AN ACR SAAB-340 CREW HAD TO RETURN LAND WHEN THEY HAD AN ACFT EQUIP PROB FALSE CARGO COMPARTMENT FIRE WARNING. EMER DECLARED.

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CLBING OUT OF NY AREA TOWARD MERIT INTXN; CARGO SMOKE WARNING ILLUMINATED AS WE CLBED THROUGH 5000 FT. MEMORY ITEMS AND 'CARGO SMOKE CHKLIST' WERE DONE IN LESS THAN A MIN. WARNING LIGHT EXTINGUISHED CONSPICUOUSLY EARLY (JUST AFTER I ACTIVATED FIRE EXTINGUISHER). I DECLARED EMER AND REQUESTED RETURN TO JFK. FO FLEW APCH AND LNDG. UPON CLRING THE RWY 4R HOLD LINE; THE ACFT WAS STOPPED; AND WE HAD THE FLT ATTENDANT OPEN THE CABIN DOOR. I DIDN'T WANT TO EVACUATE IF THERE WAS NO FIRE. FLT ATTENDANT RPTED NO HEAT OR SMOKE OR FUMES JUST BEFORE WE FLEW APCH. NOW; JUST AFTER STOPPING AND SHUTTING DOWN ENGS; THE CFR PEOPLE CONFIRMED NO FIRE; SO WE SENT THE PAX TO THE TERMINAL IN VANS. (NORMAL DEPLANING; NO EVAC.) LUGGAGE AND CARGO COMPARTMENT WAS RECHKED; THEN ACFT TAXIED TO COMPANY PARKING AREA. MY SAFETY CONCERN WAS THAT WE WERE ONTO THE LAST STEPS TO EVAC FOR A BOGUS WARNING LIGHT. IT IS A COMMON SAAB-340 PROB IN HUMID WX. HAD I NOT PAUSED TO BE SURE AN EVAC WAS NEEDED; PAX WOULD HAVE BEEN COMMANDED TO JUMP OUT OF THE ACFT ONTO A WET AND SLIPPERY TXWY NEXT TO A STILL OPEN RWY. SO IF THEY GET OUT WITHOUT INJURY; THEY COULD (IN THE HEAT OF THE MOMENT) VENTURE INTO HARM'S WAY ON RWY 4R. I THINK BETTER FIRE DETECTION IS NEEDED TO PREVENT THESE SCENARIOS; AND TFC NEEDS TO BE MOVED TO ANOTHER RWY TO ELIMINATE RISKS OF PAX-AIRPLANE COLLISIONS. MERELY EVACING HAD SOME INJURY RISKS DUE TO THE CABIN-FLOOR TO GND DISTANCE AND THE SLICK AND WINDY SURFACE CONDITIONS. I FEAR THAT SOMEONE WILL ONE DAY EVAC FOR A BOGUS CARGO SMOKE WARNING AND INJURIES WILL RESULT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR'S SAAB-340 WAS EQUIPPED BOTH WITH CARGO COMPARTMENT FIRE DETECTION AND SUPPRESSION. THE RPTR FIRED THE FIRST BOTTLE AS REQUIRED BY THE CHKLIST. HIS ACFT HAS ONLY 1 FIRE BOTTLE; WHILE OTHERS WITH HIS ACR HAVE 2. THE RPTR WAS RELUCTANT TO EVAC ON THE RWY AS THE SAAB DOES NOT HAVE SLIDES. ITS FLOOR HT IS JUST BELOW THAT HT WHERE SLIDES ARE REQUIRED. IN SAAB TRAINING; A PROB WITH FALSE CARGO FIRE WARNINGS WAS MENTIONED; ESPECIALLY ON HIGH HUMIDITY DAYS WITH TEMPS IN THE REGION OF 50 DEGS F. SOME SAAB ACFT HAVE A DUAL SENSOR SYS IN AN ATTEMPT TO ALLEVIATE THIS PROB ALONG WITH A TAIL CONE VENT SYS THAT BRINGS AIR CONDITIONING INTO THE CARGO COMPARTMENT BEFORE IT GOES THROUGH THE CABIN. THE RPTR FILED AN IRREGULARITY RPT WITH HIS ACR. HE HAS HEARD NOTHING EITHER FROM HIS ACR OR THE FAA ON THIS. THE RPTR'S ACFT HAD A DUAL SENSOR SYS WHICH WAS CHANGED BY ACR MAINT.