A respirator is a protective device that covers the nose and mouth or the entire face or head to guard the wearer against hazardous atmospheres. Respirators may be:

• Tight-fitting - that is, half masks, which cover the mouth and nose and full facepieces that cover the face from the hairline to below the chin; or
• Loose-fitting, such as hoods or helmets that cover the head completely.
• In addition, there are two major classes of respirators:
• Air-purifying, which remove contaminants from the air; and
• Atmosphere-supplying, which provide clean, breathable air from an uncontaminated source. As a general rule, atmosphere-supplying respirators are used for more hazardous exposures.