What was found
(AUS) FOLLOWING APU BATTERY FITMENT AND WHILE INSTALLATION CHECKS WERE CARRIED OUT ON THE THERMAL SWITCH, A FLASH FIRE OCCURRED WHICH SET FIRE TO THE THERMAL BLANKET LOCATED UNDER THE APU BATTERY TRAY AND ALSO CAUSED FLASH BURNS TO MAINTENANCE PERSONNEL. THEFIRE WAS CONTAINED AND QUICKLY EXTINGUISHED. THE FIRE MAY HAVE BEEN CAUSED BY COMBINATION OF AN IGNITION SOURCE FROM A PREVIOUSLY UNDISCOVERED BROKEN/CHAFFED WIRING IN LOOM ADJACENT TO APU BATTERY TRAY AND USE OF AN UNAPPROVED COOLANT SOURCE THAT WAS INFLAMMABLE.