A factual update released about the ongoing investigation of the April 26 explosion and fire at the Husky Superior Refinery in Superior, Wisconsin.
The initial explosion occurred in the refinery’s Fluid Catalytic Cracking Unit (FCCU) at 10 a.m. while the refinery was shutting down the FCCU for maintenance and inspection, according to the U.S. Chemical Safety Board (CSB).
To date the CSB determined the following:
• The explosion took place during a planned maintenance shutdown of the refinery FCCU.
• The incident occurred during a scheduled break time and many workers previously in the unit before the explosion had moved either into blast resistant buildings or away from the process unit.
• One piece of debris from the explosion flew about 200 feet, and struck a large, nearby, aboveground storage tank containing about 50,000 barrels of asphalt. The side of the tank was punctured, resulting in the release of over 15,000 barrels of hot asphalt into the refinery.
• Approximately two hours after the release, the asphalt ignited, resulting in a large fire.
• As a result of the explosion, 36 people sought medical attention, including eleven refinery and contract workers who sustained OSHA recordable injuries. In addition, a large portion of Superior, WI, ended up evacuated.
In addition to the factual report, the CSB also released an animation of the events leading up to the explosion of the FCCU.
The CSB investigation is ongoing.
Investigators continue to collect data and evidence from the site. Investigators will develop a root cause analysis of this incident based on evidence collected during the investigation. A final report, including facts, analysis, conclusions, and recommendations will be issued at the end of the investigation.