Abstract: Employees #1 and #2 were maintenance employees at a production facility where high pressure natural gas from 18 wells went through machines that separated gas from liquids. When a well was first brought on line, the flow line was routed through an indirectly fired heater where hot water around the flow line melted the paraffin in the gas. Chicksan joints (swivels) and 20 ft lengths of 2 in. diameter pipe with hammer union fittings on each end routed the flow line through the heater. Employees #1 and #2 had to replace a lead O-ring in a chicksan joint. They depressurized the system, changed the O-ring, then put the hammer union fitting back together. When they brought the well back up to approximately 4,200 psig, a 2 in. diameter threaded nipple stripped loose from a female flange, causing a chicksan joint to flail around. It struck Employee #1, killing him. Employee #2 was knocked down and bruised.