ISPE Glossary of Pharmaceutical and Biotechnology Terminology

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Biological Safety Cabinets (BSCs)

The US Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) in their Primary Containment for Biohazards: Selection, Installation and Use of Biological Safety Cabinets – Third Edition – September 2007, Section III, Biological Safety Cabinets, defines three classes of biological safety cabinets, which are the primary means of containment developed for working safely with infectious microorganisms. BSCs are designed to provide personnel, environmental and product protection when appropriate practices and procedures are followed. The three kinds of biological safety cabinets are designated as Class I, Class II, and Class III, and they have been developed to meet varying research and clinical needs:

Class I BSC – The Class I BSC provides personnel and environmental protection, but no product protection. It is similar in air movement to a chemical fume hood, but has a HEPA filter in the exhaust system to protect the environment. In the Class I BSC, unfiltered room air is drawn across the work surface. Personnel protection is provided by its inward airflow as long as a minimum velocity of 75 linear feet per minute (lfpm) is maintained through the front opening. Because product protection is provided by the Class II BSCs, general usage of the Class I has declined. However, in many cases, Class I BSCs are used specifically to enclose equipment (e.g., centrifuges, harvesting equipment or small fermenters), or procedures with potential to generate aerosols (e.g., cage dumping, culture aeration or tissue homogenation).

Class II BSC – The Class II (Types A1, A2, B1 and B2) BSCs provide personnel, environmental and product protection. Airflow is drawn into the front grille of the cabinet, providing personnel protection. In addition, the downward laminar flow of HEPA-filtered air provides product protection by minimizing the chance of cross-contamination across the work surface of the cabinet. Because cabinet exhaust air is passed through a certified HEPA filter, it is particulate-free (environmental protection), and may be recirculated to the laboratory (Type A1 and A2 BSCs) or discharged from the building via a canopy connection. Exhaust air from Types B1 and B2 BSCs must be discharged to the outdoors via a hard connection.

Class III BSC – The Class III BSC was designed for work with highly infectious microbiological agents and for the conduct of hazardous operations and provides maximum protection for the environment and the worker. It is a gas-tight (no leak greater than 1x10-7 cc/sec with 1% test gas at 3 inches pressure Water Gauge) enclosure with a non-opening view window. Access for passage of materials into the cabinet is through a dunk tank, that is accessible through the cabinet floor, or double-door pass-through box (e.g., an autoclave) that can be decontaminated between uses. Reversing that process allows materials to be removed from the Class III BSC safely. Both supply and exhaust air are HEPA filtered on a Class III cabinet. Exhaust air must pass through two HEPA filters, or a HEPA filter and an air incinerator, before discharge to the outdoors. Airflow is maintained by an exhaust system exterior to the cabinet, which keeps the cabinet under negative pressure (minimum of 0.5 inches of water gauge). “The exhaust fan for the Class III cabinet is generally separate from the exhaust fans of the facility ventilation system”.

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See also: Biosafety Level Containment Positive Pressure Personnel Suit

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