EMPLOYEE HAD MAIN MOTOR ON DREDGE OVERHEAT AND STOP. COOLANT OVERFLOWED INTO CATCH BUCKET. EE TOOK MMEASURES TO RELIEVE PRESSURE WITH COOLANT HOLDING TANK. WHEN HE THOUGHT PRESSURE WAS RELIEVE D HE REMOVED THE COOLANT TANK CAP. PRESSURE WAS NOT RELIEVED FULLY AND HOT COOLANT SPRAYED ON BACK AND ARMS CAUSING 1ST AND 2ND DEGREE BURNS.