What type of breathing system is ineffective in an oxygen deficient atmosphere?

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

Answer: (C)

An air-purifying respirator is specifically designed to filter contaminants from the air that a person is breathing. It relies on an adequate level of oxygen in the surrounding atmosphere to function properly. In an oxygen-deficient environment, these respirators cannot provide the necessary oxygen, rendering them ineffective. They only clean the air of particulates and gases but do not supply oxygen, which is vital for normal respiratory function.

In contrast, other types of breathing systems, such as self-contained breathing apparatus and supplied air respirators, provide a source of breathable air. Positive pressure respirators also ensure that the air delivered to the user is at a pressure greater than the surrounding atmosphere, which is essential in hazardous environments. Therefore, while the other options ensure that the user receives breathable air even in low-oxygen situations, the air-purifying respirator is inadequate in these circumstances due to its dependence on the surrounding atmosphere containing a sufficient amount of oxygen.