A B757-200 WHILE ACCOMPLISHING AN AIRWORTHINESS DIRECTIVE AND AN ENGINEERING AUTH TO ALL PAX SVC UNITS ONE OXYGEN CANISTER WAS FOUND PINNED.

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ON SEP/WED/04; WHILE RELAMPING A READING LIGHT AT SEAT POS X; A ZZZ1 AMT FOUND AN OXYGEN GENERATOR SAFETY PINNED WITH THE RED 'REMOVE BEFORE FLT' STREAMER ATTACHED. THE GENERATOR WAS REACTIVATED AND THE REMAINING FIRST CLASS AND COACH GENERATORS WERE INSPECTED TO INSURE THEY WERE ACTIVATED. NO OTHER GENERATORS WERE FOUND PINNED. A LOGBOOK ENTRY WAS MADE; A MAINT OPERATIONAL RPT WAS COMPLETED AND QUALITY ASSURANCE WAS NOTIFIED. THE SIGNOFF ON THE JOB INSTRUCTION CARD WAS COMPLETED UNDER AN AIRWORTHINESS DIRECTIVE ON AUG/MON/04. I AM AN AMT IN ZZZ BASE MAINT. MY SIGNATURE AND EMPLOYEE IDENT ARE IN THE SIGNOFF BLOCK. ALTHOUGH I AM ULTIMATELY RESPONSIBLE FOR THE SIGNOFF; THERE ARE SEVERAL CONTRIBUTING FACTORS FOR THE INCIDENT. FIRST; THERE ARE NUMEROUS JIC'S AND OPS FOR THE PAX OXYGEN MASK/GENERATOR REPLACEMENT/INSPECTION. CONFUSION RESULTS FROM EA'S (ENGINEERING AUTH) AND AIRWORTHINESS DIRECTIVES CONFLICTING WITH EACH OTHER. FURTHERMORE; SEVERAL AMT'S WERE ASSISTING WITH PULLING THE SAFETY PINS/STREAMERS. THE RISK OF HUMAN ERROR WAS MULTIPLIED. I AM NOT PASSING BLAME UPON ANYONE ELSE; SINCE MY SIGNATURE IS IN THE BLOCK. FINALLY; I VERIFIED THAT ALL SAFETY STREAMERS/PINS WERE PULLED BUT MAY HAVE INADVERTENTLY LEFT ONE INSTALLED. TO PREVENT THIS OCCURRENCE IN THE FUTURE; I WOULD SUGGEST HAVING SEPARATE SIGNOFFS FOR EACH ROW OF SEATS. WHEN WE INSTALL FLOORBOARDS; THERE IS A SEPARATE SIGNOFF FOR EACH FLOORBOARD. ALSO; HAVING A 'SECOND SET OF EYES' SUCH AS AN INSPECTION SIGNOFF AFTER THE MECH SIGNOFF WOULD HELP RECTIFY THE AMBIGUITY.