Abstract: On June 5, 2009, Employee #1, a sheet metal worker, was installing flex duct for the HVAC system in the carpenter's shop. Employee #1 was working above the ceiling where the joists and insulation were located. Employee #1, was using plywood sheets above the ceiling for support. While moving one plywood sheet around, he stepped on a joist block that failed and caused him to fall to the floor. The height of the fall was measured 10 feet and 4 inches and the joist block was a two-by-four board. The opening created by Employee #1 when he fell measured to be 23 inches by 46.25 inches. One nail was observed in the block and another nail was in the joist. When Employee #1 stepped on the joist block, the nails pulled out of the joist block and joist resulting in the fall. Employee #1 had a mild concussion as a result of the fall.