Abstract: At approximately 7:30 a.m. on June 12, 2012, an employee was preparing to start patching steel connections on precast concrete panels on the roof. Employee #1 and a coworker were just dropped-off by their employer on the roof. The employer started to descend the aerial lift to ground level. Employee #1 was walking north, away from the coworker, on the roof. The roof design included several holes/openings for the vessel stacks and other fixed equipment to exit the building. All the holes were covered with plywood, but not all of them were secured and none of them were labeled as "hole". Employee #1 was walking close to one of these holes with an unsecured/unlabeled cover. It was not clear yet how the plywood cover moved. However, according to interviews, it was believed that the Employee #1 moved the cover and fell through the hole in the process. The coworker heard the cover smack the roof and when he looked, the Employee #1 was not on the roof and already fallen inside the building. The employer was still on his way down when he saw someone falling and yelled to the GC that someone fell inside the building. The employee hit the top of a vessel inside the building, rolled to the vessel's edge and then fell another 31 feet to the concrete slab at ground level. Employee #1 fell about 60-feet through 34-inch diameter opening in roof and was killed.