Abstract: On October 28, 2009, Employees #1 and #2, and four coworkers were replacing the roof trusses of a building, which were made of prefabricated wood. The building consisted of slab on grade with concrete block walls and the trusses were located on each gable end. In addition, the walls had been raised an additional 5 feet. Using a rented crane to lift the trusses and working from a scissor lift and portable ladders, Employees #1 and #2, and their coworkers were installing piggy back trusses. The trusses were lifted two at a time, weighing 500 lbs, with a steel cable. However, no spreader bar was used. A guide rope was also used to help maneuver the trusses to the desired location. During the operation, the four coworkers were setting the trusses, while Employees #1 and #2 were bracing the trusses. Employee #1 worked at the peak to install bracing, and was wearing a personal fall arrest system. He was attached at the peak of the existing (original) trusses with a 6 foot lanyard. He was installing 2 foot by 4 foot lateral bracing by lying on top of the trusses. Employee #2 was standing on the back wall and installing lateral bracing. He was also wearing a personal fall arrest system. The site superintendent was standing inside, against the front wall, watching the trusses being installed. After approximately 23 of 30 new trusses were installed and 7 more remained, a storm started with strong gusts of wind and rain. This caused all the trusses to fall into the building. Employee #1 and #2 also fell, but did not hit the ground due to their harnesses. Both Employees #1 and #2 were taken to a nearby hospital, where they were hospitalized. Employee #1 was treated for a broken nose and bruises from being struck by the trusses, and Employee #2 received treatment for bruises and soreness. The accident investigation contributed the incident to the trusses failing to have any diagonal bracing installed, which was in accordance with the Building Component Safety Information Guide to good practice for handling, installing, and bracing of metal plate connected wood trusses, and was consistent with the manufacturer's instructions.