B767-300 CABIN CREW INADVERTENTLY OPENS AN ARMED DOOR; THE SLIDE PACK FALLS OUT BUT DOES NOT INFLATE.

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THE AIRPLANE ARRIVED AT GATE AT LAX WITHOUT INCIDENT. THE R ENG WAS SHUT DOWN DURING TAXI IN TO THE GATE AND THE PARKING BRAKE WAS SET. AFTER LNDG FLOWS WERE COMPLETED WITH THE L ENG STILL RUNNING AWAITING EXTERNAL PWR (THE APU WAS NOT RUNNING). I HEARD A RATHER UNUSUAL LOUD BANG WHEN THE FORWARD ENTRY DOOR WAS OPENED. I LOOKED AT THE OVERHEAD LIGHT PANEL AND SAW AN ENTRY DOORS LIGHT ILLUMINATED. EXTERNAL PWR WAS AVAILABLE SHORTLY THEREAFTER; SELECTED; THE L ENG SECURED; AND THE PARKING CHKLIST COMPLETED. I OPENED THE COCKPIT DOOR AND FOUND THE PURSER VERY CONCERNED THAT SHE HAD ACCIDENTALLY OPENED DOOR 1L WHILE IT WAS STILL ARMED. THE DOOR HAD OPENED AND THE SLIDE PACK HAD FALLEN OUT ONTO THE JETWAY WHICH HAD BEEN STOPPED APPROX 2 FT AWAY. IT WAS STILL CONNECTED TO THE ACFT BUT DID NOT INFLATE. I THEN INSTRUCTED EVERYONE TO BACK UP AND STAY AWAY FROM THE DOOR AND ASKED THE PURSER TO GO INTO THE COCKPIT TO STAY SAFE. I INFORMED THE FO WHAT HAPPENED AND ASKED HIM TO CALL MAINT IMMEDIATELY. MAINT ARRIVED IN ABOUT 3-5 MINS AND SECURED THE SLIDE SO IT WOULDN'T INFLATE. WE THEN ASKED FOR AIR STAIRS TO DEPLANE THE PAX. AT FIRST THEY ATTEMPTED TO APCH DOOR 1R FOR DEPLANING WITH THE STAIRS AND I SUGGESTED 2R INSTEAD. ALL PAX WERE DEPLANED; NOBODY INJURED; AND THE SLIDE DID NOT DEPLOY. THE PURSER HAD BEEN VERY PROFESSIONAL AND COMPETENT DURING THE ENTIRE FLT AND WAS VERY UPSET ABOUT THE INCIDENT.