Will an air purifying respirators save your life within an oxygen-deficient atmosphere?

No, an air purifying respirator will NOT save your life in an oxygen deficient atmosphere.

An air PURIFYING respirator removes bad things from air. It does not MAKE good things (like oxygen). In an oxygen deficient atmosphere, you must have a supply of oxygen. This is usually provided by an SCBA, or an air line respirator.

Underground miners have "self rescue breathers." These are a form of respirator that can make oxygen. They are very expensive, have limited uses, and work for a limited time.