Multiple process safety management system deficiencies contributed to the February 2015 explosion and near miss at the ExxonMobil Refinery in Torrance, Calif., according to a final investigation report released in May by the U.S. Chemical Safety Board (CSB). The explosion was caused by an accumulation of hydrocarbons inside of the refinery’s fluid catalytic cracking unit, where products such as gasoline are produced. A slide valve acting as a barrier to prevent hydrocarbons from flowing into the air side of the unit failed, and hydrocarbons flowed in and ignited a piece of equipment. Two workers were injured, and the explosion caused serious damage and scattered catalyst dust up to a mile away from the facility. In 2015, approximately 148,000 residents lived in the city of Torrance, which surrounds the refinery. Due to weaknesses in the refinery’s process safety management system, the fluid catalytic cracking unit was being operated without pre-established safe operating limits and criteria for shutdown, CSB found. The slide valve that failed had degraded significantly and did not work as needed during the emergency. CSB investigators also learned that workers violated corporate lockout/tagout requirements during work leading up to the incident. The CSB investigation also revealed that a large piece of debris thrown during the explosion nearly missed a tank that contained tens of thousands of pounds of modified hydrofluoric acid (MHF), which, according to NIOSH, can seriously injure or cause death at a concentration of 30 ppm. The refinery was sold by ExxonMobil in July 2016 and now operates as the Torrance Refinery Company. ExxonMobil has not responded to CSB’s requests for information regarding safeguards to prevent or mitigate a release of MHF. CSB has issued subpoenas for this information and is pursuing enforcement in federal district court. According to the agency, the refinery has had multiple incidents since the explosion in February 2015. More information, including the final report (), is available on CSB’s .