Which type of breathing apparatus offers protection only for specific, known hazards?

The air-purifying respirator offers protection only for specific, known hazards because it relies on filters to remove contaminants from the air. These devices are designed to protect against particular airborne hazards such as dust, fumes, mists, and specific gases or vapors, but their effectiveness is contingent on the identification of those hazards. Users must be aware of the specific substances present in their environment to select the appropriate filter, as air-purifying respirators do not provide oxygen in environments where oxygen levels are inadequate.

In contrast, supplied air systems deliver breathable air from a clean source, making them suitable for a wider range of applications, including environments where air quality is unknown or hazardous. Closed circuit systems recirculate exhaled air after filtering, allowing the user to utilize a limited supply of oxygen efficiently but are not limited to known hazards either. Open circuit systems expel used air after inhalation and are designed for high exertion or extended use, similarly providing protection without being limited to specific contaminants. Hence, the air-purifying respirator stands out as the option specifically restricted to known hazards.