5.4.2 Proper Use and Operation of the BSC According to Cabinet Class

Class II BSCs, when used in conjunction with GMT, provide an effective partial containment system for safe manipulation of moderate and high-risk microorganisms (e.g., Biosafety Level 2 and 3 agents).  The use of these cabinets alone is not appropriate for containment of the highest risk biohazardous agents because aerosols may accidentally escape through the open front.  As with any other piece of laboratory equipment, personnel must be trained in the proper use of the cabinet.  Strict adherence to recommended practices is as important as the mechanical performance of the equipment itself. 

Class II BSCs are classified into two types (A and B) based on construction, air flow velocities and patterns, and exhaust systems.  Basically, Type A cabinets are suitable for work with microbiological research in the absence of volatile or toxic chemicals and radionuclides, since air is recirculated within the work area.  Type A cabinets are exhausted through high efficiency particulate air (HEPA) filters into the laboratory or may be exhausted to the outside, if a "thimble" connection to the exhaust ductwork is used. 

Type B cabinets are hard-ducted to the exhaust system and contain negative pressure plena.  These features, plus an increased face velocity of 100 feet per minute, allow work to be done with toxic chemicals or radionuclides.  Type B cabinets are further sub-typed into two types, B1 and B2.  Type B1 requires 70% of the downward-flowing air stream to be exhausted to the outside and 30% recirculated. Type B2 has 100% of the downward-flowing air exhausted to the outside; no air is recirculated within the cabinet.  Call EHS for information on a comparison of the design features and applications. 

As with any other piece of laboratory equipment, personnel must be trained in the proper use of BSCs.  Of particular note are those activities that may disrupt inward directional airflow through the work opening and allow the escape of aerosolized particles from within the cabinet (e.g., repeated insertion and withdrawal of worker's arms into and from the work chamber, opening and closing laboratory doors, improper placement of materials, improper operation of equipment within the work chamber or brisk walking past the cabinet while it is in use).  These cabinets should be located away from traffic patterns and doors.  Fans, heating and air conditioning registers and other air handling devices can also disrupt airflow patterns if located adjacent to a BSC.  Strict adherence to recommended practices for use of BSCs and proper placement in the laboratory are as important in attaining the maximum containment capability of equipment as is the mechanical performance. 

IMPORTANT: Cabinets must be tested and certified at the time of installation, any time they are moved, following internal repair, and at least annually thereafter.  Cabinets must be decontaminated prior to moving.  Certification is site specific and is required before the cabinet is put into operation in the laboratory.  Please call the Associate Biosafety Officer at EHS (335-5679) with any questions regarding decontamination or certification of biosafety cabinets, or to schedule repair, certification, or decontamination.

Class III BSCs are totally enclosed, ventilated cabinets of gas-tight construction and offer the highest degree of personnel, environmental and product protection.  Class III cabinets are most suitable for work with hazardous agents that require Biosafety Level 3 or 4 containment. 

The Class III cabinet is operated under negative pressure.  Supply air is HEPA-filtered and the cabinet exhaust air is filtered by two HEPA filters in series, or HEPA filtration followed by incineration, before discharge outside the facility.   All operations in the cabinet are performed through attached rubber gloves.  Any equipment required by the laboratory activity, such as incubators, refrigerators and centrifuges must be an integral part of the system.  Double-door autoclaves and chemical dunk tanks are also attached to the cabinet system to allow supplies and equipment to be safely introduced and removed.