Biosafety cabinets are ventilated workspaces that are designed to protect laboratory personnel, products and the environment from contamination during research on infectious microorganisms. They are designated as Classes I, II and III depending expected hazards and the safety levels required.
The risks associated with work on microorganisms and the degrees of containment required are ranked in four biosafety levels. Level 1 agents do not pose risks to healthy adults or the environment. Examples are canine hepatitis and laboratory cultures of E. coli. Level 2 agents pose a moderate risk of infection to healthy humans and can be salmonella, mumps, measles, Lyme disease and scrapie. Level 3 agents could cause potentially lethal illnesses and include bacillus antracis, SARS coronovirus and yellow fever virus. Level 4 agents are highly dangerous and pose a serious risk of aerosol transmitted infections such as smallpox and Ebola virus.
Class I cabinets
A Class I biological safety cabinet is similar to a laminar fume hood and provides protection to a laboratory operator and the environment, but does not protect the product under investigation. The exhaust air is filtered through a HEPA (high efficiency particulate air) filter. Some Class I cabinets recirculate air into the laboratory but need frequent changes of HEPA filter.
Class II biological cabinets provide a vertical flow of HEPA-filtered air into the workspace and also HEPA filter the exhaust. There are four subdivisions within this class. Type A is the lowest level of containment for use on low risk agents. It is similar to a Class I cabinet and suited for laboratories where cabinets cannot be hard ducted to outside ventilation. Type B1 cabinets exhaust 30 percent of the air flow. They can be used for work on toxic chemicals and radionuclides if hard ducted to an external exhaust system. Types B2 and B3 exhaust all of the air and must be connected to a dedicated exhaust system. These can be used for investigations on Level 1, 2 and 3 agents. The Class II cabinets can be modified to accommodate special tasks. One frequent adaptation is to attach microscope eyepieces. The working surface can be modified to accommodate centrifuges and other equipment which may need containments during special investigations.
The Class III biosafety cabinet is used for the investigation of highly infectious level 4 agents and hazardous operations. It provides the maximum protection to laboratory personnel, environment and products. Exhaust air passes through two HEPA filters before release into a special ventilation system. Access for products into the cabinet is through a dunk tank and autoclave. Researchers conduct operations through use of heavy duty rubber gloves attached to gas tight ports on the side of the cabinet. A number of Class III cabinets can be custom built and attached together in a line to provide a larger workspace.
A biological safety cabinet is a primary containment device for research on infections biological agents and hazardous chemicals. They provide protection for laboratory personnel, products and the environment. The choice of cabinet class depends on the hazards posed by the products under investigation.
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