FLC OF C550 HAS A DOOR SEAL FAIL INFLT CAUSING RAPID DECOMPRESSION. DONNING OXYGEN MASKS; THEY HAVE DIFFICULTY COMMUNICATING WITH EACH OTHER AND WITH ATC.

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IN CRUISE FLT AT FL370 THE MAIN CABIN DOOR SEAL FAILED CAUSING A RAPID DECOMPRESSION. WE IMMEDIATELY DONNED OUR OXYGEN MASKS AND INITIATED THE EMER PROCS FOR OUR ACFT. FROM THE MOMENT WE DETECTED A DOOR SEAL NOISE TO THE POINT THE SEAL COMPLETELY FAILED WAS ABOUT 10 SECONDS. DURING THE EMER PROCS THE PNF AND I HAD DIFFICULT COMS DUE TO POOR QUALITY MIKE IN THE MASKS. ADDITIONALLY; AFTER 3 OR 4 ATTEMPTS BY THE PNF TO CONTACT ZAB AND DECLARE THE EMER; AN AIRLINER ON FREQ STEPPED IN AND SAID TO THE CTLR 'I THINK THEY'RE HAVING A PRESSURIZATION PROB; YOU BETTER CLR THEM ON DOWN.' WE ALREADY WERE SQUAWKING 7700; SO WE WERE CERTAIN THAT CTR WAS AWARE THERE WAS SOME TYPE OF EMER IN PROGRESS. ONCE SAFELY DOWN FROM ALT; THE PNF WENT AND CHKED ON OUR 4 PAX IN BACK -- EVERYBODY WAS OK. WE LANDED AT THE NEAREST SUITABLE ARPT WITHOUT FURTHER EVENT. FLYING DIFFERENT AIRPLANES AT TIMES; I WILL ALWAYS TAKE SOME EXTRA TIME TO CHK THE WORKING ORDER OF MIKES IN OXYGEN MASKS TO INSURE GOOD CREW COMS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE ACFT IS A CE550; CESSNA CITATION II. THE MASKS IN USE WERE THE QUICK- DONNING MASKS. RPTR BELIEVES THEY ARE THE OLD CARBON TYPE MIKE WHICH MAY BE AFFECTED BY HEAT AND MOISTURE FROM BREATHING AND THUS DEGRADED OVER TIME. TO TEST THE MIKES DURING PREFLT; BOTH CREW MEMBERS WOULD DON THE MASKS AND FLIP THE HAND SWITCH TO INTERCOM AND SPEAK TO TEST THE QUALITY OF THE XMISSIONS. BECAUSE OF THIS INCIDENT THE COMPANY HAS UPGRADED THE OXYGEN MASKS IN ITS ACFT. THE NEW ONES ARE SMALL AND COMPACT AND ARE TIGHT FITTING. THEY SQUEEZE ONTO THE FACE WITH A RUBBER BAND TYPE SEAL THAT IS TRIGGERED TO FIT TIGHT; AND HAVE A NEWER ELECTRICAL MIKE.