An employee was welding on a yoke and while un-chocking the yoke it rolled and fell off the table. The yoke hit the floor and rolled over again hitting the employee's left leg and pinning him up against the welding screen. A yoke is part of the closure on a large vessel. They are about 60 inches in diameter. They are in two pieces so the part that fell was only half of the yoke. The part of the yoke that fell weighs 1,320 pounds. Both bones in his left leg were broken at the ankle and a bone in his right foot that runs from the third toe to the ankle was also broken.