Narrative:

We departed out of ZZZ1 in clear WX. A large WX system was directly west of the airport; so our routing was to the north; until clear of the WX; then west to ZZZ. After about 10 minutes; we experienced sustained moderate turbulence as we were passing a WX cell to our left. Although we gave it a wide berth; according to what we could see on our radar; we were still encountering a very rough ride and a lot of lightning around us. The autoplt would not stay on; due to the turbulence; even when we were well past the cell as it was painting on our radar. We were at 34000 ft. Just as the ride calmed down enough to put the autoplt back on; and we were turning towards ZZZ; the cabin altitude warning horn sounded. The cabin was at 11000 ft. We donned our oxygen masks. This is where it gets fun. My mask immediately started fogging up; and the microphone didn't work. I asked the first officer to put the pressurization system in standby to see if we could catch it at 11000 ft. He couldn't hear me. In addition to the normal frenzy of this event; not being able to communicate was horrible. We did get the pressurization switched to standby; but it would not move the valve. The cabin stayed at 11000 ft; climbing slowly. We declared an emergency and started an emergency descent. As we descended the cabin stabilized at 11000 ft. We were not able to move the outflow valve until about 8000 ft. During the descent; we spoke to the flight attendants; dispatch; and ATC. ZZZ2 seemed to be the logical place to go. An important note: I was not aware that I was not transmitting at all on my mask (yes the switch was in 'mask') so when I rang three bells for the flight attendants; they all came to their interphones; but could not hear me. I was frustrated because I realized they could not hear me; and they were now very concerned because we called them and weren't on the other end of the interphone. When the mechanics looked at the oxygen mask; they found a wire that was shorting. The mask would test in its storage unit; but would only transmit in certain positions. As a result; I had to pick up the telephone interphone on the center console and move my mask out of the way to talk to them. Eventually; I just slid my headset microphone under the mask to communicate. Overall; the performance of these masks is unacceptable. It made this emergency almost unmanageable.callback conversation with reporter revealed the following information: reporter stated that the mask checked correct on preflight and the microphone and intercom worked. During the event; the mask fogged up and the interphone didn't work. Post flight inspection revealed a short in the microphone lead and when the mask was deployed; it caused the short to occur. The preflight check did not reveal the short as the mask was stowed and was not moved for the preflight. Reporter stated that it appeared to be an anomaly and that maintenance indicated that this was a rare occurrence.

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Original NASA ASRS Text

Title: B737-300 FLT CREW HAS PRESSURIZATION LOSS WHILE AT CRUISE; DECLARES AN EMER AND DOES EMER DSCNT.

Narrative: WE DEPARTED OUT OF ZZZ1 IN CLR WX. A LARGE WX SYSTEM WAS DIRECTLY W OF THE ARPT; SO OUR ROUTING WAS TO THE N; UNTIL CLR OF THE WX; THEN W TO ZZZ. AFTER ABOUT 10 MINUTES; WE EXPERIENCED SUSTAINED MODERATE TURB AS WE WERE PASSING A WX CELL TO OUR L. ALTHOUGH WE GAVE IT A WIDE BERTH; ACCORDING TO WHAT WE COULD SEE ON OUR RADAR; WE WERE STILL ENCOUNTERING A VERY ROUGH RIDE AND A LOT OF LIGHTNING AROUND US. THE AUTOPLT WOULD NOT STAY ON; DUE TO THE TURB; EVEN WHEN WE WERE WELL PAST THE CELL AS IT WAS PAINTING ON OUR RADAR. WE WERE AT 34000 FT. JUST AS THE RIDE CALMED DOWN ENOUGH TO PUT THE AUTOPLT BACK ON; AND WE WERE TURNING TOWARDS ZZZ; THE CABIN ALT WARNING HORN SOUNDED. THE CABIN WAS AT 11000 FT. WE DONNED OUR OXYGEN MASKS. THIS IS WHERE IT GETS FUN. MY MASK IMMEDIATELY STARTED FOGGING UP; AND THE MICROPHONE DIDN'T WORK. I ASKED THE FO TO PUT THE PRESSURIZATION SYSTEM IN STANDBY TO SEE IF WE COULD CATCH IT AT 11000 FT. HE COULDN'T HEAR ME. IN ADDITION TO THE NORMAL FRENZY OF THIS EVENT; NOT BEING ABLE TO COMMUNICATE WAS HORRIBLE. WE DID GET THE PRESSURIZATION SWITCHED TO STANDBY; BUT IT WOULD NOT MOVE THE VALVE. THE CABIN STAYED AT 11000 FT; CLBING SLOWLY. WE DECLARED AN EMER AND STARTED AN EMER DSCNT. AS WE DSNDED THE CABIN STABILIZED AT 11000 FT. WE WERE NOT ABLE TO MOVE THE OUTFLOW VALVE UNTIL ABOUT 8000 FT. DURING THE DSCNT; WE SPOKE TO THE FLT ATTENDANTS; DISPATCH; AND ATC. ZZZ2 SEEMED TO BE THE LOGICAL PLACE TO GO. AN IMPORTANT NOTE: I WAS NOT AWARE THAT I WAS NOT TRANSMITTING AT ALL ON MY MASK (YES THE SWITCH WAS IN 'MASK') SO WHEN I RANG THREE BELLS FOR THE FLT ATTENDANTS; THEY ALL CAME TO THEIR INTERPHONES; BUT COULD NOT HEAR ME. I WAS FRUSTRATED BECAUSE I REALIZED THEY COULD NOT HEAR ME; AND THEY WERE NOW VERY CONCERNED BECAUSE WE CALLED THEM AND WEREN'T ON THE OTHER END OF THE INTERPHONE. WHEN THE MECHANICS LOOKED AT THE OXYGEN MASK; THEY FOUND A WIRE THAT WAS SHORTING. THE MASK WOULD TEST IN ITS STORAGE UNIT; BUT WOULD ONLY XMIT IN CERTAIN POSITIONS. AS A RESULT; I HAD TO PICK UP THE TELEPHONE INTERPHONE ON THE CENTER CONSOLE AND MOVE MY MASK OUT OF THE WAY TO TALK TO THEM. EVENTUALLY; I JUST SLID MY HEADSET MIKE UNDER THE MASK TO COMMUNICATE. OVERALL; THE PERFORMANCE OF THESE MASKS IS UNACCEPTABLE. IT MADE THIS EMER ALMOST UNMANAGEABLE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE MASK CHKED CORRECT ON PREFLT AND THE MICROPHONE AND INTERCOM WORKED. DURING THE EVENT; THE MASK FOGGED UP AND THE INTERPHONE DIDN'T WORK. POST FLT INSPECTION REVEALED A SHORT IN THE MICROPHONE LEAD AND WHEN THE MASK WAS DEPLOYED; IT CAUSED THE SHORT TO OCCUR. THE PREFLT CHK DID NOT REVEAL THE SHORT AS THE MASK WAS STOWED AND WAS NOT MOVED FOR THE PREFLT. RPTR STATED THAT IT APPEARED TO BE AN ANOMALY AND THAT MAINT INDICATED THAT THIS WAS A RARE OCCURRENCE.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.