How will you know when the PBE has run out of oxygen?

• A. The hood will start deflating and condensation seen on viewing window.
• B. The oxygen gauge shows full.
• C. The intercom volume increases.
• D. The hood becomes cold to touch.

Answer: (A)

Recognizing depletion of oxygen in a PBE relies on the physical cues of the system losing pressure and moisture building inside the hood. When the oxygen supply is exhausted, the hood can no longer stay inflated, so it starts to deflate. At the same time, humidity from breath and the cooler window surfaces cause condensation on the viewing window. Seeing both the hood deflate and condensation on the window together is a clear signal that the oxygen flow has ended.

The other signs don’t fit. If the oxygen gauge showed full, that would indicate oxygen is still available, not depleted. Intercom volume changing isn’t related to the oxygen supply. The hoodFeeling cold to touch isn’t expected—these systems typically feel warm due to the exothermic oxygen-generating process, so a cold hood wouldn’t indicate depletion.