MIL-HDBK-1191
8.16.3
Space Pressurization. The required pressurization of
individual spaces, relative to adjacent spaces or corridors, is indicated
at Appendix A. Where a negative or positive pressurization are required
for a given space, that pressurization shall be maintained by the HVAC
system under all conditions of operation, including periods of reduced
ventilation or night setback.
8.16.4
Laboratory Ventilation. Exit corridors shall not be utilized
to directly supply or exhaust air from the laboratory, although "transfer"
of air to/from corridors may be utilized to establish required room
pressurization. Negative pressurization of laboratories in relation to
surrounding occupancies shall be maintained under all conditions of HVAC
system and fume hood operation.
8.16.4.1
Exhaust Systems. Laboratory equipment utilized for personnel
protection from hazardous chemical, microbiological, or radioactive
airborne particles or gases shall be provided with independent exhaust
systems in accordance with NFPA 99,(reference 8c). Exhausts from general
chemical laboratory fume hoods located within a laboratory unit may be
combined into central exhaust systems in accordance with guidance in
references 8c and 8g. Exhausts from hoods handling perchloric acid or
other strong oxidizing agents, materials or agents requiring HEPA
filtration, or exhausts which, when combined, chemically interact or change
the explosion/ignition limits, may not be combined. Additional guidance
for hood and exhaust design is contained at references 8a, 8b, 8c, 8g, 8j,
and 8q. Exhaust duct discharge height shall be above the building
recirculation cavity boundary. In all cases exhaust discharge shall have
sufficient stack height, velocity, and distance from building openings,
outside air intakes, or recirculating air currents, to preclude reentry
into the building. Air velocity in exhaust ductwork shall be sufficient to
transport the contaminant vapors, fumes, dusts, or other particulate matter
for which the fume hood(s) is designed.
8.16.4.2
Laboratory Fume Hoods, General. Fume hoods shall be located in
areas of minimal air turbulence, away from doors, windows, and traffic, to
minimize disruption of required sash airflow. HVAC system/fume hood
controls shall be designed such that operation or shutdown of any fume hood
in a given space will not disrupt the required room air balance or the
required sash airflow at other hoods operating in the space. General
purpose laboratory fume hoods that control personnel exposure to chemicals
and physical contaminants shall have a minimum sash face velocity of
0.508 m/s (100 fpm). Fume hoods shall be provided with audible and visual
alarms to indicate inadequate sash airflow conditions.
8.16.4.3
Radioactive Material/Radioisotope Hoods. Duct systems serving
hoods for radioactive material shall be constructed of acid resistant type
stainless steel for their entire length. Ductwork shall be flanged with
neoprene gasketed joints to facilitate dismantlement for decontamination.
Fume hood exhaust shall remain in constant operation, and shall be
filtered with carbon and/or HEPA filters as required to meet Nuclear
Regulatory Commission (NRC) requirements. The location of filters in the
system shall be chosen to best facilitate their safe removal, disposal, and
replacement by maintenance personnel. All filters shall be automatically
monitored to provide indication that changeout is required. All hoods
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