Biological Safety Cabinets

UTHSC-H BSC Guidance Document (pdf)
CDC/NIH Primary Containment for biohazards (pdf)

Please call Biological Safety Program (x4193) for contact information of local BSC certification companies.

Biological Safety Cabinets (BSC) are engineering controls which when proper maintained and used offer excellent primary containment when working with biological agents. There are three general classes of BSCs (Class I, II, III) each with there own intended uses and offering a greater level of security for the environment, product and worker.  

Class I - BSCs designated as Class I only provide biological protection to the user and the environment. Since Class I BSCs don't provide an adequate means of protection from cross contamination for product. There is a growing trend towards the elimination of the Class I BSC.   Class I BSCs operate at a minimum face velocity of 75 lfpm and filter all exhaust air though a HEPA filter before it is reintroduced into the laboratory or outside environment. A Class I BSC is only suitable for low to moderate risk agents.

Class II BSCs are the primary containment devices that protect the worker, product and environment from exposure to microbial agents.  BSC operation, as specified by NSF/ANSI Standard 49-2007, Annex F plus Addendum #1 needs to be verified at the time of installation and as a minimum, annually thereafter.  The purpose and acceptance level of the operational tests ensure the balance of inflow and exhaust air, the distribution of air onto the work surface, and the integrity of the cabinet ant the filters (HEPA).*

Type

Face velocity (lfpm)

Airflow Pattern

Radionuclides/ Toxic Chemicals

Biosafety Level(s)

Product Protection

Class I* open front

75

In at front; rear and top through HEPA filter

No

2,3

No

Class II
Type A1

75

70% recirculated through HEPA; exhaust through HEPA

No

2,3

Yes

Class II
Type A2

100

Same as IIA, but plena under negative pressure to room and exhaust air is ducted

Yes

2,3

Yes

Class II
Type B1

100

30% recirculated through HEPA; exhaust via HEPA and hard ducted

Yes (Low levels/volatility)

2,3

Yes

Class II
Type B2

100

No recirculation; total exhaust via HEPA and hard ducted

Yes

2,3

Yes

Class III

NA

Supply air inlets and exhaust through 2 HEPA filters

Yes

3,4

Yes

BSCs designated as Class III offer the highest level of protection to personnel and the environment. A Class III BSC is a completely enclosed air tight chamber suitable for BSL-3 and 4 work.   Exhaust air is double HEPA filtered or HEPA filtered and incinerated before discharge and supply air only makes a single pass through a HEPA. Class III BSCs must be connected to a double door incubator or chemical dunk tank to sterile or disinfect all entering and exiting items. All manipulation of items occurs through the use of rubber gloves attached to the cabinet.

* Copyright of the CDC-NIH Biosafety in Microbiological and Biomedical Laboratories, 4 th Ed.   December 2009.

While BSCs are designed to provide safe work environments some work habits can greatly affect the protection they provide. Before entry into a BSC the blowers should be turned on and allowed to run for approximately 5 minutes in order to allow the proper pressures to build up. Personnel working within BSCs should wear lab coats, with appropriate gloves that fit over the cuffs of the coat. Stools should be adjusted to a proper height and all materials needed should be gathered (in order to eliminate the number of entries into the BSC) and wiped down with 70% ethanol prior to entry. The area within the BSC should be arranged into clean and dirty zones. All aerosol production equipment should be placed in the rear of the cabinet. Waste containers should also be inside the cabinet.  One should consider the work space lay out to ensure that grilles are not blocked causing disruptions to the air flow.   When work is completed all exiting materials and the interior of the cabinet should be disinfected with an approved disinfectant. 

BSC Diagram