HE WAS OPERATING A HAND-HELD ""GOPHER"" ROOF DRILL TO INSTALL SUPPLEMENTAL ROOF BOLTS IN THE BELT ENTRY OF 8-R SECTION. AFTER DRILLING HIS HOLE THE DRILL STEEL BECAME STUCK IN THE ROOF THEN FELL OUT UNEXPECTEDLY CATCHING HIS LEFT THUMB BETWEEN THE END OF THE DRILL STEEL AND THE DRILL HEAD.