Biological Safety Cabinets


Biological Safety Cabinets (BSCs) are primary containment devices utilized in laboratories for the handling of biohazardous agents. They are routinely used for a wide variety of applications, such as human and animal tissue culture, bacterial and viral work, transfection or infection of cells with recombinant DNA (rDNA), clinical sample manipulation, and animal care (some examples pictured). Click on the links below for more information about BSCs.

The Role of Biological Safety Cabinets in Research

Clean Benches and Fume Hoods are Not Biological Safety Cabinets        

Classes of Biological Safety Cabinets

Mechanical Operation of a Biological Safety Cabinet

How to Work Safely in a Biological Safety Cabinet

Biological Safety Cabinet Certification, Repair, and Disposal

FAQs about Biological Safety Cabinets

Important Links

Contact Us


The Role of Biological Safety Cabinets in Research

BSCs are designed to protect laboratory personnel and the environment from exposure to biohazards through the combined use of laminar flow and High Efficiency Particulate Air (HEPA) filters. HEPA filters trap the Most Penetrating Particle Sizes (MPPS) of 0.3 μm with an efficiency of at least 99.97%. Larger and smaller particles are captured with greater efficiency. Thus, bacteria, spores, and viruses are removed from the air by HEPA filters.


HEPA filters are very fragile - Avoid storing items on top of the BSC and bumping the filters or exposing them to dust or liquids.

When used correctly, BSCs shield workers from the inhalation of infectious particles/microorganisms and prevent their spread into the laboratory. In addition, most BSCs (all classes and types except for Class I BSCs) protect sensitive research material from external contamination.

Clean Benches and Fume Hoods are Not Biological Safety Cabinets

Biological safety cabinets must not be mistaken with fume hoods and clean benches. Small amounts of radioactive materials or volatile chemicals can be used in certain types of BSCs (see Table 1 below). However, a BSC is not a substitute for a fume hood and should never be used with large concentrations of hazardous chemicals. Fume hoods are used to protect personnel from exposure to chemical hazards and, in general, are not suitable for work involving biohazards.

Clean benches protect research products from contamination but do not afford protection to the user. Thus, clean benches should not be used when working with potentially infectious materials, chemical hazards or radioactivity.



Classes of Biological Safety Cabinets

There are three classes of BSCs: Class I, II and III. While all three classes afford personnel and environmental protection, only Class II and III cabinets provide product protection thanks to the input of clean air from supply HEPA filters.

Class I BSCs are suitable for work involving low- to moderate-risk agents. Since incoming air is not filtered, Class I BSCs should not be used with research materials (e.g., cell lines) that must be handled under sterile conditions. Class I cabinets are used specifically to enclose equipment (e.g., centrifuges, harvesting equipment or small fermenters) or procedures with potential to generate aerosols (e.g., cage dumping, tissue homogenization or culture aeration). As outgoing air is filtered, research personnel is protected while using a Class I BSC.

Class II BSCs provide an effective partial barrier system for the safe manipulation of low-, moderate-, and high-risk microorganisms. Class II cabinets, which are the most frequently used in research and clinical laboratories, are divided into four types (Types A1, A2, B1 and B2).

The Class III BSC is a totally enclosed, gas-tight ventilated cabinet, and provides the highest level of personnel, environmental and product protection. Operations within a Class III BSC are conducted through attached rubber gloves.



Class II (left) and Class III (right) biological safety cabinets


When purchasing a biological safety cabinet, you should consider the type of work that will be conducted in it. Table 1 provides a brief description of the principal characteristics of all classes and types of BSCs.


TABLE 1: Characteristics of different classes and types of BSCs

II / A1
II / A2
No, unless thimble connected or hard ducted to the HVAC system
II / B1
Yes: low levels of volatile toxic chemicals & trace radionuclides
II / B2
Yes: volatile toxic chemicals & radionuclides
N / A



Mechanical Operation of a Biological Safety Cabinet

Main Features and Operation Panel

BSCs are equipped with an on/off switch, a blower/fan system, light(s), electrical outlets and, in those cabinets with an alarm, an alarm system bypass. All these functions are controlled through a panel located either on the front or side of the BSC.

The Magnehelic Gauge and Other Indicators

Some BSCs are equipped with a differential pressure gauge, commonly referred to as Magnehelic gauge, that measures the pressure change beween points (pictured below to the lef). If monitored routinely, the Magnehelic gauge may provide a "gross" indication of HEPA filter loading, i.e., the volume of particulate matter the filter has accumulated as the cabinet operates.

Normal gauge readings differ from cabinet to cabinet. If your BSC has a Magnehelic gauge, read it every time you use the cabinet to ensure that airflow pressure remains constant. For that purpose, turn on the blower, let it run for 5 minutes, and record the reading. If the differential pressure rises or drops by more than 0.2, a blockage or tear in the HEPA filter(s) may be interfering with the correct functioning of the BSC. Do not use the cabinet and call for service.


Other BSCs (pictured above to the right) are equipped with digital displays of inflow and downflow velocities, and other features showing the capacity of the cabinet to provide a safe working environment. No matter what type of BSC you are using, always pay attention to warning signs and alarms.


Many BSCs are equipped with an alarm system that warns users if the airflow in the cabinet gets compromised. The alarm usually goes off when the sash gets raised over the 10-inch mark, rendering user and environmental protection ineffective, or when the filters do not allow air to pass through them anymore. Do not work in the BSC if the alarm sounds continuously, since it indicates a problem with the BSC's performance. Instead, ask a specialized technician to inspect your BSC. For safety reasons, disengaging the alarm to make it stop is not allowed.

UV Lights

UVM Health and Safety has adopted the position of the NSF, NIH, CDC and the American Biological Safety Association (ABSA) in regard to the use of UV lamps within biosafety cabinets; UV lamps are neither recommended nor required in biological safety cabinets.  UVM Health and Safety believes they are not appropriate for disinfection within a BSC and are potentially dangerous when used improperly.  If you have any questions regarding our position on the use of UV light in biosafety cabinets, please contact the UVM Biosafety Officer @ 6-3618 or


Electrical devices can be used, and vacuum pumps connected, inside the BSC.

Bunsen Burner Use

Warning: Open flames are not allowed inside the BSC. In most instances, flames are not required in the near microbe-free environment provided by a BSC. If absolutely necessary, touch-plate microburners with a pilot light that provide a flame on demand may be used.


How to Work Safely in a Biological Safety Cabinet

Biological safety cabinets afford the best protection and are more effective when maintained and used properly. To accomplish this goal, it is necessary that:

  • The BSC be certified upon installation, after it is moved, after repairs and annually thereafter.
  • Researchers learn how to work safely in and maintain a biological safety cabinet.


To extend the life of your BSC and ensure a safe working environment, follow these tips:

  • Minimize the storage of materials in and around the BSC. Avoid storing items on top of the cabinet since it could damage the HEPA filters.
  • Never operate the blower with the sash closed - an excessive air inflow could rip the HEPA filters.
  • Turn the BSC off after use - do not leave it running overnight.
  • If an UV light is present, use only as needed - never have the UV on when somebody is in the room.
  • Clean any spill immediately to prevent staining of the surfaces. 
  • Never use volatile chemicals, gases or radionuculides in a biosafety cabinet that is not thimble connected or hard ducted to the laboratory HVAC system.


To operate a BSC safely and effectively, follow these instructions: 



  1. Wash your hands with soap and water and put on the appropriate PPE (at a minimum gloves and a buttoned down or disposable gown).
  2. Raise the sash to the proper height.
  3. Turn on the blower and light (turn on blower 5 min. prior to work)
  4. Wipe down the surface, walls, grills, and viewscreen of the BSC with an appropriate disinfectant.
  5. Load the cabinet with the necessary materials and reagents - Make sure that you disinfect the outer surface of medium bottles and pipettes before putting them in the BSC.
  6.  If working with sharps, place a sharps container in the BSC for safe disposal
  7. Place a non glass waste container lined with a plastic bag for all other waste materials produced during work in the BSC.  When the bag is full, decontaminate with appropriate disinfectant and move to laboratory biowaste container.



  1. Do not block the front and rear air intake grills.
  2. Do not disrupt the protective airflow pattern - Avoid rapidly moving your arms in and out of the cabinet, people walking rapidly behind you, and open laboratory doors, which may reduce the effectiveness of the BSC.
  3. Establish working areas and always work from the clean to the dirty area (see picture below).
  4. Clean spills as soon as they occur and replace broken/dirty gloves.


A typical layout for working “clean to dirty” within a Class II BSC. Clean cultures (left) can be inoculated (center); contaminated pipettes can be discarded in the shallow pan and other contaminated materials can be placed in the biohazard bag (right). Source: Biosafety in Microbiological and Biomedical Laboratories, 5th Edition.



  1. Purge the air inside the BSC for at least 5 minutes.
  2. Disinfect the materials/supplies (e.g., media bottles, pipettes) that have been inside the cabinet before taking them out.
  3. Remove and discard waste bag after thoroughly disinfecting it with the appropriate disinfectant.
  4. Wipe down the BSC.
  5. Turn off the blower and light and close the sash.
  6. Do not expose yourself unnecessarily to the UV light, since this can result in skin burns and eye lesions and, in the long term, development of melanoma.
  7. Remove PPE and wash hands.



  • To collect liquid biohazardous waste, aspirate liquid into a flask containing bleach (A) connected to a second overflow collection flask (B) and separated from the vacuum system (D) by an in-line filter (C). Biohazardous liquid waste needs to be properly neutralized before disposal. Source: Biosafety in Microbiological and Biomedical Laboratories, 5th Edition.


  • To dispose of contaminated solid waste, deposit non-sharps into regular biohazard containers (biohazard bag in biohazard container) and sharps into sharps containers only.



Biological Safety Cabinet Certification, Decontamination, Repair and Disposal


Biological safety cabinets must be tested periodically in order to ensure that they are working properly and providing a safe research environment. This process, known as certification, should be performed by a specialized technician. Certifications should be conducted according to the NSF/ANSI Standard 49 for Biosafety Cabinetry of the National Sanitation Foundation.

The NSF Biosafety Cabinetry Program was initiated more than 25 years ago at the request of regulatory organisms including the National Institutes of Health (NIH), Centers for Disease Control (CDC), and the National Cancer Institute (NCI). For more details, please visit:

As a general rule, a BSC should be certified:

  • Upon initial installation in the laboratory
  • At least once a year thereafter
  • After repairs
  • when moving it to a different laboratory.

Depending on the model, age, and condition of the cabinet, the certification process can take somewhere between 2 and 4 hours. Some of the tests conducted include:

  • Testing the inflow (air coming from the room into the BSC) and downflow (air passing through the supply filter into the work area) velocities.
  • Inspecting the HEPA filters for leakages and patching small leakages with silicon if indicated.
  • Testing the airflow smoke pattern to ensure that air is appropriate passing through the HEPA filter and also not escaping from the cabinet.

If the BSC passes the certification, the technician will issue a certification sticker that is valid for one year. If it fails, it should be decontaminated, repaired, and recertified before being used. Remember that a BSC that fails the certification cannot guarantee safe working conditions for you, your research materials, and your lab.

Decontamination, Repair and Disposal

Decontamination of a BSC is necessary when it is:

  • Being opened for repairs (e.g., internal damper adjustment, filter and motor changes) 
  • Moving from one laboratory to another
  • Being disposed of.

There are several methods to decontaminate BSCs, such as using formaldehyde, Vaporous Hydrogen Peroxide (VHP), or Chlorine Dioxide (CD, ClO2). All these methods relay in strong chemicals to ensure that biological contaminants are inactivated before the BSC is opened or moved, and effectively decontaminate not only the surfaces of the cabinet, but also internal parts. Since chlorine dioxide is less toxic than formaldehyde, and the decontamination can be performed in less time, many technicians are abandoning formaldehyde in favor of ClO2.

For health and safety purposes, only the technician is allowed in the room while the BSC is being decontaminated.




The Environmental Safety Department at UVM assists researchers in scheduling the annual certifications. For decontaminations, repairs, and additional certifications, contact the vendor directly. We encourage you to ask for quotes from several companies since their prices and availability may vary. Here is a list of vendors UVM has been working with:


TSP (UVM) 802-656-3255 Burlington, VT
ATC Associates 802-862-1980 Williston, VT
ENV Services 800-292-5255 Hicksville, NY
B&V Testing 800-851-9081 Waltham, MA


If you have any question or concern, please do not hesitate to contact Environmental Safety at:


FAQs about Biological Safety Cabinets

I need to treat my cell culture plates with volatile chemicals and / or radioactivity. What is the safest way to conduct my work?

What is the difference between a biological safety cabinet and a clean bench? Can I use the clean bench for cell culture?

My cells have gotten contaminated several times in the past few weeks. I have discarded the medium, decontaminated the incubator, etc., without any luck. What could the problem be?

A technician has told me that my BSC has failed the certification. Can I still use it?

A new lab member has never worked in a BSC. Where can he/she get some training?


Important Links and Resources

Additional information can be found in the following documents:


Contact Us

If you have any question regarding Biolosafety Cabinets or would like additional information, please contact us at:


Last updated: February 14, 2018