[1] The primary purpose of a BSC is to serve as a means to protect the laboratory worker and the surrounding environment from pathogens.

[2] This is in contrast to a laminar flow clean bench, which blows unfiltered exhaust air towards the user and is not safe for work with pathogenic agents.

These BSCs are commonly used to enclose specific equipment (e.g. centrifuges) or procedures (e.g. aerating cultures) that potentially generate aerosols.

[3]: 6 Class II cabinets provide both kinds of protection (of the samples and of the environment) since makeup air is also HEPA-filtered.

The air is then drawn underneath the work surface and back up to the top of the cabinet where it passes through the HEPA filters.

A column of HEPA filtered, sterile air is also blown downward, over products and processes to prevent contamination.

This type is not safe for work with hazardous chemicals even when exhausted with a "thimble" or canopy to avoid disturbing internal air flow.

[5] Additionally, there is the risk that contaminated air would flow into the laboratory if the exhaust system for a Type B1 or B2 cabinet were to fail.

This includes reduction of the noise level (for a more convenient working atmosphere), a height adjustable stand or stool and footrest (for optimized sitting position), panorama side windows (more light within cabinet), 10° angled front sash (enables better sitting position), strong light sources (better view within cabinet), forearm support for comfort and safety, as well as extended access openings and sloped viewing windows to improve the working conditions.

[12] However, these assertions have been formally disputed in at least one peer-reviewed article which points out that:[13] Biological safety cabinets are generally required to comply with that country or region's standards.

AS2243.3 classifies the level of risk that microorganisms pose based on their pathogenicity, mode of transmission, and host range, along with current preventative measures and effective treatments.

To avoid contamination and the risk of personnel exposure, the CDC advises investigators to follow best practices to reduce and control splatter and aerosol generation, such as keeping clean materials at least 12 inches (30 cm) from aerosol-generating activities and arranging the work flow "from clean to contaminated".

[3]: 22  In particular, open flames, not necessary within the clean environment of a Class II or III BSC, cause disruption of the airflow inside.