How can you tell O2 is flowing from the PSU unit?

• A. There is a green indicator light on the mask
• B. A green indicator light on the PSU unit shows flow for each mask
• C. Red indicator light
• D. Audible alarm

Answer: (B)

Verifying oxygen flow is done by using the indicator lights on the PSU. Each mask has a dedicated green light on the PSU unit that lights up when oxygen is flowing to that mask. This per-mask signal is the direct, visual confirmation that oxygen is being delivered. The mask itself doesn’t typically display a flow light, so relying on the PSU’s green indicators is the correct way to tell that oxygen is flowing. A red light would indicate a fault or no flow rather than normal operation, and an audible alarm might indicate a problem but does not provide the per-mask flow confirmation you get from the PSU indicator lights.