EMPLOYEE WAS REMOVING THE LEFT REAR OUTSIDE TIRE OF UNIT 622 TO BE ABLE TO WORK ON THE INSIDE DUEL TIRE. WHEN REMOVING THE LUG NUTS HE WAS MOVING THE RAD TOOL BETWEEN THE LUG NUTS USING HIS LE FT HAND TO GUIDE THE TOOL ONTO THE NEXT NUT HE ACCIDENTALLY HIT THE TRIGGER PINCHING HIS LEFT INDEX FINGER & HAND BETWEEN THE TOOL & THE WHEEL. THE TOOL CAUSED A LACERATION OF THE LEFT FINGER