Abstract: At about 1:30 p.m. on March 23, 2004, Employee #1, working for a sign manufacturing and installing company in Ontario, CA, was replacing old corrugated fiberglass panels in the roof of a building adjacent to the employer's site. At the time of the incident, Employee #1 lost his balance and inadvertently stepped on the panel he was removing and fell 13 ft through the roof to the concrete floor below. Employee #1 was transported to the Arrowhead Regional Medical Center in Colton, CA, where he remained for four days undergoing treatment of broken ribs, fractures of the right clavicle, jaw and nose, a punctured lung, and head lacerations. The task assigned to Employee #1 was non-routine.