An employee had driven a wrecker out to a job site to remove a piece of heavy equipment that was stuck in mud and wedged against a building. The employee ran winch cables, adjusted the boom, attached chains, and set up a snatch block. He began pulling the equipment out of the mud. A chain that was pulling on the heavy equipment broke, and the employee was struck in the chest by the snatch block. He sustained five broken ribs and a punctured lung.