EE WAS WORKING ON A 6"" AIR LINE UNDER THE DISCHARGE END OF ## RAW MILL. THE COMPRESSOR'S SUPPLY AIR TO THE LINE WERE LOCKED OUT, THE VALVE FROM THE RECEIVING TANK WAS CLOSED. EE WAS REMOVING A DRESSLER COUPLING FROM THE SECTION OF LINE TO BE RE-ROUTED WHEN A BLAST OF WATER AND AIR PRESSURE ESCAPED FROM LINE.