Abstract: On the day of the accident, the job superintendent (operator) was operating a Pettibone rough terrain fork lift to hoist employees in a personnel basket (man basket) to the roof of the building. The superintendent indicated that he had not received any formal training on how to operate the fork lift. The other employees working on site also indicated that they use the rough terrain fork lift to carry materials and lift employees. A coworker was working on the roof laying metal roofing material and Employee #1 was working from the basket. The coworker was wearing a personal fall protection system while up on the roof. The operator of the Pettibone rough terrain fork lift was lifting employees approximately 18 ft to the roof of a building in a personnel basket that was attached and secured to the forks of the lift. The operator extended the basket up to the roof and then left the fork lift with the load extended. The operator walked to the front of the building next to the one they were working on to go to his truck for materials. The operator indicated that the fork lift was out of his view. During this time, Employee #1 climbed out of the personnel basket and got on the roof to help a coworker secure purlin extensions to the roof. Employee #1 tried to stand back up after securing the extension and lost his balance and fell 18 ft from the roof on to the concrete floor. Employee #1 sustained internal injuries including swelling on his brain and was hospitalized for over a month and a half.