A 300-mm butterfly valve in an industrial oxygen pipeline ignited during system start-up, resulting in three fatalities. The valve was apparently stuck and the operators used pipe tongs to open it. Afterwards, hand wheel torque required to open identical valves when subjected to 35-bar pressure difference was measured. Three test valves opened easily but a high torque was required with the fourth one. This was due to a damaged PTFE sliding layer of the free shaft main bearing. Several possible causes of the fire were identified. Frictional heating could have occurred at a foreign body wedged between the disc and valve body or Fire Safe seal, or at damaged free shaft bearing. The heated metal parts would have ignited the PTFE seat or coating of the free shaft bearing, respectively. In addition, ignition of the Fire Safe seal or valve body by particle impact could have occurred due to contaminants carried by the oxygen flow or due to particles detached from the wedged foreign body. (C) 2008 Elsevier Ltd. All rights reserved.