Abstract: At approximately 3:00 p.m. on December 3, 2013, Employee #1, an apprentice laborer employed by Diablo Plumbing, Inc., and Coworkers #1 and #2, managers, were working at a multi-employer work site, the construction of the Stoneridge Creek Skilled Nursing Facility. Employee #1's employer was subcontracted to Segue Construction, Inc., the general contractor, to install underground plumbing and related plumbing trenches. The employer's workers had excavated a relatively shallow sewer trench, approximately 2 feet 6 inches deep. They then set the pipe in the trench. Their work progressed toward one end of the site, while another contractor followed behind to excavate a deeper trench and install in it the electrical utility. Employee #1 was instructed by Coworker #1, a manager, to drop back to areas where the sewer pipe had been recently installed and to tape plastic sleeving for corrosion protection to the 4-inch sanitary sewer riser. Due to the configuration of site utilities, there were several locations where the sewer and electrical trenches crossed. One of these locations was Grid Line 8, between Grid Lines M and N, where the electrical trench had been excavated crosswise to the sewer trench and approximately 3 feet from the sewer riser. The work was scheduled so that the excavation activities of the two trades were not physically conflicting. Employee #1 worked safely within the sewer trench, installing the plastic sleeving. He then exited the shallow trench to retrieve more tape. He climbed out of the sewer trench at the corner where it intersected with the deeper electrical trench. The corner broke off, and Employee #1 fell into the deeper electrical trench, a fall height of 7 feet. Although Employee #1 climbed out of the trench on his own, he was gasping for breath. Coworker #2 came over and evaluated Employee #1. Coworker #1 called for an ambulance after Employee #1 lost consciousness. The Livermore-Pleasanton Fire Department responded and transported Employee #1 to the hospital, where he was admitted and treated for bruising to the neck. This event was reported to Cal/OSHA by the employer at approximately 3:00 p.m. on December 3, 2013. It also was reported by the general contractor and the Livermore-Pleasanton Fire Department. During Cal/OSHA's subsequent investigation, it was determined that Diablo Plumbing was a plumbing contractor that performed work on a wide range of both residential and commercial projects, including related excavation work. The investigation report concluded that the employer had failed to reevaluate the trench conditions when the situation changed. The top edges and corners of the trench were beveled in many places from drying and cracking and/or minor sloughing. Where the newer, deeper electrical conduit trench was excavated at right angles to the sewer trench, the drying reentrant corners where the trenches met constituted a new hazard to Employee #1, who was working in one of these areas. The employer had failed to train Employee #1 to recognize and avoid this new hazard. The investigation found that Employee #1 could have avoided the new hazard if he had walked further away from the deeper electrical utility trench before exiting the shallower sewer trench.