Biological Safety Cabinets

Biosafety cabinets (BSCs) are categorized into three main classes—Class I, Class II, and Class III—each designed to provide varying levels of protection for personnel, products, and the environment.

Class I cabinets offer personnel and environmental protection by drawing air into the cabinet and through HEPA filters, but they do not protect the product from contamination.

Class II cabinets are the most commonly used in laboratories and provide a balance of protection for personnel, the environment, and the work material through a carefully controlled airflow system and HEPA filtration. These are further divided into types (A1, A2, B1, and B2) based on airflow and exhaust systems.

Class III cabinets, also known as glove boxes, offer the highest level of containment and are gas-tight, providing maximum protection when handling high-risk biological agents. Each class serves a specific purpose depending on the type of work and level of biosafety required.

Class I Biosafety Cabinets

Class I biosafety cabinets provide protection for personnel and the environment, but not the product being handled. Air is drawn into the front opening of the cabinet, passing over the work surface and then through a HEPA filter before being exhausted. This unidirectional airflow prevents contaminants from escaping the enclosure, protecting users from exposure to potentially hazardous materials. However, because room air enters the cabinet directly, there’s no protection for the samples or products inside. Class I cabinets are typically used for procedures involving low to moderate-risk biological agents or when personnel protection is the primary concern.

Class II Biosafety Cabinets

Class II biosafety cabinets are the most widely used in laboratories handling infectious agents or cell cultures, as they offer protection for personnel, the environment, and the product. These cabinets use a combination of inflow and downflow HEPA-filtered air to create a sterile work environment while ensuring that contaminated air does not escape into the room.

Class II cabinets are subdivided into four types—A1, A2, B1, and B2—each with specific airflow patterns and exhaust methods. For example, Type A cabinets recirculate a portion of filtered air, while Type B cabinets exhaust most or all of it, often requiring external ducting. The selection depends on the application and the materials being used, especially if volatile chemicals are involved. Types A2 and B2 are the most common.

Class II Type A2 Biosafety Cabinets

Type A2 biosafety cabinets are the most commonly used subtype in research and clinical laboratories. They provide protection for personnel, the environment, and the product by maintaining a carefully balanced airflow. Approximately 70% of the air is recirculated through a HEPA filter back into the work zone, while the remaining 30% is exhausted—either back into the room or through a canopy connection to the building's exhaust system.

Because Type A2 cabinets do not safely exhaust chemical vapors or volatile toxic substances unless properly ducted, they are best suited for microbiological work involving non-toxic or minute quantities of volatile chemicals. Their flexibility, energy efficiency, and ease of installation make them a popular choice for most biosafety applications requiring containment and sterile conditions.

Class II Type B2 Biosafety Cabinets

Type B2 biosafety cabinets, sometimes referred to as "total exhaust" cabinets, are designed for work that involves hazardous chemical vapors or radionuclides in addition to biological agents. These cabinets provide the highest level of chemical safety within the Class II category by exhausting 100% of the air through a hard-ducted external ventilation system—none of the air is recirculated. As a result, B2 cabinets require a dedicated building exhaust system and must be carefully balanced and maintained to ensure proper function. They are ideal for applications involving toxic or volatile compounds, such as in pharmaceutical research or specialized microbiological procedures where chemical and biological containment is essential.

Class III Biosafety Cabinets

Class III biosafety cabinets, also known as glove boxes or total containment units, are designed for maximum containment when working with high-risk pathogens such as those in Biosafety Level 4 (BSL-4) laboratories.

These cabinets are completely sealed and gas-tight, with access to the work area provided through attached rubber gloves. All materials enter and exit through a pass-through chamber to maintain containment. Air is HEPA-filtered both in and out of the cabinet, ensuring no contamination can escape.

Class III cabinets are essential for handling the most dangerous biological agents, providing the highest level of protection for personnel and the environment.