EE STATED HE WALKED AROUND THE PARKED SHUTTLE CAR TO CHECK THE CABLE REEL AND UPON RETURNING TO THE OPERATOR'S STATION AND STILL STANDING OUTSIDE THE DECK A PIECE OF ROCK FELL FROM BETWEEN BOL TS STRIKING HIM DIRECTLY ON TOP OF HIS HARD HAT.THE ROCK MEASURED 12""X12""X0 TO 3"" THICK AND WEIGHTED APPROX. 12 LBS.