WIDEBODY CARGO ACFT IS SPRAYED WITH DISINFECTANT; RESULTING IN ACTIVATION OF CARGO FIRE WARNING SYSTEM.

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WHILE REVIEWING THE DEP PAPERS FOR THE FLT WE NOTICED THAT THE ACFT WOULD BE SPRAYED WITH DISINFECTANT UNDER A FLT OPS BULLETIN LABELED 'DISINFECTANT SPRAY PROCS.' NO NOTIFICATIONS WERE GIVEN OF POSSIBLE FIRE ALERTS CAUSED BY THIS SPRAYING OF DISINFECTANT. THE ACFT WAS IN THE CHOCKS WITH THE APU RUNNING AND THE APU AIR ON OPERATING ALL 3 AC PACKS. THE LOAD SUPVR CAME INTO THE COCKPIT AND NOTIFIED ME THAT THEY WERE READY TO START SPRAYING THE DISINFECTANT AND THAT WE SHOULD TURN OFF OUR PACKS. WE THEN TURNED OFF THE APU AIR AND HAVING MOST OF OUR PREFLT DUTIES COMPLETE WAITED IN THE ACM AREA OF THE ACFT WITH THE CABIN L DOOR OPEN. PERSONNEL AFTER A WHILE; CAME BACK UP THE STAIRS CARRYING A PLASTIC BAG WITH 4 RED CAPPED DISINFECTANT CANS WHICH HE PLACED ON ONE OF THE COURIER SEATS. THE SAME LOAD SUPVR WHO HAD TOLD ME TO TURN OFF THE PACKS THEN TOLD ME IT WAS NOW OK TO TURN THE PACKS ON. THE FO AND I CLBED BACK INTO OUR SEATS AND WAITED FOR THE LOAD MANIFEST TO ARRIVE. WE ACTIVATED APU AIR TURNING ON THE PACKS FOR THE ENTIRE ACFT AT THAT TIME. I WAS HANDED THE LOAD MANIFEST WITH A LOAD COMPLETE TIME LISTED BY THE LOAD SUPVR. I HAD THE SD ON THE MISC PAGE AND NOTICED THAT THE LOWER AFT CARGO DOOR WAS STILL OPEN AND ALTHOUGH I HAD THE LOAD MANIFEST; IT SEEMED GND PERSONNEL WERE STILL LOADING THE ACFT. WHILE I WAS REVIEWING THE DATA ON THE LOAD MANIFEST BOTH THE FO AND MYSELF HEARD AN AUDIBLE TONE ALERT. I ASKED WHAT WAS THAT; BUT NEITHER ONE OF US HAD NOTICED ANY ALERTS OR WARNINGS DISPLAYED. I LOOKED AT THE FIRE WARNING DISPLAY AND THERE WERE NO INDICATIONS SHOWN. WITH NEITHER ME OR THE FO KNOWING WHAT CAUSED THE QUICK MOMENTARY AUDIBLE ALERT TONE I CONTINUED WITH THE REVIEWING THE LOAD MANIFEST AND LOADING THE INFO INTO THE FMS. APPROX 20 SECONDS LATER THE AUDIBLE TONE CAME BACK AND THIS TIME WITH A LEVEL 3 CARGO FIRE LOWER AFT DISPLAYED ON THE FIRE WARNING DISPLAY ALONG WITH A FLASHING CARGO FIRE AGENT DISCHARGE SWITCH AFT1. I DID NOT PUSH THE FLASHING CARGO FIRE DISCHARGE SWITCH AS THE MEMORY ITEMS FOR THIS ALERT REQUIRE; AS I ASSUMED I HAD GND PERSONNEL INSIDE THIS CARGO HOLD AND DID NOT WANT TO SUFFOCATE THEM. THE LEVEL 3 ALERT WENT AWAY BUT A LEVEL 1 ALERT 'DISCHARGE CARGO AGENT' AND THE AFT1 FLASHING CARGO DISCHARGE SWITCH CONTINUED FLASHING. AT THIS POINT I SENT THE RELIEF PLT WHO WAS IN THE COCKPIT ALSO BACK TO GET WHOEVER WAS IN THAT CARGO BAY OUT OF THE ACFT. THE FO ASKED IF HE SHOULD CALL FOR THE FIRE TRUCKS. I THOUGHT FOR A FEW SECONDS AND DECIDED THAT YES I HAD A FIRE ALERT AND THAT CALLING FOR THE FIRE TRUCKS WOULD BE THE SAFEST COURSE OF ACTION. THE FO CALLED GND CTL REQUESTING THE FIRE TRUCKS AND THEN CALLED OPS INFORMING THEM OF THE PROB. THE FO AND I THEN EVACED THE ACFT GOING DOWN THE STAIRS. I IMMEDIATELY WENT OVER TO MAINT AND TOLD THEM WHAT WAS HAPPENING. I WAS TOLD BY MAINT PERSONNEL THAT MOST LIKELY WHAT HAD HAPPENED WAS THE SPRAYING OF THE DISINFECTANT HAD TRIPPED OFF THE ALERT AND THERE WAS REALLY NO PROB; ALSO STATING THAT THIS HAD HAPPENED BEFORE IN THE PAST. I TOLD THEM THAT THE FIRE TRUCKS WERE COMING. I WOULDN'T ACCEPT THAT IT HAD HAPPENED BEFORE ANSWER. I FELT THAT THE SAFEST COURSE OF ACTION WAS TO HAVE FIRE PERSONNEL INSPECT THE ACFT. I DIDN'T NOTICE IT BUT GND CREW AT THIS TIME CLOSED THE CARGO DOOR WHILE I WAS TALKING TO THE MECHS. WHEN THE FIRE TRUCKS ARRIVED ON THE SCENE THE FIRE RESCUE PERSONNEL TALKED TO THE MECHS WHILE THE CREW AND I WAITED NEAR THE FRONT OF THE ACFT. THE FIRE CHIEF CAME UP TO ME AND TOLD ME THAT THE MECHS HAD INFORMED HIM THAT THEY THOUGHT THE SPRAYING OF THE DISINFECTANT HAD CAUSED THE CARGO FIRE LWR ALERT. THE FIRE CHIEF HAD NOT AT THIS TIME OPENED THE AFFECTED CARGO HOLD TO INSPECT IT. THE FIRE CHIEF SEEMED WILLING TO TAKE THE MECH'S VIEW AND CLR THE ACFT. I TOLD THE FIREMAN TO OPEN THE HOLD AND INSPECT IT FOR FIRE. HE LEFT AND THEN OPENED THE AFFECTED CARGO BAY LOOKING INSIDE AND FINDING NO SIGNS OF FIRE OR SMOKE DAMAGE. THE FIRE CHIEF CAME BACK TO ME AND MY CREW CLRING THE ACFT. MY CREW AND I BOARDED THE ACFT WITH THE MECHS AND SHOWED THEM THE FLASHING FIRE AGENT DISCHARGE SWITCH ON THE OVERHEAD PANEL. THE MECHS THEN TRIED TO RESET THE LIGHT WITH A CARGO FIRE TEST. THIS DID NOT WORK. THEN THE MECHS PULLED AND RESET A CIRCUIT BREAKER CLRING THE LEVEL 1 ALERT OF DISCHARGE CARGO AGENT AND ELIMINATING THE FLASHING DISCHARGE SWITCH AFT1. I SAT DOWN AND FINISHED INPUTTING THE LOAD MANIFEST INTO THE FMS. I WAS CONCERNED WITH NOW MINIMIZING ANY MORE DELAYS AND THINKING THAT SINCE THE ALERT WAS A FALSE ALARM CAUSED BY A KNOWN PROB THAT A LOGBOOK WRITE-UP WAS NOT REQUIRED. IF I HAD TO DO IT AGAIN I WOULD WRITE THE EVENT UP IN THE LOGBOOK.