Abstract: At 3:15 p.m. on September 11, 2019, two employees were preparing to install purlins on the roof trusses of a building. Employee #1 entered a Genie lift Model GS 4069 RT and attached his Guardian Diablo retractable to his Guardian harness and anchored himself to the lift. The employer elevated Employee #1 approximately 17 feet to gain access to the roof truss. Employee #1 attached a sling around the top cord of the north end of the truss. Employee #1 detached his retractable from the lift and attached it to the anchor point on the truss. Employee #1 opened the access door and stepped onto the truss. Employee #2 used an extension ladder to access the second truss adjacent to Employee #1. Employee #2 attached a sling to the truss, then attached his lanyard to his Guardian harness, and then attached the lanyard to the Guardian Diablo retractable, and anchor sling. The employees prepared to receive the first purlin from the employer, when the truss that they were standing on and anchored to collapsed. Both employees fell from the truss. Employee #1 was hospitalized to treat vertebrae fractures, bilateral pelvic fractures, sacral fractures, and right-hand fractures to the fourth and fifth digits. Employee #2 was treated without hospitalization.