EMPLOYEE WAS HOLDING A KNOCKER WRENCH & ANOTHER EMPLOYEE WAS USING A #8 SLEDGE HAMMER TO SECURE THE HOUSING ON THE VESSEL MEDIA PUMP. INJURED THOUGHT HAMMERER WAS READY FOR WRENCH TO BE REPO SITIONED. WHEN HE MOVED HIS HAND TO THE HANDLE THE FINGER WAS CAUGHT BETWEEN THE WRENCH AND THEHAMMER.