Abstract: Employee #1, a mechanic at a rock and gravel surface mining operation, was replacing a missing lug on the right rear tire of a Ford F-250 welding truck. He was working on a flat level of the mine known as the main floor which was composed of loose sand and gravel. The wheel was off of the truck, and the truck was supported with a Craftsman Professional 12-ton hydraulic jack. The top of the jack has a shallow 1/2 inch wide notch which was placed under one of the U-bolts on the left rear axle. The base of the jack was 5 inches by 4.5 inches. Directly next to the jack, toward the center of the truck, Employee #1 placed a piece of steel 4-inch square tubing onto a piece of 6-inch square tubing as blocks. Both the jack and the blocks were directly on the ground. It is uncertain but it is unlikely that the blocks were touching the axle. Employee #1 was on his right side with his legs protruding behind the wheel area. A nearby employee observed Employee #1 "banging hard" on the back of the inspection plate which covers the brake assembly. Employee #1 noticed a backward and downward motion when the truck fell. The truck did not fall completely to the ground, and was most likely stopped by the 10 inches of blocking under the axle. Employee #1 was pinned underneath the truck on his side. He managed to get onto his back and the other employee pulled him out from under the truck. Employee #1 was hospitalized for treatment of five fractures of his pelvis. Employee #1 stated that the emergency brake was off. He said he had chocked the front wheels with stones but that the stones were too small to keep the truck from moving. It is the opinion of the Division that the primary cause of this accident was the failure to adequately block the truck under repair from motion, both vertically and horizontally. This was compounded by the lack of a solid surface on which to support the jack or blocks.