MD80 FA DID NOT DISARM HER ASSIGNED DOOR UPON ARRIVAL AT THE GATE. THE DOOR SLIDE WAS ACCIDENTALLY DEPLOYED.

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CHIEF PURSER AND I BOARDED MD80 ACFT APPROX 40 MINS PRIOR TO DEP. CHKED EMER EQUIP AND ACFT FAMILIARIZATION DUE TO THE FACT THE MD80 IS NOT AN ACFT THAT IS BASED AT MY DOMICILE AND MY INITIAL TRNG WAS 14 YRS AGO. THIS HAS BEEN THE ONLY TRNG EXCEPT FOR DOOR AND WINDOW REVIEW IN RECURRENT TRNG. DURING MY REVIEW THE AIR MARSHALS BOARDED AND BEGAN THEIR BRIEFING. FIVE MINS INTO THE BRIEFING THE CAPT BOARDED AND JOINED BRIEFING. IMMEDIATELY AFTER THE BRIEFING; BOARDING COMMENCED. THE CAPT WAS NOT ABLE TO GIVE HIS BRIEFING DUE TO BOARDING. AT DOOR CLOSURE THE PURSER ARMED 1L DOOR AND I ARMED 1R DOOR AND WE CROSS CHECKED. AFTER THE SAFETY DEMO I OCCUPIED THE FORWARD INBOARD JUMP SEAT. UPON ARRIVAL THE PURSER MADE THE DOOR ARRIVAL ANNOUNCEMENT AND I DISARMED 1R DOOR AND WE CROSSCHECKED. THE PAX DEPLANED AND WE PROCEEDED TO THE NEXT GATE. WE WERE THEN INFORMED OF THE SLIDE DEPLOYMENT. WE NOW REALIZE THAT I HAD OCCUPIED THE WRONG JUMP SEAT. I FEEL THE FOLLOWING WERE CONTRIBUTING FACTORS: THIS ACFT IS NOT BASED AT MY DOMICILE NOR DO WE EVER FLY THIS EQUIP. OUR ONLY ONGOING TRNG ON EQUIP ARE DOOR AND WINDOW OPERATION DURING RECURRENT TRNG. EQUIP FAMILIARITY AND BRIEFING WITH AIR MARSHALS TOOK UP ALL TIME TILL BOARDING. THE AIR MARSHAL PROGRAM IS NEW TO US AND THE INFO EXTREMELY IMPORTANT; OUR ATTENTION WAS DIRECTED AND POSSIBLY DISTRACTED BY THIS PROC. ALL ACFT BASED AT MY DOMICILE HAVE SIMILAR JUMP SEAT ASSIGNMENTS. DUE TO ABOVE DISTRACTION WE ASSUMED THESE POSITIONS BASED ON OUR NORMAL PROCEDURES ON OTHER ACFT ASSIGNED TO OUR BASE. SINCE THIS ACFT WAS SUBSTITUTED FOR ONLY ONE FLIGHT SEGMENT I WOULD LIKE THE COMPANY EITHER CONTACT US BY PHONE OR MAIL OF THIS FACT AND MAKE US AWARE OF THE DIFFERENT PROCS.