Abstract: Employee #1, a part-time student worker at the Mandeville Center auditorium on the UC-San Diego campus, was cleaning up and setting up chairs along with a student coworker. Employee #1 went up in a pneumatically powered telescopic lift to check that the chairs were set up in a proper semi-circle, as was standard procedure at the auditorium. He got onto the platform, raised the guardrails, then extended the platform between 10 and 15 ft. The platform became unstable without its outriggers, and tipped over onto the concrete floor. Employee #1 sustained fractures to both elbows and to his left forearm, and suffered abrasions and possible head injuries. He was transported to Scripps Hospital in La Jolla, where he was hospitalized for one week. Employee #1 did not deploy the manufacturer-supplied outriggers, which were available on site, because two or three coworkers were needed to lift up the platform and install them. Apparently, it was common practice not to use the outriggers. Employee #1 and the coworker later stated that management personnel had used the aerial lift in the same manner, and that management had also previously observed them elevate the platform without the outriggers in place.