AT72 CREW HAD AN 'ELECTRIC SMOKE' WARNING AFTER BEING DEICED WITH TYPE 1 GLYCOL DEICING FLUID.

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WE WERE DEICED WITH TYPE 1 FLUID TO REMOVE MORNING FROST. I ASKED THE FO TO TURN ENG BLEED AIR VALVES TO OFF POS FOR A FEW MINS AFTER ENG START; TO PREVENT CABIN SMOKE IN CASE OF GLYCOL INGESTION. AFTER ENGS WERE RUN FOR A FEW MINS; THE BLEED VALVES WERE RETURNED TO THE NORMAL 'ON' POS. WE TAXIED FOR ABOUT 5 MINS AND CONDUCTED A ROUTINE ENG TEST AT THE END OF RWY 11. WE DEPARTED BMI WITHOUT ANY PROBS. ABOUT 10-15 MINS AFTER TKOF; WE OBSERVED AN ELECTRIC SMOKE CAPTION ALONG WITH MASTER WARNING AND REPETITIVE CHIME. IN THE ATR; AN ELECTRIC SMOKE CAPTION CAN MEAN EITHER A FIRE IN THE AVIONICS COMPARTMENT OR SMOKE IN THE ENVIRONMENTAL CTL SYS; DEPENDING ON THE ORDER THAT SMOKE IS SENSED BY THE CREW IN RELATION TO THE ACTIVATION OF THE CAPTION. SINCE NEITHER MY FO; BOTH FLT ATTENDANTS; NOR MYSELF SMELLED OR OBSERVED ANY SMOKE PRIOR TO THE CAPTION ACTIVATION; WE DETERMINED THE WARNING TO BE AN AVIONICS FIRE RATHER THAN SMOKE FROM OUR AIR CONDITIONING SYS. THEREFORE; I CALLED FOR THE ELECTRIC SMOKE CHKLIST RATHER THAN THE AIR CONDITIONING SMOKE CHKLIST. AFTER SHUTTING DOWN THE LISTED SYS IN THE CHKLIST; THE SMOKE DETECTOR CONTINUED TO SEND AN ELECTRIC SMOKE WARNING. WE NOTIFIED PEORIA DEP OF OUR PROB INDICATION; BUT NO APPARENT SMOKE; AND OUR NEED FOR A PRECAUTIONARY RETURN TO BMI. A TURN AND DSCNT WAS ISSUED AND EXECUTED IMMEDIATELY. SINCE THE ALERT WAS STILL ACTIVE; THE FO ALSO RAN THROUGH THE AIR CONDITIONING SMOKE CHKLIST. JUST PRIOR TO LNDG; THE FIRE SYS STOPPED SENSING SMOKE AND THE ALERT DISAPPEARED. WE LANDED IN BMI WITHOUT INCIDENT AND; SINCE NONE OF US SMELLED OR SAW ANY SMOKE; WE DISMISSED THE FIRE TRUCKS AND DEPLANED THE PAX IN A NORMAL FASHION AT OUR GATE. I WROTE UP THE DISCREPANCY IN THE ACFT LOGBOOK AND CALLED COMPANY MAINT AND DISPATCH. A COMPANY MECH WAS DISPATCHED ON THE NEXT FLT TO BMI. AFTER RUNNING BOTH ENGS FOR ABOUT 10 MINS WITHOUT ANY WARNING GENERATED AND NO FIRE DAMAGE OBSERVED; HE DETERMINED THAT THE ALERT MUST HAVE BEEN TRIGGERED BY EXCESS GLYCOL IN THE ENG. HE SIGNED OFF THE DISCREPANCY CORRECTIVE ACTION COLUMN AND WE DEPARTED BMI WITHOUT INCIDENT.