EMPLOYEE WAS SUPERVISING THE REPLACEMENT OF THE TIE-ROD INSIDE THE ROLLER MILL. VENTILATION INSIDE THE MILL WAS CAUSING THE BAGHOUSES VENTILATION FANS TO FAIL AND THE SYSTEM BECAME POSITIVE CREATING A DENSE CLOUD OF DUST IN THE MILL. AS THE EE RUSH OUT OF THE AREA HE TRIPPED AND FELL WITHT THE DIFFICULTY OF GETTING OUT EMPLOYEE INHALES DUST CAUSING DIFFICULTY TO BREATHE.