Abstract: On Monday, March 11, 1985, Employee #1 climbed a tubular welded frame scaffold to access the top of an insulated ceiling panel. This ceiling panel had been cut and grooved on March 10, 1985, but was not yet fully installed. The foreman had instructed the employees to erect more vertical wall panels; they needed to finish one bay compartment so that the iron workers could start working. The 24 ft ceiling panel had two 1 in. undercuts that were 10 ft 10 3/4 in. apart, matching the spacing of the vertical panels. The tops of the wall panels were intended to fit into the ceiling panel's undercut grooves, but the ceiling panel had not yet been properly positioned over the vertical panels. Because the undercuts were not positioned, the insulated ceiling panel was unstable, not securely supported by the vertical panels. When Employee #1 mounted the insulated ceiling panel to begin work, his weight caused the panel to break. He fell approximately 23 ft to the concrete floor, striking the back of his head against a steel channel that was lying on the floor. He was killed.