An update published by the U.S. Chemical Safety and Hazard Investigation Board in December provides the latest information from the agency’s investigation into the 2018 explosion and fire at the Husky Superior Refinery in Superior, Wis. On April 26, 2018, the refinery was shutting down in preparation for a five-week turnaround when the explosion and subsequent fire occurred. A portion of the city was evacuated, and 36 people sought medical attention, including 11 refinery and contract workers. According to CSB’s update, evidence suggests similarities with the February 2015 explosion at the ExxonMobil Refinery in Torrance, Calif. The 2015 explosion in Torrance was caused by an accumulation of hydrocarbons inside 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, which resulted in a piece of equipment igniting. Two workers were injured, and the explosion caused serious damage up to a mile away from the facility.  CSB’s update states that both the Superior and Torrance explosions “resulted from the inadvertent mixing of hydrocarbons with air inside the unit that found an ignition source.” In both incidents, the explosions occurred while the fluid catalytic cracking unit was not in normal operation and toward the end of an operating cycle.  The similarities between the 2015 and 2018 incidents have spurred CSB to examine areas of improvement for the industry. For more information, visit CSB’s for the Husky Energy Refinery explosion and fire. A of CSB’s update is available on the agency's website.