What is the principle of operation of biological safety cabinet?

Last Updated: June 29, 2021 10:05:34 AM PDT

Follow these guidelines for working safely in a biological safety cabinet (BSC).

Improper use of a biological safety cabinet can result in contaminated cultures and expose workers to infectious organisms.

When used correctly, a curtain of room air enters the grill at the front edge of the BSC work surface and acts as a protective barrier. The air mixes with the recirculating air stream and passes through a HEPA filter downward toward the work surface, creating a contamination-free zone.

These guidelines aim to preserve the delicate air barrier that protects both the research product and the researcher.

Hands-on training for proper use of a biosafety cabinet is available to researchers. Contact to schedule a class.

Use the cabinet as intended

• See Biological Safety Cabinets: Overview for a discussion of different types of biosafety cabinets, purpose, placement, certification, and decontamination requirements.
• Do not use the top of the cabinet for storage; this can damage the HEPA filter.
• Keep only necessary equipment or supplies inside the BSC.

Take precautions before beginning work

• Wear personal protection equipment (PPE):
  • Labcoat
  • Gloves
  • Safety glasses
• Place materials in the cabinet before beginning work if possible.

Start up procedures

• Turn off the ultraviolet sterilizer (if so equipped) as soon as you enter the room.
• Turn on all blowers and cabinet illumination lights.
• Allow 5 minutes of operation to purge the system; check the flow alarm system and visual alarm function (if so equipped).
• Decontaminate readily accessible interior surfaces with a disinfectant appropriate for the agents or suspected agents present.

Standard operation procedures

• Never have the ultraviolet light on when working at the cabinet. It can cause eye damage and skin burns.
• Avoid disrupting airflow:
  • Minimize movement (especially rapid movements) into and out of the BSC, or in areas near the BSC.
  • Do not block the front grill or rear vents with your arms or other materials.
  • Work at least 4 inches from the inside edge of the front vent.
• Bunsen burners, other continuous flame devices, or flammable gases are prohibited in biosafety cabinets.
  Safer sterilization methods exist, such as touch-plate microburners equipped with a pilot light, small electric "furnaces," or pre-sterilized loops.
  • See the BSC Open Flames and Flammable Gas Policy for alternatives to continuous flame devices and disinfecting instruments in a BSC.
• Beware of fire hazards associated with vaporized ethanol and isopropanol disinfectants.

Special precautions for ultraviolet (UV) lamps

EH&S Biosafety division strongly discourages UV lamps in BSCs.

National Institutes of Health (NIH), Centers for Disease Control and Prevention (CDC), National Science Foundation/ANSI, and the American Biological Safety Association agree that ultraviolet (UV) lamps are not recommended or necessary for decontamination in BSC’s.

If a UV lamp is used in your BSC, follow the procedures below.

Required:

• Post a warning sign on the front of the BSC indicating the presence of UV light hazards.
• The sign must say CAUTION: Turn off UV light before working.

Be aware of the hazards. Exposure to UV light can cause:

• Painful eye and skin burns
• Damaging exposure levels exist well after the output of the lamp bulb has dropped below the biocidal level.
• Deterioration of some tubing
  • This can be dangerous if you're using a touch-o-matic burner with natural gas tubing in a BSC.

Be aware of the limitations:

• Never rely on UV irradiation alone to disinfect a contaminated work area. UV is:
  • Not effective on porous materials that are opaque to the light such as wood or foam
  • Ineffective if a microbe is protected by dust, dirt, or organic matter
  • Affected by the accumulation of dust and dirt on the bulb surface
  • Effective only in direct line of site
  • UV does not work in shadowed areas, penetrate into cracks or through the grill work of a BSC
    • The spill area under the work surface of a BSC is a favorite hide out for fungal spore and hardy bacteria.
    • The UV lamp bulb remains lit long after the germicidal effectiveness is gone.

Take precautions during work:

• Turn off UV lamps while the lab is occupied. The stainless steel interior of the BSC can reflect potentially hazardous illumination out of the opening of the cabinet.
• Never have the UV lamp on while an operator is working in the cabinet.

After work is complete:

• Turn the fan off and close the sash, if possible, when the UV lamp is on.

Maintenance:

• Clean UV lamp bulbs frequently by turning off the UV lamp then wiping off the surface of the room temperature lamp bulb with 70% alcohol.
• Before replacing bulbs, clear the BSC of equipment and material, and disinfect it with 10% bleach and then clean with 70% ethanol.
• Install the bulb with gloved hands to prevent oil build up.
• Disinfect lamp bulbs before disposal as universal waste.

Shut down procedures

When you are done:

• Decontaminate and remove all items from the interior work area.
• Decontaminate readily accessible interior surfaces with a disinfectant appropriate for the agents or suspected agents present.
• Turn on ultraviolet sterilizer (if so equipped). Note: Never rely on UV irradiation of the work area alone to disinfect a contaminated work area.
• Allow 5 minutes of operation to purge the system.
• Turn off the blower.

Resources

• Decontamination and Sterilization, Office of Research Safety, Dept. of Occupational Health & Safety
• Laboratory Safety: Principles and Practices, Diane O. Fleming, Debra Hunt, 3rd ed., ASM Press
• Appendix A – Primary Containment for Biohazards: Selection, Installation and Use of Biological Safety Cabinets (PDF), CDC (see p. 290)