Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 90
Topic Requirement(s) Commentary
Biosafety
Cabinets –
Certification
and Safe
Usage -
Canada
E.2.3 Roof exhaust systems
Roof exhaust systems serving biosafety cabinets should have a stack that extends
straight upward at least 10 ft (3 m) above the roof surface to avoid re-entrainment by
the building, and should be increased in elevation when necessary to avoid the
influence of surrounding structures. Raincaps or any other structure that deflects the
straight upward flow of the discharged air should be avoided. No precipitation can
enter the stack when air is being exhausted at normal stack velocities. To take care of
precipitation during periods when system is shut off, a 1 in (2.5 cm) hole can be
drilled in the lowest point of the fan casing and the water allowed to drain onto the
roof. It is recommended that roof exhaust fans be energized by direct-connected
electric motors to avoid failures caused by slipping and breaking of belts.
Another advantage of direct-connected fans is the ability to use the motor non-
function to activate an alarm in the laboratory, whereas when a malfunctioning belted
fan is employed, the motor can be operating when the fan is idle.
Public Health Agency of Canada, Office of Laboratory Security, Biosafety
Division, Laboratory Biosafety Guidelines, 3
rd
Edition 2011:
9.3 Installation and Certification
The air curtain at the front of the cabinet is fragile and can easily be disrupted by
people walking parallel to it, by open windows, air supply registers or laboratory
equipment that creates air movement (e.g., vacuum pumps, centrifuges). BSCs
should be installed in accordance with the requirements outlined in the Canadian
Standards Association (CSA) Biological Containment Cabinets (Class I and II):
Installation and Field Testing
(8)
. They should be located away from high traffic areas,
doors and air supply/exhaust grilles that may interrupt airflow patterns. A minimum
unobstructed distance of 40 cm should be provided between the exhaust outlet on
top of the cabinet and any overhead obstructions. Whenever possible, a 30 cm
clearance should be provided on each side of the cabinet to allow for maintenance
access. For ducted cabinets, blowers on the exhaust system should be located at the
terminal end of the ductwork; failure of exhaust flow should signal an alarm to the
user. To prevent pressurization of the cabinet, an interlock system should be installed
to prevent the cabinet blower from operating whenever the exhaust flow is
insufficient; an anti-backflow device to prevent reverse airflow through the HEPA filter
may be required.
Continuous operation of BSCs helps to control dust levels and other airborne
particulates in the laboratory. If BSCs are operated only when needed in order to
conserve energy, the balancing of laboratory room air must be considered. In some
cases, room exhaust is balanced to include the air exhausted through ducted BSCs,
and these cabinets must not be turned off.
The provision of natural gas to BSCs is not recommended. Open flames in the BSC
create turbulence, disrupt airflow patterns and can damage the HEPA filter
(1)
. When
suitable alternatives (e.g., disposable sterile loops, micro-incinerators) are not
possible, touch-plate micro burners that have a pilot light to provide a flame on
demand may be used.