Also called gas masks, these respirators are more effective for a longer time than cartridge respirators. Only full-face canister respirators are available. The canister is screwed into the mask or worn on the user’s belt, back, or chest. A hose or tube connects the canister to the facepiece. Canister filter respirators are not to be used in areas considered immediately dangerous to life or health (IDLH), such as a manure pit or silo with gases.