Abstract: At approximately 3:30 p.m. on February 7, 1995, Employee #1 and a coworker were at the Henry J. Mills filtration plant in Riverside, CA, installing shoring in an excavation that was to contain an underground fuel tank . They were putting in Z-shoring, which is a type of shoring that has a manifold of valves that must be closed to hold pressure on the cylinders. The employees had used an excavator to position the shores in the trench, and pressure was applied to the cylinders by means of a hand pump. The employees decided that because the cable was too short, pressure was being applied to the cable attached to the excavator rather than to the side of the excavation. The boom of the excavator was let down to take the pressure off the cable, and the cylinders were pumped up again. The cable was then removed from one side of the shore, and Employee #1 took his weight off the cylinder. The shoring collapsed and fell into the excavation, along with Employee #1. He suffered injuries to his back and head.