A320 FLC REPORTED AN EMER EVAC SLIDE DETACHED FROM AFT L SVC DOOR DURING ACFT CATERING.

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AN EMER ESCAPE SLIDE INADVERTENTLY DETACHED FROM AFT L SVC DOOR UPON ARR IN GRAND CAYMAN (MWCR). OUR COMPANY'S PROC IS FOR THE AFT FLT ATTENDANTS TO DISARM AND XCHK EACH OTHER ON SLIDE DISARMAMENT. A FURTHER CHK FOR DISARMAMENT IS DONE IN THE COCKPIT DURING THE 'PARKING AND SECURING' CHKLIST; WHERE THE SLIDE ARMING DISPLAY IS CHKED BY THE CAPT. THERE WAS AN MEL ITEM ON OUR 'ELECTRICAL EQUIP VENTILATION;' AND ONCE WE ARRIVED AT THE GATE; AN UNEXPECTED HORN WAS SOUNDING IN THE NOSEWHEEL AREA. I WAS DISTRACTED BY THE HORN; AND EXITED THE COCKPIT TO CHK OUT THE HORN. I NEVER CALLED FOR THE CHKLIST. THE DISTR WAS ENOUGH TO HINDER MY NORMAL FLOWS. THE SLIDE NEVER INFLATED; AS ITS ARMING WAS NOTICED BY A CATERING STAFF MEMBER AS HE ATTEMPTED TO OPEN THE DOOR FROM THE INSIDE (HIS VERSION). I RECEIVED SEVERAL VERSIONS OF THE ARM/DISARM HANDLE POS; AND NONE OF THEM SEEM TO BE SIMILAR. IT IS IMPOSSIBLE TO ASCERTAIN; FROM THOSE INVOLVED; WHETHER OR NOT THE DOOR WAS LEFT ARMED; OR WHETHER THE CATERING STAFF INADVERTENTLY ARMED IT BEFORE OPENING THE DOOR. WHAT IS CERTAIN; IS THAT THE DISTR OF MYSELF AND THE FO CAUSED BY THE UNEXPECTED SOUNDING OF THE HORN BELOW; PRECIPITATED A FAILURE TO READ A CHKLIST WHICH WOULD HAVE ASSURED ME THAT ALL INDICATIONS SHOWED A DISARMED ESCAPE SLIDE.