Respirators protect the workers in two basic ways. The first is by the removal of contaminants from the air. Respirators of this type include particulate respirators, which filter out airborne particles, and air-purifying respirators with cartridges/canisters which filter out chemical vapors ;and gases. The other type of respirators protect by supplying clean respirable air from another source. Respirators that fall into this category include airline respirators, which use compressed air from a remote source, and self-contained breathing apparatus (SCBA), which include their own air supply.
Air purifying respirators are devices with air purifying filters, cartridges or canisters that remove specific air contaminants such as particulates, gases and vapors. These type of respirators include particulate or aerosol removing respirators, and gas removing respirators. Respirator types under this category include: disposable dust masks, gas marks, half- face masks, full-face masks and powered air-purifying respirators.
Air purifying respirators must only be used when there is sufficient oxygen , at least 19.5% by volume, available in the workplace environment.
Contaminants are removed as they pass through the respirator's filter, canister or cartridge using one or a combination of the following mechanism: filtration, absorption, adsorption, or chemical reaction. Air purifying respirators are available in non-powered and powered types. A powered respirator has a blower that forces ambient air through one or more filters attached to the device while the non-powered respirator filters the air as the user breaths in.
Careful selection of filters, cartridges or canisters for the air-purifying respirator must be done by a trained professional. This could be a complicated process because there are so many types and none protects against all contaminants. It is therefore necessary to do a careful risk assessment and identify the specific respiratory hazard in the workplace before selecting the most appropriate air-purifying medium Keep in mind also that the useful life of an air-purifying respirator and its filter, cartridge or canisters is limited by the concentration of the air contaminants, breathing rate of the user, temperature and humidity level in the workplace and contaminant removal capacity of the air-purifying medium.
Atmosphere-supplying respirators offer a better degree of protection as compared to air-purifying respirators. Atmosphere-supplying respirators allow users to breath uncontaminated air from a source. Unlike air-purifying respirators, atmosphere-supplying respirators could be used in toxic or oxygen deficient environments. There are two basic types of atmosphere-supplying respirators: Self-Contained Breathing Apparatus and the Supplied-Air Respirators.