EMPLOYEE WAS PULLING DRIVE UNIT WITH A CHAIN HOOKED ONTO THE SCOOP. DRIVE GOT STUCK IN MUD &CHAIN BROKE; END OF CHAIN WHIPPED BACK, STRIKINGHIM IN THE FACE. CAUSE OF INJURY--EXCESSIVE STRAIN. COMPLIANCE WITH RULES/REGS NOT A FACTORNOR EQUIPMENT A FACTOR. MINING SYSTEM A FACTOR,MINER KNOWLEDGE A FACTOR.