Understanding Biosafety Cabinets: A Guide to Classes I, II, and III

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Now, on to the article.

Understanding Biosafety Cabinets: A Guide to Classes I, II, and III

Biosafety cabinets are an important piece of equipment in many labs, providing a safe environment for researchers working with harmful biohazards and pathogens.

BSCs come in three different classes, each of which is designed for different kinds of lab work and varying levels of required safety.

Understanding the capabilities and design of each class is important when selecting the right equipment to use for your research, or if you are purchasing a new BSC for your lab.

Class I: Basic Design & Protection

  • Design and Airflow: Air is drawn into the BSC and across the work surface before being sterilized by HEPA filters and exhausted back out.
  • Safety and Protection: Class I BSCs create a safe, aerosol-free environment for lab personnel. They don’t, however, protect work samples inside the cabinet.
  • Uses and Safety Level: Best equipped for general lab work, as well as procedures like aerating cultures and enclosing certain equipment (e.g., centrifuges). Most commonly used in environments dealing with low to moderate risk agents (Biosafety Levels 1 and 2).

Class II: Common & Versatile

  • Design and Airflow: Class II BSCs create a sterile curtain of air over the entire work area, with air circulating and filtering through HEPA filters​​.
  • Safety and Protection: Comprehensive protection for the user, work surface, and external lab environment.
  • Variants and Features: Class II BSCs come in several subtypes (A1, A2, B1, B2, C1). Each subtype has a unique airflow pattern and exhaust system. In general, Class II cabinets use HEPA-filters to sterilize both inflow and downflow, which creates a suitable environment for working with many different materials and specimens.
  • Applications: These are versatile units suited for several applications, including handling pathogens, cell cultures, and allergens. Common in microbiological, clinical, pharmaceutical, and life science research labs.


    • Type A1: Mainly used for work with low to moderate risk biological agents (Biosafety Levels 1 and 2) and is not suitable for volatile or toxic chemicals. Recirculates 70% of the HEPA-filtered air and exhausts 30% back into the lab. 
    • Type A2: Similar to Type A1, but with a higher minimum inflow velocity (100ft./min. vs. 75ft./min.).  Suitable for work with Biosafety Levels 1, 2, and 3 agents, but not recommended for significant volumes of volatile or toxic chemicals. Recirculates 70% of the HEPA-filtered air and exhausts the remaining 30%.
    • Type B1: Suitable for handling low quantities of toxic chemicals and radionuclides for moderate-risk applications​​ (Biosafety Levels 1, 2, and 3). Designed with a mixed airflow pattern, where 40% of the HEPA-filtered air is recirculated and 60% is exhausted out.
    • Type B2: Also known as a total exhaust cabinet. Capable of handling all biosafety work, but is critical for any work with high volumes of toxic chemicals and radionuclides (Biosafety Levels 1, 2, 3, and 4). 100% of the HEPA-filtered air is externally exhausted, so Type B2 cabinets are often found in toxicology labs, as well as other microbiological and biomedical labs.
    • Type C1: A versatile and relatively new development in biosafety cabients with two modes of operation: Type A (air is recirculated, often for microbiological work) and Type B (connected to an exhaust system for hazardous chemicals). These are energy-efficient, cost-effective, and suitable for handling materials up to Biosafety Level 3.

Class III: Maximum Protection

  • Design and Airflow: Class III BSCs are fully sealed, meaning that all air passes through HEPA filters. These cabinets are also frequently referred to as 'glove boxes' and are equipped with built-in heavy-duty rubber gloves for handling​​ materials on the work surface.
  • Safety and Protection: Offers the highest level of protection against high-risk pathogens, preventing the user from having any direct contact with the work product.
  • Uses and Safety Level: Well-suited for all lab work, but are very important for any work with Biosafety Level 4 agents. These cabinets are common in maximum containment laboratories for handling Biosafety Level 4 agents like deadly viruses and hazardous pathogens. They are also often custom-outfitted based on a lab's unique requirements, which can include supplemental equipment like microscopes and incubators​​​​.


Remember, this guide is just a starting point. Choosing the right class of BSC is more than just understanding the difference between I, II, and III. It's about aligning the cabinet's capabilities with the specific needs of your lab work.

Whether you're handling low-risk biological agents or dealing with high-level pathogens, the right BSC will ensure a safe and efficient work environment for you and your colleagues. Make sure that you do proper research and consult with experts before purchasing a cabinet.