These are bio-enclosures that are commonly used for microbiological analysis. These cabinets are suitable for Biosafety levels I to IV where samples being handled range from non-pathogenic to those with lethal effects.
A Class II Type A1 cabinet has a positively pressurized contaminated plenum compared to a Type A2 cabinet where in the positively pressurized plenum is surrounded by a negative plenum trapping leaks inside and preventing the leak to affect the blower and the work zone. The leak containment system of an A2 cabinet makes it more safe to use than an A1. In an A2 cabinet, 70% of the air that enters the cabinet is recirculated while the remaining 30% is exhausted back to the laboratory as clean air.