Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 378
Situational Awareness; Physiological - Other; Human-Machine Interface
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Diverted; General Maintenance Action
Human Factors; Aircraft
While at cruise; the First Officer discovered that the oxygen mask harness at his station did not inflate when the triggers were squeezed and did not retract when released. The mask did provide oxygen flow but did not cradle the head or face making the mask ineffective if used hands free. After some discussion; the crew decided the best course of action was to stop enroute and have the mask replaced rather than continue to destination. We notified Dispatch and Maintenance Control via ACARS; made a logbook entry; and diverted to a nearby regular airport. Maintenance Technicians met the aircraft on arrival and replaced the mask. We then departed to our scheduled destination without further incident; arriving about 45 minutes behind schedule.Preflight procedures need to be changed to require the oxygen masks be removed from their containers to ensure they are working properly. Had a smoke; fire; or pressurization event occurred; the First Officer would not have been able to use his hands other than to hold the mask in place. Donning the Observer mask would not have allowed him to reach the flight controls.
When the First Officer's O2 mask harness failed to inflate for donning B737-700 flight crew diverted to a nearby airport to have it replaced.