Respirators protect users in two basic ways. The first is by the removal of contaminants from the air. These types of respirators include particulate respirators and air-purifying respirators (APRs). The Occupational Safety and Health Administration (OSHA) defines an APR as a respirator with an air-purifying filter, cartridge or canister that removes specific air contaminants by passing ambient air through the air-purifying element. The second way that respirators protect users is by supplying clean, respirable air from another source—atmosphere-supplying respirators. This Quick Tip provides an overview of the various types of atmosphere-supplying respirators. For a closer look at APRs, refer to Quick Tips #275: Types of Respirators, and #141: Particulate Respirators, 42 Code of Federal Regulations (CFR) Part 84.
OSHA subdivides atmosphere-supplying respirators into the following three classifications: supplied-air respirators (SARs), combination atmosphere-supplying respirators and self-contained breathing apparatuses (SCBAs). Atmosphere-supplying respirators, when used in accordance with the requirements of OSHA’s Respiratory Protection standard (29 CFR 1910.134), offer the wearer a level of protection equal to or exceeding APRs with an enhanced level of comfort. The drawbacks are that they are more expensive and harder to use and maintain than APRs.
When it comes to determining the level of protection provided by a respirator, it is important to first understand OSHA’s definitions for “Assigned Protection Factor” and “Maximum Use Concentration.” Assigned Protection Factor (APF) refers to the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program. Maximum Use Concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator. MUC is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance.
Within atmosphere-supplying respirators, APFs can range from 10, for a SAR operated in the demand mode, all the way up to 10,000 for SCBAs. In addition, because atmosphere-supplying respirators provide the wearer with fresh breathing air from a trusted source, certain classifications of atmosphere-supplying respirators are approved for oxygen-deficient conditions (oxygen levels below 19.5%) as well as for airborne concentrations of contaminants that exceed Immediately Dangerous to Life or Health (IDLH) levels.
Atmosphere-Supplying Respirator Classifications
Supplied-Air Respirators (SARs) - The basic SAR is comprised of a respirator facepiece—which could be a tight fitting half mask or full face mask, or a loose-fitting hood or helmet assembly—connected via an air supply hose to a source of breathing air. The air supply could be either a low pressure or high pressure source. A low pressure source would be an ambient pump (an air compressor designed specifically for respiratory protection applications) located in, or drawing air from, a clean environment. A high pressure supply source would be either a cylinder or “cascaded” cylinders of breathing air, or the compressed air supply within a facility as long as it is filtered and monitored to ensure it meets OSHA’s purity requirements (see below) for breathing air.