The Class I cabinet has the most basic and rudimentary design of all biological safety cabinetry available today. A stream of inward air moving into th cabinet contains aerosols generated during microbiological manipulations. It then passes through a filtration system that traps all airborne paticles and contaminants. Finally, clean, decontaminated air is exhausted from the cabinet.
The filtration system usually consists of a pre-filter and a HEPA (High Efficiency Particulate Air) filter. Although the Class I cabinet protects the operato and the environment from exposure to biohazards, it does not prevent the samles being handled in the cabinet from coming into contact with airborne contaminants that may be present in room air. Naturally, there is a possibility of cross-contamination that may affect experimental consistency. Consequently, the scope and application of Class I cabinets are limited and are largely considered obsolete. All Class I biosafety cabinets are suitable for work with microbiological agents assigned to biological safety levels 1,2 and 3.