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Class II Bio-Safety Cabinets

A ventilated cabinet for personnel, product, and environmental protection having an open front with inward airflow for personnel protection, downward HEPA filtered laminar airflow for product protection, and HEPA filtered exhausted air for environmental protection. When toxic chemicals or radio-nuclides are used as adjuncts to biological studies or pharmaceutical work, Class II cabinets designed and constructed for this purpose should be used.

Class II Type Al Cabinets (formerly designated Type A)

Maintain minimum average inflow velocity of 75 ft/min (0.38 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 plenum (i.e., a plenum from which a portion of the air is exhausted from the cabinet and the remainer supplied to the work area). May exhaust HEPA filtered air back into the laboratory or to the environment through an exhaust canopy; and May have positive pressure contaminated ducts and plenums that are not surrounded by negative pressure plenums. Type Al cabinets are not suitable for work with volatile toxic chemicals and volatile radio- nuclides.

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Class II, Type A2 Cabinets (formerly designated Type B3)

Maintain a minimum average inflow velocity of 100 ft/min (0.5 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 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 radio-nuclides required as an adjunct to microbiological studies must be exhausted through properly functioning exhaust canopies.

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BothClass II, Type A1 & A2 Cabinets

Have HEPA filtered downflow air that is a portion of the mixed downflow and inflow air from a common plenum.

May exhaust filtered air back into the laboratory or to the environment through an exhaust canopy.

Class II Type B1 Cabinets

Maintain a minimum average inflow velocity of 100 ft/min (0.5 m/s) through the work access opening.

Have HEPA filtered downflow air composed largely of uncontaminated re-circulated inflow air. Exhaust most of the contaminated downflow air through a dedicated duct exhausted to the atmosphere after passing through a HEPA filter.

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 re- circulated in the downflow air.

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Class II Type B2 Cabinets (sometimes referred to as "total exhaust")

Maintain a minimum average inflow velocity of 100 ft/min (0.5 m/s) through the work access opening.

Have HEPA filtered downflow air drawn from laboratory or the outside air i.e., downflow air is not re-circulated from the cabinet exhaust air).

Exhaust all inflow and downflow air to the atmosphere after filtration through a NEPA filter without recirculation in the cabinet or return to the laboratory.

Have all contaminated ducts and plenums under negative pressure or surrounded by directly exhausted (non-recirculation through the work area) negative pressure ducts and plenums.

Type B2 cabinets may be used for work with volatile toxic chemicals and radio-nuclides required as adjuncts to microbiological studies.

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Class III Bio-Safety Cabinets

A totally enclosed ventilated cabinet of leak-tight construction. Operations in the cabinet are conducted through attached rubber gloves. The cabinet is maintained under negative air pressure of at least 0.50" WG (120 Pa). Downflow air is drawn into the cabinet through NEPA filters. The exhaust air is treated by double NEPA filtration or by NEPA filtration and incineration