Washington State University

REV 1-96
Environmental Health and Safety

Biological Safety Cabinets

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University researchers are to ensure that biological safety cabinets operate properly. Properly operating cabinets promote safe and effective working environments.

WSU provides biological safety cabinets in laboratories as containment devices for experiments which include infectious agents, recombinant DNA, chemical carcinogens, and oncogenic viruses.

The primary factor in attaining maximum containment in biological safety cabinet is the laboratory worker's strict adherence to administrative controls and recommended practices while using biological safety cabinets.

Researchers and laboratory workers are to conform with procedures in this section (S80.10) when using biological safety cabinets.


Descriptions of Classes I and II

Class I

A Class I biological safety cabinet is an open-fronted, negative-pressure, ventilated cabinet with a minimum inward face velocity at the work opening of at least 75 feet per minute. The cabinet filters the exhaust air with a high efficiency particulate air (HEPA) 99.9+% filter. Laboratory workers may use this cabinet in three operational modes: with a full-width open front, with an installed front closure panel not equipped with gloves, and with an installed front closure panel equipped with attached rubber gloves.

Class II

A Class II vertical laminar-flow biological cabinet is an open-fronted, ventilated cabinet with an average inward face velocity at the work opening of at least 75 feet per minute. Newer models require a minimum face velocity of 100 feet per minute. This cabinet provides a HEPA-filtered, recirculated mass airflow within the work space. The cabinet also filters the exhaust air using HEPA filters. The National Sanitation Foundation at Ann Arbor, Michigan, designs, constructs, and establishes performance standards for Class II cabinets. Contact Environmental Health and Safety (EH&S) for design information or performance standards related to the Class II cabinet.

[A Class II cabinet in the microbiological laboratory offers the capability of protecting materials contained within it from extraneous airborne contaminants. This is achieved with the cabinet's HEPA-filtered and recirculated mass airflow within the work place. However, laboratory workers must use correct microbiological procedures and techniques since cabinets cannot be a substitute for poor work techniques or procedures].

Discussion of Classes I and II

When used in conjunction with good microbiological techniques, Class I and Class II biological safety cabinets provide an effective partial containment system for safe manipulation of low and moderate-risk microorganisms.

Class I and II cabinets alone are inappropriate for containment of high-risk infectious agents because aerosols can escape through the front of the cabinet.

Personnel protection provided by Class I and II cabinets depends upon inward air flow.

Laboratory workers activities may disrupt the inward directional airflow through the work opening of Class I and II cabinets and such actions may result in the accidental escape of aerosols through the front of the cabinet.

Demonstrated causes of escaping aerosol particles from within these cabinets include repeated insertion and withdrawal of the worker's arms in and from the work chamber, opening and closing doors to the laboratory or isolation cubicle, improper placement or operation of materials or equipment within the work chamber, or someone briskly walking past the biological safety cabinet while it is in use.

Class III

The Class III cabinet provides the highest level of personnel and product protection. The Class III cabinet provides this protection with a physical isolation of the space in which the cabinet maintains the infectious agent. When infectious agents indicate the use of Class III cabinets, laboratory workers must conduct all procedures involving the infectious agents within the Class III cabinet.

A Class III cabinet is a totally enclosed ventilated cabinet of gas-tight construction. Operations within the Class III cabinet are conducted through attached rubber gloves. When in use, the Class III cabinet maintains negative air pressure of at least 0.5 inches water gauge. The cabinet draws the air supply into the cabinet through HEPA filters. The cabinet filters the exhaust air with two HEPA filters, installed in a series, before the cabinet discharges the exhaust. The Class III cabinet exhaust fan is usually separate from the exhaust fans in the laboratory's ventilation system.


Refer to 4.24 for HEPA filter disposal procedures.


Laboratory supervisors must provide training in the proper use of the biological safety cabinets. The slide/sound training film developed by National Institute of Health (NIH) provides a thorough training and orientation guide. Contact EH&S to check out this film.


Independent contractors certify Class I, II and III biological safety cabinets for a fee at the time of installation and any time after the biological safety cabinet is moved or repaired. The schedule for subsequent certification is shown in the table below.

Type of Cabinet

Level of Work





Class I

Not Required



Class II

Not Required*

Every Year

Every Year

Class III

Not Required*

Every Year

Every Year

* The responsible principal investigator is to report cabinets not being utilized for biohazardous materials to the Office of Grant and Research Development (mail code 3140) and EH&S (mail code 1172). Include a list of those cabinets falling into this category. Such biosafety cabinets must also display a warning placard placed by EH&S. The placard is 3" x 5" with a black background with an orange biohazard symbol and the following warning statement:

"WARNING! Biological safety cabinet is NOT certified for use with biohazardous agents."

EH&S places the placard in the lower left hand corner of the cabinet glass view screen.

Certification Location

Cabinets must be certified in place at their operational permanent location.


EH&S provides assistance and consultation regarding installation and certification of any biological safety cabinet.


A clean bench is an open-fronted cabinet with filtered air passing horizontally over or around the research materials and directed at the researcher and surrounding laboratory.

Horizontal laminar flow "clean benches," present in a number of clinical, pharmacy, and laboratory facilities, are not a substitute for biological safety cabinets. Clean benches provide an air filtered environment for manipulation of nonhazardous materials. Clean benches protect the product but not the worker.

Clean Bench Caution

Since the operator sits in the immediate horizontal exhaust from the "clean bench," do not use clean benches with toxic, infectious, or sensitizing materials.