Biological safety cabinets (biosafety cabinets) come in several classes (I, II, and III) that offer varying levels of protection from hazardous or contagious materials. For all classes of biological safety cabinet, the air is HEPA (high efficiency particulate air)-filtered before being released as exhaust. A Class I biosafety cabinet is designed to protect the user and the environment, not the sample as negative pressure is used to pull outside air in across the workspace.
Class II biological safety cabinets are divided into four subtypes (A1, A2, B1, and B2) and have the additional feature of protecting the sample as the air supply is HEPA-filtered before passing over the workspace. The Class II subtypes differ in the amount of recirculated air within the cabinet.
Class III biosafety cabinets (also known as gloveboxes) provide maximum protection for work in biosafety level 4 containment labs. A class III biosafety cabinet is a hermetically-sealed glovebox with access through a dunk tank or double-door box that allows for decontamination.