A pipeline crew welding together a pipeline segment was using an excavator to make minor adjustments to the alignment of the pipe. The machine's controls were locked-out while the pipeline welder was working on the pipe. When an adjustment to the pipe's alignment was required, the welder stepped back from the pipe and the excavator operator was signaled to make the adjustment. The excavator operator sat down in the operator's seat and did not notice that his jacket caught on the control stick and engaged it. The excavator operator proceeded to disengage the lockout lever and the boom of the excavator immediately went into motion, pulling the pipe segment in towards the bank of the excavation. This caused the welder to be crushed between the pipe and the bank of the excavation. The welder suffered serious injuries, including broken ribs, a punctured lung and a fractured jaw.