Basic Documentation

Table Of Contents
Biological Laboratories
Siemens Industry, Inc. 79
Topic Requirement(s) Commentary
Biological
Safety
Cabinets and
Classifications
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The Class II, Type A2 BS.C (Formerly called A/B3): Only when this BSC is ducted
to the outdoors does it meet the requirements of the former Class II Type B3.8 The
Type A2 cabinet has a minimum calculated or measured inflow velocity of 100 fpm.
All positive pressure contaminated plenums within the cabinet are surrounded by a
negative air pressure plenum thus ensuring that any leakage from a contaminated
plenum will be drawn into the cabinet and not released to the environment. Minute
quantities of volatile toxic chemicals or radionuclide can be used in a Type A2
cabinet only if it exhausts to the outside via a properly functioning canopy
connection.
Class III
The Class III BSC was designed for work with highly infectious microbiological
agents and for the conduct of hazardous operations and provides maximum
protection for the environment and the worker. It is a gas-tight (no leak greater than
1x10-7 cc/sec with 1% test gas at 3 inches water gauge enclosure with a non-
opening view window. Access for passage of materials into the cabinet is through a
dunk tank, that is accessible through the cabinet floor, or double-door pass-through
box (e.g., an autoclave) that can be decontaminated between uses. Reversing that
process allows materials to be removed from the Class III BSC safely. Both supply
and exhaust air are HEPA filtered on a Class III cabinet. Exhaust air must pass
through two HEPA filters, or a HEPA filter and an air incinerator, before discharge
directly to the outdoors. Class III cabinets are not exhausted through the general
laboratory exhaust system. Airflow is maintained by an exhaust system exterior to
the cabinet, which keeps the cabinet under negative pressure (minimum of 0.5
inches of water gauge.) Long, heavy-duty rubber gloves are attached in a gas-tight
manner to ports in the cabinet to allow direct manipulation of the materials isolated
inside. Although these gloves restrict movement, they prevent the user’s direct
contact with the hazardous materials. The trade-off is clearly on the side of
maximizing personal safety. Depending on the design of the cabinet, the supply
HEPA filter provides particulate-free, albeit somewhat turbulent, airflow within the
work environment. Laminar airflow is not a characteristic of a Class III cabinet.
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