INJURED WAS ATTEMPTING TO LOOSEN A PACKER OTT OFA 2 7/8"" PIPE WITH A 36"" PIPE WRENCH ON A WOODENDECK. HE WAS ON HIS KNEES PUSHING THE WRENCH AWAY FROM HIS BODY. HE LOST HIS GRIP & THE TENSION ON THE WRENCH CAUSED IT TO COME BACK AND STRIKE HIM IN THE MOUTH.