What happened to the Class II Type A/B3 Biosafety Cabinet?
The Class II Type A/B3 Biosafety Cabinet has been replaced by the Class II Type A2 BSC
NSF InternationalmodifiedNSF/ANSI Standard 49in 2002 to replace the Type A/B3 biosafety cabinet configuration with theType A2.Type A/B3 cabinets ceased to be manufactured by all producers of Class II BSCs in the mid 2000s.
Type A/B3 cabinets were designed to recirculate their air back to the lab for work not involving chemicals.If minute amounts of chemicals were used, Type A/B3 cabinets could also be exhausted with a hard duct connection to the outside of the building – a design connection that could lead to unstable BSC airflows and the potential for positively pressurized ductwork.
A Type A2 cabinet's exhaust exhaust can be recirculated to the room or canopy connected to an external exhaust duct, like both of the configurations for a Type A/B3.However, when connected to exhaust ductwork, an A2 provides safer operation.The A2 design uses a canopy connection (sometimes called a ‘thimble' connection), which acts as a buffer between the Type A2's internal exhaust fan and the building's remote exhaust fan.NSF-approved canopy connections prevent the opportunity for positively pressurized ductwork, and eliminate the chance for the biosafety cabinet to experience airflow imbalances to inflow and downflow velocities.The design of a canopy connected A2 also includes anexhaust alarm, which notifies the user when the building's exhaust airflow is insufficient.
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