EMPLOYEE STATED HE WAS STANDING 6 FT AWAY FROM ANOTHER EMPLOYEE WHO WAS KNOCKING A FLANGE ON A WHEEL MOTOR OF A BATTERY POWERED COAL HAULER. OTHER EMPLOYEE WAS USING 8 LB HAMMER TO HIT FLANGE. EMPLOYEE MISSED AND THE HAMMER HIT INJURED ON RIGHT THUMB AND FOREFINGER. HIS HAND WAS RESTING AGAINST THE COAL HAULER FRAME.