Owing to their small size, droplet nuclei aerosols may be generated by certain laboratory procedures without the laboratory worker’s knowledge; this may result in the inhalation of infectious agents or cross-contamination of work surfaces or materials. BSCs are designed to protect people and the environment from infectious agents and, depending on their classification, offer varying degrees of protection from contamination of specimens and cultures.
The HEPA filter in the exhaust system of a BSC effectively traps infectious organisms and ensures that only microbe-free exhaust air is discharged from the cabinet. A HEPA filter mounted in the BSC above the BSC work surface protects the surface and its materials from contamination. This is often referred to as product protection.
There are three classes of BSCs: I, II and III (corresponding to standards AS/NZS 2252.1:1994, AS/NZS 2252.2:1994, NSF/ ANSI 49 – 2008 and EN 12469).¹⁸ ¹⁹ ²⁰ ²¹ According to the NSF/ANSI 49 – 2008 standard, class II BSCs have a variety of types (known as A1, A2, B1, B2); these are used to classify variations in airflow patterns, velocities, the position of the HEPA filter inside the cabinet, ventilation rates and exhaust methods.