Abstract: Employee #1, who worked for a company that performed HVAC control wiring, accompanied his foreman into a house under construction to check a wiring chase and plan a job. The foreman incorrectly presumed that Employee #1 was familiar with the work area. The two men accessed the work area by way of what would eventually be a stairwell, but which at the time was only a hole cut in the wall near the balcony on the second floor main hallway. The foreman entered first. Employee #1 watched him step down into the opening, turn left, and then move out of sight. Employee #1 followed, but when he stepped into the opening he found that the area was unlit, and that he could see neither what was in front of him nor where the foreman had gone. He listened, heard the foreman to his left, and then put one foot out to find something to stand on before he moved. Employee #1 felt what he thought was the concrete slab above the second floor hallway, took a step, and fell 10 ft through a suspended ceiling to the floor. He sustained injuries that required hospitalization.