In a laminar air flow hood, room air is drawn into a horizontal hood and passed through a prefilter to remove large contaminants like dust and lint. The air is then channeled through a HEPA filter to remove particles larger than 0.3 microns. This purified air then flows over the work surface in parallel lines at uniform velocity, or laminar flow. The constant flow of air from the hood prevents room air from entering the work area and removes contaminants introduced into the work area by material or personnel.
Biological safety cabinets protect both the personnel and environment from contamination in the preparation of hazardous drugs such as chemotherapy medication. They pass air through a HEPA filter, downwards towards the work surface and then pulled through front, back and side air vents. The majority of the air is recirculated back into the cabinet with only a minor portion passing through a secondary HEPA filter and exhausting into the room.