FAULTY PROPANE CYLINDER. EMPLOYEE WAS UNABLE TO USE FRESHLY FILLED TANK. TANK WAS LEFT UNATTENDED FOR ? MINUTES WHILE HE CHECKED OTHER TASK. ON HIS RETURN, THIN STREAM OF PROPANE FROM VENT HAD IGNITED, BURNING HOSE OFF. OVERHEAD WIRING THEN CAUGHT FIRE. EMPLOYEE, UNAWARE OF PROPANE FIRE, WAS BRINGING EXTINQUISHER FOR ELECTRICAL FIRE AND WAS BURNED AS HE ENTERED THE BUILDING.