The basic purpose of any respirator is to protect the respiratory system form the inhalation of hazardous materials contained in the atmospheric environment.
Air purifying respirators are basically of two fundamental types.
Also these two different filter elements can be used in combination with each other. Atmosphere supplying respirators function by providing an independent air source by means of a connection to a stationary breathing gas source, such as an air compressor, or by having an air source that is carried by the wearer. The first type is referred to as an air line respirator. All the above described respirators present unique design characteristics that must be tested and evaluated. Usually this is done by a set of laboratory tests that are designed to evaluate the specific performance of each individual respirator.