EE WAS WORKING ON A CEMENT AIRSLIDE CONVEYOR. THIS IS AN AIR ASSISTED GRAVITY CONVEYOR FOR FINISHED CEMENT PRODUCT. WHEN HE REMOVED A COVER ON THE AIRSLIDE, THE MATERIAL INSIDE PURGED OUT ON TO HIM COVERING HIS FACE AND EYES WITH MATERIAL AND KNOCKED HIM DOWN ONTO THE STEEL PLATFORM WHERE HE WAS STANDING ON A 4 FT LADDER.