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Oregon State University

Biosafety Cabinet types

BioSafety Cabinet - Class I

Select a Class I BSC when only personnel  protection against particulate materials is required.

Similar in operation to a conventional fume hood. A ventilated cabinet for personnel and environmental protection, having an un-recirculated inward airflow away from the operator that exhausts all air to the atmosphere after filtration through a HEPA filter. Class I cabinets are suitable for work where no product protection is required. It WILL NOT protect users against exposures to gases or vapors.


A. front opening
B. sash
C. exhaust HEPA
D. exhaust plenum

BioSafety Cabinet  - Class II

Select a Class II BSC when both product and personnel protection are required.

Class II Biological Safety Cabinets, regardless of type (i.e. Types: A2, B1, or B2) provide the same level of product and personnel protection from a biological point of view. The National Sanitation Foundation's Listing Program for compliance to NSF Std. No. 49* has subjected each type to the exactly the same testing procedures and exactly the same pass/fail criteria for all Class II cabinets.

What is the difference between the types of biological safety cabinets that affect selection? It is the amount of air that is recirculated within the cabinet.

Studies to determine the dilution within the Class II cabinet of highly volatile liquids have been conducted by the NSF Advisory Committee. Those studies indicated that the total quantity of volatiles designated as flammable which are used in a type A2 cabinet be limited to 25 ml or less. For Type B1 cabinets slightly more is permitted, if the work is carried out in the dedicated exhaust portion (i.e. rear) of the work surface. For the Type B2 total exhaust cabinet, even though there is total exhaust, quantities of volatiles must be limited due to the potential of electrical spark ignition within the cabinet's work zone.

Former Class II, type A/B3 designation has been reclassified to Class II, type A2









BioSafety Cabinet  - Class III

Select a Class III biological safety cabinet when both personnel and product protection are required, and the risk of injury to personnel is imminent with the product at hand.

A totally enclosed, ventilated cabinet of leak-tight construction. Operations in the cabinet are conducted through attached rubber gloves. The cabinet is maintained under negative air pressure of at least 0.50 in w.g. (120 Pa). Downflow air is drawn into the cabinet through HEPA filters. The exhaust air is treated by HEPA filtration or by HEPA filtration and incineration. This cabinet provides the highest level of personal protection of all the BSC’s.

Connection to building exhaust system required.


A. glove ports with O-ring for attaching arm-length gloves to cabinet
B. sash
C. exhaust HEPA filter
D. supply HEPA filter
E. double-ended autoclave or pass-through box

Note: A chemical dunk tank may be installed which would be located beneath the work surface of the BSC with access from above. The cabinet exhaust needs to be connected to the building exhaust system.


Last update 4/19/2010