Process Safety Management Lessons Learned from a Petroleum Refinery Spent Caustic Tank Explosion

No injuries or fatalities resulted from a spent caustic tank explosion in a major Midwestern USA refinery on August 14, 2007. The explosion occurred after operators initiated a routine manual procedure to safely vent hydrocarbons from spent caustic being transferred into the atmospheric-relief, cone roof storage tank. This procedure was developed in 2005 to mitigate a Process Safety Management (PSM) risk at a tank that had been in service since 1956.

An investigation was launched to determine the explosion's cause. This paper details the investigation's conclusions and corrective actions. It describes the factors that defeated a HAZOP action item's intended purpose to reduce the risk for a PSM failure, which led to a design change that had the opposite effect. Lessons learned are communicated for organizations to avoid repeating the same mistakes.