EMPLOYEE REPORTED: WORKING ON WALLACE DIESEL MANTRIP IN UNDERGROUND SHOP AREA. WHEN STEPPING FROM SIDE TO SIDE OF THE MANTRIP, HE STRUCK HIS RT. EAR AGAINST A FIRE OUTLET NIPPLE THAT WAS ALONG THE MINE ROOF. THE OUTLET CUT HIS EAR REQUIRING SUTURES. (NO LOST WORK DAYS)