WIDEBODY FREIGHT ACFT SMOKE WARNING SYSTEM ACTIVATED REPEATEDLY AND FLT CREW DECLARED EMER. LNDG AT DIVERSION ARPT WAS UNEVENTFUL AND NO EVIDENCE OF FIRE WAS DISCOVERED.

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AFTER LEVELOFF; 40 MINS INTO THE FLT; THE CABIN SMOKE LEVEL 3 ALERT ILLUMINATED; ALONG WITH THE ACCOMPANYING AURAL ALERT. WE WENT ON OXYGEN AND ACCOMPLISHED THE CHKLIST; THEN DETERMINED THAT THIS WAS PROBABLY AN ERRONEOUS WARNING AS THERE WAS NO OTHER INDICATION OF SMOKE. FURTHER; THE WARNING WAS ON AND THEN OFF; THEN ON; ETC. ALONG WITH THIS ALERT WAS AN AFT LOWER CARGO HIGH TEMP ALERT; WHICH WENT AWAY AFTER ADJUSTING THE TEMP. THIS ALL WENT AWAY AFTER A FEW MINS; AND WE WERE SATISFIED THAT THERE WAS NO FIRE/SMOKE AND THAT IT WAS PROBABLY TEMP RELATED. NOTE: THE TEMP IN ZZZ WAS IN THE HIGH 90'S; AND WHEN WE ARRIVED AT THE AIRPLANE; THERE WAS NO AIR (APU OR AIR CART); YET THE GPU PWR WAS ON AND THE ACFT WAS VERY; VERY HOT. I KNOW IT IS NOT GOOD FOR A GLASS AIRPLANE TO GET THIS HOT AND WE DISCUSSED THIS AS WE TALKED ABOUT THESE WARNINGS. WE TALKED TO OUR DISPATCHER AND MAINT ON THE SAT PHONE. AT THIS POINT WE'D BEEN AIRBORNE FOR 46 MINS. ABOUT 15-20 MINS LATER; CABIN SMOKE (LEVEL 3) AGAIN ILLUMINATED BY THE AURAL WARNING; AND THIS TIME IT WOULD NOT GO AWAY. BY NOW; WE WERE ABOUT 90 MI OUT; AND WE MADE THE DECISION TO GET THE AIRPLANE ON THE GND. I STILL DIDN'T BELIEVE THERE WAS A FIRE; AS THERE WERE NO OTHER INDICATIONS (INCLUDING POKING MY HEAD IN THE BACK ACCESS DOOR - BOTH TIMES) BUT THE ALERT WOULD NOT GO AWAY. FURTHER; THE ALERT DID NOT STAY ON. IT WENT ON AND OFF; APPARENTLY RESETTING ITSELF; SO THE AURAL TONE WOULDN'T GO AWAY. SO; WE DECLARED AN EMER WITH ATC; AND HEADED TO ZZZ. OUR WT AT THIS POINT WAS 506000 LBS; AND WE DUMPED; AS NEAR AS I CAN CALCULATE; ABOUT 37000 LBS ON OUR WAY INTO ZZZ. THEY WERE TRYING TO GIVE US AN 8000 FT RWY; AND I DIDN'T WANT TO TAKE IT IN AT EXACTLY OUR MAX LNDG WT IF I DIDN'T HAVE TO; WHICH IS WHY I MADE THE DECISION TO DUMP DOWN BEYOND THE MAX LIMIT. IT TURNS OUT THAT THEY GAVE US RWY WITH 11000 FT; SO IT ALL WORKED OUT. THE FINAL FUEL TOTAL AFTER SHUTTING DOWN WAS 79000 LBS; AND I BELIEVE THE TKOF FUEL WAS 146100 LBS. I DIDN'T GRAB THE PAPERWORK UPON EXITING THE AIRPLANE - I KNOW I SHOULD HAVE BUT AT THIS POINT I'VE BEEN AWAKE 25 HRS; AND I DIDN'T THINK TO TAKE THE PACKET. THE ALERT STAYED; PROBABLY UNTIL SHORT FINAL; AND I THINK IT FINALLY WENT AWAY. WE DID DUMP THE CABIN AS THE CHKLIST LED US TO DO; AND THE WX WAS GOOD VFR. UPON LNDG; WE CLRED THE RWY RIGHT IN FRONT OF THE RAMP; THEN WAITED FOR THE CRASH TRUCKS TO CIRCLE THE AIRPLANE LOOKING FOR SMOKE. THEY DIDN'T SEE ANY; OF COURSE; SO WE RELEASED THEM AND TAXIED TO THE RAMP. MECHS CAME OVER AND QUICKLY DETERMINED THAT A MAIN CABIN SMOKE DETECTOR HAD FAILED; AND THAT'S WHAT CAUSED THE WHOLE EVENT. HE ALSO THOUGHT IT WAS NOT A GOOD IDEA TO LET THESE THINGS SIT ON THE RAMP IN THE HOT SUN WITH NOTHING TO COOL THE INSTS. THEY UNLOADED THE PLANE; UNPLUGGED AND DEFERRED THE OFFENDING SMOKE DETECTOR; LOADED AND FUELED BACK UP; AND CONTINUED ON.