Employees at an oil rig were breaking down its blowout preventers. After removing the preventers from the wellhead, they put a wooden board on the ground to set the preventer on and keep it from getting muddy. When one employee unhooked his tagline from a preventer, the preventer shifted and the locking stem on its top struck the top of the employee's left boot. He suffered a laceration to the foot and two broken toes.