Air purifying respirators are special types of masks that cover the nose and mouth for the purpose of filtering contaminants from the air as a person breathes. These respirators are comprised of three basic parts: a mask to cover the nose and mouth, a filtering device and a cartridge. The mask itself possesses a canister to either side of the mouth. The canister contains the combined filters and cartridges. Breathing through the mask forces air to enter through the canisters, which capture contaminants — such as dust or smoke — while the cartridge removes harmful gasses or other vapors.
Many types and models of air purifying respirators exist, all designed for specific uses. The simplest example of these, a dust mask, can be disposed of after only one use. The half-face design is often used for cleaning or working in areas that have high concentrations of dust in the air. More complex designs, such as gas masks, can be used multiple times and might provide a shield for the eyes and upper face, or they might cover the entire head like a hood. Heavy-duty air purifying respirators, such as those used for construction or mining, require specific cartridges, depending on what gasses might need to be filtered.
Another type of respirator, a powered air respirator, can handle two or more gaseous contaminants, filtering them through the cartridges before delivering clean, breathable air to the user. Cartridges are manufactured to absorb specific contaminants and are color-coded to help the user select which type will best suit his or her needs. Powered air purifying respirators, such as those sometimes used in automotive paint shops, also require specific filters, depending on the particles encountered in the environment in which the the user will be working. Typically, a small fan is employed to draw the air in for cleansing.
Air purifying respirators offer a good deal of mobility for the wearer because they rely on natural respiration and eliminate the need for a portable, contained air supply. The lack of contained atmosphere means that air purifying respirators can be used only in an environment that contains enough oxygen for human survival. To enter any environment without adequate oxygen would require an atmosphere-supplying respirator with a provided air supply.