Abstract: At approximately 10:07 p.m. on July 20, 2000, Employees #1 through #3, of Quality Window Cleaning, Inc., were cleaning windows on the west side of a building. Employees #2 and #3 were working from a boatswain's chair suspended from the roof by two transportable roof rigs or roller, and descending the side of the building using descent control devices. Employee #1 was on the roof pushing the rollers back and forth to move his coworkers from window to window. Employee #1 was moving the roller on the south end of the building when one of its wheels slipped off the edge of the parapet wall. This caused the rollers, which were tied together, to fall between six and seven stories to the ground. Employees #2 and #3, whose lifelines were only attached to the suspension point on the rollers, also fell to the ground. Both sustained injuries; Employee #2 was listed in critical condition and Employee #3 was in serious condition following the accident. When the south end roller went over the edge, Employee #1 was catapulted off the roof and fell approximately 84 ft 4 in. to the ground. He was killed. Neither of the rollers was anchored to the roof.