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A Biological Safety Cabinet (BSC), also known as a biological or microbiological safety cabinet, is a ventilated laboratory enclosure designed to allow safe handling of materials that are contaminated—or may be contaminated—with infectious agents requiring specific biosafety levels. Multiple types of BSCs exist, each offering different degrees of containment and protection. Commercial production of Biological Safety Cabinets began in the 1950s.

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Purpose

The primary function of a Biological Safety Cabinet is to protect laboratory personnel and the surrounding environment from exposure to infectious agents. Air exhausted from a BSC passes through high-efficiency particulate air (HEPA) filters, which remove harmful microorganisms such as bacteria and viruses. This feature distinguishes BSCs from laminar flow clean benches, which direct unfiltered air toward the user and are therefore unsafe for work with pathogens. Most BSCs are also not suitable for use as chemical fume hoods, and fume hoods themselves do not provide the environmental protection afforded by HEPA filtration. In addition to personnel and environmental protection, many BSCs are designed to maintain the sterility of materials inside the cabinet, providing product protection.

Classes

The U.S. Centers for Disease Control and Prevention (CDC) categorizes Biological Safety Cabinets into three classes based on the level of protection they provide to personnel, the environment, and the product.

Class I

Class I Biological Safety Cabinets protect personnel and the environment but do not protect the product. The inward airflow can introduce contaminants into samples. These cabinets maintain a minimum inward air velocity of 75 ft/min (0.38 m/s) and are commonly used to contain equipment or procedures that generate aerosols, such as centrifuges or culture aeration. Class I cabinets may be either ducted to a building exhaust system or operate as recirculating (unducted) units.

Class II

Class II Biological Safety Cabinets provide protection for personnel, the environment, and the product. Both the inflow and downflow air are HEPA-filtered. There are five Class II types: A1, A2, B1, B2, and C1, all defined by NSF International Standard 49. Revisions to this standard reclassified earlier cabinet types and introduced the Type C1 in 2016. Approximately 90% of installed Biological Safety Cabinets are Type A2 units.

Class II cabinets operate using motor-driven blowers that create controlled airflow patterns. Air is drawn into the front grille to protect the operator, passes beneath the work surface, and moves upward through HEPA filters. Filtered, sterile air flows downward over the work area to protect samples, while exhaust air is HEPA-filtered before being either recirculated into the laboratory or expelled through dedicated ductwork, depending on the cabinet type.

Type A1

Type A1 cabinets have a minimum inflow velocity of 75 ft/min. Air flowing downward over the work surface splits just above the surface and mixes with incoming air. This air is routed through internal plenums, where it is either recirculated through a HEPA filter or exhausted through another HEPA filter. Because contaminated air passes through positive-pressure plenums, Type A1 cabinets are not suitable for use with hazardous chemicals, even when connected to a canopy or thimble exhaust.

Type A2

Type A2 cabinets operate at a higher minimum inflow velocity of 100 ft/min and differ from Type A1 cabinets by using negative-pressure plenums to surround contaminated positive-pressure areas. Aside from this added safety feature, their design and airflow characteristics are similar to those of Type A1 cabinets.