INJURED AND ANOTHER EMPLOYEE WERE INSTALLING BALLS IN RAW #1 MILL. THIS AREA (HOOKING UP BARRELS) IS WITHIN 20 FT OF THE HIGH BAY HOIST BARRICADED AREA. CONTRACTOR WAS HOISTING 5 SHEETS OF PLY WOOD ON HIGH BAY HOIST TO THE 4TH FLOOR WHEN THE LOAD SLIPPED AND BROKE LOOSE FROM RIGGING. PLYWOOD SHEETS FELL ALL THE WAY TO GROUND FLOOR AND SAILED OUT OF BARRICADE AREA STRIKING BOTH EMPL