Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Aircraft
I performed O2 mask test on the ground before the flight. While climbing through FL350 for FL370; I pulled out the O2 mask. Oxygen started flowing uncontrollably as if the emergency oxygen knob was turned on.I checked to make sure the emergency knob was in correct position and verified it to be working and not stuck. The 100% oxygen tab was also seemingly functional. As high pressure oxygen flow continued; we consulted the QRH; which directed to close the mask doors and engage the shut off tab; which is the tab used for mask/microphone test on the ground. This step stopped the oxygen flow; but the oxygen supply to my mask was cut by this action. We had 650PSI O2 left. After further consulting the QRH and discussing with FO; we decided to ask our flight attendant to pass the portable O2 bottle to us; requested descent to MEA (FL180; then 15000; followed by 14000 and 11500MSL) and continued to destination.  Reflecting on the event; and imagining a scenario when the mask would be needed due to rapid decompression  and malfunction like this happened; following our memory items; could have resulted in crew incapacitation. Our memory items call for masks to be donned and crew communication established before starting descent. Given the same malfunction; and assuming First Officer donned his mask; constant oxygen flow from Captain's mask would have been extremely distracting; and unless a decision was made to start the descent immediately the oxygen bottle content would be depleted very quickly; or if the flow was stopped; the Captain would have an inoperative mask.  I believe a training outlining how to handle a scenario of O2 mask malfunction during decompression; particularly emphasizing the method of quick O2 cut off to malfunctioning mask; and possibly using observer's mask if no observer is present may be useful and lifesaving.  Speculating further; it may be also useful to go over a scenario when one of the crew members initiates an emergency descent; if the other crew member can't don the oxygen mask for whatever reason during decompression event.
EMB-135 Captain reported a malfunctioning crew oxygen mask prompted a request for a lower cruise altitude.