Abstract: At approximately 11:00 a.m. on October 28, 2011, Employee #1, a dental assistant, and a second dental assistant were decorating and preparing a room for a party. Employee #1's employer, a dentist, had arranged to have an office party at the site. At the same site, employees of R.A.H. Industries, Inc., dba, Concourse Automobile Restoration (Concourse) had created an opening in the floor for the installation of a fireman's pole that was to go from the second floor to the first floor. Concourse employees had covered the opening with two 4-foot by 4-foot pieces of plywood that were not secured or marked, as required. Employee #1 and the second dental assistant were moving several items from the floor to make space for tables for the party. While Employee #1 was removing the second piece of plywood, she walked and fell through the opening. She fell approximately 14 feet from the second-story floor to the cement floor below. Employee #1 was seriously injured, with fractures to her elbow, wrist, head, and back (in two spots). She was taken to Henry Mayo Hospital, and she was hospitalized for more than 24 hours. The Los Angeles County Fire Department reported the accident to the Van Nuys District office at 11:55 a.m. on October 28, 2011. Both employers were issued accident-related citations.