Abstract: Employee #1, a second-year plumbing apprentice, was helping his employer install a hot water pipe on the fourth floor of an addition being constructed at the headquarters of the Baltimore Police Department. His employer had asked him to get a sighting on the pipe, which ran in a north-south direction across the ceiling and into an area protected by a wire rope guardrail system. The guarded area consisted of a men's lavatory, three elevator shafts, and a mechanical shaft. The hot water pipe, which was one of three pipes that Employee #1 and his employer were to install, protruded approximately 12 to 18 in. into the guarded area. When Employee #1 entered the guarded area to sight the pipe, his employer was already in it, working on the pipe in the area's north side. The employer later said that Employee #1 was in plain view as he entered the guarded area. In the process of siting the hot water pipe, Employee #1 walked backwards in a southerly direction, and fell through the 32 in. wide by 64 in. long hole in the cross-bracing of the mechanical shaft. He fell 48 ft and landed on some steel pipes at the bottom of the shaft. Employee #1 sustained a concussion, a fractured knee, and a lacerated liver, and was taken by ambulance to the Maryland Shock Trauma unit. His employer's foreman later stated that plumbers are responsible for the apprentices working under them. Although the employer has a policy of using fall protection 100 percent of the time, it was not consistently enforced, and violations were not documented. Employee #1 was not using any form of fall protection at the time of the accident.