Class II biological safety cabinets fall into four types (A1, A2, B1, B2), all of which protect the specimen, the user, and the environment from contamination. This is especially crucial for applications that require aseptic or particulate free conditions such as tissue culture experiments, and in toxicology work involving fumes and gases. All types of Class II biological safety cabinet have HEPA (high-efficiency particulate air) filters at their air supply and exhaust points. For Type A1 and A2 Class II biological safety cabinets (A2 has a higher air velocity for greater protection), 70% of the airflow is recirculated within the cabinet while 30% of the air is exhausted (usually through the top). These cabinets do not protect against vapors and gases and, therefore, are best used for applications requiring sterile conditions without the need to work with volatile chemicals. However, when a Type A2 Class II biological safety cabinet is connected to a building’s exhaust system (through an optional canopy), trace amounts of volatile chemicals and radionuclides may be used. For Type B1 and B2 Class II biological safety cabinets, more air is exhausted out of the cabinet (70% for B1, 100% for B2). These cabinets are best used for applications that require larger quantities of volatile chemicals and/or radionuclides (although limit restrictions may still apply). Type B Class II biological safety cabinets must be connected to the building’s exhaust system to protect the user from vapors and gases.
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