Immediately after O2 enters the breathing bag, where does it go next?

• A. back into the cylinder
• B. into the carbon dioxide scrubber canister
• C. into the demand valve
• D. into the inhalation hose

Answer: (D)

The gas moves forward into the inhalation hose. In a closed-circuit rebreather, the breathing bag supplies the next inhalation, and as you begin to inhale, the demand valve at the mouthpiece opens to let that gas flow into your lungs. The carbon dioxide scrubber handles CO2 from the gas after you exhale, not the fresh O2 you’re about to inhale, and there isn’t a normal path for gas to go back into the cylinder. So the immediate next step after entering the bag is the inhalation hose delivering O2 to you.