EMPLOYEE WAS IN THE PROCESS OF INSTALLING AN 8' BOLT ON OPERATOR SIDE OF A VOEST ALPINE MINER. HEAD COAL BROKE LOOSE FROM OVER TOP OF VENTILATION TUBING. HEAD COAL WAS 2"" THICK X 8"" WIDE X 12 "" LONG - COAL BOUNCED OFF THE TUBE STRIKING THE EMPLOYEE'S RIGHT FOREARM CAUSING A LACERATION.