Abstract: On May 7, 2013, Employee #1, employed by a drywall contractor, was working at a commercial warehouse building. He was working as a drywall taper, spotting screws in the drywall in the main area of the warehouse from his position on a scissor lift (aerial lift). Employee #1 fell to the concrete floor of that working level. Coworker #1, employed by an electrical subcontractor also working at the facility, found Employee #1 lying prone, unconscious and bleeding from a laceration on his forehead. Emergency services were called, and the Fullerton Fire Department responded. Employee #1 was transported to University of California Irvine Medical Center (UCI), where he was admitted for observation and treatment of a head injury. The Fullerton Fire Department reported this event to Cal/OSHA on May 7, 2013. Cal/OSHA's subsequent investigation determined that there were no witnesses to Employee #1's fall. In addition, Employee #1 did not respond to attempts to be interviewed. The investigation did establish that work at the site began at 6:00 a.m. on May 7, 2013, and that the workers all took their lunch break at 10:30 a.m. After the lunch break, Employee #1 continued with his assigned work and was alone on one side of the facility for approximately 20 minutes before he was found on the floor at approximately 12:24 p.m. by Coworker #1, the subcontractor. When found, Employee #1 was lying on the floor approximately 6 feet away from the scissor lift, which was in the down and stowed position. Employee #1 had worked as a drywall finisher for more than 11 years and had been a member of the Drywall Finishers Regional Local Union 1136 since 2001. He was certified as an aerial lift power user and had received other specialized training related to his work from the union as well as site specific safety training from the employer.