What is the indication that the Drager PBE is running low on oxygen?

• A. The alarm sounds louder
• B. The canister becomes warm
• C. The 'hissing sound' stops
• D. The mask inflates

Answer: (C)

The main idea is that the PBE’s oxygen flow is audible. When the system is supplying gas, you hear a continuous hissing as oxygen moves through the regulator into the hood. As the oxygen runs out, the regulator can no longer push gas, and the flow stops, so the hissing disappears. That absence of sound is the clear cue that the PBE is running low on oxygen. Other signs like a louder alarm, the canister feeling warmer, or the mask inflating don’t reliably indicate remaining oxygen, whereas the halt in the hiss directly signals depleted supply.