Abstract: Employees were erecting a work platform around a chimney area, bridging the platform of a tower scaffold and the roof slope. Employee #1, a mason's helper, was standing at the pulley hoistway at the southwest corner of the scaffold platform. As the pulley was hoisted 25 ft to the tower scaffold, Employee #1 apparently suffered a seizure, lost his balance, and fell backward off the elevated work platform to the ground. As he fell he struck the planks that were being hoisted and sustained a severe head injury. Employee #1 was fully trained for his assignment. He had a medical history of seizures between the ages of 8 and 16, but because he had not experienced any in recent years, he was not taking any medication. His employer provided gloves, hard hats, and other ppe as required. The platform had no standard railings at the open sides or ends. The weather was clear, cool, and dry, and all walking surfaces were dry.