Abstract: The employer was laying a 10 in. gas pipeline for a distance of 235 miles, replacing a line that had been installed in 1929. The stringing crew was unable to place pipe joints beside the trench in one area because the pipelaying machine was too big to get around some trees. The pipe bending crew had a smaller pipelayer (Caterpillar, model 561D, side-boom pipelayer) that they used to place the pipe on each side of the trees. Employee #1, a laborer on the crew, was hooking and unhooking the pipe joints being moved. The crew had placed a joint on one side of the trees and the operator backed around the tree with the side boom in a vertical position. Employee #1 was walking alongside the pipelayer. The operator started lowering the side boom, which struck Employee #1. He was knocked against a pipe joint and suffered fatal internal injuries.