ODOR IN B757-200 TURNS INTO SMOKE AND FIRE AFTER CABIN INSPECTION. EMER DECLARED DSCNT AND DIVERSION TO ALTERNATE.

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TO THE BEST OF MY RECOLLECTION THESE ARE THE FACTS SURROUNDING THE ABOVE NOTED FLT. WE WERE CRUISING AT FL370 WHEN ONE OF THE FLT ATTENDANTS ADVISED THE COCKPIT THAT THERE WAS AN UNUSUAL ODOR IN THE AFT CABIN. I SUGGESTED THAT PULLING THE CIRCUIT BREAKERS IN THE REAR GALLEY MIGHT DISSIPATE THE ODOR. SHORTLY THEREAFTER; THE FLT ATTENDANTS RPTED THE ODOR HAD DECREASED. SOMETIME LATER; THE FLT ATTENDANTS RPTED THAT THE ODOR WAS BACK. I PROCEEDED TO THE AFT CABIN TO SEE FOR MYSELF WHAT WAS TAKING PLACE. THE ODOR WAS PRESENT. AFTER RETURNING TO THE COCKPIT; WE ALSO LOWERED THE AFT CABIN TEMP. APPROX 5 MINS LATER THE FLT ATTENDANT RPTED THE ODOR WAS INCREASING AND THAT SMOKE WAS NOW COMING FROM THE FLOOR AND THAT FIRE WAS VISIBLE. I INSTRUCTED THE FO TO DECLARE AN EMER. WE BEGAN AN EMER DSCNT AND PROCEEDED TO THE NEAREST APPROPRIATE ARPT. ON FINAL APCH PRIOR TO LNDG; THE FLT ATTENDANTS RPTED THAT THEY HAD EXTINGUISHED THE FIRE; THAT THE SMOKE WAS GONE; AND THE CABIN WAS SECURED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT WAS A B757-200. THE POSTFLT INSPECTION AT THE DIVERSION ARPT; TERRE HAUTE; IN; FOUND THE SOURCE OF THE ODOR; SMOKE AND RESULTANT FIRE. IT WAS FROM A SHORT IN THE VIDEO EQUIP LINE UNDER SEAT ROWS XX AND YY IN THE AFT CABIN. THE CABIN ATTENDANT WAS ASSISTED BY A PAX IN SEAT ROW XX WHO RIPPED THE FLOOR VENT OUT OF THE WALL (THE SOURCE OF SMOKE) AND SPRAYED THE FIRE EXTINGUISHER INTO THIS AREA. THE CIRCUIT BREAKER PANEL IS LOCATED UNDER THE FLOORING OF THE ACFT AND IS NOT AVAILABLE TO THE CREW. IT WAS SURMISED THAT THERE WAS A DELAY IN THE ACTIVATION OF THE CIRCUIT BREAKERS IN DISCONNECTING THE ELECTRICAL PWR TO THESE LINES. THE CREW EXERCISED THE ABNORMAL AND EMER CHKLISTS THAT DEALT WITH FIRE AND SMOKE IN THE CABIN. THERE WAS NO CHKLIST THAT DEALT SPECIFICALLY WITH AN AUDIO OR VISUAL ELECTRICAL SYS AS SUCH. THE AIRLINE; AFTER THE POSTFLT INSPECTION; IMMEDIATELY HAD ALL B757 VIDEO SYS DEACTIVATED SUBJECT TO A FULL INSPECTION OF THE SYS. RPTR BELIEVES THAT THERE WAS A MODIFICATION TO THIS SYS BUT CAN'T BE CERTAIN. THE VIDEO SYS WAS AN 'ADD ON' ITEM AFTER THE ACFT HAD BEEN DELIVERED TO THE ORIGINAL ACR AND MAY OR MAY NOT HAVE MET THE AIRWORTHINESS STANDARDS OF THE FAA. IT WAS NOT A 'BOEING' ITEM. CAPT WAS VERY IMPRESSED WITH THE SPD OF THE AIRLINE MAINT DEPT IN CORRECTING THIS SIT. THE INITIAL ACTIONS TAKEN; THAT OF PULLING CIRCUIT BREAKERS FOR THE GALLEY AND LOWERING THE AFT CABIN TEMP WAS ASSOCIATED WITH A BELIEF THAT THE GALLEY WAS JUST PRODUCING AN ODOR AND THAT THE CABIN WAS ON THE WARM SIDE. RPTR STATED THAT THEY HAD A DIFFICULT TIME CONVINCING ATC THAT THEY WERE IN NEED OF A LOWER ALT AS ATC KEPT GIVING ALT RESTRS; NOT A DSCNT CLRNC. AS THE FLT WAS DSNDING THROUGH FL310; ATC WAS STILL ASKING THAT THEY MAINTAIN FL330. ONLY LATER DID THEY GIVE; WHEN REQUESTED; A VECTOR TO TERRE HAUTE. THERE WAS NO EMER EVAC SINCE THE RPT WAS GIVEN OF NO FIRE OR SMOKE BY THE CABIN ATTENDANT.