THE EE WAS CHANGING A LINE BLIND VALVE AT SILO #44 USING A TORQUE WRENCH. WHILE TIGHTENING THE TOP BOLT ON THE VALVE, THE TORQUE WRENCH SLIPPED OFF OF THE BOLT HEAD WHICH CAUSED THE EE'S LEFT HAND LITTLE FINGER TO BE CAUGHT BETWEEN THE TORQUE WRENCH AND THE 8"" CEMENT LINE CAUSING A LACERATION AND FRACTURED BONE. THE LACERATION REQUIRED EIGHT STITCHES.