During a decompression, what indicates whether oxygen is flowing?

The green flow indicator is a visual cue designed to show the presence and flow of oxygen in a system, particularly in aviation and emergency medical situations. When oxygen is flowing, this indicator typically displays a green color, signaling to operators and crew members that the system is functioning properly and the oxygen is available for use. This immediate visual feedback is essential in emergencies, where time and clarity are vital for decision-making.

Other options do not serve as reliable or practical indicators of oxygen flow. The compressor sound may vary depending on system performance and does not directly indicate flow. The smell of oxygen is not a method used to assess flow, as pure oxygen is odorless; any smell could indicate a problem or the presence of other substances. Cabin lights do not provide any functional indication of oxygen flow and are unrelated to the operation of the oxygen delivery system. Therefore, the green flow indicator is the best and most accurate option for determining whether oxygen is flowing.