Canisters rely on a variety of mechanisms for contaminant removal such as chemical absorption, adsorption, catalytic action, neutralization, and mechanical filtration.
Cartridges are smaller than canisters but are designed to work on the same principles.
An enclosure such as a storage tank, boiler, sewer, underground utility vault, tunnel or pit that is difficult to enter or exit and may contain atmospheric or physical hazards. Exhalation Valve A device that allows exhaled air to leave a respiratory device and prevents outside air from entering through the valve. The facepiece is supported by headbands, and contains inhalation valves, exhalation valves and connectors for the air-purifying cartridges or filters. Fume Airborne particulate formed by the evaporation of solid material e.g. metal fume emitted during welding. HEPA filters are often referred to as absolute filters and are used to remove toxic respirable sized particles from contaminated air.