BSC class I II III type A type B biological safety cabinets NIH national institute of health

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Biological Safety Cabinets (BSCs)
Bench-top or freestanding cabinets with unidirectional airflow used for handling materials that present a health hazard. The National Institutes of Health (NIH) Guidelines classify them as:

1. Class I - A negative pressure, ventilated cabinet for personnel protection having an inward flow of air away from the operator. The exhaust air is filtered through a HEPA filter (located at rear or top) either into the laboratory or to the outside. This cabinet is designed for general microbiological research with low and moderate risk agents (BL-2 and BL-3 agents), and is used in three operational modes:

a) With a full width open front. The face velocity of the inward flow of air through the full width open front is at least 75' feet per minute.

b) With an installed front closure panel (having four 6-inch diameter openings) without gloves. The face velocity of the inward flow of air through the openings will increase to approximately 150' feet per minute.

c) With an installed front closure panel equipped with arm-length rubber gloves, and inlet air pressure relief for further protection. In this configuration, it is necessary to install a make-up air inlet fitted with a HEPA filter in the cabinet.

2. Class II - A ventilated cabinet for personnel and product protection having an open front with inward airflow for personnel protection (75' to 100' feet per minute), and HEPA filtered downward unidirectional airflow for product protection. The exhaust air is filtered through a HEPA filter for environmental protection. For selection and procurement of Class II cabinets refer to standards developed by the National Sanitation Foundation, Ann Arbor, Michigan. Cabinets are further classified as:

a) Type A - Suitable for microbiological research in the absence of volatile or toxic chemicals and radionuclides (BL-2 and BL-3), with 70% recirculated air through HEPA. They are exhausted through HEPA into the laboratory or to the outdoors via a "thimble" connection to the building exhaust system.

b) Type B - Hard ducted to the building exhaust system, contains negative pressure plena, and face velocity of 100' feet per minute. Type B cabinets are further sub-typed into types: B1 (30% recirculated air through HEPA; exhaust via HEPA and hard ducted. BL2 and BL-3), B2 (No recirculation; total exhaust via HEPA and hard ducted. BL-2 and BL-3), and B3 (same as IIA, but plena under negative pressure to room and exhaust air is ducted. BL-2 and BL-3).

Classes I and II should be located away from traffic patterns and doors, airflow from fans, room air supply louvers, and other air moving devices.

3. Class III - Closed-front ventilated cabinet of gas tight construction that provides the highest level of personnel protection from infectious aerosols, as well as protection of research materials from microbiological contaminants. The interior of the cabinet is protected from contaminants exterior to the cabinet. The cabinet is fitted with arm-length rubber gloves and is operated under negative pressure of at least 0.5 inches water gauge. All supply air is filtered through HEPA filters. Exhaust air is filtered through two HEPA filters in series or one HEPA filter and incinerator before being discharged to the outside environment. Class III cabinets are most suitable for work with hazardous agents that require Biosafety Level 3 or 4 containment. Cabinets must be connected to a double-door autoclave and/or chemical dunk tank used to sterilize or disinfect all materials exiting the cabinet, and to allow supplies to enter the cabinet