A MECHANIC WAS USING A 8' FIBERGLASS LADDER TO ENTR THE FEED END OF THE #7 MILL IN THE CONCENTRATOR. THE FEET OF THE LADDER SLIPPED ON THE CONCRETE FLOOR. HE FELL 3'. HE RECENTLY BEGAN PHYSCIA L THERAPY FOR LOW BACK PAIN. A SMALL AMOUNT OF NORDBACK BUILD-U[ ON THE LADDER FEET APPARENTLY ALLOWED THE LADDER TO SLIDE.