Class II BSCs use higher air velocities to provide better protection for personnel, the environment and product. The two main types are Class II Type A1 and A2 cabinets. Both have HEPA filtered downward laminar airflow and HEPA filtered exhaust air to protect the environment. The main difference is that Type A1 cabinets recirculate about 70% of the purified air back into the work zone whereas Type A2 cabinets do not recirculate exposed air in the work zone. Type A2 cabinets are often used for handling infectious agents requiring higher levels of containment.
Class III cabinets, also called “glove boxes”, provide the highest level of protection. All manipulations of materials within the cabinet are conducted through attached rubber gloves within a closed front panel. Supply and exhaust air undergo HEPA filtration and cabinet pressure is held at a negative pressure compared to surrounding rooms. Class III units are used for hazardous, infectious materials requiring Biosafety Level 4 containment such as manipulation of highly pathogenic viruses.
Components and Design
BSCs have certain key components that facilitate their function and maintain adequate microbiological and operational safety levels. The plenum is the lower part of the cabinet that houses the blower and intake HEPA filters. Biological Safety Cabinets filtered air space maintains positive cabinet pressure. The work access opening and front window allow for materials transfer and viewing. Sliding glass sash doors or panels cover the opening and windows. An exhaust HEPA filter installed in the cabinet outlet collects materials leaving the work zone before being discharged to the outside.
Other typical design features include stainless steel or epoxy-coated interiors for easy cleaning and disinfection. They have adjustable work trays, service fixtures, and pass-through durometers and ports. Electronic control systems monitor cabinet operation parameters like blower/filter status, face velocity, and alarm conditions. A supply air diffuser distributes filtered air uniformly across the work zone while inward sloping surfaces channel outward flowing contaminated air to the exhaust plenum located at the rear of the cabinet. All components work together seamlessly to protect the operator, experiment, and environment.
Operator Training and Use
Usage of BSCs requires specialized training to ensure safe microbiological practices. Operators learn key techniques like proper aseptic work habits and containment zones. Sleeved arms should remain inside the work zone at all times to avoid reaching across contaminated and clean areas. Materials placed into the cabinet must lie flat and not block the turbulent inward flowing curtain of air.
Work using sharps or organisms requiring needles/syringes requires extra care. Liquid spills should be cleaned promptly to prevent aerosols. Inward velocity is monitored periodically as per standard operating protocols. Equipment inside the cabinet is properly decontaminated before removal or exchange. Proper door closing/opening motions prevent accidentally trapped arms. Technicians are trained to understand the cabinet design limits and recognize filter loading or failure indications. Periodic certification validates satisfactory containment criteria are being met.
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