CONTRACTOR'S EE WAS REPAIRING A HAUL TRUCK TIRE.HE INCORRECTLY PLACED HYDRAULIC RAM TO REMOVE METAL TIRE BEAD. WHEN HE PRESSURIZED THE RAM IT POPPED OFF MOUNTING & STRUCK HIM ON THE FOREHEAD. INJURED WAS AN EE OF A CONTRACTED COMPANY WHICH DOES NOT HAVE AN MSHA ID#.