06-06
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 should be selected to operate at low tip speed
(approximately at half the maximum permissible tip speed) and
maximum static efficiency.
To ensure verification, provide fan
selection data on a performance curve.
c. Keep air velocity through the exhaust ducts within the ASHRAE
recommended range of 1000 to 1200 feet per minute.
d. Select backward inclined or forward curved blade fans.
Ensure
that the fan discharge is directed upwards and the discharge
velocity of 15 m/s (3,000 fpm) is maintained.
e. Perform sound analysis for each exhaust fan and provide sound
attenuation, as required, by installing prefabricated sound
attenuators or sections of lined ductwork.
f. To ensure design air flow, a pressure independent, factory set
(but field adjustable), automatic air flow control and balancing
valve shall be provided for each fume hood and biological safety
cabinet.
This requirement is applicable even when an exhaust fan
is connected to a single fume hood or a single biological safety
cabinet.
2. H3 Radioisotope Hoods: The following minimum design criteria shall
apply:
a. Provide a dedicated exhaust system for each H3 hood.
b. The exhaust air quantities m3/min (CFM) and pressure drops (Pa)
(Inch of Water Gage) are listed below in Table 3.1:
TABLE 3.1
SIZE
EXHAUST
PRESSURE DROP
Millimeters
m3/mi.
Pa
1200 (48")
25 (875 CFM)
93 (0.375")
1500 (60")
32 (1125 CFM)
93 (0.375")
1800 (72")
38 (1375 CFM)
93 (0.375")
c. Provide a HEPA filter in exhaust air stream prior to discharge at
or above the highest point of the building.
d. Provide an alternate room exhaust air connection, so exhaust air
may be drawn from the room grille when the hood is not in
operation.
Provide automatic on/off dampers in each branch duct
and an automatic air flow control and balance valve in the common
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