EE HAS DE-ENERGIZED ELEC. POWER SOURCE & LOCKED OUT GRINDER MACHINE FOR PREVENTIVE MAINTENANCE INSPECTION. UPON REMOVING THE INSPECTION DISCHARGE HOUSING AND REMOVING/CLEANING OUT EXCESS MICA MATERIAL HE STRUCK HIS UNGLOVED RIGHT THUMB AGAINST THE SHARP EDGED BLADE OT THE GRINDER MACHINE CAUASING A LACERATION INJURY.