Abstract: Employee #1 and other employees were erecting prefabricated metal walls on the fourth floor of a multi-unit condominium project. The employees were preparing to erect an exterior wall on the north side of the building, next to the east stairwell. In the area where they were placing the wall was a 4-foot by 3-foot floor hole that was covered by two pieces of plywood, neither of which was secured to the floor. The top sheet of plywood was a full 4-foot by 8-foot sheet. The second sheet was just bigger than the floor hole. Neither sheet was marked with any indicators that they were protective coverings for a floor hole. The employees moved the 4-foot by 8-foot sheet prior to placing the wall into place. They moved this sheet so that it would not interfere with placing the wall. After the employees set the wall in place, Employee #1 secured the wall temporarily by shooting it down with a Hilti gun while other employees held it in place. After temporarily securing the wall, Employee #1 stepped back away from the wall and onto the unsecured corner of the small sheet of plywood still lying over the floor hole. This caused the plywood to give away under the pressure. Employee #1 fell through the hole and 11 feet to the concrete floor. Employee #1 sustained a fractured arm, fractured ribs, and several cuts and abrasions. Employee #1 was transported to a local hospital, where he was treated and released. Employee #1 was not wearing any fall protection, only a hard hat.