B777 GND CREW; WHILE PERFORMING MAINT ON AN EMER DOOR SLIDE; INADVERTENTLY ACTIVATES THE SLIDE AND INJURIES OCCUR TO ONE OF THE PERSONNEL.

Narrative

SHORTLY AFTER ARRIVING AT THE ACFT; I LEARNED OF A PROB WITH THE OP OF DOOR 5L. AFTER BRIEFING THE PURSER FOR THE FLT; I MADE MY WAY THROUGH THE AIRPLANE TO INTRODUCE MYSELF TO THE OTHER FLT ATTENDANTS. WHILE APCHING THE REAR CABIN; I OBSERVED MECHS WORKING ON THE DOOR AT 5L. THE SLIDE PACK COVER WAS REMOVED AND THE DOOR WAS CRACKED OPEN. 2 MECHS WERE LYING ON THE FLOOR ON BOTH SIDES OF THE DOOR HOLDING UP WHAT APPEARED TO BE THE GIRT BAR OF THE SLIDE WHILE OBSERVING THE OP OF THE MECHANISM MOVEMENT AT THE BOTTOM OF THE DOOR. A THIRD MECH WAS MOVING THE HANDLE AT THE DIRECTION OF THE OTHER 2 MECHS. ONE OF THE MECHS ON THE FLOOR ASKED THE STANDING MECH TO ARM THE DOOR AND MOVE THE HANDLE. AT THIS POINT; I TOLD THE FLT ATTENDANT TO KEEP AWAY FROM THE DOOR AND I WENT UPSTAIRS TO PREPARE THE COCKPIT FOR DEP. ABOUT THE TIME I REACHED THE COCKPIT DOOR; I HEARD OVER THE PA THAT A SLIDE HAD BEEN DEPLOYED. I WENT BACK DOWNSTAIRS TO SEE WHAT HAD HAPPENED. THE SLIDE WAS DEFLATED AND SPREAD OVER A LARGE AREA NEAR THE DOOR. ONE OF THE MECHS WAS SEATED IN AN AISLE SEAT FORWARD OF THE DOOR. THE OTHER MECHS WERE STANDING NEARBY AND ALL APPEARED TO BE SHAKEN. THE SEATED MECH APPEARED TO BE HURT. I ASKED THEM IF THEY WERE OK AND LEARNED THAT THE SEATED MECH HAD BEEN THROWN AND PINNED AGAINST THE SEATS WHEN THE SLIDE DEPLOYED. I QUICKLY WENT TO DOOR 2L TO CALL PARAMEDICS.