Abstract: At approximately 6:30 a.m. on March 12, 1997, Employee #1 was engaged in drywall work near the second-floor elevator shaft of the south wing of the central plant building. A rolling scaffold had been installed across the elevator shaft opening to facilitate the job. After completion of drywall operations in that immediate area, the scaffold was being dismantled. Employee #1 was standing close to the elevator shaft opening and extended his hand to grab part of the scaffold that was over the opening. As he did so, he leaned or pressed against the top rail of the temporary guardrail. His weight dislodged the two steel posts that were clamped to the floor slab to hold up the rail and he fell 16 ft through the guardrail into the elevator pit. Employee #1 suffered a dislocated shoulder and was transported to the Torrance (CA) Memorial Hospital. The main causal factors in this accident include (1) erecting a guardrail, including its connections and anchorage, was not capable of withstanding horizontal or vertical loads to the extent required by regulations; and (2) failure to provide the guardrail, which was likely to get heavier-than-normal stresses from workers carrying building materials, with additional strength through use of heavier stock, bracing, or other methods.