Fire from the Cascading Failure of an Oxygen Supply System

This paper discusses the investigation, findings, and root cause analysis of a fire due to the loss of oxygen containment in an ethylene oxide process.  This is one of many types of processes that may contain a high pressure oxygen supply system.  In such systems, the pressure and velocity of the oxygen stream are related to the potential for ignition of system components.  Thus, measures are taken in design, operation, and maintenance to utilize ignition resistant materials of construction. 

While more ignition resistant than carbon steel, stainless steel is still ignitable under certain process conditions in oxygen enriched atmospheres.  In this incident, unanticipated conditions led to ignition of internal parts and stainless steel components in the high purity oxygen system.  The resulting loss of oxygen containment caused a fire that destroyed the oxygen injection system and allowed a significant release of a combustible process gas stream.  While automated safety instrumented safeguards shut down the oxygen supply to the system, the ensuing fire involving the combustible process gas stream continued.  Consumption of both steel and ignition-resistant alloy components in the system during the oxygen enriched fire masked the underlying causes of the system failure.  No injuries were sustained in the incident, but the process unit sustained major damage and required a lengthy outage for repair.

Given the level of damage to the oxygen injection system, the failure analysis required rigorous and systematic investigation by a multidisciplinary team.  Through evaluation of the process data, metallurgical analysis of the damaged components, and understanding of the process dynamics, detailed hypotheses were developed, tested and refuted leaving a few most likely hypotheses explaining the cause of the incident.  The lessons learned from the incident were used to develop a system redesign and maintenance guidelines for the rebuilt unit to mitigate the likelihood of future failures.