Abstract: A crew of workers were caulking gutters and installing gratings at the skylight roof level, at a height of approximately 175 ft. Most of the skylight glass had been installed, but the workers were aware that glass was missing from some skylight units at the westernmost portion of the roof. Employee #1 was caulking the gutters between skylight grids, which involved walking backward on the glass framing sills at the sides of the gutters. He was moving backward toward the corner of a skylight unit where glass was missing when he fell through one of the triangular openings and was killed instantly. The skylight openings were not covered nor were safety belts or safety nets in use.