ROOF BOLTER OPERATOR WAS INSERTING A BOLT INTO A BOLT HOLE. AS THE BOLT WAS PUSHED IN TO THE HOLE, IT WAS BEING SPUN AT A HIGH RPM TO MIX THE RESIN. AFTER SPINNING FOR THE REQ'D TIME, THE B OLT WAS THRUST UPWARD INTO THE HOLE. AS IT WENT UP, A SPARK WAS CAUSED AND A FIST SIZED BALL OF FLAME WAS OBSERVED. IT IMMEDIATELY EXTINGUISHED ITSELF LOCATION- NO. 5 ENTRY X-CUT, MMU-001-0