Clean room work benches

Class II Bio safety Cabinet Type A1 & A2 are designed for protection of operator, product and environment from pathogenic agents and microorganisms transmitted in respiratory way and also for creation of a bacterial dust free air environment. It has a common plenum from which 30% of air is exhausted, and 70% re-circulated to the work area as the down flow. Type A cabinets exhaust air directly back to the laboratory, and they may contain positive pressure contaminated plenums. When toxic chemicals must be employed as an adjunct to microbiological processes, these cabinets should not be used. Exhaust HEPA filtration only removes airborne aerosols including biohazards, and not chemical fumes.

The Class II Type A1 has the positively-pressurized contaminated plenum bordering the ambient environment, and therefore is less safe than the Class II Type A2 that has a negative pressure surrounding the positively pressurized contaminated plenum. In case there is a leakage on the positive plenum, the leaking aerosol will be pulled by the negative pressure back to the positive plenum, and it will not leak out. Because of the safety issue, the Type A1 design is now considered obsolete. In the A2 cabinet, about 70% of air from the positive plenum is recirculated as down flow, and the remaining