A crew was preparing a 20-foot section of 12-inch high-density polyethylene (HDPE) pipe to be swung into a welder using an excavator, where it would be welded onto a longer run of pipe. One employee was facing the longer pipe in the welder while the 20-foot section was being rigged. The 20-foot section moved and struck the employee's left knee. The employee's left leg was broken below the knee.