Basic Documentation

Biological Laboratories
Siemens Industry, Inc. 81
Topic Requirement(s) Commentary
Biological
Safety
Cabinets and
Classifications
(Continued)
3.4.2.2 Class II, Type A2 cabinets (when exhausted to the environment were
formerly designated Type B3): cabinets that:
– maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the
work access opening;
– have HEPA filtered downflow air that is a portion of the mixed downflow and
inflow air from a common exhaust plenum;
– may exhaust HEPA filtered air back into the laboratory or to the environment
through an exhaust canopy; and
– have all biologically contaminated ducts and plenums under negative pressure
or surrounded by negative pressure ducts and plenums.
Type A2 cabinets used for work with minute quantities of volatile toxic chemicals
and tracer amounts of radionuclides required as an adjunct to microbiological
studies must be exhausted through properly functioning exhaust canopies.
3.4.2.3 Class II Type B1 cabinets: cabinets that:
– maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the
work access opening;
– have HEPA filtered downflow air composed largely of uncontaminated
recirculated inflow air
– exhaust most of the contaminated downflow air through a dedicated duct
exhausted to the atmosphere after passing through a HEPA filter; and
– have all biologically contaminated ducts and plenums under negative pressure
or surrounded by negative pressure ducts and plenums.
Type B1 cabinets may be used for work treated with minute quantities of volatile
toxic chemicals and tracer amounts of radionuclides required as an adjunct to
microbiological studies if work is done in the direct exhausted portion of the
cabinet, or if the chemicals or radionuclides will not interfere with the work when
recirculated in the downflow air.
3.4.2.4 Class II, Type B2 cabinets: Cabinets that:
– maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the
work access opening;
– have HEPA filtered downflow air drawn from the laboratory or the outside air
(i.e., downflow air is not recirculated from the cabinet exhaust air);
– exhaust all inflow and downflow air to the atmosphere after filtration through a
HEPA filter without recirculation in the cabinet or return to the laboratory; and
– have all contaminated ducts and plenums under negative pressure or
surrounded by directly exhausted (nonrecirculated through the work area)
negative pressure ducts and plenums.
Type B2 cabinets may be used for work with volatile toxic chemicals and
radionuclides required as adjuncts to microbiological studies.
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