Biological safety cabinets are among the most effective and commonly used primary containment devices in laboratories working with biohazardous agents. There are three classes of BSCs, each having different performance characteristics as outlined below.
The Class I BSC provides protection to personnel and to the laboratory area; however, product protection is not provided because the inlet air is not filtered. Class I BSCs are no longer being manufactured on a regular basis and most have been replaced by Class II BSCs.
The Class II BSC is a vertical laminar flow BSC that adds HEPA filtered recirculating airflow within the work space to the basic design of the Class I BSC. This enables it to protect the agents used within the cabinet (product protection) as well as the lab and the worker. It is designed for use with low- or moderate-risk agents.
The Class III BSC, commonly referred to as a glove box, is a self-contained gas-tight enclosure that provides a complete barrier between the worker and the materials in the cabinet. It is designed for use with high risk biologicals. When in use it is maintained under negative air pressure. Supply and exhaust air are HEPA filtered. Exhaust air is discharged outside the facility by fans separate from the facility's ventilation system.