Abstract: At approximately 9:15 a.m. on June 19, 2012, Employee #1, a laborer employed by Cleveland Wrecking Company, was engaged in demolishing a floating roof type storage tank, approximately 130 feet in diameter and 40 feet tall, at a non-operational PG&E power plant. He was positioned approximately 40 feet above the ground, on the platform of a Genie telescopic boom lift, Model Number S-60, Serial Number S6007-15084. Employee #1 had previously cut an entrance 24 feet high by 21 feet wide on the east side of the tank to access the inside of the tank with the lift. At the time of the accident, he had finished cutting vertically over the center of the entrance to the tank, and then had positioned the boom lift just north of the vertical cut he had made. He elevated the lift basket over the tank to signal a coworker, who was operating the excavator, to push in the wall section to the south of the cut employee #1 had made. As the coworker pushed the south wall section inward with the excavator, the wall section north of the vertical cut also collapsed inward and struck the boom lift. The boom lift was knocked backwards. It overturned and hit the floor of the tank. Employee #1 sustained blunt force trauma to his head, chest, abdomen, and pelvic area. He died from these injuries. The accident was reported to Cal/OSHA's Bakersfield District office by the employer at 11:10 a.m. on June 19, 2012. Investigation revealed that one day before the accident, Employee #1 partially removed a section of the tank girder. This girder was located 3 feet from the top of the tank and extended around the outside of the tank. The girder was removed from just north of the tank entrance to about one-fourth way around the northeast side of the tank. Removing the girder contributed to the instability of the tank. The tank wall section that was cut just prior to the accident was approximately 40 feet high and did not have any lateral support. No civil engineering data was available at the time of the incident substantiating the capability of any of the wall sections over one story or 12 feet in height to stand alone without lateral support.