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Types of Biosafety Cabinets

Biosafety cabinets are used as the primary means of containment for working safely with infectious microorganisms.  However, biosafety cabinets are only one part of an overall biosafety program, which requires consistent use of good microbiological practices.

Biosafety cabinets are designed to prevent biological exposure to personnel and the environment and may also protect experimental material from being contaminated when appropriate practices and procedures are followed. Three kinds of biosafety cabinets, designated as Class I, II and III have been developed to meet varying research and clinical needs.

Biosafety Cabinet Classifications

Type of Cabinet 

Agent Classification (Biosafety Level)

Average Inlet Velocity 


Class I

Low & Moderate Risk (BSL 2, 3)


User only

Class II A

Low & Moderate Risk (BSL 2, 3)

75 (work opening fixed)

User & material

Class II B

Low & Moderate Risk (BSL 2, 3)

100 (work opening at 8”)

User & material

Class III

High Risk (BSL 3, 4)

User & material

Biological safety cabinets use high efficiency particulate air (HEPA) filters in their exhaust and/or supply systems.  These filtered cabinets are primarily designed to protect against exposure to particulates, including biological agents used in the cabinet.  Protection against exposure from fumes generated by radionuclides and toxic chemicals is only provided by Class II, Type B biosafety cabinets, which are ducted directly to the facility exhaust.

The Class I Biosafety Cabinet

The Class I biosafety cabinet provides personnel and environmental protection, but no product protection. It has similar turbulent air flow as a chemical fume hood, but has a HEPA filter in the exhaust system to provide containment and environmental protection. This older class of biosafety cabinet is rarely seen in MUSC's biomedical and microbiological laboratories.

Class I Biosafety Cabinets

A. Front Opening
B. Sash
C. Exhaust HEPA
D. Exhaust plenum

The Class II Biosafety Cabinet 

The Class II biosafety cabinet provides protection to the user, the experimental material and the environment. The Class II biological safety cabinet is the type most commonly used in MUSC's biomedical and microbiological laboratories. Air flow is drawn from the room around the operator into the front grille of the cabinet, which provides personnel protection. In addition, the downward laminar flow of HEPA-filtered air provides protection for experimental material inside the cabinet. Because cabinet air has passed through the exhaust HEPA filter, it is contaminant-free, providing environmental protection, and may be recirculated back into the laboratory (Class II Type A) or ducted out of the building (Class II Type B).

Class II Biosafety Cabinet

A. Front Opening
B. Sash
C. Exhaust HEPA filter
D. Supply HEPA filter
E. Rear plenum
F. Blower

The Class III Biosafety Cabinet 

The Class III biological safety cabinet is most suitable for work with biohazardous agents requiring high contain (biosafety level 3 or 4). The Class III cabinet is  completely enclosed, HEPA filter-ventilated cabinet fitted with glove ports and decontamination capabilities for entry and exit of material.  It offers the highest degree of personnel and environmental protection from infectious aerosols. 

Class III Biosafety Cabinet

A. Glove ports with O-ring for attaching arm-length gloves to cabinet
B. Sash
C. Exhaust HEPA
D. Supply HEPA
E. Double-ended autoclave or pass-through box

Clean Benches

Though similar in appearance, clean benches are NOT biological safety cabinets. These cabinets intake room air which is passed through a pre-filter and a HEPA filter to remove contaminants, dust and other particles. The purified air then enters the work surface via a directed (non-turbulent) air flow. These cabinets provide product protection but do not provide user protection. Clean benches must not be used when working with any form of biohazard or other type of hazardous material as they can increase the risk of exposure.

Clean Bench

A. Front opening
B. Grille
C. HEPA filter
D. Plenum
E. Blower 
F. Supply grille

Modifications and Additional Types of Biosafety Cabinets

Some vendors provide biosafety cabinets with modifed sashes designed to accomodate microscopes.

New models of biosafety cabinets provide containment for aerosol generating equipment such as fluorescence activated cell sorters (FACS or flow sorters).

The MUSC Biosafety Cabinet Service Program

Biosafety Home


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