Abstract: Employee #1 and Employee #2 were on the roof of the existing building measuring a piece of mechanical equipment that was to be moved to the roof of the new building. They were on the west side of the building on a small roof over a loading dock which was lower than the rest of the building. The roof is about 20 ft wide by 80 ft long and has cyclones and associated piping on it. Access to the roof was through a ladder hatch on the south end and the mechanical equipment they were measuring was near the north end. There are two 8 inch cast iron pipes that run across the roof to the cyclone and the only way to get from the ladder hatch to the exhaust fan is to duck under the pipes. After making the measurements they walked back toward the hatch. Employee #2 ducked under the pipe but Employee #1 struck his head on it and fell backwards. Employee #1 was wearing a hardhat with the brim in back so he could see well. Employee #1 suffered a herniated disc in his neck and was hospitalized.