Abstract: At approximately 11:00 a.m. on July 26, 1993, Employee #1 was applying a soaping compound on the end of a corrugated PVC sewer pipe while standing in the bottom of a 5 ft wide by 20 ft long by 20 ft deep trench. The pipe was 18 in. in diameter, 12 ft long, and weighed approximately 80 lb. The pipe was suspended at its midpoint by a nylon sling attached to the bucket of a backhoe. Employee #1 was positioned inside of stacked trench boxes--two boxes measuring 4 ft by 8 ft by 16 ft and one box measuring 4 ft by 4 ft by 16 ft. The spoil base was set back the width of a Caterpillar 968 bucket with side cutters which measured 3 ft. A clod of dirt broke free of the north end of the trench, rolled into the excavator end of the trench box, and struck the PVC pipe, causing it to swing. The pipe struck Employee #1 and knocked him to his knees. He climbed from the trench by a straight ladder and 20 minutes thereafter was taken to the local hospital. When he was examined no injury was apparent, but he was admitted for overnight observation and released to duty the following day.