EE was operating a continuous miner when a piece of roof rock fell out between the rib and rib bolts. The rock was approx. 7'L,2'W, 0-5"" thick. The rock struck the back of his head and upper back. It drove him down onto the mine floor and he was partially pinned down by the rock being hung on his mine bolt. He receved abrasions and contusion to his back and leg.