GRESHAM TRUCK DRIVER ENTERED PARKING LOT AT 1:00P.M. AND WENT UP TO LOADING PLATFORM TO OPEN HATCHES. TERMINAL OPERATOR HEARD HIM OPEN THE FIRST HATCH. WHEN HE DID NOT HEAR THE SECOND HATCH OP EN HE WENT TO CHECK AND FOUND THE DRIVER FACE DOWN ON TOP OF THE TRUCK INSIDE OF A SAFETY PLATFORM. HE WAS ASSISTED BY LAFARGE EMPLOYEES WHO PROVIDED EMERGENCY TREATMENT UNTIL PARAMEDICS CAME