2.11.2.2 To be in compliance with NFPA 90A, ducts connected to the special
exhaust systems, noted below, are hazardous and shall not be housed in the
same shaft, carrying environmental supply, return, and exhaust ducts.
(a) Laboratory Hood Exhaust Systems
(b) ETO-Ethylene Oxide Sterilizers Exhaust Systems
(c) Grease-Laden Kitchen Hood Exhaust Systems
(d) Ortho/Prosthetic Laboratory Exhaust
(e) Battery Charging Rooms
2.11.2.3 All other ducts carrying make-up air, connected to special exhaust
systems, may be installed in the same shaft, which carry environmental supply
and/or return ducts.
2.11.2.4 Exhaust fans shall be located close to the discharge air to maintain
a negative air pressure in the exhaust ductwork inside the building.
2.11.3 LABORATORY HOOD EXHAUST SYSTEMS
laboratories and research services require dedicated exhaust systems. While
the type of exhaust system would depend upon the hood characteristics, the
following features shall be incorporated into the design to avoid excessive
noise levels and ensure accurate air balancing. Room noise criteria for
laboratories are NC 45.
(a) The ventilation system for the fume hood exhaust shall conform
to the
OSHA (Occupational Safety and Health Act), Regulation 29 CFR, Part
1910. The
exhaust shall be continuously monitored and an alarm system (local
audible
and visible alarm, and an alarm at the central engineering control
center
(ECC), if any, shall be provided for each fume hood and biological
safety
cabinet.
(b) The exhaust fans shall be selected to operate at low tip speed
(approximately at half the maximum permissible tip speed) and maximum static
efficiency. Provide fan selection data on a performance curve. Ensure that
the fan discharge is directed vertically upward and the discharge velocity of
15.3 m/s (4,000 fpm) is maintained. See VA Standard Detail 15822-2 for stack
installation. Minimum height of stack shall be 7-feet high as per ASHRAE.
(c) Keep air velocity through the exhaust ducts within the ASHRAE recommended
range of 5.1 to 6.12 m/s (1000 to 1200 fpm).
(d) Select backward inclined or forward curved blade fans.
(e) Perform sound analysis for each exhaust fan and provide sound
attenuation, if required. Use prefabricated sound attenuators or lined
ductwork.
(f) To ensure design airflow, a pressure independent, factory-set, field-
adjustable, automatic airflow control shall be provided for each fume hood
and a biological safety cabinet.
HVAC DESIGN MANUAL
2-31
HVAC SYSTEMS AND EQUIPMENT
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