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Introduction to Biological Safety Cabinets

The need to protect personnel, product, and the environment from exposure to hazardous contaminants and cross contamination during general laboratory procedures has never been more essential. With those needs, biological safety cabinets, therefore, has been introduced and playing an important role in any life science, clinical, pharmaceutical and industrial laboratory related sectors ever since.


What is a biological safety cabinet?

The biological safety cabinet (BSC), sometimes known as biosafety cabinet or microbiological safety cabinet (MSC), is a containment device equipped with HEPA filter(s), architected and designed to provide personnel, environment and/or product protection from biohazards.


  1. Personnel protection from harmful agents inside the cabinet
  2. Product protection from cross contamination occurred during the work, experiment or process
  3. Environment protection from contaminants escaping from the cabinet toward outside


How Biological Safety Cabinets are classified?


The classes of biological safety cabinets are classified based on their protection ability including personnel, product and environment protection, airflow velocities and patterns, and exhaust systems.


Class I  Personnel and Environment protection only

  • A Class I cabinet does not provide product protection from contaminants and any cross contamination because dirty room air is constantly drawn through front opening of the cabinet and flow across entire working area inside the cabinet.
  • Personnel protection is achieved by constant movement of air into the cabinet, and thus, make contaminants being unable to spread outside.
  • The cabinet is designed and suitable for work with microbiological agents assigned to biosafety levels 1, 2 and 3 where the only containment is required but not for product protection.
  • Due to limit of scope and application of Class I cabinets, they are mostly considered obsolete.
  • The HEPA exhaust filter installment inside the cabinet differentiates this type of BSC from conventional fume hoods which do not have HEPA filter installed, and thus, do not provide environment protection.


Class II  Personnel, Product and Environment protection

  • Inward dirty air is constantly drawn into an inlet air grille near front access opening and none of this dirty is passes over the work area in the cabinet. This mechanism provides protection to product on the work area.
  • HEPA-filtered, vertical, unidirectional airflow is commonly seen within the work area.
  • HEPA-filtered exhaust air can be either leave inside the room or exhaust to any exhaust system.
  • The certain type of cabinet that is widely used in life science, clinical, hospital and pharmaceutical sectors because of its protection abilities.
  • There are four subtypes, A1, A2, B1 and B2, for the Class II cabinets depended on different airflow patterns, velocities, exhaust methods and recirculation rate.
  • Suitable for work with agents involving biosafety level 1, 2 and 3.


Class III  Personnel, Product and Environment protection

  • The only class of cabinets provides an absolute level of safety that is suitable for work with agents assigned to biosafey level 1, 2, 3 and 4.
  • Frequently specified for work involving the most lethal biological hazards.
  • Always has physical barrier between personnel and product, e.g. gloves.
  • During operation, negative pressure relative to ambient environment is obligated to maintain full level of containment.
  • Double HEPA filtration in series or combination between one HEPA filter and air incineration are common in Class III cabinet to ensure absolute safety level.


What are biohazards and biosafety levels?

The word biohazard is a contraction of the words biological and hazard, and defined as: an infectious agent, or part thereof, presenting a real or potential risk to the well-being of man, animals and / or plants, directly through infection or indirectly through disruption of the environment.


Biosafety Levels 1 through 4 were established by the Centers for Disease Control (CDC) and the National Institutes of Health (NIH) and are combinations of laboratory practices and techniques, safety equipment and facilities. All of these levels are appropriate for the biohazard posed by the agents used and for the laboratory activity.


Biosafety Level 1

Practices, safety equipment and facilities appropriate for work with defined and characterized strains of viable microorganisms not known to cause disease in healthy adult humans. Bacillus subtilus, Naegleria gruberi, infectious canine hepatitis virus and exempt organisms under the NIH Recombinant DNA Guidelines are representative of those microorganisms meeting these criteria. The laboratory is not necessarily separated from the general traffic patterns in the building. Work is generally conducted on open bench tops using standard microbiological practices. A biological safety cabinet is generally not required for work involving these agents.


Biosafety Level 1 represents a basic level of containment relies on standard microbiological practices without special primary or secondary barriers recommended, other than a sink for hand washing.


Biosafety Level 2

Practices, safety equipment and facilities appropriate for work done with a broad spectrum of indigenous moderate-risk agents present in the community and associated with human disease in varying severity. Hepatitis B virus, HIV, the salmonella, and Toxoplasma spp, are representative of microorganisms assigned to this containment level. The differences between biosafety level 1 and 2 are:


  • Biosafety level 2 requires personnel to have specific training in handling pathogenic agents and are directed by competent scientists.
  • Biosafety level 2 requires extreme precautions to any contaminated sharp items
  • Biosafety level 2 requires all procedures with aerosol or high splash exposure that may increase the risk must be conducted in primary containment equipment, or in devices such as a Biological Safety Cabinet or safety centrifuge cups.


Biosafety Level 3

Practices, safety equipment and facilities appropriate for work done with indigenous or exotic agents with a potential for respiratory transmission, and which may cause serious and potentially lethal infection. Mycobacterium tuberculosis, St. Louis encephalitis virus, and Coxiella burnetti are representative of microorganisms assigned to this level.


At Biosafety Level 3, more emphasis is placed on primary and secondary barriers to protect personnel in the contagious area, the community, and the environment from exposure to potentially infectious aerosols. Both biological safety cabinets Class I or Class II are required for working with these biological agents.


Biosafety Level 4

Practices, safety equipment, and facilities appropriate for work done with dangerous and exotic agents that pose a high risk individual risk of life-threatening disease, which may be transmitted via the aerosol route, and for which there is no available vaccine or therapy. Viruses such as Marburg or Congo-Crimean hemorrhagic fever are manipulated at Biosafety Level 4.


At Biosafety Level 4, laboratory personnel's complete isolation of aerosolized infectious agents is achieved primarily by working in a Class III Biological Safety Cabinet or a full-body, air-supplied positive-pressure personnel suit. The facility in this biosafety level itself is generally a separate building or completely isolated zone with complex, specialized ventilation requirements and waste management systems to prevent release of viable agents to the environment.


Reference: Biosafety in Microbiology and Biomedical Laboratories, U.S. Department of Health and Human Services, HHS publication (CDC), 4th edition, April 1999.



Biosafety Level


Class I

1, 2, 3

Low to moderate risk biological agents

Class II

1, 2, 3

Low to moderate risk biological agents

Class III

1, 2, 3, 4

Low to high risk biological agents