Abstract: On May 22, 2006, Employees #1 and a coworker were installing a 10 in. diameter sewer line in an approximately 36 in. wide by 7 ft 3 in. deep trench. They finished putting in the first section of pipe and tamped it in with a mechanical tamper. The employees then had the excavator dig out for the next length, put bedding rock down, and install the second section of pipe in the trench. They were using a laser to make sure it was on grade when a coworker standing near the trench saw the north wall start to move and shouted out a warning. The wall caved in on them, completely covering the coworker and burying Employeee #1 up to his waist. Both workers were successfully extricated. Employee #1 suffered a cracked rib and bruised shoulder where he was struck by a large clod of the clay dirt. The coworker also suffered a cracked rib, as well as a small puncture to his lung, which quickly closed. Both employees returned to work within seven work days. The trench had been dug in clay soil, but a natural gas line had been installed 16 to 18 in. to the north and about 48 to 52 in. deep. This left an approximately 12 in. wide clay wall of original material between the two excavations, which is what had toppled into Employee #1's trench. In addition, the trench in which the pipe was being installed was not shored or otherwise protected against cave-ins. There had been heavy rains in the area during the night before the accident.