A closed circuit or rebreather uses a cylinder of ____ in its operation.

A closed circuit or rebreather uses a cylinder of ____ in its operation.

• A. Oxygen
• B. Compressed air
• C. Carbon dioxide
• D. Carbon

Answer: (A)

Closed-circuit breathing systems recirculate the wearer’s expired air, remove carbon dioxide, and add oxygen so the gas mixture stays breathable without being vented to the environment. The source of that breathable gas is a cylinder of oxygen, which supplies the oxygen the user consumes and allows the loop to maintain the needed oxygen concentration. This is distinct from open-circuit systems that rely on a supply of compressed air carried in a tank and vent it with every breath. Carbon dioxide is what the system removes, not what it supplies, and carbon is not a breathing gas. Therefore, the cylinder used in a closed-circuit rebreather is oxygen.

Closed-circuit breathing systems recirculate the wearer’s expired air, remove carbon dioxide, and add oxygen so the gas mixture stays breathable without being vented to the environment. The source of that breathable gas is a cylinder of oxygen, which supplies the oxygen the user consumes and allows the loop to maintain the needed oxygen concentration. This is distinct from open-circuit systems that rely on a supply of compressed air carried in a tank and vent it with every breath. Carbon dioxide is what the system removes, not what it supplies, and carbon is not a breathing gas. Therefore, the cylinder used in a closed-circuit rebreather is oxygen.