MECHANIC WORKING NUMEROUS CABIN PRIORITY WRITE-UPS; INCLUDING A MUST FIX MEL INTERPHONE PROBLEM AND DOOR 2-R INDICATION IN FLIGHT ISSUE; ON AN AIRBUS A321; INADVERTENTLY OPENS CABIN DOOR PRIOR TO DISARMING; DEPLOYING SLIDE.

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SHIFT STARTED AT XA30. WORK PACK FOR ACFT X HAD SEVERAL ITEMS TO WORK. THESE ITEMS INCLUDED 3 PRIORITY 1 ITEMS; AND OTHER MEL'S. 3 INBOUND ITEMS WERE WRITTEN IN THE LOGBOOKS. ONE OF THE INBOUND ITEMS WAS AN ITEM CONCERNING R2 CABIN DOOR INDICATION WHILE INFLT. I WORKED THE OVERNIGHT CHK FIRST WHILE MY PARTNER STARTED TO WORK THE MUST FIX MEL ON THE CABIN INTERPHONE SYS. AFTER THE OVERNIGHT CHK WAS COMPLETED; I WAS GOING TO WORK THE PRIORITY 1 FUEL FILTER CHANGES WHICH HAD NO FLT TIME LEFT TO USE. NO FILTERS WERE AVAILABLE FOR THE FUEL FILTER CHANGE. MY PARTNER NEEDED HELP WITH TROUBLESHOOTING THE INTERPHONE PROB. HE TALKED WITH MAINT CTL SEVERAL TIMES ABOUT THE INTERPHONE PROB AND ALSO THE CABIN DOOR INDICATION PROB. WE DID WORK THE DOOR PROB BY OPENING AND CLOSING EACH DOOR; AND ALSO ARMING AND DISARMING EACH DOOR/EXIT DOOR ON THE ACFT. WE COULD NOT DUPLICATE THE LOGBOOK ITEM. I LOOKED IN THE MEL BOOK FOR RELIEF WITH THE DOOR. THE DOOR COULD BE MEL'ED. THIS WAS AN OUT FOR THIS PROB. WE CONCENTRATED ON THE INTERPHONE PROB HOPING TO CLR THIS MEL. THIS WOULD ALLOW THE ACFT TO OPERATE IN MORNING. WORK ON INTERPHONE WAS INVOLVED WITH CEILING PANEL REMOVAL AND RINGING OUT WIRES FOR SHORTS OR OPENS. WORK PROGRESS WAS GIVEN TO MAINT CTL AND TO OUR LEAD MECH. THE INTERPHONE SYS WAS REPAIRED AND THE MEL CLRED NEAR THE END OF OUR SHIFT. MAINT CTL THEN DIDN'T WANT TO GIVE AN MEL ON THE DOOR INDICATION AND A NEW PLAN WAS STARTED. I HAD COMPLETED THE PAPERWORK ON THE CHK AND PREPARED A TURNOVER FORM FOR THE DOOR INDICATION PROB TO GIVE TO THE FIRST SHIFT. THE TIME WAS APPROX XH00. A NEW CABIN DOOR SENSOR AND ACFT MAINT MANUAL REF WAS RECEIVED WITH A REQUEST TO STAY AND WORK THE PROB THROUGH BY MAINT MGR. MY PARTNER STARTED THE DOOR SENSOR REMOVAL; BUT COULD NOT STAY PAST SHIFT END TIME. I ACCEPTED TO STAY TO FINISH FIXING THE ITEM. THE SENSOR WAS CHANGED; BUT THE NUT WASN'T SAFETIED DUE TO IT MAY NEED ADJUSTMENT PER ACFT MAINT MANUAL. THE DOOR WAS CLOSED AND LATCHED. I WALKED TO THE COCKPIT TO CHK THE INDICATION. IT WAS GOOD. MY LEAD ARRIVED TO HELP. I WENT BACK TO THE DOOR AND ARMED THE SLIDE. THEN RETURNED TO THE COCKPIT TO CHK THE INDICATION TO SEE IF IT WORKED. THE INDICATIONS WERE GOOD. THE NEXT STEP IN MY THINKING WAS TO TIGHTEN AND SAFETY THE NUT. THIS REQUIRES OPENING THE DOOR. I OPENED THE DOOR; BUT THE SLIDE WASN'T DISARMED FIRST. THE SLIDE DEPLOYED. I KNEW INSTANTLY WHAT I DID WRONG. I DIDN'T STOP; LOOK; DOUBLECHK BEFORE OPENING THE DOOR. MY LEAD WAS PRESENT AND NOTIFIED THE SUPVRS. DRUG AND ALCOHOL TESTS WERE GIVEN. I HAD GOTTEN UP MONDAY MORNING AND BEEN AWAKE ALL DAY TO START NIGHT SHIFT AT XA30. MANY WORK ITEMS TO DO; ONLY WORKED ON THE NECESSARY ITEMS NEEDING TO BE DONE SO THAT ACFT COULD OPERATE NEXT DAY. I KNOW THE IMPORTANCE OF FIRST FLT OF THE DAY OP. THE COMPANY NEEDS ACFT READY TO GO TO SERVE ITS CUSTOMERS.