IT APPEARS THAT ONE OF THE #1 COAL MILL ROLLS LOST THE OIL THAT LUBRICATES IT. THIS ALLOWED THE ROLL TO BECOME VERY HOT WHICH THEN PROVIDED AN IGNITION SOURCE FOR THE GROUND COAL. THE IGNITION OF COAL CAUSED THE RUPTURE DISCS IN THE COAL MILL DUST COLLECTOR TO BLOW OUT AS THEY WERE DESIGNED TO DO.