Which respiratory protection cannot be used in an oxygen-deficient atmosphere?

• A. Self-contained breathing apparatus
• B. Air-purification respirator
• C. Supplied-air respirator
• D. Powered air-purifying respirator

Answer: (B)

In an oxygen-deficient atmosphere, you must have a respirator that supplies its own breathing air. An air-purifying respirator only cleans contaminants from the surrounding air and does not add oxygen. If the oxygen level is too low, relying on that ambient air can lead to suffocation even if contaminants are removed, so it cannot be used in these conditions.

In contrast, a self-contained breathing apparatus provides its own air from a cylinder, and a supplied-air respirator delivers breathing air from an external source; both are suitable for low-oxygen or IDLH environments. A powered air-purifying respirator still relies on ambient air for oxygen, so it’s not appropriate in oxygen-deficient atmospheres.

So, the air-purifying respirator is the type that cannot be used when the atmosphere is oxygen-deficient.