Biosafety Cabinet: Definition, Classification (Class I, II, III), Working Mechanism, Application, Features.

Content hide 1 Biosafety Cabinet Definition 2 Why should we use Biosafety Cabinets? 3 Biosafety Cabinet Classification(BSC) 4 Further Reading Biosafety Cabinet...

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Biosafety Cabinet

Biosafety Cabinet Definition

The biosafety cabinet (BSC) also known as the microbiological safety cabinet or biological safety cabinet, are an enclosed, and ventilated laboratory workspace that is designed to protect the laboratory worker and the surrounding environment from infectious pathogens.

The exhaust air inside the biosafety cabinet pass through a HEPA filter and removes all the hazardous agents such as viruses and bacteria.

Why should we use Biosafety Cabinets?

We should use biosafety cabinets to;

  • To protect ourselves or laboratorians from infectious agents.
  • To protect the sample from contamination.
  • To prevent environmental contamination from infectious agents.

Biosafety Cabinet Classification(BSC)

Based on the degree of biocontainment, the biosafety cabinet is classified into three classes such as Class I Biosafety Cabinet, Class II Biosafety Cabinet, and Class III Biosafety Cabinet.

Classes of Biosafety Cabinet
Classes of Biosafety Cabinet
  • Class I
  • Class II
    • Type A
      • Type A1
      • Type A2
    • Type B
      • Type B1
      • Type B2
  • Class III

Class I Biosafety Cabinet (BSC)

  • Class I Biosafety Cabinet (BSC) only provides personnel and environment protection. It does not protect the products.
  • It is a negative-pressure, ventilated cabinet which is operated with an open front.
  • The air is exhausted from the cabinet either into the laboratory or to the outside.

Working Mechanism

The air enters into the cabinet through the front opening with a minimum velocity of 0.38 m/s. After that, it passes over the workplace and releases from the cabinet by exhaust duct. The stream of inward air carried out all the aerosols which are generated within the workplace during microbiological manipulations. 

Then the air traps all the airborne particles and contaminants when it passes through the filtration system, and releases clean, decontaminated air from the cabinet. The filtration system is made of pre-filter and a HEPA (High-Efficiency Particulate Air) filter.

Biosafety Cabinet Class 1
Biosafety Cabinet Class 1 | Image Source : WHO


  • Front opening
  • Exhaust plenum
  • Shash
  • Exhaust HEPA filter.


  • It is only used for microbiological research with low- and moderate-risk agents.
  • For Cag dumping in an animal lab.
  • Housing centrifuge, fermenters.
  • To aerate cultures which are potentially generated aerosols.

Class II Biosafety Cabinet

  • Class II Biosafety Cabinet provides personnel, environment, and product protection.
  • There are different types of Class II Biosafety Cabinet such as A1, A2, B1, and B2.

Working Mechanism

The working mechanism of the Class II Biosafety cabinet is totally different from others. For personnel protection, it contains an open front with inward airflow. To protect the product from contamination it has a downward HEPA filtered laminar airflow over the work surface. To protect the environment it has HEPA filtered exhaust air.

The inward airflow enters the cabinet with a velocity of  0.38 m/s through the front opening and then it passes through a supply HEPA filter. Next, it follows the downwards over the work surface.

During the downward, it “splits” about 6–18 cm from the work surface, one-half passes through the front exhaust grill, and the second half passes through the rear exhaust grill. The generated aerosols will be captured by this downward airflow and will pass through the front or rear exhaust grills, which will provide a maximum level of product protection.

After that, the air is released into the space between the supply and exhaust filters located at the top of the cabinet. Then the supply HEPA filter recirculates 70% air within the cabinet and the remaining 30% is released into the room environment through the exhaust filter.

Class II Type A1 Biosafety Cabinet

  • The Face Velocity is 75 fpm
  • 70% air recirculated through HEPA Filter.
  • 30% air Exhausted Through the HEPA Filter.
  • Class II Type A1 Biosafety cabinet Cannot be used for Radio Nucleotides and Toxic Chemicals
  • It is used in Biosafety Levels 2 & 3.
  • Class II Type A-I Biosafety Cabinets provides personal, product, & environment Protection.
Biosafety Cabinet Class 2 Type A1
Biosafety Cabinet Class 2 Type A1 | Image Source : WHO
  • Front opening 
  • Sash
  • Exhaust HEPA filter
  • Rear plenum 
  • Supply HEPA filter
  • Blower

Class II Type A2 Biosafety Cabinet

  • Downward Velocity Is 100 fpm.
  • 70% air recirculated through HEPA  Filter.
  • 30% air Exhausted Through HEPA Filter.
  • Type A2 Biosafety Cabinet Can be used for Radio Nucleotides and Toxic Chemicals.
  • Use for Biosafety Levels 2 & 3 User.
  • It provides Product, & Environment Protection.
  • Under Negative Pressure to room.
  • The Exhaust Air is Hard Ducted.
Biosafety Cabinet Class 2 A2
Biosafety Cabinet Class II Type A2
  • The front opening
  • Sash
  • Exhaust HEPA filter
  • Supply HEPA filter
  • Positive pressure plenum
  • Negative pressure plenum 

Class II Type B1 Biosafety Cabinet

  • The Downward Velocity is 100 fpm.
  • 30% air is recirculated through HEPA Filter.
  • 70% air Exhausted Through the HEPA Filter.
  • It Can be used for Radio Nucleotides and Toxic Chemicals (Low Levels / Volatility).
  • It is designed for Biosafety Levels 2 & 3 Users.
  • It provides Product, & Environment Protection.
Biosafety Cabinet Class 2 Type B1
Biosafety Cabinet Class 2 Type B1 | Image Source : WHO
  • The front opening.
  • Sash.
  • Exhaust HEPA filter.
  • Supply plenum.
  • Supply HEPA filter.
  • Blower.
  • Negative pressure exhaust plenum.

Class II Type B2 Biosafety Cabinet

  • The Downward Velocity 100 fpm.
  • No Re-circulation 100% air Exhausted Through HEPA Filter
  • It Can be used for Radio Nucleotides and Toxic Chemicals 
  • It is designed for Biosafety Levels 2 & 3User
  • Provides Product, & Environment Protection 
  • The Exhaust HEPA Filtered.
  • Exhaust Hard Ducted out.
Biosafety Cabinet Class 2 B2
Biosafety Cabinet Class II Type B2
  • The front is opening
  • Sash
  • Exhaust HEPA filter
  • Supply HEPA filter
  • Negative pressure exhaust plenum
  • Contain Supply blower 
  • filter screen.

Class III Biosafety Cabinet

Class III Biosafety Cabinet is designed for work with BSL-4 pathogenic agents. It provides maximum protection to persons and the environment. It is an aerosol-tight enclosure with a non-opening, completely sealed.

Working Mechanism

Class III Biosafety cabinet provides a maximum level of personal, environmental, and product protection. These are gas-tight chambers made of welded metal, there are heavy-duty rubber glove ports in the front cabinet which used to perform the work.

In Class III Biosafety cabinets the supply air is HEPA filtered and before release from the cabinet the air is passed through two HEPA filters. There is a dedicated exhaust system exterior to the cabinet to maintain the negative pressure within the cabinet interior.

Some time Class III Biosafety cabinets contain a double-door autoclave two decontaminate the material within the cabinet.

Biosafety Cabinet Class 3
Biosafety Cabinet Class 3 | Image Source : WHO


  • Contain glove ports with an O-ring for attaching arm-length gloves to the cabinet.
  • Sash
  • Exhaust HEPA filter
  • Supply HEPA filter
  • Double-ended autoclave or pass-through box.


  • To examine the high-risk agents.
  • To Work with highly infectious or hazardous experimental materials.
  • To study the emerging diseases.
  • To Study the diseases that are near eradication.
  • Weighing and diluting chemical carcinogens.

Further Reading

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