THE DIGESTION OPERATOR ASSISTANT WAS USING AN 8 LB. SLEDGEHAMMER TO CLOSE AN 8""X10"" ANGLE VALVE ON #4-6 HEATER. THE AREA AROUND THE VALVE WAS RESTRICTED DUE TO PROCESS PIPING. AS HE SWUNG THE HAMMER TO CLOSE THE VALVE, HE MISSED THE VALVE & STRUCK A DRAIN VALVE HANDLE, CAUSING THE DRAIN VALVE TO OPEN. HOT LIQUID ESCAPED AND STRUCK HIS LEGS. HE RECEIVED 2ND DEGREE BURNS.