Abstract: Employee #1 was part of a crew preparing to install a "Y" connection on a sewer line pipe for a new building project. A 17 ft deep trench had been partially backfilled around the pipe so that two trench boxes pinned together, one 8 ft long and another 4 ft long, could be placed in the hole with between 18 and 24 in. between them and the bottom. The top edges of the excavation had been sloped so that the boxes extended 18 in. above the sloped edge. A track hoe had been used to position the boxes and Employee #1 was then sent in to make initial preparations for the connection. The track hoe bucket had been left with an end still inside one of the boxes. The backhoe either malfunctioned or the operator accidentally hit the control, causing the bucket to lurched and to pull the trench boxes toward the backhoe. The opposite end of the boxes became dislodged from the compacted dirt alongside the installed pipe, allowing the attached boxes to drop approximately 2 ft into the hole. Employee #1 was bent over examining the pipe when a brace on the trench box struck the back of his head, knocking him to the ground. He was transported to the hospital, where he was treated and released.