper containment of the filters for final disposal. Airflow through the filter
housing shall be shut down during filter changeout.
4.2.4
Testing and Maintenance
All of the requirements of Sections 6.3, 6.4, and
8.0 for containment and airflow testing and all of
the requirements of Sections 9.2 and 9.3.2 for air
cleaning performance shall be followed.
4.3
Special Purpose Hoods
Special laboratory chemical hoods shall be
designed in accordance with ANSI/AIHA® Z9.2
and the latest edition ACGIH®’s Industrial
Ventilation: A Manual of Recommended Practice.
Special purpose hoods are defined as any not conforming to the specific types described in this standard. Special hoods may be used for operations for
which other types are not suitable (e.g., enclosures
for analytical balances, for histology processing
machines, gas vents from atomic absorption, or gas
chromatography equipment). Other applications
might present opportunities to achieve contamination control with less bench space or less exhaust
volume (such as special mixing stations, sinks,
evaporating racks, heat sources, or ventilated work
tables).
Additional information on special exhaust system
design and operation can be found in
Semiconductor Exhaust Ventilation Guidebook by
Jeff Burton and “Development of a Program for
Performance Evaluation of University Specialty
Local Exhaust Systems for Compliance with the
OSHA Lab standard” (Hallock et. al., Appl. Occup.
Env. Hyg. 11(3):170–77 (1995).
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5
Laboratory Ventilation System Design
5.1
Laboratory Design
5.1.1
Spatial Layout
Laboratory designers shall consider effects on
safety when establishing floor plans and spatial
layout.
The laboratory ventilation system affects contamination control. Spatial layout, in terms of physical barriers, and the flow of personnel and material also
affects contamination control. Laboratory design
should address these issues from consistent view.
One useful design concept is a progression of
spaces from ‘clean to dirty’ or ‘low to high hazard.’
This can lead to placement of barriers between office
space and a laboratory corridor, or to an ante-room
between the corridor and the laboratory.
The location of laboratory chemical hoods and other
hoods or vented openings with respect to open windows, doorways, and personnel traffic flow directly
influences the containment ability. Cross currents,
drafts, and spurious air currents from these sources
may decrease a hood’s containment ability.
Users should be aware that cross drafts may disturb
capture efficiency even when the sash is partially
closed.
Laboratory designers should consider how hood
location affects path of egress from the laboratory.
Designers should consider arranging exhaust
devices, and gathering heat producing equipment in
ways that reduce the energy expense associated with
safe ventilation and effective heating and cooling.
5.1.2
Noise
Ventilation system designers shall consider
acoustical emission when selecting air moving
devices. (fans) Generation of excessive noise
shall be avoided in laboratory ventilation systems.
Fan location and noise treatment shall provide for
sound pressure level (SPL) in conformance with
local ambient noise criteria.
The acoustic character of the ventilation system
should help create a pleasant working environment.
Sound from the ventilation system should not interfere with laboratory operations. It may be used to
mask undesirable noise such as vehicular traffic,
noisy equipment, or low discourse.
The primary references for design criteria and methods will be found in ASHRAE publications listed below.
Chapter 7 on Sound and Vibration from the ASHRAE
2005 Handbook – Fundamentals
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Chapter 47 on Sound and Vibration Control from
ASHRAE 2007 Handbook – HVAC Applications
Noise associated with mechanical ventilation and
exhaust systems generally originates with fans, duct or
damper vibration, and air noise caused by excessive air
velocity or turbulence. Therefore, the primary design
focus should be on preventing excessive noise generation. Where possible, it is good practice to locate high
static pressure fans remote from occupied spaces.
Use good duct design procedures. Avoid abrupt duct
turns without turning vanes, change duct dimensions
gradually, and generally follow procedures given in the
latest ASHRAE Handbooks chapters on duct design. The
careful use of vibration isolators, inertia blocks, and suitable fan speed and outlet velocities is indicated. Variable
volume systems have found wide application in laboratories. However it is important to be aware that variable
sound levels may focus unwanted attention on the ventilation system. Frequently laboratories have large and
numerous fans, and then special care must be taken to
comply with location regulations and good practice with
regard to noise contamination of adjoining properties.
NOTE: Such regulations vary but provide for sound pressure level (SPL) in the range of 50 dBA and limit the
increase in SPL above background levels when the ventilation systems are operating.
System design should provide for control of exhaust system
noise (combination of fan-generated noise and air-generated noise) in the laboratory. Systems should be designed to
achieve an acceptable SPL and frequency spectrum [room
criteria, (RC), or noise criteria (NC)] as described in the
ASHRAE 2007 Handbook – HVAC Applications. The recommended range for hospital laboratories is 50 – 35; higher RC ranges might be acceptable for other types of laboratories. NC curves above 55 might result in unacceptable
speech interference in the laboratory.
Use of porous or flammable sound-absorbing interior lining of exhaust ductwork usually is unacceptable.
Ventilation designers may also consider the sound
caused by operation of ventilation control devices, especially when installed in an open ceiling.
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5.2
Laboratory Airflow Management
5.2.1
Differential Pressure and Airflow
Between Rooms
As a general rule, airflow shall be from
areas of low hazard to higher hazard unless
the laboratory is used as a barrier facility,
such as a Clean Room, or an isolation or
sterile laboratory, or other special-type laboratories. When flow from one area to
another is critical to emission exposure
control, airflow monitoring devices shall be
installed to signal or alarm that there is a
malfunction.
Air shall be allowed to flow from laboratory
spaces to adjoining spaces only if
• There are no extremely dangerous and
life-threatening materials used in the
laboratory;
• The concentrations of air contaminants
generated by the maximum credible
accident will be lower than the exposure limits required by 2.1.1.
‘Space pressurization’ or ‘directional airflow’ between
spaces is one of many tools available to limit exposure to
laboratory hazards. Effectively applied, it opposes migration
of air contaminants; it does not eliminate it. Air moves
between spaces in response to many phenomena, including thermal effects, movement of people and direct drafts
from the ventilation system. Effective pressurization overcomes many of those drivers, most of the time. In a laboratory with ordinary construction, and a properly functioning
ventilation system, air can move briefly the wrong direction.
(Very special techniques for construction and operation can
eliminate migration. Such facilities are outside the scope of
this standard.)
Safety professionals and users should understand pressurization as an imperfect secondary barrier, and consider it in
the context of other exposure control measures. This includes
consideration of ordinary work practices, distribution and storage of materials, and operation of the primary barriers. It also
includes consideration of emergencies, and accidents.
Pressure within a Lab Room or other space is defined as
the differential pressure between that space and adjacent
space(s). This differential pressure causes air to flow in the
desired direction, which is typically from areas of relatively
low (risk of) contamination and in the direction of increasing
(risk of) contamination. The resulting Transfer Air (TA) flow
occurs at all the openings in the room boundary: space
around the doors, gaps between wall, floor and ceiling
materials and penetrations for ducts, pipes and wires. This
directional air flow through the envelope reduces the likelihood of air contaminants moving in the wrong direction. In
most laboratories a negative pressure (containment) tends
to prevent contaminants from migrating outside the room. In
other applications such as Clean Rooms or Sterile
Laboratories a positive pressure (barrier) tends to prevent
contamination by air from outside the Room.
The flow rate of Transfer Air depends on the differential
pressure and the effective leakage area around the doors
and through envelope. If the room envelope is tightly
sealed, the leakage area is small, and there is very little
Transfer Air flow for a given pressure. If the room is not so
tight, the leakage area is larger, and more Transfer Air flows
for the same differential pressure.
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When a door to the laboratory is open, the effective leakage area is very large. The differential pressure and the
desired containment are lost. Net airflow may continue in
the intended direction as a result of the airflow offset, but
the average velocity is very low. It is impractical to maintain a differential pressure across an open door. Air is
likely to move both directions through the large opening,
which is one reason contaminants may migrate, despite
proper ventilation.
The quantity of Transfer Air is also generally equivalent to
the “airflow offset” which is defined as the volumetric difference between Supply Air (SA) to the space and
Exhaust (or Return) Air (RA) flows driven by the mechanical ventilation systems.
The desired directional airflow between
rooms shall be identified in the design and
operating specifications.
For a building with laboratories or other critical spaces it
is recommended that an “airflow map” of the building be
produced. This floor plan indicates the Transfer Air
Volume through each boundary, or the required relative
pressure relationship between across it. It should also
show the Supply Air Volume, the Exhaust (or Return) Air
Volume for each space. The flow rates must balance for
each room (TA=SA-EA) and for large common areas
such as corridors. These air volumes are summed to size
fans and other mechanical equipment.
Ventilation system designers use several approaches to
control laboratory pressurization. Methods include flow
offset control, direct pressure control and combinations
of those two. ASHRAE (Applications Handbook 2007,
Page 14–12) describes each method in detail and compares them, indicating the circumstances that favor each
one. Flow offset control is the most commonly applied
approach and is illustrated in the following example.
A lab designer chooses a value for the offset between
supply and exhaust. For example, the lab Exhaust Air
volume is 1000 L/s (2118 CFM) and the Supply Air
Volume is 900 L/s (1906 CFM). This is defined as a “-100
L/s (-212 CFM) offset.” This -100 L/s offset draws 100 L/s
of Transfer Air into the room. If the flows were reversed
(Supply greater than Exhaust) the offset would be+100
L/s (+212 CFM).
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Flow control accuracy is crucial to the performance of a
pressurization system based on the airflow offset.
Designers explicitly specify the accuracy needed for the
mechanical flows in and out of the room after quantifying the effect of inaccuracy on the flow offset and resulting pressurization.
The leakage of the room envelope is just as important.
The quantity of offset air to maintain a desired room
pressure depends on the effective leakage area of the
room, through the doors and envelope.
In some projects, delivering an effective pressurization
system includes specifying and testing the tightness of
the room envelope. The construction process may
explicitly include steps to adjust the observed leakage
area. Rooms that leak too much are far more common
than rooms that are too tight. Sometimes it is necessary
to seal the envelope more carefully before the room can
be effectively pressurized.
Typically, the leakage area is not known. Designers rely
on their experience and published design resources,
(ASHRAE Handbook Fundamentals, 2005, Page 27.23)
to estimate it. Then during the construction, TAB and
Commissioning Phase, air flow and pressure measurements confirm the design. If necessary, the Transfer Air
Volume can be adjusted and the sealing of critical
rooms can be corrected to produce the desired Room
Pressure Differential.
When rooms are constructed very tightly, the low room
leakage means that small changes in the room offset air
volume cause significant changes in the differential
pressure to the adjacent spaces. Controlling a very tight
room by volumetric offset requires especially precise
and stable volumetric air flow control. If the room envelope is too tight for volumetric offset, direct pressure
control is a practical alternative.
In special cases designers open a hole in the envelope
and fit it with an air balancing device to control the volume of transfer air, and in some cases, a HEPA filter to
prevent contamination. Such measures only apply to
special high containment laboratories or barrier facilities
that employ rigorous construction methods for the structure, envelope, seals, penetrations and finishes.
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5.2.1.1 Ante-rooms and Airlocks
When health and safety professionals are concerned with containing contaminants during
use and operation of the doors to the room,
designers shall evaluate the application of airlocks and ante-rooms.
An ante-room (or vestibule) stands between the laboratory and the adjacent corridor. This can improve the
effectiveness of the pressurization system, reducing
the likelihood that entry and exit by personnel will
cause contaminants to move in the wrong direction.
An airlock shall consist of a vestibule or small
enclosed area that is immediately adjacent to
the laboratory room and having an airtight
door at each end for passage. Airlocks shall be
applied in such a way that one door provides
access into or out of the laboratory room, and
the other door of the airlock provides passage
to or from a corridor (or other non-laboratory
area). Airlock doors shall be arranged with
interlocking controls so that one door must be
fully closed before the other door may be
opened.
An airlock is distinguished from a more common
vestibule or ante-room by the interlocked, airtight
doors.
Airlocks are utilized to prevent undesirable airflow from
one area to another in high hazardous applications,
which are generally outside the scope of this standard.
5.2.1.2 Critical Air Balance
If the direction of airflow between adjacent
spaces is deemed critical, provision shall be
made to locally indicate and annunciate inadequate airflow and improper airflow direction.
5.2.2
Diversity
A designer, applying the concept of ventilation
load diversity, shall consider the following
issues:
• Capacity of any existing equipment;
• Expansion considerations;
• Maintenance department’s ability to
perform periodic maintenance
• Minimum and maximum ventilation rates
for each laboratory;
• Quantity of hoods and researchers;
• Requirements to maintain a minimum
exhaust volume for each hood on the
system;
• Sash management (sash habits of users);
• Thermal loads;
Diversity is a system design concept that can justify
sizing components for a total load that is less than the
sum of the individual peak demands. A system that is
designed with full flow capacity for all hoods is
designed for 100% Usage Factor or 100% diversity.
Both existing and new facilities can benefit from applying diversity to the HVAC design if individual laboratory
chemical hoods are used at different times of day.
Diversity may allow existing facilities to add laboratory
chemical hood capacity without adding new mechanical equipment. In new construction, diversity allows the
facility to reduce capital equipment expenditures and
space requirements by downsizing equipment and
other infrastructure.
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•
•
•
•
Type, size, and operating times of facility;
Type of laboratory chemical hood controls;
Type of ventilation system, and
Use patterns of variable volume hoods.
The following conditions shall be met in order to
design a system diversity:
• Acceptance of all hood-use restrictions by
the user groups. Designers must take into
account the common work practices of the
site users.
• A training plan must be in place for all laboratory users to make them aware of any
limitations imposed on their freedom to
use the hoods at any time.
• An airflow alarm system must be installed
to warn users when the system is operating beyond capabilities allowed by diversity.
• Restrictions on future expansions or flexibility must be identified.
5.2.3
Lab users can undermine diversity assumptions if they
leave fume hood sashes open. Common approaches
for ensuring diversity include VAV hoods, sash management aids such as building management system
trending and automated sash closers, and hood use
detection.
Designing with diversity may limit the number of hoods
in use or limit the sash openings, thus creating potential for overexposures to personnel, and prevention of
future expansion opportunities. Therefore, diversity
should be applied carefully in all situations. Certain
diversity approaches may be undesirable for certain
circumstances:
• Sash management is difficult to predict and often
unreliable. Dependence on historical sash management patterns may be insufficient for any
given facility. Turnover among laboratory users
may reduce the future commitment to sash management. The use of building management systems to monitor sash management may help, but
this requires significant commitment by operating
personnel to effectively regulate the users.
Automatic sash closers—designed to improve
sash management habits—may be overridden
and lose their effect on diversity.
• Laboratories with extremely high use patterns—
such as teaching labs—may be candidates for
full-flow or very high-usage factor designs.
Laboratory Ventilation—Emergency
Modes
A hazard assessment (see Section 2.4) shall
be performed to identify credible emergency
conditions that may occur.
Each laboratory room should be evaluated with
respect to the potential for hazardous chemical spills,
accidental gas release, or a fire occurrence.
When the type and quantity of chemicals or
compressed gases that are present in a laboratory room warrant a special, emergency ventilation mode, the room shall be equipped with
provision(s) to initiate emergency notification
and emergency ventilation.
If the type and quantity of chemicals and gas present
could pose a toxicity or fire hazard if accidentally
spilled, released, or ignited, the room occupants
should have a means to signal for an appropriate
emergency response as well as initiate appropriate
emergency ventilation. The means to signal an emergency may be a dedicated switch or pull station, or it
may be a phone. The signal may come from automatically monitored Eye Wash Stations of Emergency
Showers. Naturally, the benefit of such provisions is
limited to incidents that an occupant is present to
observe.
Emergency situations (see current version of
NFPA 92A) that shall be anticipated and the
appropriate ventilation system responses shall
include:
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• CHEMICAL EMERGENCY – A means
such as a clearly marked wall switch, posted emergency phone number, or other
readily accessible device shall be provided
to enable the room occupants to initiate
appropriate emergency response.
For rooms served by VAV ventilation systems,
the Chemical Emergency mode of operation
shall maximize the room ventilation (air change
per hour) rate. For rooms served by 2-state ventilation systems that utilize a reduced ventilation
level for energy savings, the Chemical
Emergency mode of operation shall apply the
maximum ventilation rate.
The intent of the chemical emergency provision is to
utilize the ventilation system to maximize the dilution
and removal of chemical fumes and vapors, and prevent migration of such fumes and vapors to other
building areas. This response is intended to address
a serious chemical spill or related incident that has
the potential for releasing large amounts of hazardous fumes or vapors within the room.
In addition to initiating the emergency ventilation
modes, it is desirable that the emergency situation
be simultaneously indicated to appropriate facility
personnel at one or more designated locations.
Operation of the room ventilation system in a
chemical emergency mode shall not reduce the
room ventilation rate, room negative pressurization level, or hood exhaust airflow rate.
• FIRE – Any manual or automatic means of
detecting fire (such as a pull station or
smoke detector) in a laboratory room shall
also activate an appropriate fire emergency
mode of operation for the room and/or
building ventilation system.
The selected fire emergency mode shall operate all supply and exhaust equipment in the
room in a manner that promotes egress, retards
the spread of fire and smoke, and complies with
applicable fire safety codes and standards.
The intent of the fire emergency ventilation mode is
to promote safe egress. This means apply negative
pressurization in the room of fire origin in order to
retard the spread of smoke and toxic fire gases to
other parts of the facility but do not pressurize to the
extent that the force needed to open the door is
excessive. (Also refer to the current versions of
NFPA 92A and NFPA 45.)
The common practice of cutting off supply air to a
fire zone does not apply to some laboratories. The
combination of a high exhaust rate and no supply
can depressurize a room so far that some occupants
would be unable to open the doors. The initial design
of the laboratory ventilation system must include
analysis of flow rates, pressure levels and forces on
the door to ensure that egress is possible.
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Note: There are other failures and abnormal events
(e.g. drop out of supply fans due to freeze stat
alarms) that can cause excessive space pressure differences. Each of these scenarios should be identified and addressed in the design of the supply air,
exhaust air, and smoke management system so that
safe laboratory and building egress is maintained
under all conditions.
Depending on the chemicals used, the risk of fire
may be heightened upon a spill or gas release. Such
situations may justify initiating a fire alarm and summoning the local fire department to respond even if a
fire has not started.
5.3
Supply Air
5.3.1
Supply Air Volume
If laboratories are to be maintained with a negative pressurization and directional airflow from
the corridor into the laboratory, supply air volume shall be less than the exhaust from the
laboratory.
When laboratories are to be maintained with a
positive pressurization and directional airflow,
supply air volume shall be more than the
exhaust from the laboratory.
To maintain the desired space pressurization,
the supply air volume shall respond to applicable dynamic events including:
•
•
•
•
changes in desired ventilation rate,
flow changes in VAV exhaust devices,
temperature control demands, and
temporary deficit of exhaust system capacity.
In general, return air is not used in laboratories with
hazardous chemicals or biological hazards. The difference between the air supplied by the ventilation system and that exhausted is the Transfer Air described in
Section 5.2.1. It serves to resist the escape of airborne
hazardous materials from the laboratory room.
Energy recovery systems should be evaluated to
reduce the energy needed to condition a large outside
air intake.
The ventilation rate selected for a laboratory depends
on the following concerns:
• control of the thermal and psychrometric environment (ASHRAE Laboratory Design Guide,)
• dilution and displacement of contaminants not
captured by exposure control devices,
• effective operation of exposure control devices,
such as laboratory hoods (See Sections 3 and
4,) and
• space pressurization (See Section 5.2.1.)
Typically, the air flow rate is selected to satisfy the concern requiring the greatest flow. This rationale applies
from room to room during the design process, and
may apply from moment to moment in an active ventilation control system.
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From a practical point of view, the ventilation
designer may restrict the range of air flow rates
based on the capability of the ventilation equipment and associated control system.
The laboratory ventilation system shall be
designed to remove and dilute air contaminants in
accordance with the Laboratory Ventilation
Management Plan.
Current information about the costs of ventilation
indicates that it costs approximately $3 to $9 per
cfm-year. This cost includes the energy required to
move and condition the supply and exhaust air.
The costs can vary based on geography and
depend on the cost of energy for given area.
Minimizing airflow reduces energy use and operating costs.
The quantity of dilution (or displacement) ventilation required is a subject of controversy.
Numerous studies make it clear that the air flow
rate is just one factor affecting contaminant levels in the room. Frequently, other factors have
been shown to make a bigger difference than
some changes in the air flow rate. These factors
include the mechanical arrangement of the supply and exhaust devices, thermal effects, occupant movement and the motion and location of
doors.
(Manning, et al. 2000, ASHRAE Transactions, DA00-14-3: Analysis of Air Supply Type and Exhaust
Location in Laboratory Animal Research Facilities
Using CFD
Klein, et al. 2009, JCHAS, Laboratory air quality
and room ventilation rates
Smith and Yancey-Smith, 2009, JCHAS,
Specification of Airflow Rates in Laboratories)
The ventilation rate must also satisfy the general
codes and standards that apply to the occupancy
class.
These studies do not show that the flow rate does
not matter. On the contrary, they have shown that
the flow rate certainly does affect contaminant levels, but that there is no air change rate that is
always appropriate.
Usually a laboratory ventilation system surpasses
the codes and standards that apply to the building
in general. For example, the OA ventilation per person usually exceeds the requirements of ASHRAE
Standard 62.1.
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5.3.2
Supply Air Distribution
Supply air distribution shall be designed to
keep air jet velocities less than half, preferably
less than one-third of the capture velocity or
the face velocity of the laboratory chemical
hoods at their face opening.
For most laboratory chemical hoods, this requirement
will mean 50 fpm (0.25 m/s) or less terminal throw
velocity at 6 ft (1.8 m) above the floor. For laboratories
with very small volumes of hood exhaust this may be
achieved by correct selection and placement of conventional aspirating supply diffusers. For rooms with
greater supply air requirements, either perforated ceilings or special large-capacity radial diffusers may be
necessary. These special laboratory diffusers systems
are preferable from a safety viewpoint to auxiliary air
hoods because the ventilation air can also be used to
sweep gases and vapors from the room into the laboratory chemical hoods. The large capacity radial diffusers are available from several manufacturers
designed specifically for laboratory use. These diffusers have capacities of up to 100 cfm (47.2 L/s) per
square foot of diffuser and come in 1ft 1ft (0.3 m 0.3
m), 2 ft 2 ft (0.6 m 0.6 m), 1 ft 4 ft (0.3 m 1.2 m),
and 2 ft 4 ft (0.6 m 1.2 m) sizes with nonaspirating
design and omnidirectional radial flow patterns.
Supply air diffusers where practical should be located
close to the personnel corridor and entry door to the
laboratory and far from the major exhaust devices. This
location promotes unidirectional flow, sweeping contaminants into the exhaust devices and helping further
protect the corridor from airborne hazardous materials.
The ideal arrangement locates hoods and exhaust
devices away from entry doors and exit corridors and
locates supply air diffusers close to entry doors and
exit corridors.
5.3.3
Supply Air Quality
Supply systems shall meet the technical
requirements of the laboratory work and the
requirements of the current version of
ANSI/ASHRAE Standard 62.1.
Additional design information can be obtained using
Computational Fluid Dynamics (see Memarzadeh,
1996).
The outside air should be drawn from the least contaminated location available. Wind studies are often used
to select relative placement of air intakes and exhaust
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5.4
Exhaust
5.4.1
Exhaust System Classification
Designers shall review existing regulations and
code requirements for the project location.
International Mechanical Code (IMC) – Section 510 –
Hazardous Exhaust Systems:
In cases where Section 510 of the
International Mechanical Code applies,
designers shall consult the current version of
IMC 510.
Many building codes based on the IMC define
Hazardous Exhaust Systems in a way that sometimes
includes laboratory exhaust systems. In the past, the
designation has been an obstacle to HVAC designers.
Since 2006, revisions to the IMC make that designation less of a burden. In particular, the code more readily permits manifolding, and usually eliminates the
need for fire suppression.
Most states have adopted this section into their state
mechanical code. Section 510.2 of this code provides
a definition based decision process to determine
whether Section 510 applies to their design. The
exceptions in Section 510.4 serve to more readily permit manifolding of laboratory exhaust, when appropriate. The exception in Section 510.7 addresses an
exemption for laboratory ducts from requirements for
automatic suppression.
The laboratory definition and exception language for
laboratories are changes that were first published in
the 2004 Supplement to the International Codes and
the 2006 International Mechanical Code. These
changes were made to support safety and efficiency in
general, and to permit manifolding where appropriate.
5.4.2
Exhaust System Ductwork
5.4.2.1 Design
Laboratory exhaust system ductwork shall
comply with the appropriate sections of current
versions of the Sheet Metal and Air
Conditioning Contractors’ National Association
(SMACNA) standards.
Systems and ductwork shall be designed to
maintain negative pressure within all portions
of the ductwork inside the building when the
system is in operation.
It is permissible to locate exhaust fans in a normally
unoccupied enclosed space such as a roof penthouse
when the fan discharge ductwork is well sealed and the
enclosed space is adequately ventilated.
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Exhaust ductwork shall be designed in accordance with the current versions of ANSI/AIHA®
Z9.2,
the
ASHRAE
Handbook
–
Fundamentals, and NFPA 45.
Branch ducts shall enter a main duct so that
the branch duct centerline is on a plane that
includes the centerline of the main duct. For
horizontal main ducts, branch ducts shall not
enter a main duct on a plane below the horizontal traverse centerline of the main duct.
Horizontal runs of branch ducts shall be kept at
a minimum.
Longitudinal sections of a duct shall be a continuous seamless tube or of a continuously
welded formed sheet. Longitudinal seams that
are formed mechanically shall be utilized only
for light duty systems with no condensation or
accretion inside the duct. Spiral ducts may be
one gauge lighter than the required gauge of
longitudinal seam duct, except the spiral duct
gauge shall always meet the abrasive wear
resistance requirements.
Traverse joints shall be continuously welded or
flanged with welded or Van Stone flanges.
(When nonmetallic materials are used, joints
shall be cemented in accordance with the
manufacturer’s procedures.) If the duct is coated with a corrosion-resistant material, the
coating shall extend from the inside of the duct
to cover the entire face of the flange. Flange
faces shall be gasketed or beaded with material suitable for service.
When nonmetallic materials are used, joints cemented
in accordance with the manufacturer’s procedures may
be considered equivalent to welding.
If condensation within the duct is likely, all horizontal duct runs shall be sloped downward at
least 1 in. per 10 ft in the direction of the airflow
to a suitable drain or sump.
Exhaust duct sizes should be selected to ensure sufficiently high airflow velocity to retard condensation of
liquids or the adherence of solids within the exhaust
system.
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Exhaust airflow volume shall be sufficient to
keep the temperature in the duct below 400°F
(204°C) under all foreseeable circumstances.
In some cases, accumulation of solid material within
the duct system may be prevented by providing water
spray nozzles in the duct at frequent intervals and
sloping the duct down to an appropriate receptor (e.g.,
a wet dust collector).
This temperature limit applies in case of ignition of a
spill of flammable liquid that in turn requires an estimate of the maximum credible accident that would
generate heat.
All duct connections to the exhaust fan shall be
consistent with good ventilation design practice. As an alternative, the duct connections
may be made by means of inlet and outlet
boxes. If circumstances such as space limitations prevent the implementation of the preceding requirements, then applicable speed and
power corrections shall be made by applying
the “System Effect Factor" (see AMCA 201-90).
Where optimum duct connections cannot be
made due to space or other limitations, suitable
alternative means shall be substituted to compensate for the space limitations.
If adequate duct connections cannot be provided at the fan, the fan shall be equipped with
inlet and outlet boxes furnished by the fan manufacturer. The manufacturer shall furnish performance curves for the fan with the inlet and
outlet box(es) as part of the fan.
If neither adequate connections nor inlet/outlet
boxes are present, the fan speed and power
requirements represented in the fan rating table
shall be corrected by the “System Effect
Factor.”
If variable air volume (VAV) laboratory chemical hoods
are used, satisfying this criterion might require a heat
sensor arrangement to signal the VAV controls system
to increase the exhaust airflow. An alternative solution
would be to provide a higher temperature exhaust system design or a high-temperature combustion flue
design for the portions of the exhaust system in which
temperatures might exceed 400°F (204°C) in conjunction with the current version of NFPA 86.
For good inlet and outlet duct design refer to the Air
Movement and Control Association’s Fan Application
Manual Part 1, the ACGIH® Laboratory Ventilation
Manual, and the ASHRAE Handbook – Fundamentals.
An adequate outlet duct connection has the same
requirements as an air inlet duct except it need be only
3 diameters in length and no vortex breaker is necessary.
Transition fittings at the inlet and outlet should have a
15° or less included angle in any plane.
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5.4.2.2 Materials
Exhaust system materials shall be in accordance
with the current version of ACGIH’s Industrial
Ventilation: A Manual of Recommended Practice,
the ASHRAE Handbook – Fundamentals, and
NFPA 45.
Computation of this factor requires data on the fan’s
“blast area” and must typically be obtained from the
manufacturer.
Exhaust system materials shall be resistant to
corrosion by the agents to which they are
exposed. Exhaust system materials shall be noncombustible if perchloric acid or similar oxidizing
agents that pose a fire or explosive hazard are
used.
Solid metal ductwork has good fire characteristics but
in some cases has inferior corrosion resistance for
some chemicals. Solid plastic ductwork generally has
good corrosion resistance but may not be acceptable
to the local fire authority. An economical material that
can be used when appropriate and if proper care is
used in installation and maintenance is a metal duct
with a protective coating. However, because of the
thin coatings generally used, pinhole defects in the
coating may be relatively common, which would
eventually lead to a very small amount of leakage.
Any mechanical damage or scratching of the coating
in installation or maintenance would have to be
immediately and properly repaired or the bare metal
revealed in the scratch will be eaten away. Owner’s
representatives must spend more time and money
during installation to make sure contractor coats all
exposed metal during initial installation and similar
care must be exercised whenever the coated exhaust
duct is modified during renovations.
5.4.3
Manifolds
5.4.3.1 Combined Exhaust Systems
Two or more exhaust systems may be combined into
a single manifold and stack, if the conditions of
5.4.3.2 are met.
Manifold exhaust systems frequently have significant
advantages over individual (single-hood/single-fan)
systems and are encouraged.
Exhaust systems may combine all lab exhaust, or
may segregate general room exhaust from fume
hood exhaust. This decision can affect options for
heat recovery and air cleaning.
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Manifold and individual systems have the following
characteristics:
Manifold Systems:
Advantages:
• Contaminant concentrations from individual hoods
are diluted by the air from all the other hoods on
the manifold before being released into the atmosphere.
• 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.
• High mass of discharge makes it less susceptible to
wind.
• Operating costs are lower.
• Opportunity to install redundant fans is increased
and may only require one additional fan (i.e., cost
to provide redundancy is reduced.)
• Opportunity to install emergency power is increased
while the cost is reduced.
• Opportunity to utilize diversity is increased.
• Opportunity to efficiently utilize 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 application of a single hood (i.e., from
a standard laboratory chemical hood to radioisotope hood or perchloric acid hood) is difficult.
• Controls for system static pressure, capacity control, etc., are more complex than individual systems.
• Fan failure affects all hoods on the system and
redundancy is required.
• May be difficult to apply in existing buildings.
• The ability to provide treatment (i.e., scrubbing, filtering, etc.) for an individual exhaust source
requires an in-line scrubber and additional static
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pressure for the entire manifold or in the specific
hood branch.
Individual Systems:
Advantages:
• Changing the application of a single hood (i.e., from
a standard laboratory chemical hood to radioisotope hood or perchloric acid hood) is easily accomplished.
• Fan failure affects only a single hood.
• Less complex system.
• The ability to provide treatment (i.e., scrubbing, filtering, etc.) for an individual exhaust source is easily accomplished.
Disadvantages:
•
•
•
•
•
•
•
•
•
•
•
•
•
Applying diversity is difficult.
Energy recovery is not financially feasible.
First costs are higher.
Impossible to locate all 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 limitations and is more expensive.
Providing emergency power is difficult and more
expensive.
Providing future capacity for expansion requires
additional ductwork, equipment, and utilities.
Maintenance costs are higher.
Requires a larger number of roof penetrations and
roof leak potential is increased.
Shaft space requirements are higher.
There is no dilution of the source effluent before
releasing it to the atmosphere.
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Large Systems:
Large and/or diverse systems that have several types
of hoods often benefit from a hybrid approach where a
manifold is designed to handle a majority of the hoods
and individual exhaust systems are installed for those
that cannot or should not be manifolded such as perchloric acid or radioisotope hoods.
Adverse Chemical Reaction Potential:
Contrary to popular belief, the probability of two or
more reagents from different sources combining in the
manifold to produce an explosion is extremely small but
should be evaluated for special cases involving large
quantities of materials.
Consider the minimum manifold with two hoods connected to a single fan: Reagent A is spilled in Hood A,
covering the entire work surface and producing maximum evaporation and duct concentration while
Reagent B is similarly spilled in Hood B. Reactive
chemistry experts attempting to devise worst-case
binary reaction assure us that although these two
chemicals, when mixed in liquid or solid form, will certainly explode, when mixed in concentrations less than
10,000 ppm (1%) in air, it is unlikely that an explosive
reaction can be initiated or sustained (Hitchings,
unpublished data). The last statement notwithstanding,
assuming that a reaction can be initiated, the result
would be only a slight adiabatic temperature increase
in the duct.
The ability of chemicals from different sources to form
toxic products is similarly limited by low concentrations
that become lower and lower the closer they get to the
fan in manifold systems.
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5.4.3.2 Manifold Requirements
Laboratory chemical hood ducts may be combined into a common manifold with the following exceptions and limitations:
Flow regulating devices that are pressure-independent
devices also allow changes to be made in the system
without the need to rebalance the entire system.
Each control branch shall have a flow-regulating device to buffer the fluctuations in pressure
inherent in manifolds.
Manifolding of perchloric acid hoods is discouraged
because nonvertical ductwork is implied by connecting
one or more hoods together and nonvertical ducts are
difficult to wash down properly using duct-mounted
spray heads.
Perchloric acid hoods shall not be manifolded
with nonperchloric acid hoods unless a scrubber is installed between the hood and the manifold.
Where there is a potential for ductwork contamination from hood operations as determined
from the Hazard Assessment of Section 2.4,
radioisotope hoods shall not be manifolded
with nonradioisotope hoods unless an appropriate air-cleaning system is provided between
the hood and the manifold: HEPA filter and/or
carbon bed filters for gases.
Installing in-line filtration is impractical in most situations because it increases the overall static pressure
for the entire system unless a booster fan is installed
with the HEPA filters, which increases a leak potential.
Manifolding of radioisotope hoods is discouraged due
to the potential contamination of the entire exhaust
system in the event of HEPA filtration failure and the
possibility of pressurizing the exhaust manifold with the
booster fan.
HEPA filters only cover radioactive dust, not radioactive gases.
Systems that use heavy digestions or other operations
that could cause condensation in the duct may not be
appropriate for a manifold system. The high potential of
condensation imposes drainage problems throughout
the system rather than just for the hoods that may have
high condensation.
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5.4.3.3 Compatibility of Sources
Exhaust streams that contain concentrations
of flammable or explosive vapors at concentrations above the Lower Explosion Limit (LEL) as
well as those that might form explosive compounds (i.e., perchloric acid hood exhaust)
shall not be connected to a centralized
exhaust system. Exhaust streams comprised
of radioactive materials shall be adequately filtered to ensure removal of radioactive material before being connected to a centralized
exhaust system. Biological exhaust hoods
shall be adequately filtered to remove all hazardous biological substances prior to connection to a centralized exhaust system.
5.4.3.4 Exhaust System Reliability
Unless all individual exhausts connected to the
centralized exhaust system can be completely
stopped without creating a hazardous situation, provision shall be made for continuous
maintenance of adequate negative static pressure (suction) in all parts of the system.
This requirement could be satisfied by one or both of
the following provisions:
• Multiple operating fans so the loss of a single fan
does not result in loss of total system negative
static pressure.
• Spare centralized system exhaust fan(s) that will
rapidly and automatically be put into service upon
failure of an operating fan by repositioning isolation
dampers and energizing the standby fan motor.
Emergency backup power should be provided to all
exhaust fans and the associated control system.
As an alternative, if the hood is completely
turned off, the hood shall be emptied and
decontaminated and provisions shall be implemented to prevent the hood from back-drafting.
Before considering complete shutdown of the hood, the
following 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 independent of the sash position.
The VAV hood shall be provided with an emergency switch that allows the hood exhaust volume to return to the maximum.
Note this requires careful planning for a system with
less than 100% diversity (See Section 5.1.2).
If the maximum exhaust volume of the variable air volume hoods in one room exceeds 10% of the room air
supply volume, and if the laboratory is designed for
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controlled airflow between the laboratory and adjacent
spaces, automatic flow control devices should be provided to reduce the supply air volume by the same
amount that hood exhaust volume is reduced.
At present, this system requires sophisticated testing
equipment and training of maintenance personnel.
5.4.3.5 Biological Safety Cabinets
Biological safety cabinets manifolded with
chemical laboratory chemical hoods shall have
either:
1) A thimble connection (also known as a
canopy connection), or
Thimbles allow the exhaust flow to continue exhausting
airflow from the room when the biological safety cabinet is off thus avoiding continuous dust loading of the
biological safety cabinet filters.
Secondly, this prevents the exhaust system from
becoming positively pressurized by the internal fans in
the biological safety cabinets in the event that the
exhaust system should fail.
2) An air flow control device and an interlock/alarm for these devices shall be installed
between the cabinet outlet and the exhaust
manifold.
Where Hazard Evaluation and Analysis determines that the installation calls for direct connection (hard ducted) of the biological safety
cabinet (e.g., Class II–Type B) to an exhaust
manifold system to allow work with toxic chemicals or radionuclides, interlocks and alarms
shall be provided to prevent the biological
safety cabinet from operating its normal starting mode or to immediately warn the operator
in the event of an exhaust system failure
(CDC-NIH, 1999).
Thirdly, continuous exhaust through the thimble connection may be important for room air balance as well
as removing the heat load of laboratory equipment.
For direct (hard ducting) of Class II Type B cabinet, the
exhaust flow balance is critical for the needed inflow
velocity of the biological safety cabinet.
Where the installation calls for direct connection of the
biological safety cabinet (e.g., Class II–Type B), interlocks and alarms should be provided to prevent the biological safety cabinet from shutting down and to immediately warn the operator in the event of an exhaust
system failure. Thimble connections can be improperly
designed and are sometimes difficult to balance and
draw in a small amount of room air. However, they are
recommended over the direct connection and operation interlock design so that worker and product protection are maintained even in the event of an exhaust
system failure. Interlocks, if activated during an exhaust
system failure involving radioactive materials, could
cause worker or product exposure. A non-manifolded
dedicated exhaust system connection directly vented
to the atmosphere may be needed for work with these
types of hazardous materials.
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Constant volume control devices maintain a constant
exhaust rate from all types of biological safety cabinets
regardless of changes in exhaust system static pressure.
Refer to NSF 49 for testing and certification of biological safety cabinets.
5.4.3.6 Static Pressure
The static pressure in the exhaust system shall
be lower than the surrounding areas throughout the entire length, with the exception noted
in Section 5.3.1.1.
This prevents contaminated air from leaking out of the
duct into the building.
5.4.3.7 Fire Dampers
Fire dampers shall not be installed in exhaust
system ductwork (NFPA 45).
The accidental activation of a fire damper will shut off
airflow from one or more laboratory chemical hoods
and may cause worker injury or exposure.
The activation of a fire damper caused by a fire in a laboratory chemical hood will shut off airflow from that
hood making it impossible to remove the combustion
products from the hood and forcing the hood to
become positively pressurized. This condition makes it
likely that the fire will escape the fire-resistant hood into
the laboratory.
With the exhaust flow from one or more hoods shut off,
the laboratory may become positively pressurized with
respect to the corridor, encouraging the spread of the
combustion products, and perhaps the fire, from the
laboratory to adjoining spaces.
5.4.3.8 Fire Suppression
Fire sprinklers shall not be installed in laboratory chemical hood exhaust manifolds.
Studies of actual exhaust systems have demonstrated
that the spray cone produced by sprinkler heads can
actually act as a damper and reduce or prevent airflow
in the duct past the sprinkler head (Hitchings and
Deluga, personal communication). Like a fire damper,
this may produce a lack of flow at one or more laboratory chemical hoods at the moment when it is needed
most.
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5.4.3.9 Continuous Operation
Exhaust systems shall operate continuously to
provide adequate ventilation for any hood at
any time it is in use and to prevent backflow of
air into the laboratory when the following conditions are present:
A “motorized damper” may need to be provided at the
fan to isolate the system from a stack effect.
• Chemicals are present in any hood
(opened or unopened).
• Exhaust system operation is required to
maintain minimum ventilation rates and
room pressure control.
• There are powered devices connected to
the manifold. Powered devices include,
but are not limited to: biological safety
cabinets, in-line scrubbers, motorized
dampers, and booster fans.
5.4.3.10 Constant Suction, Redundancy
and Emergency Power
Manifolds shall be maintained under negative
pressure at all times and be provided with at
least two exhaust fans for redundant capacity.
Emergency power shall be connected to one
or more of the exhaust fans where exhaust
system function must be maintained even
under power outage situations.
5.4.4
The manifold fans and controls should be designed so
that sufficient static pressure is available to each connected exhaust source for all conditions that do not
exceed the system diversity. Since each critical connected source (i.e., laboratory hoods) should have continuous performance monitors, exceeding system
capacity should also result in flow alarms.
Exhaust Fans
Each fan applied to serve a laboratory exhaust
system or to exhaust an individual piece of laboratory equipment (e.g., a laboratory chemical
hood, biosafety cabinet, chemical storage,
etc.) shall be adequately sized to provide the
necessary amount of exhaust airflow in conjunction with the size, amount, and configuration of the connecting ductwork. In addition,
each fan’s rotational speed and motor horsepower shall be sufficient to maintain both the
required exhaust airflow and stack exit velocity
and the necessary negative static pressure
(suction) in all parts of the exhaust system.
If flammable gas, vapor, or combustible dust is
present in concentrations above 20% of the
Lower Flammable Limit, fan construction shall
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be as recommended by the current version of
AMCA’s 99-0401, Classifications for Spark
Resistant Construction.
Laboratory exhaust fans shall be located as
follows:
• Physically outside of the laboratory building
and preferably on the highest level roof of
the building served. This is the preferred
location since it generally minimizes risk of
personnel coming into contact with the
exhaust airflow.
• In roof penthouse or a roof mechanical
equipment room that is always maintained at
a negative static pressure with respect to the
rest of the facility, and provides direct fan discharge into the exhaust stack(s).
Under most operating conditions, centrifugal fans
will leak small amounts of system gases at the fan
shaft. Also, fan discharge ducts typically are under
positive pressure and any air leaks would discharge
into the room. Locating laboratory exhaust fans as
required helps ensure that any leakage will be
effectively removed and will not migrate within the
building.
It is permissible to locate exhaust fans in a normally unoccupied enclosed space such as a roof penthouse when the fan discharge ductwork is well
sealed and the enclosed space is adequately ventilated.
All laboratory exhaust fans shall include provisions to allow periodic shutdown for inspection
and maintenance. Such provisions include:
• Isolation dampers on the inlet side of all centralized exhaust system fans that have individual discharge arrangements or their own
individual exhaust stacks.
• Isolation dampers on both the inlet and outlet
sides of all centralized exhaust system fans
that discharge into a common exhaust stack
or plenum.
• Ready access to all fans, motors, belts, drives, isolation dampers, associated control
equipment, and the connecting ductwork.
• Sufficient space to allow removal and
replacement of a fan, its motor, and all other
associated exhaust system components and
equipment without affecting other mechanical equipment or the need to alter the building structure.
The requirements for inspection access and serviceability are intended to ensure that laboratory
exhaust systems can be kept and maintained in
proper operating condition. If a centralized exhaust
system has multiple fans and a fan replacement is
necessary, the process should not require disconnecting piping or removing other building encumbrances that might lead to an indefinite postponement of the required work.
See Section 8.1, Operations During Maintenance
Shutdown, for necessary requirements and guidance.
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5.4.5
Discharge of Contaminated Air
The discharge of potentially contaminated air that contains a concentration more than the allowable breathing air concentration shall be
• direct to the atmosphere unless the air is treated
to the degree necessary for recirculation (see
Section 9.3),
• discharged in a manner and location to avoid
reentry into the laboratory building or adjacent
buildings at concentrations above 20% of allowable concentrations inside the laboratory for routine emissions or 100% of allowable concentrations for emergency emissions under wind conditions up to the 1%-wind speed for the site, and
• in compliance with applicable federal, state, or
local regulations with respect to air emissions
5.4.6
The in-stack concentrations of contaminants
allowed under such regulations typically range
from 100 to 1000 times higher than safe breathing concentrations.
The 1% wind speed is the value exceeded at
the site only 1% of time, according to historical
weather records.
Exhaust Stack Discharge
The exhaust stack discharge shall be in accordance
with the current version of ASHRAE Handbook –
HVAC Applications, and the chapter or section dealing
with Building Air Intake and Exhaust Design.
In any event the discharge shall be a minimum of 10 ft
(3 m) above adjacent roof lines and air intakes and in
a vertical up direction.
Necessary measures must be taken to protect
the laboratory building and adjacent buildings
from toxic materials reentry.
The 10 ft (3 m) height above the adjacent roof
line called for by this standard is primarily
intended to protect maintenance workers from
direct exposure from the top of the stack. However, this minimum 10 ft (3 m) height may be
insufficient to guarantee that harmful contaminants won’t enter the outside air intake of the
building or of nearby buildings.
After initial installation, the exhaust stack is
unchanged for the lifetime of the hood. It is
uncertain that the lifetime hood usage can be
accurately projected. In most cases, consistent
discipline in safe hood procedures cannot be
assured. Accordingly, it is prudent to use conservative guidelines in the location and
arrangement of the hood discharge.
The basic challenge in locating the hood discharge is to avoid re-entrainment of effluent
into any building air intake or opening and to
minimize exposure of the public. The selection
of stack height is dependent on the building
geometry and airflow pattern around the build-
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ing and is as variable as meteorological conditions.
An excellent resource is Chapter 44 of the ASHRAE
2007 Handbook – HVAC Applications. Among the factors to consider in establishing stack configuration,
design, and height are: toxicity, corrosivity, and relative
humidity of the exhaust, meteorological conditions,
geometry of the building, type of stack head and cap
design, adjacency of other discharged stacks and
building intake, discharge velocity, and receptor population.
Exhaust stack discharge velocity shall be at
least 3000 fpm (15.2 m/s) is required unless it
can be demonstrated that a specific design
meets the dilution criteria necessary to reduce
the concentration of hazardous materials in the
exhaust to safe levels (See Section 2.1) at all
potential receptors.
A discharge velocity of 2500 fpm (12.7 m/s) prevents
downward flow of condensed moisture within the
exhaust stack. It is good practice to make the terminal
velocity at least 3000 fpm (15.2 m/s) to encourage
plume rise and dilution.
Aesthetic conditions concerning external
appearance shall not supersede the requirements of Sections 5.4.5 and 5.4.6.
In case there is a conflict, the requirements of Section
5.3.4 take priority. Some solutions that may be used
are:
Any architectural structure that protrudes to a
height close to the stack-top elevation (i.e.,
architectural structure to mask unwanted
appearance of stack, penthouses, mechanical
equipment, nearby buildings, trees or other
structures) shall be evaluated for its effects on
re-entrainment
The air intake or exhaust grilles shall not be
located within the architectural screen or mask
unless it is demonstrated to be acceptable.
These factors affect the dilution of the exhaust stream
and the plume trajectory. High discharge velocity and
temperature increase plume rise, but high velocity is
generally less effective than increased stack height.
• An evaluation of the stack design that will account
for the effects of problem structures should be
undertaken. The evaluation should provide estimates of the expected concentration levels of
exhaust contaminants at surrounding air intakes.
Appropriate physical modeling (wind tunnel, mockup or water flume) or numerical modeling using
appropriate methods (Computational Fluid
Dynamics or other advanced numerical methods)
should be undertaken as discussed in Chapter 44
of the ASHRAE 2007 Handbook – HVAC
Applications. The limitations of the technique utilized
should be understood and evidence should be provided that the results are conservative or accurate
for the case being modeled. When physical modeling is used, procedures discussed in the EPA
Guideline for Modeling of Atmospheric Diffusion
(Office of Air Quality Planning and Standards, EPA600/8-81-009, April 1981) should be employed.
• Treatment of the discharge gas may permit a
lower and esthetically acceptable stack. The technology of gas-treating equipment is outside the
scope of this standard except as described in
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Section 9.2.
• Appendix 3 is provided to assist the designer in
understanding stack height determination and
evaluation methods.
5.4.7
Recirculation of Room Exhaust Air
Non-laboratory air or air from building areas
adjacent to the laboratory is permitted as part of
the supply air to the laboratory if its quality is
adequate.
In many laboratory settings, the laboratory is purposely kept at a slight negative differential pressure
with respect to adjacent building spaces. In this situation, air flows from the adjacent spaces into the laboratory through building cracks and doorways, at least
when open. This may be highly desirable; if not, this
flow can be reduced, but not completely eliminated, by
use of double-door anterooms, with corresponding
consumption of interior space and some hindrance to
traffic.
5.4.7.1 General Room Exhaust
Air exhausted from the general laboratory
space (as distinguished from laboratory chemical hoods) shall not be recirculated to other
areas unless one of the following sets of criteria
is met:
1) Criteria A
Some laboratories have no general exhaust, so there
is no flow to consider recirculating.
Devices that are intended to provide heating and/or
cooling by recirculating the air within a laboratory
space (i.e., fan coil units) are exempt from this
requirement
• The concentration of air contaminants generated by maximum credible accident will
be lower than short-term exposure limits
required by 2.1.1;
• There are no extremely dangerous or lifethreatening materials used in the laboratory; and
• The system serving the laboratory chemical hoods is provided with installed redundancy, emergency power, and other reliability features as necessary, or
2) Criteria B
• Provision of 100% outside air, whenever
continuous monitoring indicates an alarm
condition;
• Recirculated air is treated to reduce contaminant concentrations to those specified in
2.1.1; and
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• Recirculated air is monitored continuously
for contaminant concentrations or provided with a secondary backup air-cleaning
device that also serves as a monitor (via
a HEPA filter in a series with a less efficient filter, for particulate contamination
only). Refer to Section 9.3.1.
5.4.7.2 Hood Exhaust
Exhaust air from laboratory hoods shall not be
recirculated to other areas.
Hood exhaust air meeting the same criteria as
noted in Section 5.4.7.1 shall only be recirculated to the same work area where the hood
operators have control of the hood work practices and can monitor the status of air cleaning.
For most laboratories, recirculation of laboratory chemical hood air should be avoided. Laboratory chemical
hood air usually contains significant amounts of materials with differing requirements for removal. Providing
air-cleaning equipment to permit safe recirculation represents a high capital and operating cost, especially
when redundancy and monitoring requirements are
considered.
Refer to the current version of NFPA 45 for its position
on recirculation of laboratory chemical hood air when
using flammables.
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, shall
refer to the applicable ANSI/ASHRAE 110
defined performance tests or to a test standard
recognized to be equivalent.
Specification and procurement of laboratory
fume hoods shall be based on “As
Manufactured” ANSI/ASHRAE 110 defined
performance tests conducted on a representative hood (or prototype hood) that demonstrate
Some “single purpose” laboratories might find it practical to recirculate laboratory chemical hood air; the
requirements are similar to those in Section 5.3.7.1 criteria B. See Section 4.2 for more information.
ANSI/ASHRAE 110 defines three different test scenarios, “As Manufactured, As Installed and As Used.”
”As Manufactured” tests, usually performed at the hood
manufacturer’s facility, are conducted to determine
whether the hood is adequately designed to provide
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adequate hood containment.
The performance tests to be witnessed, referenced
or otherwise shall include
•
•
•
•
•
•
•
airflow visualization tests,
auxiliary 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 volume conditions where exhaust and air supply flow
are stable and exhibit no more than 5% variation
from set-point.
the required level of performance. In addition, the
tests are conducted to determine appropriate
operating specifications. It is only necessary to
perform these tests on one hood for each unique
hood design or mode.
Credible catalog data on the fundamental performance and capabilities of a hood as it comes from
the manufacturer are useful. The designer can then
specify the unit with confidence that it will perform
as per the manufacturer’s catalog data. It is recommended that the manufacturers’ tests be conducted
or witnessed by the laboratory owner and design
professional, and/or independent third party.
The containment tests should be conducted over
the range of possible operating configurations
afforded by the hood design (i.e., sash position, baffle configurations, etc.) and at different target face
velocities or exhaust flow rates to determine operational boundary conditions and hood limitations.
Proper containment of a laboratory fume hood is
affected by a number of factors including design of
the hood, design of the laboratory, and design and
operation of the ventilation systems. Controlled
tests enable elimination of one variable: design of
the hood. Therefore, performance problems
encountered after installation can be attributed to
other factors.
Where possible, containment tests should be conducted according to methods described in the
most recent ANSI/ASHRAE 110 standard equal to
or more challenging than the standardized test.
ANSI/ASHRAE 110 does not specify a face velocity. The standard yields a performance rating in the
form of AM yy, AI yy, or AU yy where, AM means
“as manufactured,” AI means “as installed,” and AU
means “as used.” The symbol yy represents the
average 5-minute concentration of tracer gas measured in the breathing zone of a mannequin used
to simulate a hood user.
The ANSI/ASHRAE 110 standard recommends a
gas generation rate of 4 L/m. However, other generation rates (i.e., 1 L/m or 8 L/m) can be specified
by the design professional or responsible person
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(2.3) when deemed appropriate.
Testing at different operating configurations will help to
identify operational limitations or worst-case operating
conditions. This information helps the design professional in their work and can then be relayed to the
hood users to ensure proper work practices that minimize potential for exposure.
6.1.2
Performance Tests
The following performance tests shall be conducted as indicated and as prescribed in the
commissioning plan, laboratory ventilation
management plan, or as directed by the
responsible person.
6.1.2.1 Airflow Visualization Tests
Airflow visualization tests shall be conducted
as described in the ANSI/ASHRAE 110–1995,
Method of Testing Performance of Laboratory
Fume Hoods.
The tests shall consist of small-volume generation and large-volume generation smoke to
identify areas of reverse flow, stagnation zones,
vortex regions, escape, and clearance.
Visible escape beyond the plane of the sash
when generated 6 in. (15.2 cm) into the hood
shall constitute a failure during the performance test.
Smoke tests are valuable because they indicate the
direction of airflow through the opening and within the
hood enclosure when the smoke plume is visible.
Smoke particles are rapidly diluted to the extent where
they may not be visible even though significant concentrations may exist in the invisible plume. Smoke
tests should be used only as an indication of flow
direction and absence of visible smoke should not be
interpreted as an absence of smoke. Users of smoke
should note that smoke tubes and candles can be
caustic and detrimental to the user, test equipment,
and apparatus in the hood.
Attempts to improve airflow patterns should be attempted by adjusting the baffles and slot widths, redirecting
room air currents, or changing the opening configuration by moving the sash panels. Closure of the sashes
resulting in an opening smaller than the design opening
may represent a “restricted use” condition.
Often the most devastating area for reverse flow is
behind the airfoil sill on bench-top-mounted hoods. An
improperly designed airfoil or lack of an airfoil will
cause reverse flow along the work surface within 6 in.
(15.2 cm) of the sash plane. Reverse flow in this region
is particularly worrisome as the wake zone that develops in front of a hood user could overlap with the
reverse flow zone.
Dynamic challenges should be evaluated.
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6.1.2.2 Auxiliary Air Velocity Tests
For auxiliary air hoods, the face velocity shall be
measured with the auxiliary air turned off unless
room pressurization would change significantly to
affect exhaust flow. Where exhaust flow would be
affected by turning off the auxiliary airflow, auxiliary air must be redirected from the hood opening
so as not to interfere with flow into the hood while
conducting the face velocity traverse.
The velocity of the auxiliary air exiting the auxiliary
air plenum shall be measured to determine the
magnitude and distribution of air supplied above
the hood opening.
The average auxiliary air velocity shall be determined from the average of grid velocities measured across the plenum outlet.
Hood face velocity is usually defined as air speed in
a direction normal to the plane of the hood face
opening. For auxiliary air hoods in standard operation, the directional component of the air velocity is
not normal to the hood face plane. Accurate determination of the flow direction and derivation of the
horizontal and vertical components of the velocity
vector require very sophisticated instrumentation
because of the low air speeds involved. Hence,
measuring the hood’s face velocity with the auxiliary air shut off is an acceptable measure of hood
exhaust volume, if turning off the auxiliary air does
not upset the room air balance enough to reduce
significantly the volume extracted by the hood
exhaust system.
Face velocity measurements should be determined
with the supply air off or with special devices
designed to eliminate the effect of the auxiliary air
at the hood face. For example, supply air from the
auxiliary air plenum can be temporarily redirected
away from the sash opening by use of a portable
baffle, hand held or otherwise placed beneath the
supply air discharge without blocking off the supply
air flow.
NOTE: The 90% capture efficiency should be tested by material balance by introducing a tracer gas
into the auxiliary airstream and sampling the hood
exhaust. Flow volume and sampling should be in
accordance with EPA methods 1, 2, and 17 (40
CFR 60, Appendix A) or by other methods mutually agreed on by all parties.
The auxiliary air supply plenum located above the
top of the hood face and external to the hood
should be designed to distribute air across the
width of the hood opening so as not to affect containment.
Excessive auxiliary air velocity can interfere or
overcome air flowing into the hood opening and
cause escape from the hood.
The downflow velocities should be measured
approximately 6 in. (15.2 cm) above the bottom
edge of the sash positioned at the design opening
height.
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6.1.2.3 Cross-Draft Velocity Tests
Cross-draft velocity measurements shall be
made with the sashes open and the velocity
probe positioned at several locations near the
hood opening to detect potentially interfering
room air currents (cross drafts). Record measurement locations.
Over a period of 10–30 sec., cross-draft velocities shall be recorded approximately 1 reading
per second using a thermal anemometer with
an accuracy of +5% at 50 fpm (0.25 m/s) or
better.
The average and maximum cross-draft velocities at each location shall be recorded and not
be sufficient to cause escape from the hood.
Cross draft velocities shall not be of such magnitude and direction as to negatively affect
containment.
More test locations may be required or can be useful
for determining cross-draft velocities past the hood
opening. Vertical and horizontal components of crossdraft velocities should be measured at each location.
Increasing face velocity may not make the hood more
resistant to cross drafts. However, increasing face
velocity may:
• Increase the required volume of room air supply
and increase difficulties with ensuring proper
room air distribution.
• Increase exhaust of expensive conditioned air.
Excessive cross-draft velocities (>50% of the average
face velocity) have been demonstrated to significantly
affect hood containment and should be identified and
alleviated. Ideally, cross-draft velocities should be less
than 30%.
If the supply tracks the exhaust, measure the cross
drafts at the maximum conditions.
6.1.2.4 Exhaust Flow Measurements
The volumetric flow exhausted from a laboratory fume hood shall be determined by measuring the flow in the exhaust duct using industry-approved methods.
See the current version of ACGIH®’s Industrial
Ventilation: A Manual for Recommended Practice, or
ANSI/ASHRAE 41.2–1987 (RA 92), for measuring flow.
The hood exhaust flow should be adjusted to achieve
the target average face velocity at the design opening
and to achieve the specified flow with the sash closed.
Typically, exhaust flow can be predicted from the area
of the opening multiplied by the design face velocity.
However, infiltration of air into the hood through openings other than the face may require approximately
5–10% more exhaust flow than calculated. The exhaust
flow and variance from the calculated flow should be
determined to enable proper specification of flows for
design of the ventilation systems.
Failure to determine the total exhaust flow required to
achieve the desired average face velocity may result in
under sizing of the exhaust system or improper specification of supply volume to achieve required lab pressurization or differential airflow.
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Calculation of exhaust flow from face velocity measurements multiplied by hood face area is not a measurement of exhaust flow and due to the reasons stated above, true exhaust flow can vary significantly from
the calculated exhaust flow. In addition, the accuracy of
face velocity measurements can affect the accuracy of
the average face velocity used to calculate exhaust
flow. Face velocities measured at the plane of the sash
opening using hot-wire anemometers or pressure grid
assemblies can be subject to significant error due to
turbulence at the opening and direction of airflow over
the probes where average face velocities could vary
from actual by 5–20%.
6.1.2.5 Face Velocity Tests
Once adequate performance has been established for a particular hood at a given benchmark face velocity using the methods
described herein, that benchmark face velocity shall be used as a periodic check for continued performance as long as no substantive
changes have occurred to the hood or other
aspects that affect hood performance.
Substantive changes include: changes in hood setup;
hood face velocity control type, set point, range, and
response time; exhaust system static pressure, control
range and response time; the hood operating environment including lab/furniture geometry, supply air distribution patterns, and volume; and room pressure control range and response time.
Face velocity measurements shall be made
with the sash in the Design Sash Position. The
Design Sash Position is the maximum opening
or configuration allowed by user standards,
SOPs, or the Chemical Hygiene Plan,
whichever is applicable, and used in the
design of the exhaust system to which the
hood is connected.
The face velocity of a combination sash is sometimes
determined with the sash closed and the horizontal
windows open. For "set-up" conditions, the determination of the actual face velocity may not be unique. The
face velocity of combination sash hoods should identify the sash position where the tests were conducted.
The sash position at which benchmark face
velocity is measured shall be recorded with the
face velocity measurement and reproduced
each time measurements are taken.
It is important to use the same sash position for successive periodic performance measurements.
A decrease in the average face velocity below
90% of the benchmark velocity shall be corrected prior to continued hood use.
This magnitude of decrease may impair performance.
Face velocity increases exceeding 20% of the
benchmark shall be corrected prior to continued use.
An increase in individual hood average face velocity
not exceeding 20% of the benchmark face velocity will
probably not significantly alter hood performance and
is acceptable with no corrective action. It should be
noted, however, that there is an unnecessary increase
in operating cost with increased face velocities.
Increases exceeding 20% and the accompanying
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increase in supply flow rates may degrade performance
due to increased impingement and cross-draft velocities. In addition, an increase in face velocity at the measured hood may indicate a decrease in face velocity at
other hoods in the exhaust systems.
In constant volume systems, the face velocity will
increase with reduced sash height. Although the face
velocity could be three times or more than the design
face velocity, the hood performance does not usually
deteriorate because the hood opening is reduced
(which often improves performance) and the lowered
sash acts as a partial barrier.
Supply and exhaust system capacities should be
observed in the event of hood face velocity increases as
volume shifting may occur, depriving other hoods of
adequate airflow.
Periodic dynamic testing should be performed when
significant changes have occurred or to evaluate the
response of a VAV system.
The average face velocity alone is inadequate to
describe hood performance. Face velocity is not a measure of containment but only the speed of air entering
the face opening. Hood performance should be determined from tests of hood containment. Average face
velocity should only be used as an indicator of proper
system operation.
Refer to section 3.3.1, for information about analysis of
face velocity data and recommended criteria.
The average face velocity shall be determined
by the method described in the current version
of ANSI/ASHRAE 110 Method of Testing
Performance of Laboratory Fume Hoods.
Face velocity measurements shall be made by
dividing the hood opening into equal area grids
with sides measuring no more than 12 in. (30.5
cm). The tip of the probe shall be positioned in
the plane of the sash opening and fixed (not
handheld) at the approximate center of each
grid. Grid measurements around the perimeter
The accuracy of face velocity measurements can be
affected by numerous factors including instrument
accuracy, measurement technique, hood aerodynamics, room air conditions (cross drafts), and exhaust flow
stability. Average face velocities and grid velocities can
be significantly affected by turbulence (temporal variation) and direction through the opening (spatial variation). Multiple readings taken over time at each grid
location are recommended to provide more accurate
velocity measurements. Cross drafts can also bias face
velocity data by creating turbulence at the opening and
variations in face velocity readings.
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of the hood opening shall be made at a distance
of approximately 6 in. (15.2 cm) from the top,
bottom, and sides of the opening enclosure.
Multiple readings at each grid point will help determine
more accurate average face velocities when turbulent
air is present at the hood opening. Multiple readings
can be acquired with the use of time constants for
meters so equipped or use of a data logger or data
acquisition system attached to a computer.
The average face velocity shall be the average
of the grid velocity measurements.
Manufacturers have been defining the sash plane somewhat subjectively, thus making it difficult for users to compare face velocity data and AM containment test results.
This definition from ANSI/ASHRAE 110 aims to lessen
the subjectivity in AM as well as AI and AU testing.
Each grid velocity shall be the average of at
least 10 measurements made over at least 10
seconds.
The plane of the sash shall be defined as the
exterior surface of the outer most glass panel.
6.1.2.6 Hood Static Pressure Measurements
The hood static pressure shall be measured
above the outlet collar of the hood at the flows
required to achieve the design average face
velocity.
For test method, refer to current version of
ANSI/ASHRAE 41.3. Hood static pressure is a measure of the resistance imposed on the exhaust system
by the hood. Determination of hood static pressure is
required to ensure proper system design. Typical hood
static pressures range from 0.1 to 0.75 in.wg (25 to 187
Pa) at face velocities between 80 to 120 fpm (0.41 to
0.61 m/s). However, the hood static pressure will
depend on the hood design and exhaust flow.
6.1.2.7 Tracer Gas Containment Tests
The tracer gas containment tests shall be conducted as described in the ANSI/ASHRAE
110–1995, Method of Testing Performance of
Laboratory Fume Hoods or by a test recognized to be equivalent.
A control level for 5-minute average tests at
each location conducted at a generation rate
of 4 L/m shall be no greater than 0.05 ppm for
"as manufactured” tests and 0.10 ppm for “as
installed” (AM 0.05, AI 0.1).
Escape more than the control levels stated
above shall be acceptable at the discretion of
the design professional in agreement with the
responsible person (2.4.2). The “as used” 0.10
ppm level or more is at the discretion of the
responsible person (2.3).
Tracer gas tests enable the ability to quantify the potential for escape from a laboratory fume hood.
The test data need to be made available by the manufacturer for each specific model and type of hood so a
potential buyer can verify proper containment or compare one manufacturer’s hood containment against
another.
Values for control level may not be suitable for establishing hood safety, as the tracer gas test methods may
not adequately simulate actual material use, risk, or
generation characteristics. In addition, the tracer gas
test does not simulate a live operator, who may
increase potential for escape due to operator size,
movements near the hood opening, or improper hood
use.
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Hood containment should be evaluated at different
mannequin heights to represent workers of different
height.
AM 0.05 can be achieved with a properly designed laboratory fume hood. It should not be implied that this
exposure level is safe. Safe exposure levels are application specific and should be evaluated by properly
trained personnel (SEFA 1-2002).
6.1.3
Test Instrumentation
All test instrumentation utilized for the tests
prescribed throughout this section shall be in
good working order and shall have been factory calibrated within 1 year of the date of use.
(See 8.6.1, Air Velocity, Air Pressure,
Temperature and Humidity Instruments)
6.2
Commissioning of Laboratory
Ventilation Systems
6.2.1
Commissioning Process
All newly installed, renovated, or moved hoods
shall be commissioned to ensure proper operation prior to use by laboratory personnel.
6.2.2
Commissioning tests are conducted to ensure that laboratory ventilation systems operate according to
design specifications and are capable of meeting control objectives under resulting operating conditions. The
extent of the commissioning process depends on the
complexity of the systems along with the anticipated
risk associated with work to be conducted in the laboratory.
Commissioning Authority
The commissioning process shall be overseen
by a responsible person or commissioning
authority.
The commissioning authority should be someone who
represents the interests of the system owner and
should be knowledgeable in the design and operation
of laboratory ventilation systems. In addition, the commissioning authority should be experienced with collection and analysis of test data.
The commissioning authority may develop the commissioning plan in conjunction with information provided by potential equipment suppliers and contractors,
owner personnel, and project design professionals.
A commissioning team consisting of personnel directly
involved in the design, installation, and use of the new
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or renovated systems should assist the commissioning
authority. A commissioning team might include:
•
•
•
•
•
•
•
•
•
6.2.3
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.
Commissioning Plan
A written commissioning plan shall accompany
design documents and be approved by the
commissioning authority in advance of construction activities.
The commissioning plan shall be available to
all potential suppliers and contractors prior to
bid along with the other project documents.
The conceptual design phase of the project generally
includes a statement of performance objective and criteria for establishing proper operation of proposed systems. The statement of performance provides an operational definition of performance that can be measured
after installation and startup to validate or verify proper
operation. The commissioning plan describes the tests
that will be conducted to verify proper operation of the
systems.
A commissioning plan shall address operation
of the entire ventilation system where the
hoods, laboratories, and associated exhaust
and air supply ventilation systems are considered subsystems.
The plan shall include written procedures to
verify or validate proper operation of all system
components and include:
• Laboratory Fume Hood Specification and
Performance Tests
• Preoccupancy Hood and Ventilation
System Commissioning Tests
• Preoccupancy Laboratory Commissioning
Tests
For example, an operational definition for proper performance of a new hood system might include: the new
hood operated with the vertical sliding sash at a height
of 28 in. (71.1 cm) must have an average face velocity
between 80–120 fpm (0.41 to 0.61 m/s) and provide
containment below a control level of AU 0.1 ppm as
determined by methods described in the
ANSI/ASHRAE 110–1995, Method of Testing
Performance of Laboratory Fume Hoods.
A laboratory fume hood system includes all associated
subsystems such as the hoods, ducts, dampers, automated controls, filtration, fan, motor, and exhaust
stacks. In laboratories, the air supply system is considered part of the hood system when operation can affect
hood performance.
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It is imperative that the commissioning plan be completed and that is part of the project design documents.
It should not be developed after the bid process or
signing of contracts because it may substantially
impact the individual contractor laboratory costs and
scheduling. If it is developed after the bid date, whatever requirements it imposes on a contractor could be
contested as being invalid since it was not available at
the time of bid.
Design changes made subsequent to construction
must be reflected in a revised commissioning plan.
6.2.4
Commissioning Documentation
Preliminary and final commissioning documents shall be issued to the appropriate
party(s) by the Commissioning Authority.
The documents should detail the status of the ventilation systems relative to maintaining a safe facility environment.
The documents shall include:
The document should clearly indicate, based upon the
ventilation system functionality, which laboratory rooms
and equipment (i.e., chemical laboratory hoods,
biosafety cabinets, etc.) are ready for safe use, any
areas or equipment that are not safe for use or occupancy, and other safety-related ventilation system
details.
•
•
•
•
Commissioning Test Data;
Copy of Test and Balance Report;
Design Flow Specifications;
Laboratory and System Drawings for Final
System Design;
• List of Ventilation System Deficiencies
uncovered and the details of how (and if)
they were satisfactorily resolved.
Operational deficiencies and other problems
uncovered by the commissioning process shall
be communicated to the responsible party
(i.e., installer, subcontractor, etc.) for prompt
correction.
6.3
Commissioning Fume Hoods and
Different Types of Systems
6.3.1
Laboratory Fume Hoods
If practical, the exhaust flowrate from hoods
shall be tested by measuring the flow in the
duct by the hood throat suction method or by
flow meter.
Unreasonable delays or unsatisfactory follow-up
should be communicated to the owner as well as any
contractors in the tier to which this subcontractor is
responsible.
See the current edition of the ACGIH®– Industrial
Ventilation: A Manual of Recommended Practice. If a
flowmeter is used, care should be taken to ensure that
the element has not been compromised by chemical
action or deposition of solids.
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If flow measurement in the duct is not practical,
velocity at the hood face or opening shall be
measured at a sufficient number of points to
obtain a realistic average velocity, and multiplied by the open area in the plane of the
velocity measurements to obtain the flowrate.
NOTE: Fine dust, for example, might adhere to the
throat of a venturi meter and change its inside dimension, which is critical to the measurement.
If the flowrate is more than 10% different from
design, corrective action shall be taken
6.3.2
Single Hood CAV Systems
Commissioning tests on single hood, constant
air volume (CAV) systems shall consist of:
•
•
•
•
Fan Performance Tests;
Exhaust Duct Measurements;
Hood Performance Tests; and
Hood Monitor Calibration.
Ensuring proper operation of a laboratory fume hood
requires proper design, installation, and operation of all
components of the exhaust systems and many times
the air supply systems as well.
Using a “top-down” approach, the fan should be adjusted to exhaust the specified volume of air.
Fan Performance Tests shall include measurement of fan speed, fan static pressure, motor
speed, and amp draw.
The exhaust flow should be measured in the exhaust
duct according the methods described in the current
version of ANSI/ASHRAE 41.2 or as described above.
Exhaust duct measurements shall consist of
exhaust flow measurement and hood static
pressure measurement.
Fan performance and exhaust measurements should
be conducted by a certified Test-and-Balance firm.
Hood performance tests shall consist of tests
described in Section 6.1.2.
The hood monitor shall be calibrated and
adjusted after hood performance has been
determined as satisfactory. Safe operating
points shall be clearly identified for the hood
user.
6.3.3
Multiple Hood CAV Systems
Commissioning of multiple hood, constant air
volume systems shall include:
• Fan Performance Tests;
• Verification of proper test, adjustment,
and balance of branch exhaust flow and
static pressures (exhaust flow and static
pressure for each branch shall be recorded after final balancing is complete);
Multiple hood systems should be balanced using an
iterative approach where dampers or controllers are
adjusted until flow through each hood is in accordance
with design specifications.
Hood performance tests should follow completion of
system balancing, measurement of branch exhaust
flows, and branch static pressures.
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• Hood Performance tests as described
above in Sections 6.1.2; and
• Hood and System Monitor Calibration
6.3.4
Determine that sash position of one hood does not
affect flow through another hood.
VAV Laboratory Fume Hood Systems
VAV hood systems shall be commissioned
prior to use by laboratory personnel to ensure
that all system components function properly
and the system operates as designed under all
anticipated operating modes (defined under
the VAV section).
Performance of laboratory fume hoods connected to
variable air volume systems (VAV) can be affected by
numerous factors associated with proper design, calibration, and tuning of the control systems. It is imperative that all components of the VAV system be in proper operating condition to ensure proper hood performance.
The commissioning procedures for VAV systems shall include:
Commissioning tests should be specified to verify that
the VAV systems operate according to design specifications. Some of the data, such as sensor calibrations,
can be acquired through the process of installing the
VAV controls or through the Testing, Adjustment and
Air Balance process (TAB).
• Verification of VAV Sensor Calibration;
• VAV Hood Performance Tests;
• VAV Laboratory and Ventilation System
Tests; and
• Verification of System Diversity.
Documentation collected outside the commissioning
tests, such as manufacturer’s tests on system components, should be available in advance of commissioning tests for comparison with test data and inclusion
with final commissioning documents.
6.3.4.1 VAV Sensor Calibration
VAV sensors shall be capable of accurate
measurement and control within 10% of actual
at the design maximum and minimum flow
conditions.
Numerous sensors can be employed in a typical VAV
laboratory fume hood systems such as sash position
sensors and room differential pressure sensors, to
name a few. The accuracy of the sensors depends on
proper methods to measure the physical parameters
and ability to adjust calibration. Sensors that report
inaccurate information will not only be misleading when
monitoring system operation but may result in unsafe
hood and laboratory conditions.
Part of the process of installing VAV controls and balancing system airflows should involve calibration of
sensors and documentation of it.
At a minimum, commissioning tests should test a representative sample of sensors to verify accurate reporting of information.
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6.3.4.2 VAV Hood Performance Tests
In addition to hood performance tests
described for evaluation of CAV hood systems,
commissioning tests on VAV hood systems
shall include measurement of flow or face
velocities at different sash configurations and
VAV Response and Stability tests.
Flow or face velocity measurements shall be
conducted at a minimum of two separate sash
configurations.
In the majority of VAV hood systems, the purpose of
the VAV control system is to adjust airflows to compensate for changes in sash configurations or system
operating mode (occupied/unoccupied, night setback,
etc.). The VAV control system must be capable of quick
and precise adjustment of flows without experiencing
major overshoot or undershoot (10% of steady-state
value).
VAV Response and Stability tests shall include
continuous measurements and recording of
flow while opening and closing the sashes for
each hood (calibrated flow sensors or measurement of slot velocity within the hood can
be used as an indicator of flow).
Commissioning tests should be used to verify that VAV
systems provide satisfactory control of airflows in
response to sash movement or changes in operating
modes.
VAV Response shall be sufficient to increase
or decrease flow within 90% of the target flow
or face velocity in a manner that does not
increase potential for escape.
A response time of < 3 sec. after the completion of the
sash movement is considered acceptable for most
operations. Faster response times may improve hood
containment following the sash movement.
VAV Stability shall be sufficient to prevent flow
variations in excess of 10% from design at
each sash configuration or operating mode.
6.3.4.3 VAV Ventilation System Tests
The VAV hood controls shall provide stable
control of flow in the exhaust and supply ducts
and variation of flow must not exceed 10%
from design at each sash configuration or
operating mode.
On a plenum system determine what happens to
exhaust flow when one fan is not operating.
6.3.4.4 Verification of System Diversity
System diversity shall be verified prior to use
of laboratory fume hoods. The tests shall be
designed to verify that users will be alerted
when system capacity is exceeded and unsafe
conditions may exist.
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6.3.5
Laboratory Airflow Verification Tests
Tests to verify and commission the laboratory
shall consist of:
• Air supply measurements;
• General room exhaust flow measurement
(if applicable);
• Room differential pressure measurement;
and
• Calculation of the difference between total
area (laboratory, zone, etc.) supply and
total exhaust.
All ventilation system alarm and monitoring
provisions associated with occupant safety
shall be verified for proper functionality.
The laboratory commissioning tests are used to ensure
proper air supply and exhaust for each laboratory or
zone.
TAB data once verified can be substituted where
appropriate.
This includes local monitoring provisions for such items
as hood airflow or room differential pressure as well as
remote and central monitoring provisions for such
parameters.
6.3.5.1 CAV Laboratory Room Tests
These tests shall ensure that the ventilation
system design airflow is being maintained
within the allowable tolerance in:
• All hood exhausts;
• All other bench-top and equipment
exhaust provisions that may be present;
• The room general exhaust if present;
• The room supply; and
• Room air cross currents at the hood face
opening.
If a specific room differential pressure (dP) has
been specified, the dP shall be measured to
ensure that it is within its allowable range.
If a room differential airflow is specified, actual
room differential airflow shall be determined to
ensure that is within allowable maximum and
minimum limits and in the proper direction.
If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.),
each individual mode shall be enabled and
applicable parameters (i.e., room supply, room
total exhaust, etc.) shall be performed for each
separate mode.
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Room ambient conditions (temperature,
humidity, air currents, etc.) shall also be measured to ensure they are being maintained
under the conditions specified.
6.3.5.2 VAV Laboratory Room Tests
These tests shall ensure proper performance
of the VAV ventilation system and its associated controls such that:
• The room general exhaust provides the
specified range of airflow.
• The room supply provides the specified
range of airflow.
• Room air cross currents at the laboratory
hood face opening are within limits.
If a specified room dP has been specified, the
dP shall be measured to ensure that it is being
controlled within its allowable range with all
doors closed and at minimum and maximum
room exhaust airflow.
If a room differential airflow is specified, actual
room differential airflow shall be determined to
ensure that it is within allowable maximum and
minimum limits and direction at minimum and
maximum room exhaust airflow.
If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.)
conditions shall be evaluated for each mode.
Room ambient conditions (temperature,
humidity, air currents, etc.) shall also be measured to ensure they are being maintained
under the conditions specified.
The VAV systems shall be capable of maintaining the offset flow required between
exhaust and supply to achieve the desired
area pressurization within the desired time
specified.
For most operations, 10 seconds will be an acceptable
time to achieve the desired area pressurization but a
Hazard Evaluation should be conducted to determine
the acceptable time.
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6.4
Ongoing or Routine Hood and
System Tests
Routine performance tests shall be conducted
at least annually or whenever a significant
change has been made to the operational
characteristics of the hood system.
A hood that is found to be operating with an
average face velocity more than 10% below
the designated average face velocity shall be
labeled as out of service or restricted use and
corrective actions shall be taken to increase
flow.
ANSI/ASHRAE 110–1995 may be used in the laboratory as an accepted test with specific values for the
control levels (and the release rate if you depart from
the standard). It also may be used for routine periodic
testing, but it is somewhat expensive and other less rigorous tests may be adequate if conditions have not
changed since commissioning tests.
In addition to the hood tests, periodic testing at a minimum of 1-year intervals should ensure that:
• All other room exhaust provisions are within specifications;
• Room differential pressure is within specifications
(if applicable);
• Room differential airflow is within specifications (if
applicable).
Each hood shall be posted with a notice giving
the date of the routine performance test, and
the measured average face velocity. If it is
taken out of service it shall be posted with a
restricted use or out- of-service notice. The
restricted use notice shall state the requisite
precautions concerning the type of materials
permitted or prohibited for use in the hood.
Periodic tests concerning face velocity or hood exhaust
volume are valid indications of hood operation provided no changes have been made in that hood structure,
supply air distribution, or other factors listed above that
affect hood performance.
The hood sash should not be lowered below design
position to increase face velocity during routine tests. A
decrease in face velocity at the design opening may be
indicative of a problem with operation of the exhaust
system.
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7
Work Practices and Training
7.1
General Requirements
The user shall establish work practices that
reduce emissions and employee exposures.
The laboratory’s Chemical Hygiene Plan should discuss proper work practices.
The user shall not modify the interior or exterior components of the hood without the
approval of the Chemical Hygiene Officer,
Responsible Person, or other appropriate
authority in the organization.
The following list concerns only those work
practices that relate directly to hood performance and applies only when hazardous
materials are to be used in the hood.
Many work practices affect the overall safety and
health in the laboratory.
• The user shall not lean into the hood so
that his/her head is inside the plane of
the hood, as defined by the sash, without
adequate respiratory and personal protection.
• Equipment and materials shall not be
placed in the hood so that they block the
slots or otherwise interfere with the
smooth flow of air into the hood.
• All work shall be conducted at least 6 in.
(15.24 cm) behind the plane of the sash
(hood face).
• The horizontal sash or panels shall not be
removed.
• The hood shall not be operated without
the back baffles in place.
• Flammable liquids shall not be stored permanently in the hood or the cabinet under
the hood unless that cabinet meets the
requirements the current editions of
NFPA 30 and NFPA 45 for flammable liquid storage.
During setup or hood maintenance, this provision is not
necessary, provided there are no sources of chemicals
in the hood and the hood is decontaminated.
When large equipment must be placed in a laboratory
chemical hood, placing the equipment on a stand to
allow air to flow under the stand can reduce the significance of any airflow disturbance.
Marking the work surface with a tape or other means,
to indicate the 6 in. (15.24 cm) line, will assist the user
in identifying the limits of usable space.
In some cases, while the hood is empty, the sash could
be removed for setup procedures.
Although the storage of acids does not pose the same
hazard as flammable solvents, the storage of acids
under the hood should be in acid-resistant cabinets.
Because of the high hazard associated with the storage of chemicals in front of the user at the hood, some
laboratories prohibit the storage of flammable materials
under the hood. Individual policies are often site specific; hence, the Chemical Hygiene Officer should
always be consulted.
In some laboratory design, the normal sash position is
not full open. When the sash is raised above the design
level, the hood could lose adequate control.
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• The sash or panels shall be closed to the
maximum position possible while still
allowing comfortable working conditions.
• Hood users shall be trained to close the
sash or panels when the hood is not in
use.
• The hood user shall not operate with the
sashes opened beyond the design opening.
• Pedestrian traffic shall be restricted near
operating hoods.
• Rapid movement within the hood shall be
discouraged.
• The hood shall not be operated unless
verified it is working.
7.2
When a person walks past a laboratory chemical hood
he or she sets up a wake that can aspirate contaminants from the laboratory chemical hood. Proper location of the hood and administrative controls are
required to minimize this potential hazard.
Posting
Each hood shall be posted with a notice giving
the date of the last periodic field test. If the
hood failed the performance test, it shall be
taken out of service until repaired, or posted
with a restricted use notice.
The intent is to ensure that those using the hood know
its current status and where to get help or further information.
The notice shall state the partially closed sash
position necessary for safe/normal operation
and any other precaution concerning the type
of work and materials permitted or prohibited.
Other information that should be posted may include
flowrates, fan numbers, an indication that the system is
VAV or less than 100% diversity and an emergency
phone number.
7.3
Operating Conditions
Hoods shall be in operation whenever hazardous volatile materials are being used or
stored inside.
7.4
A hood that is more than 10% below the standard operating conditions, either because of inadequate face
velocity, or poor distribution of the face velocity should
be immediately reported to the responsible safety person. The hood should not be used unless specific conditions for safe use can be identified and posted such
as its maximum sash opening. Hoods should only be
turned off when all materials are removed from the
interior and only if the hood does not provide general
exhaust ventilation to the space.
Training
Hood users shall be trained in the proper operation and use of a hood.
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8
Preventive Maintenance
Inspection and maintenance shall follow a
Preventive Maintenance (PM) Program developed by the user.
PM programs should be “preventive” in nature.
The written PM Program should identify potential hazards and problems associated with laboratory operations and designate appropriate PM procedures to minimize such hazards and problems. This could include,
for example, routine inspection of fan belts to ensure
that hood exhaust ventilation fans are turning at the
designed speeds, that hoods are being cleaned to minimize buildup of hazardous chemicals in the hoods, evidence of tampering with performance equipment or
blast gates, and so forth.
The written program should identify standard operating
procedures to be followed during PM activities.
The “responsible person” identified in Section 2.3
should be involved in the development and operation of
the PM program.
Preventive maintenance shall be performed
on a regularly scheduled basis.
8.1
Operations During Maintenance
Shutdown
Operations served by equipment being shut
down for inspection or maintenance shall be
safely discontinued and secured during such
maintenance.
“Secured” condition will vary from case to case. It might
consist of ceasing operation, or requiring removal from
the premises of all flammable and highly toxic materials.
Lock-out/tag-out procedures shall be implemented.
All ventilation equipment should be de-energized and
labeled as such with appropriate signage before starting any repair work.
Laboratory workers shall be notified in
advance of inspection and maintenance operations.
8.2
Housekeeping Before and After
Maintenance
All toxic or otherwise dangerous materials on
or in the vicinity of the subject equipment shall
be removed or cleaned up before maintenance. Any hazardous materials and any
other debris shall be cleaned up before operations resume.
If possible, equipment to be removed should be decontaminated. If the maintenance activities involve contact
with potentially contaminated parts of the system,
these parts should be evaluated first by appropriate
methods.
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8.3
Safety for Maintenance Personnel
Maintenance personnel shall be trained and
required to use appropriate PPE (such as respirators, goggles or faceshields, gloves, and
protective clothing) during parts of the work
involving potential hazard.
A procedure shall be established to notify hood
users before any maintenance is to be performed so work in the hood can be halted during maintenance.
8.4
Work Permits and Other
Communications
A written work permit system or other equally
effective means of communication shall be
established whenever any PM or unscheduled
maintenance;
There may be situations in the United States where
OSHA’s hazardous energy control standard (29
CFR1910.147) conceivably be applied to the situations
being addressed in this section.
• could affect the safety of maintenance
personnel, hood users or others
• could jeopardize the integrity of the experiments/procedures/etc., underway in the
affected hood(s.)
Such system(s) shall be designed to suit the
circumstances and address the following:
• a means to communicate when systems
are returned to normal operations,
• oversight by the responsible person as
defined in this standard,
• signed or otherwise endorsed and communicated by the person(s) to do the
work, his/her supervisor, and communicated to any and all hood users and others affected by the work,
• the nature of the work and the health and
safety precautions, and
Allowable variance from design conditions,
or conditions determined otherwise satisfactory, shall be:
• For air velocity, +10%;
• For ventilation air pressure or differential
pressure, +20%; For pneumatic control
system air pressure, <5%; and
• For electronic control system, +2% of fullscale values.
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• the date(s), time(s) and affected location(s) of the work.
Records shall be maintained in accordance
with the organizations records retention policy.
8.5
Records
Records shall be maintained for all inspections
and maintenance. If testing involves quantitative values (such as hood throat suction) the
observed values shall be recorded. Inspection
forms designed for the several categories of
testing shall be provided and shall include the
normal values for the parameters tested.
8.6
Testing and Monitoring Instruments
8.6.1
Air Velocity, Air Pressure, Temperature
and Humidity Measurements
Pressure instrumentation and measurement
shall be in compliance with ANSI/ASHRAE
41.3–1989. Temperature instruments and
measurement techniques shall be in compliance
with ANSI/ASHRAE 41.1–1986 (RA 01). All
Velocity
Accuracy
Below 100 fpm
(0.51 m/s)
5 fpm (0.025 m/s)
100 fpm (0.51 m/s)
and higher
5% of signal
Pressure
Accuracy
0.1 in.wg (25 Pa)
0% of signal
Between 0.1 in. wg
(25 Pa) and 0.5 in.
wg (125 Pa)
Interpolate linearly
0.5 in.wg (125 Pa)
and higher
Records should be kept for at least 1 year or until the
next required test is performed.
Instruments of a “primary standard” nature (i.e., standard pitot tubes, flow tube manometers, draft gauges,
etc.) – if used with fluids for which they are designed
and tested for leaks – require no further calibration.
Performance measurement equipment can be used to
determine many different system changes requiring
attention (e.g., exhaust filtration loading, damper
changes, fan operation, etc.) and provides real-time
indication of system performance.
Pressure indicating manometers can lose indicating
fluids due to leaks or evaporation. These devices
should be checked on a regular basis. Fluids should be
refilled and the device re-leveled as needed.
5% of signal
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instruments using electrical, electronic, or
mechanical components shall be calibrated no
longer than 12 months before use or after any
possible damage (including impacts with no
apparent damage) since the last calibration.
The accuracy of a scale used for a given parameter shall meet the following requirements:
Pitot-static tube measurements shall be in
accordance with ANSI/ASHRAE’s Method of
Test Measurement of Flow of Gas, 41.7–1984
(RA 00). Inclined manometers shall be selected so that the nominal value of the measured
parameter is at least 5% of full scale. U-tube
manometers shall not be used for pressures
less than 0.5 in.wg (125 Pa). Pitot tubes other
than standard shall be calibrated.
Temperature measurement instrumentation
shall have an accuracy of +0.5°F or +1°C over
the entire measurement range.
Humidity measurement instrumentation shall
have an accuracy of +3.0% relative humidity
over the entire measurement range.
8.6.2
Air Contaminant Monitors
Air contaminant monitors shall be tested at least
monthly or more often, if experience or manufacturer’s recommendations so indicate. Such testing shall include the sensing element, zero drift,
and actuation of signals, alarms, or controls.
Continuous air monitors shall be calibrated per
manufacturer’s specifications or more frequently if experience dictates.
8.6.3
Tolerance of Test Results
Allowable variance from design conditions, or
conditions determined otherwise satisfactory,
shall be:
• For air velocity, +10%;
• For ventilation air pressure or differential
pressure, +20%; For pneumatic control
system air pressure, <5%; and
• For electronic control system, +2% of fullscale values.
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8.6.4
Other Test Instruments
Other instruments (such as voltmeters and
tachometers) shall be checked for function and
accuracy against a “known source” before use
and follow manufacturer’s recommendation,
when provided, for periodic calibration.
8.7
Monitoring Fans, Motors, and Drives
8.7.1
Visual Inspection
Fans, blowers, drive mechanisms, and stack
systems shall be visually checked at least
semi-annually.
Key problematic observations are abnormal noise or
vibration, bearing noise, excessive temperature of
motors, lubricant leaks, etc.
Inspections should focus on key problematic issues
with the fans, blowers, and drive apparatus looking for
abnormal noise, vibration, bearing noise, excessive
temperature, high amperage of motors, and signs such
as lubricant leaks, etc.
8.7.2
V-belt Drives
V-belt drives on non-redundant fans serving
exposure control devices without performance
monitoring equipment shall be stopped and
inspected monthly for belt tension, signs of belt
wear, sheave wear, checking, or excessive
amperage pull on the motor.
Stack inspection should include the following:
• Ensuring that any tags, labels, etc., used to associate 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 still in accordance
with design.
Belt guard shall be reinstalled after any removal.
This will probably require removing the belt guard.
8.7.3
Lubrication
Blowers, drives, and other necessary components shall be lubricated at intervals and with
lubricants recommended by the manufacturer.
8.8
The use of performance monitoring equipment (See
Section 8.10) allows for maintenance as required
rather than on any time-based interval.
Critical Service Spares
The ventilation system management plan shall
address the need of providing for critical service issues and keeping spare parts on hand.
Lead time for parts should be considered such that
periodic inspection schedules are not affected.
Maintenance supplies and spares should be planned
considering factors such as:
• Availability of spares or replacements,
• Economic cost of facility 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 shall have
contingency plans in place.
For critical equipment of 100 horsepower (74.6 kW) or
larger, consideration should be given to providing temperature and vibration sensors to give early warning of
problems.
Key instrumentation should include at least one spare
performance monitoring device.
8.10
Performance Monitoring Equipment
All hoods and exposure control devices shall
be equipped with a flow indicator, flow alarm,
or face velocity alarm indicator as applicable to
alert users to improper exhaust flow. When
these devices are marked and labeled so the
hood operator can easily interpret the equipment reading and know when to shut down a
hood and request maintenance.
9
Air Cleaning
9.1
Supply Air Cleaning
Performance monitoring equipment allows the hood
user to check and monitor the reliability of the hood
system compared to normal. The performance equipment should be on an annual pm. The performance
equipment should be calibrated and relabeled so the
hood operator can readily understand the findings.
Laboratory air supply systems seldom require air
cleaning for health and safety reasons. Supply air
cleaning usually is provided, however, for technical reasons, usually to reduce the contamination from atmospheric dust and dirt. See ASHRAE 1999 Handbook –
HVAC Applications.
9.2
Exhaust Air Cleaning
Air-cleaning systems for laboratory exhaust
systems, where required, shall be designed or
specified by a responsible person to ensure
that air-cleaning systems will meet the performance criteria necessary for regulatory compliance. See the current version of ASHRAE
Handbook—Fundamentals.
Exhaust air might require cleaning for one or more reasons (See Sections 4.2 and 5.3). Air-cleaning equipment covers a wide range of physical and chemical
mechanisms beyond the scope of this standard and its
proper application is, in general, not included.
Air-cleaning performance monitoring is typically limited
for many hazardous materials. Chemical specific
detectors located downstream of adsorption media,
pressure drop indicators for particulate filters, and/or
periodic stack sampling for contaminant emissions may
be required to monitor for regulatory compliance.
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9.3
Filtration for Recirculation
Air-cleaning systems for recirculating general
exhaust or hood exhaust from laboratories
shall meet the design and installation requirements in the current version of ANSI/AIHA®
Z9.7.
Recirculation of process air shall be returned
to the same room where the process is located and control of the process is supervised.
In practical terms, recirculation of exhaust air usually is
economical only if the air needs to be cleaned of low
concentrations of:
• Particulate material that can be removed by static
(i.e., not self-cleaning) filters;
• Gases and vapors that can be removed efficiently
by adsorption media.
Filter installations shall be tested for leaks and
have all leaks repaired or the filter replaced
before use.
The flow rate through the filters shall be maintained at design specifications not to exceed
100% of the rated flow capacity of the filters.
9.3.1
Particulates
Air-cleaning filtration systems for recirculating
exhaust air contaminated with toxic particulates shall be filtered through a particulate filtration system specified following the standard
performance and design criteria of the
ASHRAE Systems and Equipment to meet the
objectives described in General Requirements
within the Laboratory Ventilation Management
section of this standard.
The properties and behavior of airborne particulates
cover a wide range and may include dusts, fumes,
mists, smoke, etc. Special caution should be taken
when utilizing recirculating particulate air-cleaning systems when condensation or evaporation of hazardous
particulate materials can take place in the air stream.
See the Institute of Environmental Sciences
Recommended Practice for Laminar Flow Clean Air
Devices.
The filter assembly should be provided with a damper
and control that:
• Indicate the static pressure differential separately
across the primary and secondary filters and the
pressure differential across both filters and the
damper;
• Actuate a damper motor (or allow manual activation) to open the damper from an initial partially
closed position when filters are clean to a fullopen position when filters are fully loaded; and
• Actuate a signal or alarm when the pressure drop
across either the primary or secondary filter
reaches 0.01 in.wg (2.5 Pa) more than the ratedloaded pressure drop.
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Also see the ASHRAE 2001 Handbook 
Fundamentals for additional information on the theory
and need for application of air cleaning equipment for
the emission control of hazardous materials from work
operations.
9.3.2
Gases and Vapors
Adsorption or other filtration media used for
the collection or retention of gases and vapors
shall be specified for a limited use. Specific
hazardous materials to be collected, airflow
rate, temperature, and other relevant physical
properties of the system shall be incorporated
into the selection of filtration media.
The intent of this section is to specify the need to have
a method for detecting filter breakthrough before a hazardous contaminant is released to the laboratory environment. Any method that provides early, accurate, and
reproducible detection for the contaminants present is
acceptable.
Activated carbon and other adsorption media are available in a number of configurations as filter housings.
Media may be sprayed onto another filtration media as
a thin coat or be packed into thin panels less than 2 in.
(5.1 cm) in depth. Also, deep- bed filters, typically cylindrical in shape and up to several feet in diameter and
length, are utilized to provide adequate retention time
for gas adsorption.
A reliable and adequately sensitive monitoring
system shall be utilized to indicate adsorbent
breakthrough. The sensitivity of the monitoring
system shall be a predetermined fraction of
the TLV® or appropriate health standard of the
contaminant being adsorbed but shall not be
more than 25% of the TLV®.
The breakthrough time of the contaminant,
before the effluent reaches no more than 50%
of the TLV®, shall be sufficient, based upon
system capacity design to allow a work operation shut down or parallel filter switch-over,
thus proving a fresh filter.
For toxic gases and vapors, the filtration system shall be designed and sized for capacity to
ensure adequate collection and retention for a
worst-case scenario when in the event of a
spill or other major release, adequate warning
is provided for personnel to stop work or enact
other emergency procedures.
An important characteristic of adsorption media is that
upstream layers perform the adsorption function; with
the result that breakthrough of unadsorbed gas occurs
rather quickly without gradual reduction of adsorption
efficiency. Prediction of breakthrough in deep beds can
be accomplished by periodic withdrawal of media samples from incremental depths of the bed, but this is
impractical in the shallow beds used in panels or in
smaller cylindrical cartridges. Saturation of the active
adsorption sites occurs progressively through the layer
of carbon and depends on the burden of adsorbate,
which typically is variable. Therefore, breakthrough of
contaminant on the downstream side of the carbon
layer is difficult to predict.
Other gas and vapor filtration systems use absorbents
such as potassium permanganate that are impregnated onto the media that transform, oxidize, or otherwise
treat the specific air contaminant to remove the hazardous material from the air stream.
A particulate filter should be located upstream of the
adsorption filter to serve as a pre filter to prevent particulate loading on the adsorption filter.
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9.3.3
Handling Contaminated Filters
When required, contaminated filters shall be
unloaded from the air-cleaning system following
safe work practices to avoid exposing personnel
to hazardous conditions, to avoid contamination
of downstream ductwork and to ensure proper
containment of the filters for final disposal.
Airflow through the filter housing shall be shut
down during filter change-out.
9.4
Testing and Monitoring
9.4.1
Recirculation – Particulate Filter
Systems
Recirculation air filters shall be inspected and
tested as per Section 9.3.1 before initial use
and then at least once per year.
Inspections and testing shall be done after any
system maintenance or modification that disturbs
the filter housing, filter seals, and/or filter media.
9.4.2
The Hazard Assessment should include recommended
work practices and procedures to conduct filter
change-outs when filters have been exposed to hazardous materials. Hazardous waste disposal requirements should be identified where needed.
Care should be taken during filter replacement to minimize the release of hazardous materials from the filters.
The most common and recommended practice employs
the use of bag-in/bag-out systems. Another approach
involving the careful introduction of encapsulants
upstream of the filter just prior to shut down and filter
changes has been described in various documents. An
example is CAG-005–2007 Servicing Hazardous Drug
Compounding Primary Engineering Controls.
All air filters should be provided with differential pressure gauges. Gauges should be read at intervals of 1
week (or at other intervals, based on experience) and
inspected visually at the same time. If the pressure differential equals or exceeds the rated maximum, the filters should be changed at the first opportunity.
Recirculation – Adsorption and
Absorption Filter Systems
Recirculation systems that utilize activated
carbon adsorption or chemical absorption filters shall be tested as per Section 9.3.2 at
intervals no longer than 1 month initially and
then based on experience with the particular
installation and a schedule shall be prepared.
9.4.3
Air Pollution Control Equipment
Air pollution control equipment shall be inspected visually at intervals no longer than 1 week
and, if necessary, at shorter intervals. Specific
tests and repairs shall be in accordance with
the manufacturer’s recommendations or in
compliance with applicable regulations.
The variety of generic types of pollution control equipment, combined with the many different configurations
on the market, make it inappropriate to set forth specific requirements.
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APPENDIX 1
Definitions, Terms, and Units
There are many terms and definitions associated
with laboratory ventilation that have special meaning. The following are definitions of terms or units
used in this document:
A2.1 adjacent roof line: For the purposes of
determining the laboratory chemical hood stack
height, the adjacent roof will be within 6 feet horizontally of the nearest outer point of the exhaust
fan stack. This criterion is intended to protect maintenance workers from direct exposure to their
breathing zone, hands, feet, and other parts of their
body. Parts of the building that are within 6 feet horizontally of the exhaust fan stack are exempted if it
would be impossible for a person to stand or cling
to the surface in question.
A2.2 air changes per hour (ACH): A common
means for expressing a volumetric airflow through
a room. Each ACH for a room is intended to represent an amount of air equal to the gross volume of
the air passing through the room each hour. An
ACH rate for a room can be converted to volumetric airflow by multiplying the ACH number times the
gross volume of the room. For instance, for an ACH
of 10, a room with a gross volume of 2400 cubic
feet has a volumetric airflow of 400 cfm (10 2400
÷ 60). The air change rate depends on exhaust flow
for a negatively pressurized room and on supply
flow for a positively pressurized room. This term
does not reflect actual mixing factors and therefore
does not indicate the effective air exchange rate in
the room. See the ACGIH® publication, Industrial
Ventilation Manual for further information on mixing
factors.
A2.3 air lock: An intermediate chamber
between two dissimilar spaces with airtight doors
or openings to each of the spaces. The doors are
interlocked to ensure that there is always at least
one of them closed.
A2.4 auxiliary air hood: A laboratory chemical
hood with an external supply air plenum at the top
of the laboratory chemical hood. The auxiliary air
plenum provides a makeup airstream comprised of
unconditioned or only minimally conditioned outside air to substantially reduce the amount of con-
ditioned room air exhausted by the laboratory
hood.
A2.5 bypass hood (constant air volume
bypass laboratory hood): A laboratory hood
design that incorporates an opening (bypass area)
in the upper portion of the laboratory hood structure. When the movable sash is fully open, the sash
blocks off this bypass area and all of the airflow into
the laboratory hood must pass through the open
face area. However, as the sash is being closed to
reduce the open face area, at a specific point an
amount of bypass area is being uncovered. The
increase in the bypass area opening offsets the
decrease in the face area opening, thus providing
an alternate path (the uncovered bypass area) for
air to flow into the laboratory hood. When utilized
with a constant air volume ventilation system, the
bypass area keeps the laboratory hood face velocity relatively constant and from increasing to an
objectionably high value as the sash is lowered.
A2.6 capture velocity: The air velocity at a
point in space of sufficient magnitude to overcome
room air currents and draw the air and any contaminants at that point into the hood.
A2.7 chemical hygiene officer: An employee
who is designated by the employer and who is
qualified by training or experience to provide technical guidance in the development and implementation of the provisions of the Chemical Hygiene
Plan. This definition is not intended to place restrictions on the position description or job classification that the designated individual shall hold within
the employer's organizational structure.
A2.8 constant air volume (CAV) ventilation
system: A ventilation system designed to maintain
a constant quantity of airflow within its ductwork.
The airflow quantity is typically based upon the
amount required to handle the most extreme conditions of outdoor-weather-related heat gain or loss
and internal building loading. Although relatively
simple, a constant volume ventilation system typically requires the maximum ongoing energy usage
since the system always operates at maximum
capacity.
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A2.9 design sash position: The maximum
open area of the hood face that achieves the
desired face velocity during any work inside the
hood that produces airborne contaminants.
of the laboratory hood and discharges the exhaust
directly into the room. Ductless laboratory hoods
are of limited size and capacity in comparison to
conventional ducted laboratory hoods.
A2.10 dilution ventilation: Ventilation airflow
that dilutes contaminant concentrations by mixing
with contaminated air, as distinguished from capturing the contaminated air.
A2.14 exhaust air: Air that is removed from an
enclosed space and discharged to atmosphere.
A2.11 discharge velocity: The speed of the
exhaust air normally expressed in feet per minute
(meters/second) at the point of discharge from a
laboratory exhaust system. Since laboratory
exhaust system fans may be configured to discharge into a vertical exhaust stack or may utilize
fans specifically designed to discharge directly
upward, the discharge velocity normally refers to
the air velocity as it leaves the last element of the
exhaust system. Since the top of an exhaust stack
may be conical (or other type of configuration), the
velocity of the exhaust air at the point of discharge
may differ from the velocity of the air within the vertical stack itself. The term “stack velocity” is sometimes used when referring to the speed of the
exhaust airstream as it is discharged into the outside air.
A2.12 diversity factor: A percentage factor that
is applied to establish the theoretical maximum
exhaust airflow quantity that is required at any point
in time. For example, in an exhaust system consisting of three hoods, the diversity factor would be
1/3 if at any point in time only 1 hood were being
used. Applying a diversity factor to the theoretical
maximum required capacity of an HVAC system is
often considered in the design of a VAV system.
Incorporating a diversity factor enables downsizing
HVAC system components and thus results in a
smaller capacity ventilation system. The overall
intention of applying a diversity factor when designing a VAV ventilation system is to achieve a lower
life cycle cost (e.g., lower system first cost and/or
lower system energy costs).
A2.13 ductless hood: A laboratory hood that is
not connected to an exhaust system that discharges the laboratory hood exhaust outdoors.
Rather, a ductless laboratory hood incorporates an
exhaust fan and exhaust filters as an integral part
A2.15 face velocity: The air velocity at the plane
of and perpendicular to the opening of a laboratory chemical hood.
A2.16 floor-mounted hood (walk-in hood): A
larger-size laboratory hood with sash and/or door
arrangement that enables access from the floor to
the top of the hood interior. The name unfortunately is a misnomer and although the design and
height of these hoods may allow it, users should
not walk into any hood that may represent a significant exposure hazard. Walk-in laboratory hoods
enable larger equipment and apparatus (e.g.,
equipment on carts, gas cylinders, etc.) to be more
readily put in and set up within the laboratory hood.
A2.17 glovebox: A controlled environment work
enclosure providing a primary barrier from the work
area. Operations are performed through sealed
gloved openings to protect the user, the environment, and/or the product.
A2.18 hazardous chemical – Encompasses 1)
regulatory definitions such as found in 29 CFR
1910.1450 (which appears to almost mistakenly
refer exclusively to health hazards) and 29 CFR
1910.1200 (which refers to both health and physical hazards), and 2) other accepted definitions
such as offered by OSHA on its safety and health
topics web page http://www.osha.gov/SLTC/hazardoustoxicsubstances/index.html.
A2.19 HEPA: High Efficiency Particulate Air (filter) for air filters of 99.97% or higher collection efficiency for 0.3 m diameter droplets of an approved
test aerosol (e.g., Emory 3004) operating at a rated
airflow.
A2.20 laboratory: It is difficult to provide a strict
definition for laboratory. Some entire institutions
are formally named “Laboratory.” The general concept for application of this standard is a facility in
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which the amounts of chemicals handled are small
[perhaps 22 or 44 lbs (10 or 20 kg), except for storage of supplies], where much of the work involves
manual manipulation of small containers or benchtop apparatus, and where the work is not routine
production of goods.
When this standard is used as a reference document in specifying design and construction (or
modification) of a facility, it is suggested that the
parties involved in the activity agree whether the
facility is to be considered a laboratory. The
Occupational Safety and Health Administration, in
29 CFR 1910.1450 (subpart 2, paragraph
191.1450) [4], provides a definition of “laboratory”
for regulatory purposes.
A2.21 laboratory fume hood: a box-like structure with typically one open side, intended for
placement on a table, bench, or floor. The bench
and the hood may be one integral structure. The
open side is provided with a sash or sashes that
move vertically and/or horizontally to close the
opening. Provisions are made for exhausting air
from the top or back of the hood and adjustable or
fixed internal baffles are usually provided to obtain
proper airflow distribution across the open face
A2.22 makeup air (replacement air): Any combination of transfer air and air provided by a ventilation system to replace air being exhausted from a
laboratory hood, canopy hood, room, or space.
A2.23 perchloric acid hood: A laboratory hood
constructed and specifically intended for use with
perchloric acid or other reagents that may form
flammable or explosive compounds with organic
materials of construction. A perchloric acid hood as
well as its exhaust system must be constructed of
all inorganic materials and be equipped with a
water washdown system that is regularly used to
remove all perchloric salts that may precipitate and
collect in the laboratory hood and in the exhaust
system. The exhaust fan must also be of a sparkresistant design to ensure against ignition of any
perchlorate deposits in the exhaust system.
A2.24 recirculation: Air removed or exhausted
from a building area and ducted back to an air-handling system where it is mixed with outside fresh
air. This air mixture is then conditioned and utilized
for ventilation. Since air removed from a space is
more often close to the temperature and humidity
of the building interior than outside air, the recirculation process enables achieving a greater reduction in heating and cooling energy than if 100%
outside air was utilized (also see return air).
A2.25 reentry: The flow of contaminated air that
has been exhausted from a space back into the
space through air intakes or openings in the walls
of the space.
A2.26 replacement air: See makeup air.
A2.27 responsible person: An individual who
has the responsibility and authority for the design
and implementation of the ventilation management
plan. This person may be the Chemical Hygiene
Officer or work in conjunction with the Chemical
Hygiene Officer.
A2.28 return air: Air being returned from a space
to the ventilation fan that supplies air to a space.
A2.29 room air balance: A general term describing the requirement that a laboratory room have
the proper relationship with respect to the total
exhaust airflow from the room and the supply
makeup airflow. The relationship of these airflows
also establishes the pressure differential between
the laboratory room and adjacent rooms and
spaces.
A2.30 room ventilation: The volumetric airflow
through a room expressed in terms of cfm or L/sec.
A2.31 special purpose hood: An exhausted
hood, not otherwise classified for a special purpose such as but not limited to capturing emissions from equipment such as atomic absorption
gas chromatographs; liquid pouring, mixing, or
weighing stations; and heat sources. These hoods
might not meet the design description of various
types of laboratory chemical hoods discussed
here. They may be exterior hoods, receiving
hoods, or enclosing hoods, as described in the latest ACGIH Industrial Ventilation: A Manual of
Recommended Practice.
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A2.32 – transfer air – air that moves between
spaces in a building, driven by the ventilation system.
A2.33 variable air volume—two-position ventilation system: A constant air volume ventilation
system (sometimes also referred to as a “two-position variable air volume system”) that is designed to
provide two separate levels of airflow. The higher
level of airflow is provided when a facility is normally occupied such as during regular work hours.
The lower level of airflow is utilized during unoccupied times (e.g., nighttime, holidays, etc.) when
ventilation needs and internal loads require less
airflow.
A2.34 variable volume hood: A hood designed
so the exhaust volume is varied in proportion to the
opening of the hood face by changing the speed of
the exhaust blower or by operating a damper or
control valve in the exhaust duct.
A2.35 variable air volume (VAV) ventilation
system: A type of HVAC system specifically
designed to vary the amount of conditioned air supplied and exhausted from the spaces served. The
amount of air supplied and intended to meet (but
not exceed) the actual need of a space at any point
in time. In general, the amount of air that is needed
by a space is determined by the required rate and
the amount of airflow necessary to maintain comfortable conditions (temperature and humidity).
A2.36 velocity: Magnitude and direction of air
motion. As used in this standard, if the direction is
omitted it is implied to be perpendicular to the
plane of the airflow cross section. If the direction is
important, it will be stated.
A2.39 units and abbreviations:
AAALAC – Association for Assessment and
Accreditation of Laboratory Animal Care
ABSA – American Biological Safety Association
ACD – air-cleaning device
AMCA – Air Movement Control Association
ACGIH® – American Conference of Governmental
Industrial Hygienists
AGS – American Glovebox Society
AIHA® – American Industrial Hygiene Association
USAMRICD – United States Army Medical
Research Institute of Chemical Defense
ASME – American Society of Mechanical
Engineers
ASHRAE – American Society of Heating,
Refrigerating and Air Conditioning Engineers
AI – as installed
AM – as manufactured
AU – As used
CAV – constant air volume
CETA – Controlled Environment Testing
Association
CFD – computational fluid dynamics
A2.37 volumetric airflow rate: The rate of airflow expressed in terms of volume (cubic feet or
liters) per unit of time. These are commonly
expressed as cubic feet per minute (cfm) in USCS
units or liters per second (l/s) in SI units. (Also see
room ventilation.)
A2.38 Walk-in hood: See floor-mounted hood.
cfm – cubic feet per minute
dBA – (A scale) decibels
dP – differential pressure
fpm – feet per minute
in.wg – inches water column (gauge)
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IEST – Institute of Environmental Sciences
and Technology
PPE – personal protective equipment
RC – room criteria curves
ISEE – International Society of Explosives
Engineers
REL – Recommended Exposure Levels
ISPE – International Society for Pharmaceutical
Engineering
SEFA – Scientific Equipment and Furniture
Association
JIC – joint industry codes (hydraulic equipment)
SMACNA – Sheet Metal and Air Conditioning
Contractors National Association
MAK – maximum allowable concentration
SPL – sound pressure level
NFPA – National Fire Protection Association
TA – Transfer Air
NC – noise criteria curves
TAB – testing, adjusting and air balancing
NEC – National Electrical Code
TLV® – Threshold Limit Value
NFC – National Fire Code
TWA – time weighted average
NIOSH – National Institute for Occupational
Safety and Health
NSF – National Sanitation Foundation
VAV – variable air volume
WEEL® – Workplace Environmental Exposure
Levels
PEL – Permissible Exposure Limit
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APPENDIX 2. Referenced Standards and
Publications
The following standards and associated publications, when referenced in this document, constitute
provisions of this American National Standards
Institute, Inc. At the time of publication, the editions
indicated were the most current. However, since
standards and associated publications are subject
to periodic revision, parties to agreements based
on this American National Standard are encouraged to ensure that they reference the current editions of these documents.
ACGIH®: Industrial Ventilation: A Manual of
Recommended Practice, 27th edition. Cincinnati,
OH: American Conference of Governmental
Industrial Hygienists, 2001.
ACGIH®: Threshold Limit Values (TLV®) For
Chemical Substances and Physical Agents.
Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, 2012.
AGS-G001–2007: Guideline for Gloveboxes, 3rd
edition. Santa Rosa, CA: American Glovebox
Society, 2007.
AMCA 99–2010: Standards Handbook. Arlington
Heights, IL: Air Movement and Control Association,
1986.
AMCA 200-95 (RA 2007): Fan Application Manual,
Part I, Fans and Systems: AMCA Classification for
Spark Resistant Construction. Arlington 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 Hygiene
Association, 2001.
ANSI/AIHA® Z9.7–1998: Recirculation of Air from
Industrial Process Exhaust Systems. Fairfax, VA:
American Industrial Hygiene Association, 1998.
ANSI/AIHA®
Z9.11–2008:
Laboratory
Decommissioning. Fairfax, VA: AIHA®, 2008.
ANSI/ASHRAE 41.1–1986 (RA 01): Standard
Method for Temperature Measurement. Atlanta,
GA: American Society of Heating, Refrigerating
and Air Conditioning Engineers, 1991.
ANSI/ASHRAE 41.2–1987 (RA 92): Standard
Methods for Laboratory Air Flow Measurement.
Atlanta, GA: American Society of Heating,
Refrigerating and Air Conditioning Engineers,
1992.
ANSI/ASHRAE 41.3–1989: Standard Method for
Pressure Measurement. Atlanta, GA: American
Society of Heating, Refrigerating and Air
Conditioning Engineers, 1989.
ANSI/ASHRAE 41.7–1984 (RA 00): Method of
Test Measurement of Flow of Gas. Atlanta, GA:
American Society of Heating, Refrigerating and Air
Conditioning Engineers, 2000.
ANSI/ASHRAE 52.1–1992: Gravimetric and DustSpot Testing Procedure for Testing Air-Cleaning
Devices Used in General Ventilation for Removing
Particulate Matter. Atlanta, GA: American Society
of Heating, Refrigerating and Air Conditioning
Engineers, 1992.
ANSI/ASHRAE 52.2–2007: Method of Testing
General Ventilation Air-Cleaning Devices for
Removal Efficiency by Particle Size. Atlanta, GA:
American Society of Heating, Refrigerating and Air
Conditioning Engineers, 2007.
ANSI/ASHRAE 62.1–2010: Ventilation for
Acceptable Indoor Air Quality. Atlanta, GA:
American Society of Heating, Refrigerating and Air
Conditioning Engineers, 2010.
ANSI/ASHRAE 110–1995: Method of Testing
Performance of Laboratory Fume Hoods. Atlanta,
GA: American Society of Heating, Refrigerating
and Air Conditioning Engineers, 1995.
ASHRAE 2009 Handbook – Fundamentals
(Inch-Pound edition). Atlanta, GA: American
Society of Heating, Refrigerating, and AirConditioning Engineers, Inc., 2009.
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ASHRAE 2011 Handbook – HVAC Applications
(Inch-Pound edition). Atlanta, GA: American
Society of Heating, Refrigerating, and AirConditioning Engineers, Inc., 2011.
Braun, K.O. and K.J. Caplan: “Evaporation Rate
of Volatile Liquids, Final Report, 2nd edition.
EPA Contract Number 68-D8-0112”, PACE
Laboratories Project 890501.315. Washington,
D.C.: U.S. Dept. of Commerce, NTIS, December
1989.
Controlled Environment Testing Association.
CAG-005-2007, Servicing Hazardous Drug
Compounding Primary Engineering Controls,
Controlled Environment Testing Association, 1500
Sunday Drive, Suite 102, Raleigh, NC 27607,
http://www.cetainternational.org/reference/CAG00
5-v15.pdf
CDC-NIH: Biosafety in Microbiological and
Biomedical Laboratories, Appendix A, CDC-NIH,
5th edition, Atlanta, GA: Centers for Disease
Control and Prevention, 2009.
EPA-600/8-81-009: Guideline for Modeling of
Atmospheric Diffusion. Office of Air Quality
Planning and Standards, April 1981.
Harnett, P.B.: Empirical data and modeling of a
flammable spill in a chemical fume hood do not
support the need for fire suppression within the
chemical fume hood ductwork. Chem. Health Safe.
10(4):11–14 (2003).
“Hazard Communication,” Code of Federal
Regulations. Title 29, Part 1910.1200, 1988.
HVAC Duct Construction Standards: Metal and
Flexible, Merrifield, VA: Sheet Metal and Air
Conditioning Contractors’ National Association,
2005.
IMC-2012: International Mechanical Code. Falls
Church, VA: International Code Council, 2012.
Institute of Environmental Sciences and
Technology (IEST), Laminar Flow Clean Air
Devices, IEST-RP-CC-002-86 Arlington Heights,
IL, http://www.iest.org
Ivany, R., M. First, and L.J. DiBerardinis: A New
Quantitative Method for In-Place Testing of
Laboratory Hoods. Am. Ind. Hyg. Assoc. J.
50(5):275–80 (1989).
Klein, R.C., C. King, and P. Labbie: Solvent vapor
concentrations following spills in laboratory chemical hoods. Chem. Health Safe. 11(2):4–8 (2004).
Klein, R.C., et al.: Laboratory air quality and room
ventilation rates. J. Chem. Health Safety
16(5):36–42 (2009).
Kolesnikov, A., R. Ryan, and D.B. Walters: Use of
Computational Fluid Dynamics to Optimize Airflow
and Energy Conservation in Laboratory Hoods and
Vented Enclosures. Washington, D.C.: EPA Labs
for the 21st 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: EPA
Labs for the 21st Century, October 2002.
Labconco Corp.: Development of the Labconco
Protector®
Xstream®
High
Performance
Laboratory Fume Hood. Kansas City, MO:
Labconco Corporation, 2009.
LEED: Leadership in Energy and Environmental
Design. U.S. Green Building Council.
Manning, A., et al.: Analysis of Air Supply Type
and Exhaust Location in Laboratory Animal
Research Facilities Using CFD. ASHRAE
Transactions DA-00-14-3 (2000).
Memarzadeh, F.: Methodology for Optimization of
Laboratory Hood Containment, Volumes I and II.
Bethesda, MD: National Institutes of Health, 1996.
NFPA 30–2008: Flammable and Combustible
Liquids Code. Quincy, MA: National Fire Protection
Association, 2000.
NFPA 45–2011: Standard on Fire Protection for
Laboratories Using Chemicals. Quincy, MA:
National Fire Protection Association, 2011.
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NFPA 86–2007: Standards for Ovens and
Furnaces. Quincy, MA: National Fire Protection
Association, 2007.
NFPA 92A–2009: Recommended Practice for
Smoke Control Systems. Quincy, MA: National Fire
Protection Association, 2009.
NSF 49–2004: Class II (Laminar Flow) Biohazard
Cabinetry. Ann Arbor, MI: National Sanitation
Foundation, International, 2004.
“Occupational Exposure to Hazardous
Chemicals in Laboratories,” Code of Federal
Regulations Title 29, Part 1910.1450, 1988.
Parker, A.J. and P.J. DiNenno: “Evaluation of
Fixed Extinguishing System Effectiveness in
Continuously 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 Fume
Reentry and Adverse Health Effects.” Symposium
Paper at ASHRAE Summer Meeting, Honolulu, HI,
June 23-26, 2002. To be published in 2002
ASHRAE Transactions.
Ratcliff, M.A. and E. Sandru: Dilution Calculations
for Determining Laboratory Exhaust Stack Heights.
ASHRAE Transactions 105(1):Ch-99-7-2 (1999).
SEFA-1-2002: Scientific Equipment and Furniture
Association, 2001.
Sharp, G.P.: “A Review of U.S. and European
Empirical Research, Theoretical Calculations, and
Industry Experience on Fume Hood Minimum Flow
Rates.” International Institute of Sustainable
Laboratories (I2SL) E-Library, http://www.i2sl.org/
elibrary/ index.html, 2009.
Smith, T.C. and S.M. Crooks: Implementing a
Laboratory Ventilation Management Program.
Chem. Health Safety 3 : 12 (1996).
Smith, T.C. and S. Yancey-Smith: Specification of
Airflow Rates in Laboratories. J. Chem. Health
Safety 16(5):27–35 (2009).
Tronville, P. and R.D. Rivers: International standards: filters for buildings and gas turbines,
Filtration & Separation, Volume 42, Issue 7,
September 2005, Pages 39-43, ISSN 0015-1882,
DOI: 10.1016/S0015-1882(05)70623-6.
“Test Methods,” Code of Federal Regulations
Title 40, Part 60, Appendix A, 1989.
UMC–2012: Uniform Mechanical Code. Whittier,
CA: International Conference of Building Officials
and Los Angeles, CA: International Association of
Plumbing and Mechanical Officials, 2012.
U.S. Nuclear Regulatory Commission, U.S.
Department of Energy, U.S. Environmental
Protection Agency, and U.S. Department of
Defense: Multi-Agency Radiation Survey and Site
Investigation Manual (MARSSIM) (EPA 402-R-97016), 2001.
Ventilation Test according to DIN 12 924 Part 1:
Fume Cupboard DIN 12 924 TA 1500 x 900 – 900,
Fume
hood
Test
report
by
Waldner
Laboreinrichtungen GmbH & Co. for mc6 - Bench
Mounted Fume Cupboard: Test Report No.159,
May 2000.
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APPENDIX 3. Selecting Laboratory Stack
Designs
Necessary measures must be taken to protect the
laboratory building and adjacent buildings from reingestion of toxic laboratory chemical hood exhaust
back into a building air supply system. The 10 ft
(3.05 m) minimum stack height called for in the
body of this standard is primarily intended to protect maintenance workers from direct contamination from the top of the stack. However, the minimum height of 10 ft is not enough by itself to guarantee that harmful contaminants would not be reingested. Similarly, a minimum 3000 fpm (15.3 m/s)
exit velocity is specified in the body of this standard, but this exit velocity does not guarantee that
re-ingestion will not occur.
This appendix describes general stack design
guidelines and three analysis methods for determining an adequate stack design. The first analysis
method is termed the "Geometric" method, which
ensures that the lower edge of an exhaust plume
stays above the emitting building and associated
zones of turbulent airflow. The geometric method is
fully described here and is accompanied by an
example. The second analysis method, briefly
described, predicts exhaust dilution at downwind
locations. The dilution equations are not presented
here but can be obtained from the ASHRAE
Handbook  HVAC Applications. A dilution criterion
is presented in this appendix to judge the adequacy of the predicted dilutions in minimizing re-ingestion. The third analysis method described is wind
tunnel or water flume modeling.
General Guidelines
Laboratory chemical hood exhaust stacks should
have vertical, unobstructed exhaust openings. The
Building Air Intake and Exhaust Design chapter of the
ASHRAE Handbook – HVAC Applications describes
appropriate rain protection devices. Goosenecks,
flapper dampers, and rain caps are unacceptable as
they deflect the exhaust sideways or downward, making it much more likely that re-ingestion will occur.
The stack must reach high enough to ensure that
the exhaust plume is sufficiently diluted when it
reaches sensitive areas such as building air
intakes, entrances, operable windows, and outdoor
plazas. The appropriate stack height is a function of
the plume height for the exhaust system being
designed and the subsequent dispersion, or concentration levels at the aforementioned sensitive
locations. The dispersion modeling process
(numerical or physical modeling) is discussed in a
later section. The plume rise should be calculated
using the equations that compute plume rise versus downwind distance. If two exhaust systems
give the same plume height at the same downwind
distance, the dispersion and resulting concentration levels will be identical. It should be noted that
by adding 5 to 10 ft to the stack height and
decreasing the exit velocity, the same plume rise
(and dilution) can be achieved which can lead to
the fan energy savings.
For a given exhaust flow rate, reducing the exit
diameter with an exhaust nozzle is recommended
to increase the exit velocity and rise or throw of the
exhaust over the building. However, exit velocities
much larger than 3000–4000 fpm (15.3 to 20.4
m/s) may result in high noise and vibration. Too
small of a nozzle, or one with too rapid a decrease
in area, could result in excessive pressure loss in
the exhaust and the resulting combination of
reduced flow due to fan system effect and reduced
dilution and safety.
Combining exhausts into a common stack, either
by manifolding exhausts or with very close grouping of stacks, will enhance the rise of the exhaust
plume. Close grouping of stacks can be used for
specialty exhausts that cannot be manifolded
because of their chemical nature. Manifolding or
combining exhausts can generally give greater
benefit than installing an exhaust nozzle on a stack
serving a single laboratory chemical hood.
Manifolding of exhausts can also provide some
internal dilution of fume hood exhausts when the
majority of chemical emissions are from an upset
condition or large release from a single laboratory
chemical hood. Such upset or large release conditions are the primary cause of odor complaints and
potential health effects. However, this internal dilution is partially offset by the decreased atmospheric
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dilution due to the larger plume size. Nevertheless,
manifolding of exhausts is still beneficial and recommended.
Variable exhaust flow rates, used to reduce energy costs, can periodically result in low exit velocities. Minimum exit velocities below 1500 fpm (7.65
m/s) are discouraged because for such low exit
velocities, high winds can cause the exhaust to
travel down the side of the stack instead of rising
vertically. A dispersion modeling assessment can
define the minimum exhaust velocity and volume
flow needed to avoid fume reentry. If this assessment shows a higher exhaust velocity and/or volume flow is needed, there are other methods to
achieve the desired dispersion:
• Variable flow geometry
• Induction of outdoor air
• Staging of multiple fans on a common inlet
plenum
• Use of a control system and on-site weather
station so that low velocities can be set during
low wind and high velocities during high winds.
Adding outdoor air to the exhaust is the most common approach because it provides the larger
plume rise and some internal dilution.
Air intake placement is as important as stack
design. Intakes on the side of the building or at
grade will usually provide greater protection from
rooftop exhausts. Intakes on the roof may work if
placed a sufficient distance from the exhausts.
When only a single tall stack is present, an intake
location near the base of the stack may be a good
location. The advantage of this location is diminished if there are sources of toxic or odorous
exhausts at other locations on the roof. Nearby
intakes elevated above a laboratory exhaust stack
should be avoided.
Rooftop obstacles, such as parapets or architectural fences, and penthouses on the same roof as
the hazardous exhaust stack can also act as adjacent buildings causing wind flow disturbances that
reduce the rise of the exhaust. Note that it is the difference in roof heights that is particularly important
when analyzing the adjacent building effect.
First Stack Design Method—The Geometric
Method
The ASHRAE Handbook—HVAC Applications
describes the geometric method. This simplified
method is intended to be conservative, but there
are limits on its applicability. The ASHRAE
Handbook also describes those limits.
The geometric method is designed for isolated rectangular buildings that do not have taller buildings,
dense taller trees, or taller hills close to the laboratory building. Also air intakes on the emitting building should be no higher than the top of the physical
exhaust stack opening. Provided these conditions
are met, the geometric method can be applied as
follows:
1) Calculate the length of the recirculation zone (R)
downwind of the building for each of the four basic
approach wind directions. For a given direction, R =
(Bsmall 0.67) (Blarge 0.33), where Bsmall is the smaller of
the building height and width, and Blarge is the larger of the two. As used here, the recirculation zone
height is the height of the emitting building.
Table A2 presents recirculation zone length for various building dimensions.
2) Calculate the plume rise (throw) due to exhaust
momentum and add it to the stack height, to obtain
the effective stack height.
hf =
0.9[FmUH/U*]1/2
UHßj
{}
2
Fm = Ve d
4
ßj =
1
3
+
UH
Ve
is the final plume rise, where
is the momentum flux, ft4/s2 (m4/s2)
is the jet entrainment coefficient
UH / U* = 2.5ln(H/z0) is the well-known logarithmic
wind profile equation,
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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)
of the basic approach wind directions. Table A3
shows flowrates required to meet the geometric
method, given a 10 ft (3.5 m) stack height and a
3000 fpm (15.3 m/s) exit velocity (as per this standard), a 1%-wind speed of 15 mph (24 k/h), and
various horizontal distances to clear. The horizontal distance is the distance between the stack and
the downwind building edge plus the recirculation
zone length.
zo = surface roughness length, ft (m)
The same method can be used to determine a
taller stack that also complies.
Table A1 describes various zo values for a range of
sites. For example if zo equals 0.5 m and H = 11 m,
substituting into the logarithmic wind profile equation gives UH/U* = 8.3.
Example Calculation for the First Stack Design
Method—The Geometric Method
Table A1: Terrain Factors
Terrain
zo, ft (m)
Flat, water, desert
0.03 (0.01)
Flat, airport, grassland
0.16 (0.05)
Suburban
2.0 (0.6)
Urban
6.0 (2.0)
A laboratory building is 100 ft (30.5 m) wide, 200 ft
(61 m) long, and 60 ft (18.3 m) high. A manifolded
laboratory exhaust with a flowrate of 10,000 cfm
(4.7 m3/s) is located in the center of the roof. For
wind approaching the 100 ft (30.5 m) wide side,
Bsmall is 60 ft (18.3 m) and Blarge is 100 ft (30.5 m).
The length of the recirculation zone is R =
(600.67)(100 0.33) = 71 ft (21.7 m). The horizontal
distance that must be cleared by the plume equals
100 ft (30.5 m) from the center to the edge of the
building plus 71 ft (21.7 m) for the recirculation
zone, or 171 ft (52.2 m). The required effective stack
height to clear the building and recirculation zone is
171/5 (using the 5:1 slope) = 34.2 ft (10.4 m).
3) The effective height of the stack is the physical
stack height plus the added plume rise due to
momentum.
The added stack height due to momentum is calculated next. The stack diameter is 2.06 ft (.63 m)
based on a 3000 fpm (15.3 m/s) exit velocity and a
10,000 cfm (4.7 m3/s) flow rate. Using a 15 mph
(24 k/h), 1320 fpm (6.7 m/s) 1%-wind speed, the
added stack height = 3 °F 2.06 °F 3000/1320 = 14
ft (4.3 m). Given a physical stack height of 10 ft
(3.05 m) based on the minimum required to meet
this standard, the effective stack height is 14 + 10
ft = 24 ft (7.32 m).
4) The geometric method, as stated here, specifies
that the bottom of an exhaust plume should clear
the emitting building, including penthouses, and
the recirculation zone downwind of the building.
The bottom of the plume extends downward at a
5:1 slope (5 units horizontal and 1 unit downward)
from the effective stack height (physical height plus
added plume rise). This should be done for all four
The required effective height computed above is
34.2 ft (10.4 m), which is not met with a 10 ft (3.05
m) physical stack height. The designer can
increase the physical height to 20 ft (6.1 m). As an
alternative, the designer can increase the momentum of the air by introducing outside air to the system. If the physical stack height remains at 10 ft
(3.05 m), the diameter would need to increase to
The 1%-wind speed is a high wind speed exceeded only 1% of the time. These wind speeds are
available for numerous locations in the ASHRAE
Handbook—Fundamentals, Chapter Climatic
Design Information.
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Table A1
Length of Downstream Recirculation Zone (feet and meters)
Each story is 15 ft (4.6 m) high
Bldg.
Dimensions
1 Story
2 Stories
3 Stories
4 Stories
5 Stories
6 Stories
7 Stories
Height in
Feet (meters)
15 ft
(4.6 m)
30 ft
(9.1 m)
45 ft
(13.7 m)
60 ft
(18.3 m)
75 ft
(22.9 m)
90 ft
(27.4 m)
105 ft
(32.0 m)
50 ft
(15.2 m)
22.3ft
(6.8 m)
35.5 ft
(10.8 m)
46.6 ft
(14.2 m)
53.1 ft
(16.2 m)
57.2 ft
(17.4 m)
60.7 ft
(18.5 m)
63.9 ft
(19.5 m)
75 ft
(22.9 m)
25.5 ft
(7.8 m)
40.6 ft
(12.4 m)
53.3 ft
(16.2 m)
64.6 ft
(19.7 m)
75.0 ft
(22.9 m)
79.7 ft
(24.3 m)
83.3 ft
(25.4 m)
100 ft
(30.5 m)
28.1 ft
(8.6 m)
44.6 ft
(13.6 m)
58.6 ft
(17.9 m)
71.0 ft
(21.6 m)
82.5 ft
(25.1 m)
93.2 ft
(28.4 m)
101.6 ft
(31.0 m)
150 ft
(45.7 m)
29.8 ft
(9.1 m)
51.0 ft
(15.5 m)
67.0 ft
(20.4 m)
81.2 ft
(24.7 m)
94.3 ft
(28.7 m)
106.5 ft
(32.5 m)
118.1 ft
(36.0 m)
200 ft
(61.0 m)
29.8 ft
(9.1 m)
56.1 ft
(17.1 m)
73.6 ft
(22.4 m)
89.3 ft
(27.2 m)
103.7 ft
(31.6 m)
117.1 ft
(35.7 m)
129.9 ft
(39.6 m)
250 ft
(76.2 m)
29.8 ft
(9.1 m)
59.6 ft
(18.2 m)
79.2 ft
(24.1 m)
96.1 ft
(29.3 m)
111.6 ft
(34.0 m)
126.1 ft
(38.4 m)
139.8 ft
(42.6 m)
300 ft
(91.4 m)
29.8 ft
(9.1 m)
59.6 ft
(18.2 m)
84.2 ft
(25.7 m)
102.0 ft
(31.1 m)
118.5 ft
(36.1 m)
133.9 ft
(40.8 m)
148.5 ft
(45.3 m)
500 ft
(152.4 m)
29.8 ft
(9.1 m)
59.6 ft
(18.2 m)
89.4 ft
(27.2 m)
119.2 ft
(36.3 m)
140.3 ft
(42.8 m)
158.5 ft
(48.3 m)
175.7 ft
(53.6 m)
1000 ft
(304.8 m)
29.8 ft
(9.1 m)
59.6 ft
(18.2 m)
89.4 ft
(27.2 m)
119.2 ft
(36.3 m)
149.0 ft
(45.4 m)
178.8 ft
(54.5 m)
208.5 ft
(63.6 m)
Length or
Width
Formula for figure is:
Length of downstream recirculation zone is Bsmall(0.67) °F Blarge(0.33) where Bsmall is the smaller of
height and width or length and Blarge is the larger of the two (from ASHRAE, 1997).
Where Blarge is > 8 Bsmall, use Blarge = 8 Bsmall
3.5 ft (1.1 m), increasing flow rate to about 30,000
cfm (14.1 m3/s). Also, increasing to 30,000 cfm
(14.1 m3/s) will increase in-stack dilution by a factor of 3:1. This in-stack dilution, whether achieved
by manifolding exhausts in the building or by
adding roof air, can be very valuable to achieving
safe results. The other wind direction (aimed
toward the long side of the building) should be
checked, but for this example this wind direction is
the worst case.
High volume flow in itself is not a guarantee of adequate dilution. For a given source spill rate in kilograms/second, a higher exhaust volume flow Qe
increases the in-stack dilution, but somewhat
reduces the atmospheric dilution because the
atmosphere is now presented with a larger volume
of gas to disperse.
Tables A2 and A3 assist in estimating a stack
height that ensures that the plume avoids recirculation zones and the edge of the building.
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Table A2
Volume Necessary to Achieve Throw Off Edge of Building and
Recirculation Zone, cfm and L/s
Assume stack is 10 ft (3.0 m) high and fan exit velocity is 3000 fpm (15.2 m/s) with 15 mph
(24.1 km/h) wind speed
Distance to Edge of
Feet to throw
Building and Recirc. Zone horizontally
Meters to throw
horizontally
Flow needed,
cfm
Flow needed,
L/s
75
22.9
1,267
598.0
100
30.5
5,068
2392.0
150
45.7
20,272
9567.3
200
61.0
45,612
21526.5
250
76.2
81,088
38269.3
300
91.4
126,699
59795.3
Second Stack Design Method—The Numerical
Method
A more detailed analysis that accounts for dilution
within the plume can be used if the required stack
heights or flowrates are too large from the geometric method. Minimum dilution can be predicted
using equations from the ASHRAE Handbook—
HVAC Applications. The equations are not discussed in detail here. These equations apply only
to intakes below stack top. The stack height used in
these equations is the physical stack height only.
“Effective stack height,” including the effect of
plume rise, should not be used. The EPA screening
dispersion model, SCREEN3, can also be used in
certain situations to supplement the ASHRAE
Handbook equations.
The numerical methods are continually evolving.
Designers are advised to consult current sources
for specific calculations. The discussion here illustrates issues; it does not teach a design procedure.
For the example case discussed above [10 ft (3.05
m) stack, diameter = 2.06 ft (0.628 m), exit velocity
= 3000 fpm (15.24 m/s), flowrate = 10,000 cfm (4.7
m3/s), receptor at end of wake recirculation zone
171 ft (52.2 m) away], the predicted minimum dilution from the ASHRAE Handbook is 455:1. If the
diameter is increased to 3.5 ft (1.07 m) associated
with a larger flow rate of 30,000 cfm (14.1 m3/s),
the minimum dilution decreases to 264:1.
At first glance, the smaller flowrate stack that yields
the larger dilution would seem to be preferred.
However, the larger 30,000 cfm (14.1 m3/s),
flowrate provides an internal dilution of 3:1 compared to the original 10,000 cfm (4.7 m3/s). When
comparing the two cases, the larger flowrate case
has a total dilution of 3 °F 264 = 792:1, which is better than the lower flowrate case and would provide
lower chemical concentrations at an air intake for a
given chemical release rate. Allowable spill rate to
meet the 0.05 ppm at the receptor location would be
11.2 L/m of toxic vapor. The original design with d =
2.06 ft (0.63 m) has a higher dilution Dcrit of 455 but
the reduced volume flow only allows a spill volume
rate of 6.4 L/m. In effect, the factor of 3 volume flow
increase in the stack with the fan allows about a factor of 1.75 increase in allowable spill rate.
In conceptual terms, exit velocity and volume flow
rate are "equal partners" in plume rise and the
resulting increase in safety through greater dilution.
However, in practical terms, exit velocities can only
be increased by doubling or tripling while manifolding or adding roof air to the stack can easily result
in a 10-fold increase in dilution.
Dilution in the context of dispersion of laboratory
exhaust is a deceptively difficult concept because
one must account for both the dilution within the
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exhaust system, De, which is present at the stack
and the dilution from the stack to a downwind location, D. The concept can be simplified by normalizing D by the volume flow rate through the exhaust
stack, Q. By normalizing D, only the dispersion,
which occurs between the exhaust stack and the
downwind location, needs to be considered.
The normalized value can be presented in one of
two ways, either as a normalized dilution or a normalized concentration value. A normalized dilution
value can be obtained by multiplying D by the ratio
of the actual volume flow rate and a standardized
volume flowrate [i.e., 1000 cfm (4.7 m3/s) °F (Qact /
Qstd)]. The result is a dilution value that is independent of the actual volume flowrate through the
exhaust stack, making it possible to compare the
effectiveness of various exhaust stacks with different volume flowrates, because all of the values are
referenced to the same 1000 cfm (0.47 m3/s) volume flowrate.
A normalized concentration value is obtained by
applying the definitions of concentration and dilution provided in the ASHRAE Handbook—HVAC
Applications, [C/m = 1/ (D * Q)]. The result is a normalized concentration value that is the ratio of the
concentration present at the downwind location
and the mass emission rate of the emitted chemical, expressed in units of µg/m3 per g/s. This value
is completely independent of the volume flowrate
through the exhaust stack, and thus can be used to
readily compare the effectiveness of exhaust
stacks with various volume flowrates. Another
advantage of this method is that if the emission
rate of a chemical is known, you can simply multiply the emission rate by the C/m value to obtain a
pollutant concentration. This concentration can
then be compared directly with established health
and odor limits.
Design Criteria
When designing stacks with the numerical method,
it is necessary to have a design criterion for selecting a stack design. Development of a dilution criterion can be difficult since the types and quantities
of laboratory chemicals can vary significantly from
laboratory to laboratory. As a starting place, it is
suggested here to have the stack provide protection similar to what a laboratory chemical hood
would provide a worker standing at the hood. As
described in this standard, a laboratory chemical
hood should have an ANSI/ASHRAE 110 test performed by a manufacturer, and the ANSI/ASHRAE
110 rating should be AM 0.05 or lower. This rating
translates to the worker being exposed to 0.05 ppm
or lower of tracer gas while 4 liters per minute (4
L/min.) of tracer gas are being emitted from within
the laboratory chemical hood. The same 4 L/min. of
tracer gas are being emitted from the laboratory
chemical hood exhaust stack. The recommended
design criterion is that the 0.05 ppm concentration
also be the maximum concentration at the air
intake. (The time constant for exposure concentrations mentioned in this standard is measuring over
a 10-minute span of time.)
The detailed calculations are not presented here,
but it can be confirmed that the 4 L/min. emission
rate and an allowable air intake concentration of
0.05 ppm corresponds to a normalized concentration design criterion of 750 µg/m3 per g/s or a
2800:1 dilution for a 1000 cfm (0.47 m3/s) flowrate
exhaust, 280:1 for a 10,000 cfm (4.7 m3/s) flow
rate, and a 93:1 dilution for a 30,000 cfm exhaust.
These suggested design criteria is somewhat more
lenient than the smaller criteria suggested in the
ASHRAE Handbook—HVAC Applications, Chapter
Laboratories, which has recommended that air
intake concentrations should be less than 3 ppm
due to an evaporating liquid spill in a fume hood
and exhausted at a rate of 7.5 L/s. The ASHRAE
criteria translate to a normalized concentration
design criterion of 400 µg/m3 per g/s or a 5000:1
dilution for a 1000 cfm flowrate exhaust. For facilities with intense chemical utilization, design criteria
specific for that facility can be developed using the
chemical inventory.
In the stack examples above, the 10,000 cfm (4.7
m3/s) case had a predicted dilution of 455:1, which
meets the 280:1 criterion for a 10,000 cfm (4.7
m3/s) flowrate. The 30,000 cfm (14.1 m3/s) case
had a predicted dilution of 264:1, which also meets
the 93:1 criterion for this flowrate, by a larger margin than the 10,000 cfm (4.7 m3/s) stack.
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Graphical Solution Referenced for the Second
Stack Design Method Using the Halitsky Criteria
Two graphical solutions can be consulted that show
a solution to the dilution calculations. The first is
Ratcliff and Sandru (ASHRAE Transactions, 105,
part 1, paper Ch-99-7-1, 1999) and the second is
Petersen, Cochran, and LeCompte (to be published in 2002 ASHRAE Transactions). The solutions in both papers are for a Halitsky Criteria spill,
0.028 ppm, rather than the criterion derived from
the ANSI/ASHRAE 110 test specification. Quite a
bit of expertise is required to interpret the graphs.
As an example, in the second paper, one point calculated and shown on the graph is that a zero
height stack with a flow of 50,000 cfm (23.5 L/s)
and an exit velocity of 3000 fpm (15.24 m/s) would
require an offset distance of 120 ft (36.6 m) to the
nearest receptor site using the 0.028 ppm exposure limit at the receptor. These graphs were
derived from Chapter 43 of ASHRAE 1999
Handbook—Applications Manual equations for critical wind speeds and dilutions. Zero-height stacks
are quite common because stacks that end below
parapet walls, below the height of adjacent penthouses, or that end below adjacent screen walls or
screens will act as a zero-height stack. Receptor
sites would include operable doors and windows,
and any location where pedestrian access was
allowed as well as to outside air intakes.
Third Stack Design Method—Physical Modeling
Using the Wind Tunnel or Water Flume
If the stack heights determined from the first two
methods described above are undesirable or if the
geometry or topography of the building site makes
simple analysis methods unreliable, a scale model
of the building and surroundings should be physically modeled in an atmospheric wind tunnel or
water flume. Physical modeling provides more
accurate, and typically less conservative, predictions than the numerical or geometric methods.
Physical modeling is the safest method to choose
stack heights in new buildings or in buildings being
retrofitted.
Wind-tunnel modeling is often the preferred
method for predicting maximum concentrations for
stack designs and locations of interest when energy and equipment optimization is desired. It is the
recommended approach because it gives the most
accurate estimates of concentration levels in complex building environments. A wind-tunnel modeling study is like a full-scale field study, except it is
conducted before a project is built. Typically, a
scale model of the building under evaluation, along
with the surrounding buildings and terrain within a
1000-ft radius, is placed in an atmospheric boundary layer wind tunnel. A tracer gas is released from
the exhaust sources of interest, and concentration
levels of this gas are then measured at receptor
locations (i.e., air intakes, operable windows, etc.)
of interest and converted to full-scale concentration
values. Next, these values are compared against
the appropriate health or odor design criteria outlined in Section 5.3.4 to evaluate the acceptability
of the exhaust design. ASHRAE (2009) and Snyder
(1981) provide more information on scale-model
simulation and testing methods.
Dilution criteria are still necessary to evaluate the
results of physical modeling. The design criteria
discussed above provide initial guidance. A more
complete evaluation of appropriate design criteria
should be conducted when the chemical usage is
expected to exceed minimal levels. In addition, the
design criteria should take into account the 20%
factor outlined in Section 5.3.4.
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APPENDIX 4. Audit Form for ANSI/AIHA®
Z9.5–2012
( ) 2.1.3 Dilution ventilation is provided to control
the buildup of fugitive emissions and odors in the
laboratory.
Laboratory Ventilation
2.2 Chemical Hygiene Plan
Audit item numbers refer to Standard paragraphs.
Compliance with the Standard should only be
claimed when all applicable provisions or elements
of the Standard are met. Note: Mark (X) all those
that genuinely apply.
2 Lab Ventilation Management Plan
2.1 General Requirements
( ) 2.2 The laboratory develops a Chemical
Hygiene Plan according to the OSHA Laboratory
Standard (29 CFR 1910.1450).
( ) The plan addresses the laboratory operations
and procedures that might generate air contamination in excess of the requirements of Section
2.1.1.
( ) 2.1 Management has established a Laboratory
Ventilation Management Plan (LVMP) to ensure
proper selection, operation, use, and maintenance
of laboratory ventilation equipment.
( ) These operations are performed inside a hood
adequate to attain compliance.
( ) The LVMP has been implemented to
ensure proper operation of the lab ventilation systems, help protect laboratory personnel working
with potentially hazardous airborne materials, provide satisfactory environmental air quality and
maintain efficient operation of the laboratory ventilation systems.
( ) 2.3 In each operation using laboratory ventilation systems, the user designates a “responsible
person.”
( ) 2.1.1 Adequate laboratory chemical hoods,
special purpose hoods, or other engineering controls are used when there is a possibility of
employee overexposure to air contaminants generated by a laboratory activity.
( ) Laboratory worker chemical exposures are
maintained below applicable published or inhouse exposure limits.
( ) Chemical “hazard determinations” are conducted by chemical manufacturers and importers
as required by the Occupational Safety and
Health Administration's (OSHA) Hazard
Communication standard, specifically, 29 CFR
1910.1200(d).
( ) 2.1.2 The specific room ventilation rate is
established or agreed upon by the owner or their
designee.
2.3 Responsible Person
2.4 Roll of Hazard Assessments
( ) 2.4.1 Employers ensure an ongoing system for
assessing the potential for hazardous chemical
exposure.
( ) Employers promote awareness that laboratory
hoods are not appropriate control devices for all
potential chemical releases in laboratory work.
( ) The practical limits of knowing how each ventilation control is being used in the laboratory are
considered when specifying design features and
performance criteria.
( ) The responsible person defined in Section 2.3
is consulted in making these judgments.
( ) The employer establishes criteria for determining and implementing control measures to reduce
employee exposures to hazardous chemicals; particular attention is given to the selection of control
measures for chemicals that are known to be
extremely hazardous.
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( ) Laboratory chemical hoods are functioning
properly and specific measures are taken to
ensure proper and adequate performance.
( ) 2.4.2 The following items are considered and
decisions made regarding each element's relevance following the hazard assessment process:
( ) Vendor qualification;
( ) Adequate workspace;
( ) Design sash opening and sash configuration
(e.g. , for laboratory chemical hoods);
( ) Diversity factor in VAV-controlled laboratory
chemical hood systems;
( ) Manifolded or individual systems;
( ) Redundancy and emergency power;
( ) Hood location;
( ) Face velocity for laboratory chemical hoods;
( ) The level of formality given to system
commissioning;
( ) Tracer gas containment "pass" criteria;
( ) Alarm system (local and central monitoring);
( ) Air cleaning (exhaust pollution controls);
( ) Exhaust discharge (stack design) and dilution
factors;
( ) Recirculation of potentially contaminated air;
( ) Differential pressure and airflow between
spaces and use of airlocks, etc.;
( ) Fan selection;
( ) Frequency of routine performance tests;
( ) Preventive maintenance; and
( ) Decommissioning.
equipped with a safety viewing sash at the face
opening.
( ) Sashes are not removed when the hood is in
use.
( ) 3.1.1.1 Where the design sash opening area
is less than the maximum sash opening area, the
hood is equipped with a mechanical sash stop.
( ) A means of communicating when openings
are in excess of the design sash opening area is
provided.
( ) The Chemical Hygiene Plan clearly instructs
the hood users to position the sash so that the
opening is no greater than the design opening
while using the hood for protection.
( ) 3.1.1.2 Vertical sashes are designed and operated so as not to be opened more than the design
opening when hazardous materials are being
used within the hood.
( ) 3.1.1.3Horizontal sashes arfe designed so as
not to be opened more than the design opening
width when hazardous materials are being generated in the hood.
( ) 3.1.1.4 If a combination sash provides horizontally moving panels mounted in a frame that
moves vertically, the above requirements are met.
2.5 Complete and permanent records are
maintained for each laboratory ventilation
system.
( ) 3.1.1.5 All users are trained in good work
practices, including the need to close the sash
when not in use.
3 Laboratory Fume Hoods
( ) All users of VAV systems shall be trained in
the proper uses of the sash, the energy consequences of improper use, and the need to close
the sash when the operation does not require its
use.
3.1 Design and Construction
( ) 3.1 The design and construction of laboratory
chemical hoods conform to the applicable guidelines presented in the latest edition of ACGIH®
Industrial Ventilation: A Manual of Recommended
Practice, and the most current codes, guidelines
and standards, and any other applicable regulations and recommendations.
( ) 3.1.1 The laboratory chemical hood is
( ) Automatic sash positioning systems have
obstruction sensing capable of stopping travel
during sash closing operations without breaking
glassware, etc.
( ) Automatic sash positioning allows manual
override of positioning with forces of no more than
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10 lbs (45 N) mechanical both when powered and
during fault modes during power failures.
emergency contingency plans are in place.
In addition:
3.2 Hood Types
( ) 3.2.1 Auxiliary air hoods meet the requirements in Section 3.3.
( ) All inside hood surfaces use materials that will
be stable and not react with perchloric acid to form
corrosive, flammable, and/or explosive compounds
or byproducts;
In addition:
( ) The supply plenum is located externally and
above the top of the hood face;
( ) The supply jet is distributed uniformly across
the hood width;
( ) The auxiliary air does not disrupt hood containment or increase potential for escape.
( ) 3.2.2 Bypass hoods have a route for air entering the hood (the bypass mechanism) opens as
the sash closes.
( ) The bypass mechanism shall be designed to
minimize potential ejection of liquid or solid material outside the hood in the event of an eruption
inside the hood.
( ) 3.2.3 Conventional hoods meet the requirements in Section 3.3.
( ) 3.2..4 Floor-mounted hoods meet the requirements in Section 3.3.
( ) 3.2.5 Perchloric acid hoods are specifically
designed to safely handle certain types of perchloric acid work and are actually used for such
work.
( ) Perchloric acid hoods are used for handling
anhydrous perchloric acid (> 85% concentration.)
( ) All procedures conducted in a perchloric acid
hood are reviewed by an immediate supervisor.
( ) All procedures using a perchloric acid hood
are performed by trained personnel, knowledgeable and informed about the hazards and properties of these substances, and are provided with
appropriate protective equipment after suitable
( ) All interior hood, duct, fan, and stack surfaces
are equipped with water washdown capabilities;
( ) All ductwork is constructed of materials that will
be stable to and not react with perchloric acid
and/or its byproducts and will have smooth welded
seams;
( ) No part of the system is manifolded or joined to
nonperchloric acid exhaust systems;
( ) No organic materials, including gaskets are
used in the hood construction unless they are
known not to react with perchloric acid and/or its
byproducts;
( ) Perchloric acid hoods are prominently labeled
“Perchloric Acid Hood, Organic Chemicals
Prohibited.”
( ) 3.2.6 VAV hoods meet the requirements in
Section 3.3.
( ) Variable exhaust flow from a laboratory hood
has implications for room ventilation which are
addressed according to Section 5.
3.3 Hood Airflow and Monitoring
( ) 3.3.1 The average face velocity of the hood is
sufficient to capture and contain the hazardous
chemicals for which the hood was selected, and
follows guidance in Section 2.4 and as generated
under as-used conditions.
( ) An adequate face velocity is is not the only criterion to achieve acceptable performance and is
not used as the only performance indicator.
( ) Hood containment is verified as appropriate
for the hazard being controlled (e.g., visual meth-
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ods such as smoke, face velocity testing, exposure assessments, tracer gas containment testing,
etc.)
( ) 4.1.1 Gloveboxes are not used for manipulation of hazardous materials with the face or
other panels open or removed.
( ) 3.3.2 The flow rate of Constant Volume hoods
and the minimum flow rate of Variable Air Volume
hoods is sufficient to prevent hazardous concentrations of contaminants within the laboratory
fume hood.
( ) In addition to maintaining proper hood face
velocity, laboratory hoods maintain a minimum
exhaust volume to ensure that contaminants are
properly diluted and exhausted from a hood.
( ) The following considerations are taken into
account (as applicable) when setting the minimum
hood flow rate: hood interior corrosion, need to
affect directional airflows, fume hood density,
hood design, hood materials, generation or emission rates, exhaust parameters.
( ) The hood flow rate is set within the operating
range of the hood exhaust equipment and the
associated control system.
( ) Ventilation system designers coordinate the
operating range of the fume hood flow rate with
the operating ranges of the other air supply and
exhaust devices in the room.
3.3.3 Flow Measuring Devices
( ) All hoods are equipped with a flow indicator,
flow alarm, or face velocity alarm indicator to alert
users to improper exhaust flow.
( ) The flow-measuring device is capable of indicating that the air flow is in the desired range, and
capable of indicating alarms when the flow is high
or low by 20%.
( ) The device is calibrated at least annually and
whenever damaged.
4
Other Containment Devices
4.1 Gloveboxes
( ) 4.1.2 Materials: Interior cracks, seams, and
joints are eliminated or sealed.
( ) 4.1.3 Utility valves and switches are in conformance with applicable codes.
( ) When control of utilities from inside the glovebox is required, additional valves and switches are
provided outside the glovebox for emergency
shutoff.
( ) 4.1.4 Proper application of ergonomic principles is met by referring to Chapter 5.10,
“Guidelines for Gloveboxes,” AGS-G001–1998.
( ) 4.1.5 The design of the glovebox provides for
retaining spilled liquids so the maximum volume
of liquid permitted in the glovebox will be retained.
( ) 4.1.6 Containment gloveboxes are provided
with exhaust ventilation to result in a negative
pressure inside the box that is capable of containing the hazard to acceptable levels.
( ) 4.1.7 The air or gas exhausted from the glovebox is cleaned, and discharged to the atmosphere
in accordance with the general provisions of this
standard and pertinent environmental regulations.
( ) Air-cleaning equipment is sized for the maximum airflow anticipated when hazardous agents
are exposed in the glovebox and the glovebox
openings are open to the extent permitted under
that condition.
( ) If the air-cleaning device (ACD) is passive,
provision is made for determining the status of the
ACD, as noted in Section 9.3. If the ACD is active,
instrumentation is provided to indicate its status.
( ) The ACD is located to permit ready access for
maintenance.
( ) Provision is made for maintenance of the ACD
without hazard to personnel or the environment
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and so not to contaminate the surrounding areas.
( ) 4.1.8 Exhaust piping is in accordance with the
principles described in ACGIH® Industrial
Ventilation: A Manual of Recommended Practices,
ANSI/AIHA® Z9.2, and the ASHRAE 1997
Handbook − Fundamentals.
( ) All piping within the occupied premises is
under negative pressure when in operation.
( ) Materials are resistant to corrosion by the
agents to be used.
( ) 4.1.9 A glovebox pressure monitoring device
with a means to locally indicate adequate pressure relationships to the user is provided on all
gloveboxes.
( ) If audible alarms are not provided, documented training for users in determining safe pressure
differentials is required.
( ) Pressure monitoring devices are adjustable
and subject to periodic calibration.
( ) 4.1.10 A written decommissioning plan following the procedures outlined in the latest edition of
ANSI/AIHA® Standard Z9.11 Laboratory
Decommissioning is developed.
( ) Before the access panel(s) of the glovebox are
opened or re moved, the interior contamination is
reduced to a safe level.
( ) If the contaminant is gaseous, the atmosphere
in the box is adequately exchanged to remove the
potentially hazardous gas.
( ) If the contaminant is liquid, any liquid on surfaces is wiped with suitable adsorbent material or
sponges until visibly clean and dry.
( ) Used wipes are placed in a suitable container
before being removed from the glovebox.
( ) If the contaminant is a powder or dust, all
internal surfaces are cleaned and wiped until visi-
bly clean and the exterior surfaces of the gloves
also are wiped clean.
( ) Precautions to prevent personnel hazard and
contamination of the premises are made if the
ducting is to be opened or dismantled.
( ) When there is any uncertainty about the effectiveness of the contamination reduction procedures, personnel involved in opening the panels of
the glovebox are provided with appropriate
Personal Protective Equipment or clothing.
( ) 4.1.11 A high containment glovebox conforms
to all the mandatory requirements of 4.1.1 through
4.1.10, and
( ) Is provided with one or more air-lock passthrough ports for inserting or removing objects or
sealed containers without breaching the physical
barrier between the inside and outside of the
glovebox.
( ) Maintains negative operating static pressure
within the range of -0.5 to -1.5 in. wg (–124 to
–373.5 Pa) such that contaminant escape due to
“pinhole-type" leaks is minimized.
( ) Maintains dilution of any flammable vapor-air
mixtures to <10% of the applicable lower explosive limit.
( ) Prevents transport of contaminants out of the
glovebox.
( ) 4.1.12 A medium containment glovebox conforms to all the mandatory requirements of
Sections 4.1.1 through 4.1.10, and is not provided
with pass-through airlocks, and is provided with
sufficient exhaust ventilation to maintain an inward
air velocity of at least 100 fpm (0.51 m/s) through
the open access ports, and creates a negative
pressure of at least 0.1 in. w g (2.49 Pa) when
access ports are closed.
( ) 4.1.13 Special case containment gloveboxes
are tested for the intended use and found
adequate for that purpose.
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( ) 4.1.14 An isolation and containment glovebox
is used to control special atmosphere work when
either the controlled atmosphere and/or the contained agents are hazardous.
( ) Design and construction and materials conforms
to the requirements for high, medium, or special
case containment gloveboxes as necessary.
( ) If the controlled atmosphere gas is hazardous,
the airlocks are provided with a purge air exhaust
system that, by manipulation of valves, creates a
purge flow of room air sufficient to provide at least
5 air changes per minute, with good mixing, to the
interior space of the airlock.
( ) Operation of an isolation and containment
glovebox conform to high, medium, or special
case containment requirements as necessary and
the airlock purge system is operated for sufficient
time to dilute any hazardous gas in the airlock to
safe concentrations before the outer door is
opened.
( ) Care is exercised when placing certain hazardous liquids in an evacuated airlock or interior
of a glovebox when a decrease in pressure could
affect the boiling point of the liquid, causing it to
go to gaseous state.
4.1.15 An overall operation and maintenance program is documented for each application of the
glovebox to provide users with necessary information on periodic maintenance and testing of glovebox system components.
4.2. Ductless Hoods
( ) Ductless hoods meet the general requirements of Sections 3.1 and 3.3 as applicable.
( ) A Hazard Evaluation and Analysis is conducted as directed in ANSI/AIHA® Z9.7 and Section
2.1.1 of this Standard.
( ) Compliance with the general requirements of
Sections 2, 3.3 and 5.3.6.2, are evaluated by
qualified persons.
( ) Ductless hoods that do not meet the requirements specified in Sections 9.3 and
9.4 are used only for operations that normally
would be performed on an open bench without presenting an exposure hazard.
( ) Ductless hoods have signage prominently
posted on them to inform operators and maintenance personnel about the allowable chemicals
used in the hood, type and limitations of filters in
place, filter changeout schedule, and that the
hood recirculates air to the room.
( ) 4.2.1 Ductless hoods utilizing air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates must meet the
requirements of Section 9.3.1.
( ) 4.2.2 Ductless hoods utilizing adsorption or
other filtration media for the collection or retention
of gases and vapors are specified for a limited
use and meet the requirements of Section 9.3.2.
( ) Ductless hoods employing filters for removing
gases and vapors have written documentation
(records) that the manufacturer has approved the
specific application of the hood prior to usage.
( ) The manufacturer provides a list of chemicals
approved to be used in the hood with their retention capacities.
( ) Proper disposal of unused and used (contaminated) adsorption filters is considered as part of
the decision to use ductless hood employing
such.
( ) 4.2.3 Contaminated filters are unloaded from
the air-cleaning system following safe work practices to avoid exposing personnel to hazardous
conditions and to ensure proper containment of
the filters for final disposal.
( ) Airflow through the filter housing is shut down
during filter change-out.
( ) 4.2.4 All of the requirements of sections 6.3,
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6.4, 6.5.3.1 and 8.0 for containment and airflow
testing and all of the requirements of sections 9.2
and 9.3.2 for air cleaning performance shall be
followed.
4.3 Special Purpose Hoods
( ) 4.3 Special laboratory chemical hoods are
designed in accordance with ANSI/AIHA® Z9.2
and ACGIH® Industrial Ventilation: A Manual of
Recommended Practices.
5
Laboratory Ventilation System Design
mizes the room ventilation (air changes per hour)
rate and, if appropriate, increases negative room
pressurization.
( ) For rooms served by CAV ventilation systems
that utilize a reduced ventilation level for energy
savings, the chemical emergency mode of operation ensures that the room ventilation and negative pressurization are at the maximum rate.
( ) Operation of the room ventilation system in a
chemical emergency mode does not reduce the
room ventilation rate, room negative pressurization level, or hood exhaust airflow rate.
5.1 Lab Design
5.2 Lab Airflow Management
( ) 5.1.1 Laboratory designers consider effects on
safety when establishing floor plans and spatial
layout.
( ) Laboratory chemical hoods are located so
their performance is not adversely affected by
cross drafts.
( ) Windows in laboratories with hoods shall be
fully closed while hoods are in use (emergency
conditions excepted).
( ) 5.1.2 Generation of excessive noise is avoided
in laboratory ventilation systems.
( ) Fan location and noise treatment provide for
SPL in conformance with local ambient noise
criteria.
( ) 5.1.4 When the type and quantity of chemicals
or compressed gases that are present in a laboratory room could pose a significant toxic or fire
hazard, the room is equipped with provision(s) to
initiate emergency notification and initiate the
operation of the ventilation system in a mode consistent with accepted safety practices.
( ) A hazard assessment is performed to identify
the credible emergency conditions that may occur.
( ) For rooms served by VAV ventilation systems,
the chemical emergency mode of operation maxi-
5.2.1. ( ) As a general rule, airflow is from areas of
low hazard to higher hazard and exceptions are
documented.
( ) When flow from one area to another is critical
to emission exposure control, airflow-monitoring
devices are installed to signal or alarm a malfunction.
( ) Air is allowed to flow from laboratory spaces to
adjoining spaces only if:
( ) There are no extremely dangerous and lifethreatening materials used in the laboratory;
( ) The concentrations of air contaminants generated by the maximum credible accident will be
lower than the exposure limits required by 2.1.1.
( ) The desired directional airflow between rooms
is identified in the design and operating specifications.
( ) 5.2.1.1 Airlocks are utilized to prevent undesirable airflow from one area to another in high hazardous applications, or to minimize volume of supply air required by Section 5.1.1.
( ) Airlocks are applied in such a way that one
door provides access into or out of the laboratory
room, and the other door of the airlock provides
passage to or from a corridor (or other non-laboratory area).
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( ) Airlock doors are arranged with interlocking
controls so that one door must be fully closed
before the other door may be opened.
( ) 5.2.1.2 If the direction of airflow between adjacent spaces is deemed critical, provision is made
to locally indicate and annunciate inadequate airflow and improper airflow direction.
( ) 5.2.2 The following issues are evaluated in
order to design for diversity:
( ) Use patterns of hoods;
( ) Type, size, and operating times of facility;
( ) Quantity of hoods and researchers;
( ) Sash management (sash habits of users);
( ) Requirements to maintain a minimum exhaust
volume for each hood on the system;
( ) Type of ventilation system;
( ) Type of laboratory chemical hood controls;
( ) Minimum and maximum ventilation rates for
each laboratory;
( ) Capacity of any existing equipment;
( ) Expansion considerations;
( ) Thermal loads; and
( ) Ability to perform periodic maintenance.
( ) The following conditions are met in order to
design a system diversity:
( ) Acceptance of all hood-use restrictions by the
user groups, which take into account the
common work practices of the site users.
( ) When the type and quantity of chemicals or
compressed gases that are present in a laboratory room could pose a significant toxic or fire hazard, the room is equipped with provision(s) to initiate emergency notification and initiate the operation of the ventilation system in a mode consistent
with accepted safety practices.
( ) Emergency situations (see current version of
NFPA 92A) that are anticipated and the appropriate ventilation system responses are provided, as
follows:
( ) For a CHEMICAL EMERGENCY – A means
such as a clearly marked wall switch, , or other
readily accessible device is provided to enable the
room occupants to initiate appropriate emergency
notification and simultaneously activate the ventilation system’s chemical emergency mode of
operation if one exists.
( ) For rooms served by VAV ventilation systems,
the Chemical Emergency mode of operation maximizes the room ventilation (air change per hour)
rate.
( ) For rooms served by 2-state ventilation systems that utilize a reduced ventilation level for
energy savings, the Chemical Emergency mode
of operation applies the maximum ventilation rate.
( ) A training plan is in place for all laboratory
users to make them aware of any limitations
imposed on their freedom to use the hoods at any
time.
( ) Operation of the room ventilation system in a
chemical emergency mode does not reduce the
room ventilation rate, room negative pressurization level, or hood exhaust airflow rate.
( ) An airflow alarm system is installed to warn
users when the system is operating beyond capabilities allowed by diversity.
( ) For FIRE – Any manual or automatic means of
detecting fire (such as a pull station or smoke
detector) in a laboratory room also activates an
appropriate fire emergency mode of operation for
the room and/or building ventilation system.
( ) Restrictions on future expansions or flexibility
are identified.
5.2.3 Lab Ventilation – Emergency Modes
( ) A hazard assessment (see Section 2.4) is performed to identify credible emergency conditions
that may occur.
( ) The selected fire emergency mode operates
all supply and exhaust equipment in the room in a
manner that promotes egress, retards the spread
of fire and smoke, and complies with applicable
fire safety codes and standards.
5.3 Supply Air
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5.3.1 Supply Air Volume
( ) If laboratories are to be maintained with a
negative pressurization and directional airflow
from the corridor into the laboratory, supply air
volumes are less than the exhaust flowrate from
the laboratory.
( ) When laboratories are to be maintained with a
positive pressurization and directional airflow, supply air volume is more than the exhaust from the
laboratory.
( ) To maintain the desired space pressurization,
the supply air volume responds to applicable
dynamic events including:
•
•
•
•
changes in desired ventilation rate,
flow changes in VAV exhaust devices,
temperature control demands, and
temporary deficit of exhaust system capacity.
( ) The laboratory ventilation system is designed to
remove and dilute air contaminants in accordance
with the Laboratory Ventilation Management Plan.
( ) The ventilation rate also satisfies the general
codes and standards that apply to the occupancy
class.
5.3.2 Supply Air Distribution and Quality
( ) Supply air distribution is designed to keep air
jet velocities less than half, preferably less than
one-fourth of the capture velocity or the face
velocity of the laboratory chemical hoods at their
face opening.
( ) In cases where Section 510 of the
International Mechanical Code applies, designers
consult the most current version of IMC 510.
5.4.2 Exhaust System Ductwork
( ) Laboratory exhaust system ductwork complies
with the appropriate sections of current versions
of the Sheet Metal and Air Conditioning
Contractors’ National Association (SMACNA)
standards.
( ) Systems and ductwork are designed to maintain negative pressure within all portions of the
ductwork inside the building when the system is in
operation.
( ) Exhaust ductwork is designed in accordance
with the current versions of ANSI/AIHA® Z9.2, the
ASHRAE Handbook – Fundamentals, and NFPA
45.
( ) Branch ducts enter a main duct so that the
branch duct centerline is on a plane that includes
the centerline of the main duct.
( ) For horizontal main ducts, branch ducts do not
enter a main duct on a plane below the horizontal
traverse centerline of the main duct. Horizontal
runs of branch ducts shall be kept at a minimum.
( ) Longitudinal sections of a duct are a continuous seamless tube or of a continuously welded
formed sheet.
( ) Longitudinal seams that are formed mechanically are utilized only for light duty systems with
no condensation or accretion inside the duct.
( ) Supply systems meet the technical requirements of the laboratory work and the requirements of the latest version of ANSI/ASHRAE
Standard 62.1.
( ) Spiral ducts can be one gauge lighter than the
required gauge of longitudinal seam duct if the
spiral duct gauge always meets the abrasive wear
resistance requirements.
5.4 Exhaust System Classification
( ) Traverse joints are continuously welded or
flanged with welded or Van Stone flanges.
5.4.1 ( ) Designers reviews existing regulations
and code requirements for the project location.
( ) When nonmetallic materials are used, joints
are cemented in accordance with the manufactur-
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er’s procedures.
NFPA 45.
( ) If the duct is coated with a corrosion-resistant
material, the coating extends from the inside of
the duct to cover the entire face of the flange.
( ) Exhaust system materials are resistant to corrosion by the agents to which they are exposed.
( ) Flange faces are gasketed or beaded with
material suitable for service.
( ) If condensation within the duct is likely, all horizontal duct runs are sloped downward at least 1
in. per 10 ft in the direction of the airflow to a suitable drain or sump.
( ) Exhaust airflow volume are sufficient to keep
the temperature in the duct below 400°F (204°C)
under all foreseeable circumstances.
( ) All duct connections to the exhaust fan are
consistent with good ventilation design practice.
As an alternative, the duct connections may be
made by means of inlet and outlet boxes.
( ) If circumstances such as space limitations
prevent the implementation of the preceding
requirements, then applicable speed and power
corrections are made by applying the “System
Effect Factor" (see AMCA 201-90).
( ) Where optimum duct connections cannot be
made due to space or other limitations, suitable
alternative means are substituted to compensate
for the space limitations.
( ) If adequate duct connections cannot be provided at the fan, the fan is equipped with inlet and
outlet boxes furnished by the fan manufacturer.
( ) The manufacturer furnishes performance
curves for the fan with the inlet and outlet box(es)
as part of the fan.
( ) If neither adequate connections nor inlet/outlet
boxes are present, the fan speed and power
requirements represented in the fan rating table
are corrected by the “System Effect Factor.”
( ) Exhaust system materials chosen in accordance
with the current version of ACGIH’s® Industrial
Ventilation: A Manual of Recommended Practice,
the ASHRAE Handbook—Fundamentals, and
( ) Exhaust system materials are noncombustible
if perchloric acid or similar oxidizing agents that
pose a fire or explosive hazard are used.
5.4.3 Manifolds
( ) Laboratory chemical hood ducts are combined
into a common manifold with the following exceptions and limitations:
( ) Each control branch has a flow-regulating
device to buffer the fluctuations in pressure inherent in manifolds.
( ) Perchloric acid hoods are not manifolded with
nonperchloric acid hoods unless a scrubber is
installed between the hood and the manifold.
( ) Where there is a potential for ductwork contamination from hood operations as determined
from the Hazard Assessment of Section 2.4,
radioisotope hoods are not manifolded with nonradioisotope hoods unless an appropriate air-cleaning system is provided between the hood and the
manifold: HEPA filter and/or carbon bed filters for
gases.
( ) Exhaust streams that contain concentrations
of flammable or explosive vapors at concentrations above the Lower Explosion Limit (LEL) as
well as those that might form explosive compounds (i.e., perchloric acid hood exhaust) are not
connected to a centralized exhaust system.
( ) Exhaust streams comprised of radioactive
materials are adequately filtered to ensure
removal of radioactive material before being connected to a centralized exhaust system.
( ) Biological exhaust hoods are adequately filtered to remove all hazardous biological substances prior to connection to a centralized
exhaust system.
( ) Unless all individual exhausts connected to
the centralized exhaust system can be completely
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stopped without creating a hazardous situation,
provision is made for continuous maintenance of
adequate negative static pressure (suction) in all
parts of the system.
devices connected to the manifold, and powered
devices include, but are not limited to: biological
safety cabinets, in-line scrubbers, motorized
dampers, and booster fans.
( ) As an alternative, if the hood is completely
turned off, the hood is emptied and decontaminated and provisions are implemented to prevent the
hood from back-drafting.
( ) Manifolds are maintained under negative pressure at all times and be provided with at least two
exhaust fans for redundant capacity.
( ) A VAV hood is provided with an emergency
switch that allows the hood exhaust volume to
return to the maximum.
( ) Biological safety cabinets manifolded with
chemical laboratory chemical hoods have either:
(1) A thimble connection or (2) An air flow control
device and an interlock/alarm for these devices
installed between the cabinet outlet and the
exhaust manifold.
( ) Where Hazard Evaluation and Analysis determines that the installation calls for direct connection (hard ducted) of the biological safety cabinet
(e.g., Class II–Type B) to an exhaust manifold
system to allow work with toxic chemicals or
radionuclides, interlocks and alarms are provided
to prevent the biological safety cabinet from operating its normal starting mode or to immediately
warn the operator in the event of an exhaust system failure (CDC-NIH, 1999).
( ) The static pressure in the exhaust system is
lower than the surrounding areas throughout the
entire length, with the exception noted in Section
5.3.1.1.
( ) Fire dampers are not installed in exhaust system ductwork (NFPA 45).
( ) Fire sprinklers are not installed in laboratory
chemical hood exhaust manifolds.
( ) Exhaust systems operate continuously to provide adequate ventilation for any hood at any time
it is in use and to prevent backflow of air into the
laboratory when the following conditions are present: Chemicals are present in any hood (opened
or unopened), exhaust system operation is
required to maintain minimum ventilation rates
and room pressure control, there are powered
( ) Emergency power is connected to one or
more of the exhaust fans where exhaust system
function must be maintained even under power
outage situations.
5.4.4 Fans
( ) Each fan serving a laboratory exhaust system
or to exhaust an individual piece of laboratory
equipment (e.g., a laboratory chemical hood,
biosafety cabinet, chemical storage, etc.) is adequately sized to provide the necessary amount of
exhaust airflow in conjunction with the size,
amount, and configuration of the connecting ductwork.
( ) In addition, each fan’s rotational speed and
motor horsepower are sufficient to maintain both
the required exhaust airflow and stack exit velocity and the necessary negative static pressure
(suction) in all parts of the exhaust system.
( ) If flammable gas, vapor, or combustible dust is
present in concentrations above 20% of the
Lower Flammable Limit, fan construction is as
recommended by the most current version of
AMCA’s 99-0401, Classifications for Spark
Resistant Construction.
( ) Laboratory exhaust fans are located as follows
• Physically outside of the laboratory building
and preferably on the highest level roof of the
building served. (This is the preferred location
since it generally minimizes risk of personnel
coming into contact with the exhaust airflow.)
• In roof penthouse or a roof mechanical equipment room that is always maintained at a
negative static pressure with respect to the
rest of the facility, and provides direct fan discharge into the exhaust stack(s).
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( ) All laboratory exhaust fans include provisions
to allow periodic shutdown for inspection and
maintenance. Such provisions include:
• Isolation dampers on the inlet side of all centralized exhaust system fans that have individual discharge arrangements or their own individual exhaust stacks.
• Isolation dampers on both the inlet and outlet
sides of all centralized exhaust system fans
that discharge into a common exhaust stack
or plenum.
• Ready access to all fans, motors, belts, drives, isolation dampers, associated control
equipment, and the connecting ductwork.
• Sufficient space to allow removal and replacement of a fan, its motor, and all other associated exhaust system components and equipment without affecting other mechanical
equipment or the need to alter the building
structure.
Design.
( ) In any event the discharge is a minimum of 10
ft (3 m) above adjacent roof lines and air intakes
and in a vertical up direction.
( ) Exhaust stack discharge velocity is at least
3000 fpm (15.2 m/s) (unless it can be demonstrated that a specific design meets the dilution criteria
necessary to reduce the concentration of hazardous materials in the exhaust to safe levels (see
Section 2.1) at all potential receptors.)
( ) Esthetic conditions concerning external
appearance do not supersede the requirements of
Sections 5.4.5 and 5.4.6.
( ) Any architectural structure that protrudes to a
height close to the stack-top elevation (i.e., architectural structure to mask unwanted appearance
of stack, penthouses, mechanical equipment,
nearby buildings, trees or other structures) is evaluated for its effects on re-entrainment.
5.4.5. Discharge of Contaminated Air
( ) The discharge of potentially contaminated air
that contains a concentration more than the allowable breathing air concentration is:
( ) The air intake or exhaust grills are not located
within the architectural screen or mask unless it is
demonstrated to be acceptable.
5.4.7 Recirculation
• direct to the atmosphere unless the air is
treated to the degree necessary for recirculation (see Section 9.3),
• discharged in a manner and location to avoid
reentry into the laboratory building or adjacent
buildings at concentrations above 20% of
allowable concentrations inside the laboratory
for routine emissions or 100% of allowable
concentrations for emergency emissions
under wind conditions up to the 1%-wind
speed for the site, and in compliance with
applicable federal, state, or local regulations
with respect to air emissions
5.4.6 Exhaust Stack Discharge
( ) The exhaust stack discharge is in accordance
with the current version of ASHRAE Handbook –
HVAC Applications, and the chapter or section
dealing with Building Air Intake and Exhaust
( ) Air exhausted from the general laboratory
space (as distinguished from laboratory chemical
hoods) is not recirculated to other areas unless
one of the following sets of criteria is met:
3) Criteria A
• The concentration of air contaminants generated by maximum credible accident will be
lower than short-term exposure limits required
by 2.1.1;
• There are no extremely dangerous or lifethreatening materials used in the laboratory;
and
• The system serving the laboratory chemical
hoods is provided with installed redundancy,
emergency power, and other reliability features as necessary, or
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4) Criteria B
• Provision of 100% outside air, whenever continuous monitoring indicates an alarm condition;
• Recirculated air is treated to reduce contaminant concentrations to those specified in
2.1.1; and recirculated air is monitored continuously for contaminant concentrations or provided with a secondary backup air-cleaning
device that also serves as a monitor (via a
HEPA filter in a series with a less efficient filter, for particulate contamination only; refer to
Section 9.3.1) and exhaust air from laboratory
hoods shall not be recirculated to other areas.
( ) Hood exhaust meeting the same criteria as
noted in Section 5.4.7.1 is only recirculated to the
same work area where the hood operators have
control of the hood work practices and can monitor the status of air cleaning.
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 the
applicable ANSI/ASHRAE 110 defined performance tests. or to a test standard recognized to
be equivalent.
( ) Specification and procurement of laboratory
fume hoods are based on “As Manufactured”
ANSI/ASHRAE 110 defined performance tests
conducted on a representative hood (or prototype
hood) that demonstrate adequate hood containment.
( ) The performance tests to be witnessed, referenced or otherwise include:
•
•
•
•
airflow visualization tests,
auxiliary 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 are conducted under constant volume conditions where exhaust and air supply flow
are stable and exhibit no more than 5% variation
from set-point.
6.1.1 Performance Tests
( ) The following performance tests are conducted as indicated and as prescribed in the commissioning plan, laboratory ventilation management
plan, or as directed by the responsible person.
6.1.1.1 Airflow Visualization Tests
( ) Airflow visualization tests are conducted as
described in the ANSI/ASHRAE 110–1995,
Method of Testing Performance of Laboratory
Fume Hoods.
( ) The tests consist of small-volume generation
and large-volume generation smoke to identify
areas of reverse flow, stagnation zones, vortex
regions, escape, and clearance.
( ) Visible escape beyond the plane of the sash
when generated 6 in. (15.2 cm) into the hood constitutes a failure during the performance test.
6.1.1.2 Auxiliary Air Velocity Tests
( ) For auxiliary air hoods, the face velocity is
measured with the auxiliary air turned off unless
room pressurization would change significantly to
affect exhaust flow. Where exhaust flow would be
affected by turning off the auxiliary airflow, auxiliary air is redirected from the hood opening so as
not to interfere with flow into the hood while conducting the face velocity traverse.
( ) The velocity of the auxiliary air exiting the auxiliary air plenum is measured to determine the
magnitude and distribution of air supplied above
the hood opening.
( ) The average auxiliary air velocity is determined from the average of grid velocities mea-
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sured across the plenum outlet.
measurements are taken.
6.1.1.3 Cross-Draft Velocity Tests
( ) A decrease in the average face velocity below
90% of the benchmark velocity is corrected prior
to continued hood use.
( ) Cross-draft velocity measurements are made
with the sashes open and the velocity probe positioned at several locations near the hood opening
to detect potentially interfering room air currents
(cross drafts). Record measurement locations.
( ) Over a period of 10–30 sec., cross-draft velocities are recorded approximately 1 reading per
second using a thermal anemometer with an
accuracy of +5% at 50 fpm (0.25 m/s) or better.
( ) The average and maximum cross-draft velocities at each location are recorded and not be sufficient to cause escape from the hood.
( ) Cross draft velocities are not of such magnitude
and direction as to negatively affect containment.
6.1.1.4 Exhaust Flow Measurement
( ) The volumetric flow exhausted from a laboratory fume hood is determined by measuring the
flow in the exhaust duct using industry-approved
methods.
6.1.1.5 Face Velocity Tests
( ) Once adequate performance has been established for a particular hood at a given benchmark
face velocity using the methods described above,
that benchmark face velocity is used as a periodic
check for continued performance as long as no
substantive changes have occurred to the hood or
other aspects that affect hood performance.
( ) Face velocity measurements are made with
the sash in the Design Sash Position. The Design
Sash Position is the maximum opening or configuration allowed by user standards, SOPs, or the
Chemical Hygiene Plan, whichever is applicable,
and used in the design of the exhaust system to
which the hood is connected.
( ) The sash position at which benchmark face
velocity is measured is recorded with the face
velocity measurement and reproduced each time
( ) The average face velocity is determined by the
method described in the current version of
ANSI/ASHRAE 110 Method of Testing
Performance of Laboratory Fume Hoods.
( ) Face velocity measurements are made by
dividing the hood opening into equal area grids
with sides measuring no more than 12 in. (30.5
cm).
( ) The tip of the probe is positioned in the plane
of the sash opening and fixed (not handheld) at
the approximate center of each grid.
( ) Grid measurements around the perimeter of
the hood opening are made at a distance of
approximately 6 in. (15.2 cm) from the top, bottom, and sides of the opening enclosure.
( ) The average face velocity is the average of the
grid velocity measurements.
( ) Each grid velocity is the average of at least 10
measurements made over at least 10 seconds.
( ) The plane of the sash is defined as the exterior surface of the outer most glass panel.
6.1.1.6 Hood Static Pressure Measurement
( ) The hood static pressure is measured above
the outlet collar of the hood at the flows required
to achieve the design average face velocity.
6.1.1.7 Tracer Gas Containment Tests
( ) Ttracer gas containment tests are conducted as
described in the ANSI/ASHRAE 110–1995, Method
of Testing Performance of Laboratory Fume Hoods
or by a test recognized to be equivalent.
( ) A control level for 5-minute average tests at
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each location conducted at a generation rate of 6
L/m is no greater than 0.05 ppm for "as manufactured” tests and 0.10 ppm for “as installed” (AM
0.05, AI 0.1).
( ) Escape of emissions more than the control
levels stated above are acceptable at the discretion of the design professional in agreement with
the responsible person (2.4.2).
( ) The “as used” 0.10 ppm level or more is at the
discretion of the responsible person (2.3).
( ) Face velocity increases exceeding 20% of the
benchmark are corrected prior to continued use.
6.1.2 Test Instrumentation
( ) All test instrumentation utilized for the tests
prescribed throughout this section are in good
working order and have been factory calibrated
within 1 year of the date of use. (See 8.6.1 Air
Velocity, Air Pressure, Temperature and Humidity
Instruments)
along with the other project documents.
( ) A commissioning plan addresses operation of
the entire ventilation system where the hoods, laboratories, and associated exhaust and air supply
ventilation systems are considered subsystems.
( ) The plan includes written procedures to verify
or validate proper operation of all system components and include:
• Laboratory Fume Hood Specification and
Performance Tests
• Preoccupancy Hood and Ventilation System
Commissioning Tests
• Preoccupancy Laboratory Commissioning
Tests
6.2.4 Commissioning Documentation
( ) Preliminary and final commissioning documents are issued to the appropriate party(s) by
the Commissioning Authority.
The documents include:
6.2 Commissioning of Laboratory Ventilation
Systems
6.2.1 Commissioning Process
( ) All newly installed, renovated, or moved hoods
are commissioned to ensure proper operation
prior to use by laboratory personnel.
6.2.2 Commissioning Authority
( ) The commissioning process is overseen by a
responsible person or commissioning authority.
6.2.3 Commissioning Plan
( ) A written commissioning plan accompanies
design documents and is approved by the commissioning authority in advance of construction
activities.
•
•
•
•
Commissioning Test Data;
Copy of Test and Balance Report;
Design Flow Specifications;
Laboratory and System Drawings for Final
System Design;
• List of Ventilation System Deficiencies uncovered and the details of how (and if) they were
satisfactorily resolved.
( ) Operational deficiencies and other problems
uncovered by the commissioning process are
communicated to the responsible party (i.e.,
installer, subcontractor, etc.) for prompt correction.
6.3 Commissioning Fume Hoods and Different
Types of Systems
6.3.1 Laboratory Fume Hoods
( ) The commissioning plan is available to all
potential suppliers and contractors prior to bid
( ) If practical, the exhaust flowrate from hoods
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are tested by measuring the flow in the duct by
the hood throat suction method or by flow meter.
( ) If flow measurement in the duct is not practical, velocity at the hood face or opening are measured at a sufficient number of points to obtain a
realistic average velocity, and multiplied by the
open area in the plane of the velocity measurements to obtain the flowrate.
( ) If the flowrate is more than 10% different from
design, corrective actions are taken.
6.3.2 Single Hood CAV Systems
( ) Commissioning tests on single hood, constant
air volume (CAV) systems consist of:
•
•
•
•
Fan Performance Tests;
Exhaust Duct Measurements;
Hood Performance Tests; and
Hood Monitor Calibration.
( ) Fan Performance Tests include measurement
of fan speed, fan static pressure, motor speed,
and amp draw.
( ) Exhaust duct measurements consist of
exhaust flow measurement and hood static pressure measurement.
( ) Hood performance tests consist of tests
described in Section 6.1.2.
• Verification of proper test, adjustment, and
balance of branch exhaust flow and static
pressures (exhaust flow and static pressure
for each branch shall be recorded after final
balancing is complete);
• Hood Performance tests as described above
in Sections 6.1.2; and
• Hood and System Monitor Calibration.
6.3.4 VAV Laboratory Fume Hood Systems
( ) VAV hood systems are commissioned prior to
use by laboratory personnel to ensure that all system components function properly and the system
operates as designed under all anticipated operating modes (defined under the VAV section).
( ) The commissioning procedures for VAV systems include:
• Verification of VAV Sensor Calibration;
• VAV Hood Performance Tests;
• VAV Laboratory and Ventilation System Tests,
and
• Verification of System Diversity.
6.3.4.1 VAV Sensor Calibration
( ) VAV sensors are capable of accurate measurement and control within 10% of actual at the
design maximum and minimum flow conditions.
6.3.4.2 VAV Hood Performance Tests
( ) The hood monitor is calibrated and adjusted
after hood performance has been determined as
satisfactory.
( ) Safe operating points are clearly identified for
the hood user.
6.3.3 Multiple Hood CAV Systems
( ) Commissioning of multiple hood, constant air
volume systems include:
• Fan Performance Tests;
( ) In addition to hood performance tests
described for evaluation of CAV hood systems,
commissioning tests on VAV hood systems
include measurement of flow or face velocities at
different sash configurations and VAV Response
and Stability tests.
( ) Flow or face velocity measurements are conducted at a minimum of two separate sash configurations.
( ) VAV Response and Stability tests include continuous measurements and recording of flow while
opening and closing the sashes for each hood
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(calibrated flow sensors or measurement of slot
velocity within the hood can be used as an indicator of flow).
( ) VAV Response is sufficient to increase or
decrease flow within 90% of the target flow or
face velocity in a manner that does not increase
potential for escape.
6.3.4.3 VAV Ventilation System Tests
( ) The VAV hood controls provide stable control
of flow in the exhaust and supply ducts and variation of flow do not exceed 10% from design at
each sash configuration or operating mode.
6.3.4.4 Verification of System Diversity
( ) System diversity is verified prior to use of laboratory fume hoods.
( ) The tests are designed to verify that users will
be alerted when system capacity is exceeded and
unsafe conditions may exist.
( ) VAV Stability is sufficient to prevent flow variations in excess of 10% from design at each sash
configuration or operating mode.
6.3.5 Laboratory Airflow Verification Tests
( ) Tests to verify and commission the laboratory
consist of:
• Air supply measurements;
• General room exhaust flow measurement (if
applicable);
• Room differential pressure measurement; and
• Calculation of the difference between total
area (laboratory, zone, etc.) supply and total
exhaust.
( ) All ventilation system alarm and monitoring provisions associated with occupant safety are verified
for proper functionality.
6.3.5.1 CAV Laboratory Room Tests
( ) These tests ensure that the ventilation system
design airflow is being maintained within the allowable tolerance in:
• All hood exhausts;
• All other bench-top and equipment exhaust
provisions that may be present;
• The room general exhaust if present;
• The room supply; and
• Room air cross currents at the hood face
opening.
( ) If a specific room differential pressure (dP)
has been specified, the dP is measured to ensure
that it is within its allowable range.
( ) If a room differential airflow is specified, actual
room differential airflow is determined to ensure
that is within allowable maximum and minimum
limits and in the proper direction.
( ) If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.), each
individual mode is enabled and applicable parameters (i.e., room supply, room total exhaust, etc.)
are performed for each separate mode.
( ) Room ambient conditions (temperature,
humidity, air currents, etc.) are also measured to
ensure they are being maintained under the conditions specified
6.3.5.2 VAV Laboratory Room Tests
( ) These tests ensure proper performance of the
VAV ventilation system and its associated controls
such that:
• The room general exhaust provides the specified range of airflow.
• The room supply provides the specified range
of airflow.
• Room air cross currents at the laboratory
hood face opening are within limits.
( ) If a specified room dP has been specified, the
dP is measured to ensure that it is being controlled within its allowable range with all doors
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closed and at minimum and maximum room
exhaust airflow.
( ) If a room differential airflow is specified, actual
room differential airflow is determined to ensure
that it is within allowable maximum and minimum
limits and direction at minimum and maximum
room exhaust airflow.
7
Work Practices
( ) Hood users are trained in the proper operation
and use of hood.
( ) The user establishes work practices that
reduce emissions and employee exposures.
( ) If the room has more than one ventilation control mode (i.e., occupied/unoccupied, etc.) conditions are evaluated for each mode.
( ) The user does not modify the interior or exterior components of the hood without the approval
of the Chemical Hygiene Officer, Responsible
Person, or other appropriate authority in the organization.
( ) Room ambient conditions (temperature,
humidity, air currents, etc.) are measured to
ensure they are being maintained under the conditions specified.
( ) The following work practices are followed
when hazardous materials are used in the hood:
( ) VAV systems are capable of maintaining the
offset flow required between exhaust and supply
to achieve the desired area pressurization within
the desired time specified.
6.4 Ongoing or Routine Hood and System
Tests
( ) Routine performance tests are conducted at
least annually or whenever a significant change
has been made to the operational characteristics
of the hood system.
( ) A hood that is found to be operating with an
average face velocity more than 10% below the
designated average face velocity is labeled as out
of service or restricted use and corrective actions
are taken to increase flow.
( ) Each hood is posted with a notice giving the
date of the routine performance test, and the
measured average face velocity.
( ) If it is taken out of service, it is posted with a
restricted use or out- of-service notice.
( ) The restricted use notice states the requisite
precautions concerning the type of materials permitted or prohibited for use in the hood.
( ) The user does not lean into the hood so that
his/her head is inside the plane of the hood, as
defined by the sash, without adequate respiratory
and personal protection.
( ) Equipment and materials are not placed in the
hood so that they block the slots or otherwise
interfere with the smooth flow of air into the hood.
( ) All work is conducted at least 6 inches behind
the plane of the sash (hood face).
( ) The horizontal sash or panels are not
removed.
( ) The hood is not operated without the back baffles in place.
( ) Flammable liquids are not stored permanently
in the hood or the cabinet under the hood unless
that cabinet meets the requirements of NFPA 30
and NFPA 45 for flammable liquid storage.
( ) The sash or panels are closed to the maximum position possible while still allowing comfortable working conditions.
( ) Hood users are trained to close the sash or
panels when the hood is not in use.
( ) The hood user does not operate with the
sashes opened beyond the design opening.
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( ) Pedestrian traffic is restricted near operating
hoods.
( ) 8.3 Maintenance personnel are trained and
required to use appropriate PPE during work
involving potential hazards.
( ) Rapid movement within the hood is discouraged
( ) The hood is not operated unless it is verified
that it is working.
( ) Rapid movement of the sash or panels is discouraged.
( ) 7.1 Each hood is posted with a notice giving
the date of the last periodic field test.
( ) If the hood failed the performance test, it is
taken out of service until repaired, or a restricted
use notice is posted on the hood.
( ) The notice states the partially closed sash
position necessary for safe/normal operation and
any other precaution concerning the type of work
and materials permitted or prohibited.
( ) 7.2 Hoods are in operation whenever hazardous volatile materials are being used or stored
inside.
8
Preventive Maintenance
( ) Inspection and maintenance follow a written
I&M Program developed by the user.
( ) Preventative maintenance is performed on a
regularly scheduled basis.
( ) 8.1 Operations served by equipment being shut
down for inspection or maintenance are safely discontinued and secured during such maintenance.
( ) Laboratory workers are notified in advance of
inspection and maintenance operations.
( ) 8.4 A written work permit system is established whenever the integrity of a potentially contaminated ventilation system is to be breached.
( ) Such work permits are designed to suit the circumstances, and at least address the following
factors:
( ) The permit system is overseen by a Responsible
Person, as defined in this standard, and is signed
by the person(s) to do the work, their supervisor,
and any other supervisors affected by the work;
( ) The nature of the work, and the health and
safety precautions, aredescribed;
( ) The time and place of the work are described;
( ) The same persons who signed the permit (or
their counterparts on a different shift) sign off
when the work is complete;
( ) Completed work permits are filed by an appropriate management function and retained for a
minimum of 3 years or as specified by individual
organizational policy.
( ) 8.5 Records are maintained for all inspections
and maintenance.
( ) If testing involves quantitative values, the
observed values are recorded.
( ) Inspection forms designed for the several categories of testing are provided and include the
normal values for the parameters tested.
( ) 8.2 All toxic or otherwise dangerous materials
on or in the vicinity of the subject equipment is
removed or cleaned up before maintenance.
( ) 8.6.1 Pressure instrumentation and measurement are in compliance with ANSI/ASHRAE 41.3.
Temperature instruments and measurement techniques are in compliance with ANSI/ASHRAE 41.1.
( ) Any hazardous materials and any other debris
are cleaned up before operations resume.
( ) All instruments using electrical, electronic, or
mechanical components are
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calibrated no longer than 12 months before use or
after any possible damage (including impacts with
no apparent damage) since the last calibration.
( ) 8.7.3 Blowers, drives, and other critical
machine elements are lubricated at intervals and
with lubricants recommended by the manufacturer.
( ) The accuracy of a scale used for a given parameter meets the following requirements:
( ) 8.8 Ventilation system management plan
addresses the need to provide critical service
issues and keep spare parts on hand.
(
(
(
(
(
(
(
(
) Velocity − fpm Accuracy
) Below 100 (5 m/s) 5 fpm (0.25 m/s)
) 100 (5 m/s) and higher 5% of signal
) Pressure − in. wg Accuracy
) 0.1 in. wg (25 Pa) 10% of signal
) 0.5 in. wg (125 Pa) and higher 5% of signal
) Between 25 and 125 Pa, interpolate linearly.
) Pitot-static tube measurements are in
accordance with ANSI/ASHRAE 41.7– 1984
(RA 91).
( ) Inclined manometers are selected so that the
nominal value of the measured parameter is at
least 5% of full scale. U-tube manometers should
not be used for pressures less than 0.5 in. wg.
( ) 8.9 All critical service instrumentation has contingency plans in place.
9
Air Cleaning
( ) 9.2 Air-cleaning systems for laboratory
exhaust systems, where required, are designed or
specified by a Responsible Person to ensure that
air-cleaning systems will meet the performance
criteria necessary for regulatory compliance.
( ) 9.3 Air-cleaning systems for recirculating general exhaust or hood exhaust from laboratories
meet the design and installation requirements of
ANSI/AIHA® Z9.7.
( ) Pitot tubes other than standard are calibrated.
( ) 8.6.2 Air contaminant monitors are tested at
least monthly or more often, if experience or manufacturer¹s recommendation indicates.
( ) Such testing includes the sensing element, zero
drift, and actuation of signals, alarms, and controls.
( ) Continuous air monitors are calibrated per
manufacturer¹s specifications or more frequently if
experience dictates.
( ) Recirculation of process air is returned to the
same room where the process is isolated and
control of the process is supervised.
( ) 9.3.1 Air-cleaning filtration systems for recirculating exhaust air contaminated with toxic particulates are filtered through a two-stage particulate
filtration system specified as following the standard performance and design criteria of the
ASHRAE systems and equipment to meet the
objectives of 2.4.1.
( ) 8.6.3 Other instruments (such as voltmeters
and tachometers) are checked for function and
accuracy against a “known source” before use
and follow manufacturer’s
( ) Filter installations are tested for leaks and
have all leaks repaired or the filter
recommendation, when provided, for periodic calibration.
( ) The flowrate through the filters is maintained
at design specifications and does not exceed
100% of the rated flow capacity of the filters.
( ) 8.7.1 Fans, blowers, and drive mechanisms
are visually inspected weekly.
( ) 8.7.2 V-belt drives are stopped and inspected
monthly for belt tension and signs of belt wear or
checking.
replaced before use.
( ) 9.3.2 Adsorption or other filtration media used
for the collection or retention of gases and vapors
are specified for a limited use.
( ) Specific hazardous materials to be collected,
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airflow rate, temperature, and other relevant physical properties of the system are incorporated into
the selection of filtration media.
( ) A reliable and adequately sensitive monitoring
system is utilized to indicate adsorbent breakthrough. The sensitivity of the monitoring system
is a predetermined fraction of the TLV® or appropriate health standard of the contaminant being
adsorbed but is not more than 25% of the TLV®.
( ) The breakthrough time of the contaminant,
before the effluent reaches no more then 50% of
the TLV®, is sufficient, based upon system capacity
design to allow a work operation shut down or
parallel filter switch-over, thus proving a fresh filter.
( ) For toxic gases and vapors, the filtration system is designed and sized to ensure adequate
collection and retention for a worst case scenario
when in the event of a spill or other major release.
( ) Adequate warning is provided for personnel to
stop work or enact other emergency procedures.
unloaded from the air-cleaning system following
safe work practices to avoid exposing personnel
to hazardous conditions and to ensure proper
containment of the filters for final disposal.
( ) Airflow through the filter housing is shut down
during filter change-out.
( ) 9.4.1 Recirculation air filters are inspected and
tested as per Section 9.3.1 except that provisions
are mandatory.
( ) 9.4.2 Activated carbon beds or panels are
tested as per Section. 9.3.2 at intervals no longer
than 1 month initially and then, based on experience with the particular installation, a schedule is
prepared.
( ) 9.4.3 Air pollution control equipment is inspected visually at intervals no longer than 1 week and,
if necessary, at shorter intervals.
( ) Specific tests and repairs are in accordance with
the manufacturer’srecommendations or are in compliance with applicable regulations.
( ) 9.3.3 When required, contaminated filters are
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• Minimum Design and Operating Specifications
APPENDIX 5 Sample Table of Contents for
Laboratory Ventilation Management Plan
Section IV – System Design and Operation
Foreword
Purpose
Scope
• Systems Safety
• Laboratory Design  Minimum Specifications
• Laboratory Ventilation Systems  Minimum
Specifications
PART A – Standards and Procedures
Section I Facility Organization
• Roles and Responsibilities
Section II – Characterizing Hazardous Procedures
• Categorizing Laboratory Hazards and
Procedures
• Effluent Characteristics
• Hazard Information Summary
Section III – Selection and Performance
of Hoods
• Laboratory Hoods
° Chemical Fume Hoods
° Biological Safety Cabinets
° Ventilation Balance Enclosures
° Laminar Flow Fume Hoods
° Snorkels
° Canopies
° Ventilation Enclosures
° Gloveboxes
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 Drawings
Basis of Design
Operating Specifications
TAB and Commissioning Reports
Test and Maintenance Data
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ANSI/AIHA STANDARDS
American National Standard for
ANSI/AIHA Z9.5–2012
Laboratory Ventilation
BY THE ANSI/AIHA Z9.5 SUBCOMMITTEE
Every laboratory will benefit from this outline of laboratory
ventilation requirements and practices. Chapters include
performance tests, air cleaning, preventive maintenance,
and work practices. Five appendices covering definitions,
terms and units are included. Those involved in laboratory
management, including chemical hygiene officers, campus
and institutional health and safety staff, industrial hygienists,
and environmental health and safety staff will benefit from
this standard.
STOCK NUMBER: LVEA12-437
A Publication by
American Industrial Hygiene Association
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