The type of breathing system that CANNOT BE utilized in an oxygen deficient atmosphere is a(n):

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

Answer: (A)

In an oxygen-deficient atmosphere, you must have a breathing system that provides breathable air independent of the ambient oxygen level. An air-purifying respirator filters contaminants from the outside air but does not add oxygen to it. If the surrounding air has too little oxygen, you could still suffocate even though contaminants are removed. That’s why an air-purifying respirator cannot be used in low-oxygen conditions.

The other options are designed to supply breathing air from a separate source or carry their own air supply. A supplied-air respirator delivers breathing air from a hose-connected external source, so the worker isn’t relying on the local oxygen level. A self-contained breathing apparatus carries its own compressed air in a cylinder, providing oxygen-rich air regardless of the environment. A powered air-purifying respirator still relies on ambient air (filtered and blown into the facepiece) and does not supply oxygen, so it’s also not suitable for oxygen-deficient atmospheres.