TWO EMPLOYEES WERE REMOVING COVER FOR COAL ROLL REMOVAL. ONE WENT TO THE MAINTENANCE SHOP TO GET A SLING FOR LIFTING THE COVER. WHILE HE WAS GONE, THE EMPLOYEE REMOVED THE BOLTS FROM THE COVER AND TURNED AROUND TO PICK UP SOMETHING. THE COVER CAME LOOSE HITTING HIM IN THE BACK OF HIS LEFT LEG JUST ABOVE THE CALF. SCRAPES & SORENESS LATER DIAGNOSED AS A TEAR BY THE TREATING DOCTOR.