Abstract: At approximately 5:45 p.m. on December 22, 1990, Employee #1 was installing dust collectors in the SAB construction area. As the end of the work day approached, employees began to put away their tools. Employee #1 was last seen securing a portable ladder near his work area. Near the ladder were two sheets of 4 ft by 8 ft plywood leaning against the guardrails, and a sheet of plywood lying on a grating, adjacent to the leaning plywood. It appeared to Employee #1 that the plywood on the grating fell from the leaning position against the guardrail. He went over to pick it up, unaware that it was actually covering a 43 1/4 in. diameter floor opening, and fell 34 ft to the concrete floor. He was killed. No one actually saw him pick up the plywood, but witnesses saw him falling.