Abstract: At 7:49 a.m. on August 10, 2019, Employee #1, a millwright, was working for the maintenance department at a sawmill. Employee #1 and three coworkers, two maintenance colleagues and one maintenance supervisor, were working on the third level of the sawmill building. They were tasked with removing a log sweeper arm machine on the production line and installing two new log sweeper arms in its place. Employee #1 was standing on the conveyor of one of the log production lines. He was installing a 1.5-inch metal bolt into a slot of the frame that held the new log sweeper arm in place. As Employee #1 was tightening the bolt using the open end of double-ended metal hand wrench, the connection at the bolt head slipped, which caused him to lose his balance. Employee #1 fell backwards through a two-foot by three-foot floor opening gap area where the bucksaw had been retracted. He fell approximately 12 feet, then he slid down an inclined plane and came to rest on the first level backstop. His head contacted a metal surface of the conveyor line. Employee #1 sustained a laceration on his forehead extending to the side above his left ear that required 17 stitches. He was hospitalized.