Class III cabinets biosafety cabinet provides an absolute level of safety, which cannot be attained with Class I and Class II cabinets. All Class III biological safety cabinets are usually of welded metal construction and are designed to be gas-tight. Work is performed through glove ports in the front of the cabinet.
During routine operation, negative pressure relative to the ambient environment is maintained within the cabinet. This provides an additional fail-safe mechanism in case physcl containment is compromised.
On all Class III BSCs, a supply of HEPA-filtered air provides product protectio and prevents cross contamination of samples. Exhaust air is usually HEPA-filtered and incinerated. Alternatively, doubl HEPA-filtration with two filers in series may be utilized. Materials are usually transferred into the cabinet using a pass-through unit installed at the side of the work area. Class III cabinets usually exhaust air back to the laboratory; however, air may aso be exhausted via a dedicated ductwork system to the external environment. When a dedicated ductwork system is employed, they are also suitable for work employing toxic chemicals as an adjunct to microbiological processes. All Class III biosfaety cabinets are suitable for work with microbiological agents assigned to biological safety levels 1, 2, 3 and 4. They are frequently specified for work involving the most lethal biological hazards.