A four-person investigative team from the U.S. Chemical Safety Board continues to investigate the April 26 explosion at the Husky Energy oil refinery in Superior, Wis.
The refinery was shutting down in preparation for a five-week maintenance turnaround when the incident occurred. The initial explosion caused property damage and loss of containment of an asphalt tank. The contents of the tank spilled out and the material combusted. Several workers sought medical attention, and thousands of residents near the refinery were asked to evacuate due to heavy smoke.