Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 144
Topic Requirement(s) Commentary
Recirculated
Air and Cross
Contamination
National Fire Protection Association, Standard NFPA 45, 2011
8.3.1 Laboratory ventilation systems shall be designed to ensure that chemical
fumes, vapors or gasses originating from the laboratory shall not be recirculated.
8.3.2 The location and configuration of fresh air intakes shall be chosen so as to
avoid drawing in chemicals or products of combustion coming from either the
laboratory building itself or from other structures and devices.
A.8.3.2 Special studies such as air-dispersion modeling might be necessary to
determine the location of air intakes for laboratories away from the influence of
laboratory exhaust and other local point source emissions.
8.4.1 Air exhausted from chemical fume hoods and other special local exhaust
systems shall not be recirculated.
8.4.2.2 Devices that could result in recirculation of exhaust air or exhausted
contaminants shall not be used unless designed in accordance with Section 4:10:1,
“Nonlaboratory Air,” and Section 4:10.2, “General Room Exhaust,” of ANSI/AIHA
Z9.5, Laboratory Ventilation.
A.8.4.2 Consideration should be made of the potential contamination of the fresh air
supply by exhaust air containing vapors of flammable or toxic chemicals when using
devices for energy conservation purposes.
8.4.4 Air exhausted from laboratory units and laboratory work areas in which
chemicals are present shall be continuously discharged through duct systems
maintained at a negative pressure relative to the pressure of normally occupied
areas of the building.
8.4.5 Positive pressure portions of the lab hood exhaust system (e.g. fans, coils,
flexible connections and ductwork) located within the laboratory building shall be
sealed airtight or located in a continuously mechanically ventilated room.
8.4.12 Air exhausted from chemical fume hoods and special exhaust systems shall
be discharged above the roof at a location, height, and velocity sufficient to prevent
re-entry of chemicals and to prevent exposures to personnel.
A.8.4.12 Exhaust stacks should extend at least 3 m (10 ft) above the highest point
on the roof to protect personnel on the roof. Exhaust stacks might need to be much
higher to dissipate effluent effectively, and studies might be necessary to determine
adequate design. Related information on stack height can be found in Chapter 14,
Airflow Around Buildings, of the ASHRAE Handbook of Fundamentals.
(Continued on Next Page)
Note that as written, NFPA 8.4.1 specifically
prevents the recirculation of fume hood
exhaust but not laboratory room air.
Recirculation of laboratory room air is
permissible if the specific requirements of
ANSI/AIHA Z9.5 are met.
The cost to install exhaust filtering and
cleaning systems that would adequately
remove hazardous fumes (and the associated
risk of a failure in such a system) generally
makes it an impractical consideration.
Air cleaning to remove hazardous particulate
for safe discharge of the exhaust air into the
atmosphere (as may be required by the local
and federal EPA) should not be confused with
removing all toxic gasses, vapors etc. as
would be required for re-circulation of the
exhaust air within a facility.
2.1.1 States as follows: “The containment and
capture of a laboratory chemical hood shall be
considered adequate if, in combination with
prudent practice, laboratory worker chemical
exposures are maintained below applicable
in-house exposure limits, OSHA PELs,
NIOSH RELs, ACGIH TLVs, etc.