Class II cabinets provide product, operator and environment protection. They are suitable for general microbiological work with agents assigned to biosafety levels 1, 2 and 3. Class II cabinets are recommended for most applications and are the most common and cost-effective systems available on the market today.
Like Class I biosafety cabinets, Class II cabinets have a stream of inward air moving into the cabinet. This is known as the inflow and it contains aerosols generated during microbiological manipulations. However, unlike Class I cabinets, the inflow on Class II cabinets is taken in through air grilles towards the front of the work surface nearest the operator. None of the unfiltered air infiltrates the actual working zone of the cabinet and therefore contamination of product samples is not a concern.
A feature unique to Class II BSCs is a vertical laminar (unidirectional) HEPA/ULPA-filtered air stream that descends downward from the interior of the cabinet. This continuously flushes the cabinet interior of airborne contaminants and protects samples being handled within the cabinet from contamination. This is known as the downflow. Nearer to the level of the work surface, the downflow splits with some air entering grilles towards the back of the cabinet, with the remainder taken in through grilles across the horizontal work surface of the cabinet nearest the operator.
There are two major world standards for Class II Biological Safety Cabinets; US NSF49 Standard and European EU12469.