EMPLOYEE WAS IN THE PROCESS OF MEASURING THE DISTANCE FROM COAL RIB TO THE FIRST BOLT TO BE INSTALLED. EMPLOYEE WAS USING A PINNER STEEL BY LAYING IT BETWEEN THE BOOM OF THE BOLTING MACHINE AN D THE RIB. AS THE EMPLOYEE SWUNG THE BOOM THE PINNER STEEL WEDGED AND WAS FORCED OUTWARD, HITTING HIM IN THE MOUTH.