EMPLOYEE WAS WELDING 1/4"" PLATES 8"" SQUARE OVER HOLES THAT HAD WORN THROUGH THE CONVEYOR PANS. THE POSITION OF THE PANS WERE IN FRONT OF AND SLIGHTLY OVERHEAD. THE PLATES WERE IN A STACK BY HI S FEET. HE BENT DOWN TO PICK UP A PLATE, TACKED IT IN PLACE AND THEN WELDED IT OUT. NEAR THE END OF HIS SHIFT, HE NOTICED HIS BACK WAS SORE. HE ASKED FOR MEDICAL TREATMENT ON 1/23/04.