Abstract: At approximately 2:30 a.m. on April 13, 2010, Employee #1 was walking to her locker to retrieve her belongings at the end of her work shift. She slipped on a puddle of dirty mop water on the floor, adjacent to a sink located in the Janitorial Equipment Room. When she slipped, she fell on her right knee as she attempted to break the fall. She was not carrying anything in her hands. When her knee struck the tiled floor, Employee #1 heard something crack and experienced great pain. Earlier that day, janitors had dumped out waste water containing a residual of Floor Cleaner 33 from their mop buckets into the sink. Employee #1 estimated that there were six cups of waste water on the floor where she fell. Employees routinely lift the 15 pound mop buckets, which are usually approximately half full of waste water, to dump out the waste water into the high set sink, the rim of which sits approximately three feet from the floor. Employee #1 stated that she observed water in the same general area of the floor next to the sink almost every day. The floor having been recently waxed may have been a factor that contributed to her fall. There were no floor mats in the room and there were no signs to warn employees of the spill and or the slip hazard. After the injury, an ambulance arrived and transported Employee #1 to Kaiser Permanente Los Angeles Medical Center, where she was admitted on April 13, received surgical treatment for a fractured right patella, and was discharged on April 15, 2010.