EE WAS INSTALLING BOLT IN ROOF TO CHECK HYD. PRESSURE ON THE ROOF BOLTER. WHEN INSTALLING THE 2ND BOLT TO CHECK PRESSURE A PIECE OF ROCK FELL FROM THE TOP & HIT HIS RT. HAND WHILE LAYING ON TH E DRILL POT CUTTING HIS MIDDLE FINGER ON HIS RT.HAND. ROCK MEASURED 18""ROUND & 2""THICK. HEIGHT IN THIS AREA 62"".