Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 413; Flight Crew Type 7000
Troubleshooting; Workload; Distraction; Time Pressure
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted; Flight Crew Overcame Equipment Problem
Aircraft; Equipment / Tooling; Human Factors
During crew bathroom break at FL390; I attempted to put on my oxygen mask as the F/O (First Officer) was leaving the flight deck. One of the red quick don toggles broke as I was putting on the mask. Oxygen was continuously flowing out of the broken area where the toggle use to be. I was able to stop the flow by closing the mask door and pressing the reset. I took the second observer mask to use while the F/O was out. The mask barely reached the Captains seat and also didn't allow for establishing communications in the event of a pressurization issue. I contacted Dispatch and Chief Pilot Operations Center to discuss the issue and decided the safest course of action was to descend and divert. Dispatch recommended [an alternate] and FL 190 so we would be below landing weight. Upon further consideration the safest course would have been to descend directly to 10;000 ft. We accomplished the divert and landing with no further issues.
B737 Captain reported an inflight failure of the oxygen mask toggle switch; necessitating a descent and diversion to a suitable airport.