Abstract: At approximately 7:20 a.m. on August 26, 1999, Employee #1 and coworker were welding on the top of two separated vessels. These vessels were shorter than usual and were mounted on two sets of the positioning devices. Each vessel was driven separately. The positioning device included powered drive wheels and idler wheels. The drive wheels pushed the idler wheels while turning the vessel via friction. At the time of accident, Employee #1 was slowly rotating the vessel to the next position to be welded. Suddenly, an unstable condition occurred and the tank moved. As a result, the vessel came off the rolls of the positioning device. Employee #1 was thrown from the vessel. When tank number One tipped over, it hit Employee #1's head and shoulder. Then, it hit tank number Two and knocked it off the positioning device. Employee #1's head was crushed between these two tanks and Employee #1 was killed at the scene. When tank number One hit tank number Two, a coworker felt tank number Two moving. He immediately jumped off from the ladder and sprained his ankle.