A biological safety cabinet (BSC) is a critical piece of laboratory equipment designed to protect laboratory workers, the surrounding environment, and samples from exposure to harmful biological agents. These cabinets provide a controlled environment by using airflow systems to prevent contamination, ensuring both safety and accuracy in experiments involving pathogens, toxins, and other hazardous biological materials. Available in different classes based on their design and intended use, BSCs are essential for maintaining hygiene and preventing the spread of infectious agents in research, healthcare, and diagnostic settings. In this article, we will discuss the definition and types of BSC and its various applications in laboratories.

What is a biosafety cabinet?

A biosafety cabinet is a closed, ventilated laboratory work area designed to protect users, the environment, and the materials being handled from infectious pathogens and other biological hazards. Biosafety cabinets minimize the escape of contaminants by combining laminar airflow and HEPA filtration. Biosafety cabinets are the primary safety barrier for biological safety in laboratories and are the most critical safety protection equipment in laboratories.

The Working Principle of a Biological Safety Cabinet

The primary principle of a biological safety cabinet involves drawing air from inside the cabinet through ducts to maintain a negative pressure environment. This prevents gases from escaping the cabinet, thereby protecting personnel. External air is filtered through a high-efficiency air filter before entering the cabinet to prevent contamination of samples during processing. Additionally, air from inside the cabinet is also filtered through a high-efficiency air filter before being released into the atmosphere to protect the environment.

Types of Biological Safety Cabinets:

BSCs are classified into three grades: I, II, and III.

  1. Class I biological safety cabinet: Provides protection for personnel and the environment, but does not protect the products inside the cabinet. Suitable for work involving low to medium-risk media.
  2. Class II biological safety cabinet (BSC): Provides protection for personnel, the environment, and products. They are further divided into A1, A2, B1, B2, and C1 types, each with specific airflow patterns and applications.
    Grade II biological safety cabinets are further divided into Type A and Type B:
    Type A is subdivided into Type A1 biological safety cabinets and Type A2 biological safety cabinets
    Type B is subdivided into Type B1 biological safety cabinets and Type B2 biological safety cabinets
  3. Class III biological safety cabinet: Also known as a glove box, this type of cabinet provides the highest level of protection for personnel, the environment, and products. They are used for handling high-risk biological agents.

What is the purpose of a biosafety cabinet

In any laboratory, a biological safety cabinet (BSC) is essential for handling infectious pathogens or hazardous materials. BSCs are designed to protect laboratory personnel and the environment, and are critical for ensuring safety and maintaining the integrity of research work. Additionally, certain types of biological safety cabinets can provide extra protection for products or research materials.

Class I Biological Safety Cabinet

Class I biological safety cabinets are used to protect personnel and the environment, but do not provide protection for the test samples. Suitable for applications where protection of the test sample is not required. Air passing through the sample area is filtered through a high-efficiency filter and 100% exhausted into the laboratory environment.

Applications: Used as special sealed equipment (such as centrifuges, harvesting equipment, or small fermentation equipment) or for processes that may generate aerosols (such as aerated culture or tissue mixing). Equivalent to a safety ventilation cabinet.

Class II biological safety cabinet

Class II biological safety cabinets are designed to protect personnel, samples, and the environment, and meet the requirements for biological safety cabinets handling pathogens of hazard levels I, II, and III. Safety cabinets with a front window operating port allow operators to perform procedures inside the cabinet through the front window. Contaminated airflow is filtered through a high-efficiency filter before being discharged into the protected environment.

Class II safety cabinets are classified into four types—A1, A2, B1, and B2—based on the proportion of exhaust airflow to the total system airflow and internal structural design.

Class II Type A1 Biological Safety Cabinet

The incoming airflow through the work window and the vertical airflow in the work area mix and enter the upper chamber of the safety cabinet. The minimum average airflow velocity through the front window operating port is 0.40 m/s. 70% of the air is recirculated, and 30% is exhausted to the indoor or outdoor environment. It is not suitable for experiments involving volatile toxic chemicals or volatile radioactive nuclides.

Class II A2 Biological Safety Cabinet

The incoming airflow through the work window and the vertical airflow in the work area mix and enter the upper chamber of the safety cabinet. The minimum average airflow velocity at the front window operating port is 0.50 m/s. 70% of the air is recirculated, and 30% is exhausted.

Application: When conducting microbiological experiments using trace amounts of volatile toxic chemicals and radioactive nuclides as auxiliary agents, a suitable exhaust hood must be connected.

Class II B1 Biological Safety Cabinet

The incoming airflow through the work window and the vertical airflow in the work area mix and enter the upper chamber of the safety cabinet. The minimum average airflow velocity at the front window operating port is 0.5 m/s. 70% of the airflow is filtered and exhausted to the outdoors, 70% of the air is supplemented from the outside, and 30% of the airflow is filtered and recirculated.

Application: Type B1 safety cabinets can be used for microbiological experiments involving trace amounts of volatile toxic chemicals and radioactive nuclides as auxiliary agents.

Class II B2 Biological Safety Cabinet

All airflow in the work area originates from the laboratory or outdoors, and exhaust air is filtered through a high-efficiency filter before being directly discharged outdoors. The minimum average airflow velocity at the front window operating port is 0.50 m/s. Incoming and downward airflow is filtered through a high-efficiency filter and discharged into the atmosphere via a dedicated exhaust duct; it is not allowed to return to the safety cabinet or laboratory. 100% of the airflow is filtered and discharged externally; 100% of the air is supplemented from the outside; no airflow is recirculated.

Application: The B2-type safety cabinet can be used for microbiological experiments involving volatile toxic chemicals and radioactive nuclides as auxiliary agents.

Class III Biological Safety Cabinet

A fully enclosed, leak-proof ventilation cabinet that meets the requirements for handling biological hazards of Classes I, II, III, and IV pathogenic agents. There are no open observation windows, and personnel perform operations inside the safety cabinet through gloves that are tightly connected to the cabinet body. Inflow air velocity: ≥0.7 m/s. Class III safety cabinets are typically installed only in laboratories with the highest containment levels, which have controlled access, special ventilation requirements, or other support systems (e.g., high-pressure steam).

Purpose: Used for handling microbial materials of hazard level 4, providing the best individual protection. All interfaces are sealed (hands can only reach the work surface through sturdy rubber gloves connected to the cabinet), with supply air filtered through a HEPA filter and exhaust air filtered through two HEPA filters.

How to properly use a biosafety cabinet

  1. The vertical movable window of the biosafety cabinet should open and close smoothly, without any sticking or jamming at any position within its range of motion. There should be no noticeable lateral or front-to-back swaying, and the sliding motion should be smooth. Switches and buttons should operate flexibly and reliably, with all components securely fastened and no loosening, and indicators should be accurate.
  2. Before starting work, pre-position experimental materials and avoid placing too many instruments.
  3. Arrange items from the clean zone to the contaminated zone in parallel, with specimens on the left and reagents on the right.  
  4. From the start of work until completion, the safety cabinet should operate for at least 4 minutes to complete the “purification” process.  
  5. While working in the work area and with the biological safety cabinet in normal operation, there should be no noticeable mechanical vibration noise.  
  6. Do not block the front and rear air grilles to minimize airflow interference.  
  7. Clean and disinfect spills promptly.
  8. Use disposable inoculation loops or sterilize inoculation loops using an electric heater (infrared sterilizer recommended).
  9. Place waste materials inside the biosafety cabinet during operations.
  10. Avoid using open flames inside the biosafety cabinet, as open flames can cause airflow turbulence and disrupt the HEPA filter’s airflow pattern toward the work surface.
  11. Use and maintain the equipment in accordance with the manufacturer’s instructions.