Abstract: At approximately 2:30 p.m. on October 14, 2010, Employee #1, a cameraman, and Employee #2 and #3, stagehand riggers were helping to erect and set-up a mobile stage for a music festival in the park. The mobile stage was designed and engineered to be contained within a semi-truck. Its sections would unfold and the various components would be attached onto the roof and other parts of the stage. Once the components were attached, the roof would be raised. The roof was supported by two telescoping towers located on opposite sides and trusses were attached on each of the four corners of the roof. Employee #1 was helping to construct a video wall prior to starting his shift. Employees #2 and #3 were doing rigging work on the stage. The roof dropped a few feet, and both towers tilted to one side. Employees #1, #2, and #3 were on the stage, but jumped off at the sound of the collapse. One of the trusses was driven through the stage floor and into the ground. Employee #1 fractured his left ankle, sprained his right knee, and was hospitalized for two days. Employee #2 bruised the right side of his calf. Employee #3 sprained both knees. Employees #2 and #3 were taken to Kaiser Hospital and were released after a few hours.