THE INJURED WAS WALKING THRU THE X-CUT 2 TO 3 IN THE LAST OPEN BREAK ON THE 006-0 MMU, WHEN A PIECE OF ROOF ROCK FELL STRIKING THE INJURED AND KNOCKING HIM TO THE FLOOR. THE ROCKS BIGGEST DIMENSIONS WERE 58"" LONG 49"" WIDE 4 1/2"" THICK. THE INJURIES THAT RESULTED WERE BRUISES AND STRAINS TO THE CHEST AND BACK, NO BROKEN BONES.