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Process Safety Management System Issues Lead to an Explosion

On May 3, 2017 the Chemical Safety Board (CSB) released its final report into the 2015 explosion that occurred at the ExxonMobil refinery in Torrance, California within the facility’s electrostatic precipitator (ESP). An ESP is a pollution control device that removes particles from a gas stream using an induced electrostatic charge from charged plates. The refinery used the ESP in their fluid catalytic cracking (FCC) unit to remove catalyst particles. The accident was caused when undetected hydrocarbons back-flowed through piping from the FCC unit to the ESP causing it to ignite.

Despite the fact that the FCC unit was shut down for planned maintenance, it was not sufficiently disconnected from the rest of the equipment at the facility. The planned maintenance caused a pressure deviation that aided the backflow of hydrocarbons and the subsequent explosion. The refinery did not have proper hydrocarbon detection equipment that would have been able to alert the employees of the leak.

The CSB conducted an investigation and published a detailed report of the causes of the accident. They found that a lack of proper process safety management lead to the explosion. The refinery did not have safe operating limits or process conditions for shutting down the FCC unit. The refinery failed to conduct a sufficient hazard analysis, but used procedures from a similar operation from 2012. The procedures from 2012 were not accurate for these new unit conditions and thus safeguards were not in place to prevent the backflow of hydrocarbons. Additionally, ExxonMobil did not conform to specific standards for operating process equipment in a refinery.

Fortunately, no one was killed in this accident, but four workers were injured. There were also hydrofluoric acid (HF) tanks near by that were almost hit from flying debris. HF is a toxic chemical and if the tanks were hit by debris a larger explosion could have occurred causing more serious injuries and death. These accidents are an industry-wide problem due to the lack of hydrocarbon detection equipment. There have been four other similar incidents since this 2015 explosion that has caused regulators in California to reconsider refineries’ use of HF and discuss an alternative to be used in the alkylation process.

If you are interested in more information about this specific incident, please visit: If you would like to discuss process safety management procedures at your facility to prevent such tragedies from occurring please contact Suzanne Custons ( or Maria Maciejewski ( of Baron Environmental.

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