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CSB Team Investigating Husky Energy Explosion Focusing on Refinery’s Gasoline-Converting Unit


Federal investigators looking into last week’s massive Husky Energy explosion in Superior, Wisconsin, have zeroed in on its origins.

Initial Explosion Occurred in Refinery’s FCCU

Tom Zoeller, a senior advisor with the U.S. Chemical Safety Board (CSB), told Wisconsin Public Radio that an initial explosion in the facility’s fluid catalytic cracking unit (FCCU) ignited a series of explosions and fires that injured 20 workers and forced the temporary evacuation of nearly everyone in Superior, a city of roughly 27,000 people.

Shrapnel from the first explosion pierced a nearby tank, spilling asphalt which ignited.

Metallurgical Analysis Ordered to Determine Cause of FCCU Failure

The FCCU is the area of a refinery where crude oil is converted into gasoline and other petroleum-based products.

The 4-person CSB team tasked with investigating the Husky Energy explosion is working to determine what caused the initial blast. Among other things, they have ordered a metallurgical analysis of the FCCU to learn why it failed.

“What they will look to determine is were there cracks in the metal, fatigue in the metal, that weakened it during the process of the shutdown when there were temperature or pressure changes that the metal failed and gave way, causing it to break apart,” Zoeller said.

Zoeller noted that the team had not yet been able to inspect the blast site because the refinery units are still too unstable. However, they expect to get in by the end of next week.

Husky Energy Refinery Was Being Prepped for 5-Week Shut-Down

The April 26th explosion occurred around 10:00 a.m., as workers were preparing the Husky Energy refinery for a 5-week shut-down for cleaning.

As many as 20 workers on site were injured, including 11 who were taken to area hospitals.  The remaining were treated at the scene.

According to Husky Energy, most of those injured at the refinery were employed by the company contracted to clean the facility.

Six other people were treated at a local emergency room Thursday evening for minor injuries related to the evacuation.

Explosion Risk Increases During Refinery Shut-Downs

Zoeller noted that refinery shut-downs and start-ups are particularly dangerous periods.

“There needs to be greater attention to detail because you’re dealing with products and systems that work with different pressures and temperatures,” he said. “Those, if they’re not closely monitored, can create problems.”

The CSB investigated a similar incident at BP’s Texas City, Texas refinery in 2005, after a massive explosion killed 15 people and injured 180 workers.

The initial blast occurred as crews were working to restart a depressurization tower. The tower over-pressurized, igniting the explosion.

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