The U.S. Chemical Safety Board (CSB) team investigating an explosion at the Husky Energy oil refinery in Superior, Wisconsin has narrowed its focus to equipment within the refinery’s Fluid Catalytic Cracking, or FCC, unit. The April 26, 2018 blast injured approximately 20 employees and caused an evacuation of residents in the surrounding area.

When the incident occurred, the refinery was preparing to enter a 5-week maintenance turnaround, during which time equipment is shut down so that it can be opened, inspected, and repaired as needed. The initial explosion took place within the FCC unit, which “cracks” heavy, high boiling point hydrocarbon molecules into smaller molecules with lower boiling points. CSB is reviewing documentation pertaining to the FCC unit.

The explosion caused property damage and loss of containment of an asphalt tank. The contents of the tank spilled out and the material combusted.

Other areas of inquiry

The FCC unit is not the only aspect of the refinery being examined:

• The CSB team has photo-documented a large percentage of the refinery and conducted interviews with approximately 50 Husky Energy employees and contractors who were working at the facility on the day of the incident. (The CSB said it is getting the cooperation it needs for its investigation from Husky Energy, the International Union of Operating Engineers and other trade unions that represent workers at the plant.)
• The agency has retained a metallurgical expert to help identify what metallurgical testing will be necessary to determine the initial cause of the explosion and will work with Husky and other agencies to determine the protocols for the testing.     
• The CSB has collected and will analyze the large amount of debris which was scattered in and around the refinery complex.