What Is A Biosafety Cabinet?

Nuaire is a manufacturer of biosafety cabinets. This image is from one of their brochures.. Copyright (c) Nuaire

Definition and Purpose

A biosafety cabinet is an enclosed cabinet usually supported by a bench that enables a scientist to work with material contaminated with pathogens. These pathogens could be harmful if they were experimented with in open air, so the biosafety cabinet provides protection to the scientist handling the material and anyone else in the lab area.

Biosafety cabinets are also referred to as biological safety cabinets or microbiological safety cabinets.

They look similar to laboratory fume hoods.

Some pathogens require more containment than others, so the U.S. Centers for Disease Control & Prevention, along with the American Biological Safety Association and NSF International, have classified biosafety cabinets into three levels of protection categories. The classification levels are dictated by the level of protection the biosafety cabinet provides to the people and environment surrounding the cabinet, and the level of protection the biosafety cabinet provides the material being handled inside the cabinet.

Therefore, the primary purpose of a biosafety cabinet is to protect the lab worker and the surrounding environment from the potential dangers of the material being handled inside the cabinet.

The secondary purpose of the cabinet is to maintain the sterility of the material inside the cabinet.

How They Work

How, and to what degree, the air is filtered as it exits the biosafety cabinet is a major factor in the level of protection it provides.

HEPA (high efficiency particulate air) filters remove bacteria and viruses from the air as it is exhausted from the cabinet. 

HEPA filters have a limited lifetime and therefore need to be checked periodically and eventually replaced. Since the filter's job is to capture harmful viruses and bacteria from the air inside the cabinet so that it does not get exhausted into the outside air, the filters are contaminated and should be handled with care by trained professionals wearing proper personal protective equipment.

Another component that may be installed in a biosafety cabinet is an ultraviolet light bulb. Scientists have shown for over 100 years that UV light has a specific spectrum within it that can kill DNA and RNA in germs and viruses, thus making it impossible for them to reproduce and spread. And unlike physical disinfectants, such as germicidal wipes, liquids, or sprays, UV light leaves no residue or surface wear and abuse.

Like filters, UV light bulbs have a limited lifetime and therefore need to be checked and replaced when they lose their effectiveness.

Class I

This entry-level cabinet classification provides protection to the lab workers and to the environment. Class I biosafety cabinets do not protect the material being handled inside the cabinet. In other words, sterility is not maintained. In some experiments, this is acceptable, and thus Class I cabinets are suitable.

  • Air flowing into the cabinet may contaminate the product material inside the cabinet
  • Airflow velocity into the cabinet is maintained at 75 ft/min
  • Common uses: contain equipment like centrifuges
  • Class I biosafety cabinets may be either connected by duct to the building exhaust system, or unducted and therefore filtering and recirculating the air back into the lab

Class II

Class II protects the people, the environment, and the material samples in the cabinet. These cabinets have a fan installed in the top of the cabinet to create a curtain of sterile air over the material being handled by the scientist.

The air is then forced under the cabinet's work surface, flows up to the top of the cabinet where it passes through the HEPA filter system. 70% of this cleaned air recirculates through the supply HEPA filter, and 30% flows out of the exhaust HEPA filter. This ratio of filtration, air flow, and exhaust is safe for moderate risk biologicals.

There are biosafety cabinets within the Class II category however, that are designated to handle more toxic substances. In these cases, the airflow ratio switches to 30% of the cleaned air is recirculated and 70% is exhausted out of the exhaust HEPA filter.

Class III

This is the highest level classification for biosafety cabinets. They are typically only found in maximum containment labs, where highly dangerous pathogens are handled.

  • Gas-tight cabinet enclosure
  • All materials enter and leave the cabinet through a dunk tank or double-door autoclave
  • A gloves installed into the wall of the cabinet allows a lab worker to handle the hazardous materials without risking direct skin contact 

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