An employee and a coworker were conducting a lift using an overhead gantry crane. The coworker was operating the crane and lifting the load, so the employee began to leave the danger zone. As he was walking, he tripped and fell over a 4x4 spacer that was permanently set on the floor. As he was falling, his hard hat fell off and he struck his head against a rack of aluminum pipes (finished product), suffering a head laceration that required stitches.