Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 6
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Landed in Emergency Condition; General Declared Emergency; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Chart Or Publication; Human Factors; Procedure
Maintenance had replaced crew O2 bottle and First Officer Mask Regulator in ZZZ. [We were] approaching an intersection; arranged for a bathroom break. First Officer found his oxygen inoperative and the crew bottle at zero. Coordinated for a descent and ran QRH. Procedure is under MISC and is not in index [of QRH]. Suggest it be added to [QRH] index under 'O': Oxygen System malfunction. Declared an emergency and we were cleared direct to ZZZ1. Landed without incident; cancelled Emergency on landing. Taxiied to gate. Aircraft Out of Service (OTS). Leak was slow enough it was not possible for crew to detect before takeoff. If crew O2 bottle has been replaced two days in a row. Delay departure for a period of time before release for Crew O2 Leak Check. Airline Transport Pilot (ATP).
In cruise; FL300; approximately 150 miles east of ZZZ; I noticed the crew O2 supply was depleted. Informed Captain who declared an emergency; we executed QRH actions. Landed safely at ZZZ.
A Captain and First Officer report about the loss of their crew O2 bottle pressure that read 'Zero' in cruise at FL300. Maintenance had replaced the crew O2 bottle and First Officer's oxygen mask regulator on their MD-83 aircraft prior to departure.