An employee was standing on a piece of equipment called a K-brace, approximately 3.5 feet off the ground. He was working to assemble part of the K-brace. He was driving a metal pin with a sledgehammer and put the sledgehammer on the ground. He then hopped off the K-brace backward and struck the handle of the sledgehammer as he came to the ground. The employee was hospitalized with a laceration to his left buttocks and a fractured tailbone.