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Class II Biosafety Cabinet Types: A2, B1 and B2 Explained

What “Class II” means

A Class II biosafety cabinet provides operator, product and environmental protection using HEPA-filtered downflow over the work surface and HEPA-filtered exhaust. The types differ in how much air is recirculated versus exhausted, and in how the cabinet is vented.

Type A2

About 70% of the air is recirculated and 30% is exhausted through a HEPA filter. An A2 can exhaust into the room or be connected to building exhaust through a thimble (canopy) connection. It suits microbiological work and minute amounts of volatile or toxic chemicals and radionuclides.

Type B1

About 70% of the air is exhausted and 30% recirculated, and the cabinet is hard-ducted to the outside. Work involving minute amounts of volatile chemicals is performed toward the rear exhaust grille.

Type B2 (total exhaust)

100% of the air is exhausted to the outside with no recirculation, through a dedicated hard-ducted exhaust system. B2 cabinets handle work with volatile, toxic chemicals and radionuclides in larger quantities.

How to choose

Biologicals only → Type A2. Minute volatile chemicals → A2 (ducted) or B1. Significant volatile or toxic chemicals → B2. Always confirm your venting requirements with your facility. See our Class II biosafety cabinets.

Frequently Asked Questions

What is the difference between A2 and B2?

An A2 recirculates about 70% of its air and can be used unducted or thimble-connected. A B2 exhausts 100% of its air to the outside with no recirculation, for higher volatile-chemical use.

Which type for cytotoxic or hazardous drugs?

For hazardous drugs under USP 800 you need an externally vented Class II cabinet. See our USP 797 & 800 guide and the CYTO-PURE cabinet.

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