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Safe Laboratory Practices
Laboratory Biosafety Level Criteria
Table1: Summary of  Recommended Biosafety  Levels for Infectious Agents
Table1a: Summary of Vertebrate Animal Biosafety Levels (ABSL)
Biological Emergencies
Biosafety Cabinets (BSC's)
Types of BSC's
Comparison of BSC's Characteristics
Selection of a BSC Through Risk Assessment
IBC Application Forms

Comparaison of BSC Characteristics

BSC Class Face Velocity Airflow Pattern Applications
Nonvolatile Toxic Chemicals and Radionuclides Volatile Toxic Chemicals and Radionuclides
I 75 In at front; exhausted through HEPA to the outside or into the room through HEPA
             (see Fig. 2)
II, A 75 70% recirculated to the cabinet work area through HEPA; 30% balance can be exhausted through HEPA back into the room or to the outside through a thimble unit YES NO
II, B1 100 Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter YES YES (minute amounts (2))
II, B2 100 No recirculation; total exhaust to the outside through hard-duct and a HEPA filter YES YES (small amounts)
II, B3 100 Same as II, A, but plenums are under negative pressure to room; exhaust air is thimble-ducted to the outside through a HEPA filter YES YES (minute amounts (2))
III N/A Supply air inlets and hard-duct exhausted to outside through two HEPA filters in series YES YES (small amounts)

(1) Installation may require a special duct to the outside, an in-line charcoal filter, and a spark proof (explosion proof) motor and other electrical components in the cabinet. Discharge of a Class I cabinet in to a room should not occur if volatile chemicals are used.

(2) In no circumstances should the chemical concentration approach the lower explosion limits of the compound.

Reproduced from "Biosafety in Microbiological and Biomedical Laboratories, BMBL 4th Edition" with permission from the Center for Disease Control (CDC).
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