Abstract: At approximately 2:45 p.m. on April 6, 1998, Employee #1, a full time carpenter, and three coworkers were nailing plywood sheeting on the 12 ft 6 in. high, 6,400 sq ft second-floor mezzanine of a building. At the end of the shift, Employee #1 and coworkers were at the west side of the building and left the mezzanine by walking across a 2 by 4 diagonal/plank known as a truss joist. Employee #1 was walking backward down the plank when it became displaced and he fell, injuring his left knee joint. He was transported to the hospital, where he underwent surgery to insert a metal plate in his knee. Employee #1 was released three days later.