Biological Safety Cabinets

UTHealth BSC Guidance Document (link)
CDC/NIH Primary Containment for biohazards (pdf)

Please call Biological Safety Program (x8170) for contact information of local BSC certification companies.

Biological Safety Cabinets (BSC) are engineering controls which, when properly maintained and used, offer excellent primary containment when working with biological agents. There are three general classes of BSCs (Class I, II, and III) each with their own intended uses, and each 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 fpm 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 designated as Class II are the primary containment devices used in laboratories that protect the worker, product and environment from exposure to microbial agents. BSC operation, as specified by NSF/ANSI Standard 49-2016, Annex F plus Addendum #1 needs to be verified at the time of installation and as a minimum, and annually thereafter. The purpose and acceptance level of the operational tests ensure the correct balance of inflow and exhaust air, the distribution of air onto the work surface, and the integrity of the cabinet and the filters (HEPA).*

BSC Class, Type

Face velocity (lfpm)

Airflow Pattern

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

Yes

Yes (If exhausted outdoors) 1,2

II,
A1

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 (minute amounts)

Yes (minute amounts)1,2

II,
A2

100

Same as II, A1, but plenums are under negative pressure to room; exhaust air is thimble-ducted to the outside through a HEPA filter

Yes

Yes (minute amounts)1,2

II,
B1

100

Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter

Yes

Yes (minute amounts)1,2

II,
B2

100

No recirculation; total exhaust to the outside through hard-duct and a HEPA filter

Yes

Yes (minute amounts)1,2

II,
C1

100

Exhaust cabinet air must pass through a HEPA filter before being exhausted to the outside through a duct, or back into the room through canopy. 

Yes

Yes (minute amounts)1,2

 III

NA

Supply air inlets and hard-duct exhausted to outside through two HEPA filters in series

Yes

Yes (minute amounts)1,2

1Installation 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 or Class II, Type A2 cabinet into a room should not occur if volatile chemicals are used.
2In no instance should the chemical concentration approach the lower explosion limits of the compounds.
Adapted from The National Academies; Prudent Practices in the Laboratory (2011)

Class III: 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. 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 sterilize 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, 5th Ed. December 2009.

While BSCs are designed to provide safe work environments some work habits can greatly affect the security they provide. Before entry into a BSC, the blowers should be turned on and run for approximately 5 minutes in order to allow for the proper pressures to build up. Steps to ensure safe use of a BSC include:

  • Wear a lab coat and appropriate gloves that fit over the cuffs of the coat
  • Gather all needed materials at once to reduce the number of entries into the BSC
  • Wipe all materials down with 70% ethanol prior to entry into BSC
  • Arrange work space inside of BSC into clean and contaminated zones. Work from clean to dirty
  • Place aerosol generating equipment in the rear of the cabinet
  • Place materials in the BSC in such a way that they do not block grilles, disturbing airflow

Upon completion of work, disinfect all materials exiting the BSC as well as the surfaces inside of the BSC 

BSC Cabinet