Abstract: On May 23, 2003, Employee #1 and his supervisor were assigned to repair water damage to a ceiling in an apartment complex. Upon arriving at the apartment complex, they were informed that a plumbing problem had created a hole in the ceiling in the living room of apartment Number 116. They went to the apartment and set up a 3-foot and a 6-foot ladder. The supervisor then went outside to his truck. Employee #1 said when his supervisor went outside, "I got on the 3-foot ladder, on the second step. I grabbed a two-by-four ceiling stud with my left hand and started trimming the sheet rock with my right hand. I was using a sheet rock knife to trim the hole. The sheet rock was dry and covered with paint. But there was a wet spot hidden by the paint. When the knife hit the wet spot, it went through very quickly and struck my left hand; cutting it from the mid-joint of my thumb (on the back side) to my wrist." An on-site manager witnessed the incident and called the Alameda County Fire Department. Paramedics treated Employee #1 at the scene and transported him to Eden Medical Center for further treatment. Investigators concluded that Employee #1 was injured because the knife he was using unexpectedly accelerated through a hidden wet spot in a piece of ceiling drywall. The unexpected acceleration of the knife caused him to lose control of it and ultimately strike his left thumb. The impact of the knife blade against his hand caused a laceration from the middle of the back of his thumb to the base of his wrist.