THE INJURED WAS INSTALLING A ROOF BOLT WHEN A PIECE OF ROOF ROCK (5' X 2' X 8"" THICK) FELL INBY THE ATRS WHEN ONE END STRUCK THE GROUND IT FLAPPED THE OTHER END TOWARD THE INJURED STRIKING HIM ON THE LEFT LEG AND ANKLE, IT SCRATCHED HIS LEG AND SHATTERED HIS ANKLE BONE.