EE WAS REMOVING TROUGH ROLLERS PREPARING FOR NATIONAL BELT TO CHANGE A CONVEYOR BELT. THE NATIONAL BELT EE'S WERE PLACING A LARGE TOOL BOX ONTHE CATWALK. WHEN ONE OF THE HOOKS WAS TAKEN LOO SE, THE TOOL BOX SLIPPED DOWN THE CATWALK AND STRUCK EE ON THE LEG AND WAIST.