In which type of atmosphere do air-purifying respirators NOT provide protection?

Air-purifying respirators are designed to filter out specific contaminants from the air, allowing individuals to breathe safely when exposed to certain hazardous conditions. However, these respirators rely on having a sufficient amount of oxygen in the atmosphere to function properly.

In oxygen-deficient atmospheres, which contain less than 19.5% oxygen, air-purifying respirators cannot provide adequate protection because they do not supply oxygen—they only filter contaminants from the air that is available. If the oxygen levels are below the safe threshold, a respirator will not be effective, as there is not enough breathable air for the user.

Thus, for environments where the oxygen level is compromised, alternative breathing apparatuses, such as self-contained breathing apparatus (SCBA), are necessary to ensure adequate oxygen supply and protection from any hazardous exposures.