What was found
OXYGEN LINE CONNECTING NR 3 CYL TO AC OXYGEN PRESS PLUMBING RUPTURED AT SWEDGE WHILE OTHER MAINT WAS BEING PERFORMED. ALL 4 OXYGEN CYL WERE SELECTED TO OFF BEFORE COMPLETE DEPLETION OCCURRED. AS PRECAUTION ALL REMAINING ORIGINAL PRESSURIZED OXYGEN SUPPLY LINES BETWEEN OXYGEN CYL AND THE OXYGEN SYS CONT PANEL WERE REPLACED WITH NEW LINES IAW AMM. ALL LINES REPLACED WERE VISUALLY INSP. NOTED THAT ONE OF THESE LINES HAD BEGAN TO DEVELOP BLISTER AT ONE OF CONNECTORS. A MFG ENGINEER WORKING THIS ISSUE REPORTED THAT LINE WITH THE BLISTER FAILED (RUPTURED) AT APPROX HALF OF THE CERTIFIED PSI RATING. RUPTURE OF ANY ONE OF THESE LINES ALLOW UNCONTROLLED RELEASE OF ENTIRE OXYGEN SUPPLY INTO HIGHLY ELECTRONIC ENVIRMT.