Abstract: On January 24, 2014, Employee #1, a carpenter, and Coworker #1, a project superintendent who also was Employee #1's direct supervisor, both employed by a general building contractor, were working at a residential remodeling project. Employee #1 and Coworker #1 were building a catwalk to be used for installing a mechanical unit in the attic. Coworker #1 was up in the attic, nailing down pieces of plywood to create the catwalk. Employee #1 was working on the level below, cutting 22-inch by 24-inch pieces of plywood for the catwalk. Employee #1 told Coworker #1 that he (Employee #1) was going to bring a piece of plywood up to Coworker #1. There was an extension ladder that led from a stairwell to the attic. As Employee #1 ascended the extension ladder while carrying the plywood, he lost his balance on the fifth rung and fell into the stairwell. Coworker #1 immediately called his supervisor and had someone else call for emergency services. Coworker #1 then grabbed his first aid kit from the truck and administered first aid to Employee #1. The San Francisco Fire Department responded and transported Employee #1 to San Francisco General Hospital, where he was admitted and treated for fractures of the facial bones. Employee #1 underwent surgery and remained hospitalized for two days. This event was reported to Cal/OSHA by the San Francisco Fire Department at approximately 2:26 p.m. on January 24, 2014. Cal/OSHA began its investigation on January 27, 2014. Among those interviewed were Coworker #1 and the owner of the construction company.