How do Class II Cabinets work?
A Class II cabinet maintains three protective airflows at once. Room air is drawn through the front grille at an inflow velocity of about 0.38–0.51 m/s, forming an air curtain that keeps aerosols inside. A second stream of HEPA-filtered air flows downward over the work zone at about 0.25–0.35 m/s to protect the sample from contamination. Exhaust air passes a second HEPA filter before recirculation or discharge. The proportion recirculated defines the type: Type A2 returns about 70 % and exhausts 30 %, Type B1 exhausts about 70 %, and Type B2 exhausts 100 % without recirculation. A pressure or airflow sensor and alarm warn of loss of flow, and a negative-pressure plenum may surround the contaminated ductwork. Filter integrity and airflow are verified by aerosol testing at certification. The work surface is stainless steel, and a sash limits the operator's access to the work zone.
Which Class II Cabinets variants are available?
- Class II Type A2 Biosafety Cabinet — A Class II Type A2 biosafety cabinet recirculates about 70 % of HEPA-filtered air and exhausts 30 % to the room.
- Class II Type B2 Biosafety Cabinet — A Class II Type B2 biosafety cabinet exhausts 100 % of its air to the atmosphere through a dedicated duct, with no recirculation.
- Class II Type B1 Biosafety Cabinet — A Class II Type B1 biosafety cabinet exhausts about 70 % of its air through a dedicated duct and recirculates the rest.
- Class II Type A1 Biosafety Cabinet — A Class II Type A1 biosafety cabinet recirculates about 70 % of its HEPA-filtered air and protects the work.
- Class II Type C1 Biosafety Cabinet — A Class II Type C1 biosafety cabinet is convertible, switching between recirculating and exhaust modes as the workload changes.
How do I choose the right variant?
Start from the biological risk assessment and the chemicals used. Type A2 suits most microbiology, cell culture and sterile work where no volatile toxic chemicals or radionuclides are involved. Choose Type B2 when volatile toxic chemicals, radionuclides or large amounts of vapour must be exhausted to atmosphere without recirculation. Type B1 is used when small amounts of volatile chemicals are handled and a dedicated exhaust exists. Type A1 is limited to non-toxic, non-volatile work because its plenum is under positive pressure. Type C1 is convertible and can switch between recirculating and exhaust modes as the workload changes. Confirm internal width and height for equipment, decide on recirculating or ducted exhaust, and verify certification to EN 12469 or NSF/ANSI 49. Plan annual recertification and filter replacement.
Where are Class II Cabinets used?
Class II Cabinets are specified in cell culture and aseptic technique, clinical microbiology and diagnostics, pharmaceutical sterility testing, virology and molecular biology and vaccine and biologics production.
Which standards and certifications apply?
Work with Class II Cabinets is commonly governed by EN 12469 (biosafety cabinets), NSF/ANSI 49 (biosafety cabinetry), ISO 14644-1 (cleanroom classification), EU GMP Annex 1 (sterile manufacturing), GB 19489 (biosafety laboratory requirements) and IEC 61010-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Place the cabinet at least 30 cm from walls, doors and air diffusers, since cross-drafts above 0.15 m/s degrade the air curtain. Move arms slowly and avoid rapid movements that break the inflowing air. Do not place items over the front grille, because this blocks inflow and reduces protection, and keep large equipment towards the rear. Recertify at least annually and after filter change, fan repair or relocation, using aerosol leak, airflow and inflow velocity tests. For B2 and ducted types, confirm the exhaust fan is dedicated and interlocked, and verify make-up air. Clean surfaces with compatible disinfectants, use UV only as a supplement, and never work with toxic chemicals in an A2 cabinet without a vapour assessment.
