Miner operates a WDM Drill, noticed drill bit was dulling, went to Drill Pad area, to change out bit. Miner struck old bit w/2 lb hammer due to being stuck, metal hammer wasn't strong enough and a piece broke off, imbedding itself in upper G.I. area of miner, with downward angle. Piece had to be surgically removed by Specialist/Surgeon. Surgery successful on removal.