Federal Investigators Update Refinery Explosion Investigation

Updated: August 02, 2018 05:14 PM

A federal agency has released an update on its investigation into the explosion and fire at the Husky oil refinery in Superior.

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According to the Chemical Safety and Hazard Investigation Board, 36 people sought medical attention after the April 26 incident, which is more than had previously been reported. The people have been released from the hospital. An update released Thursday says eleven of the injuries were considered recordable under Occupational Safety and Health Administration regulations.

The explosion happened in the refinery's fluid catalytic cracking unit about four hours after workers began a planned shutdown of the unit.  Investigators said Thursday during start ups and shutdowns it more hazardous for things like this to happen. 

"Process unit start-ups and shutdowns are significantly more hazardous than normal oil refinery or chemical facility operations. Start up and shut downs involve many non-routine procedures," said Dr. Kristen Kulinowski, Interim Executive with the U.S. Chemical Safety and Hazard Investigation Board.

The report says it occurred during a scheduled break and many workers had moved away from the unit before the explosion.

A video shown at the news conference explained how the explosion happened in the refinery's Fluid Cataylitc Cracking Unit. 

Within the FCCU unit slide valves control the flow of material between the reactor which contains flammable hydro carbons and a regenerator which contains air. It is important to prevent mixing the hydrocarbons and air. However, investigators say conditions existed for the two to mix causing the explosion. That then led to a piece of debris to flying 200 feet striking a tank with 50,000 barrels of asphalt and releasing over 15,000 barrels of hot asphalt into the refinery, resulting in the fire.

Lead Investigator Mark Wingard, says a worn slide valve was likely the cause.

"Based on the process data and physical evidence, it seems like it wasn't sufficient to maintain that barrier," said Wingard. "At this point we can't speak to the inspection of maintenance that's been done ( on the valve equiptment) but that's something were certainly looking into."

when asked about the potential risks of the hydrogen fluoride tanks in the explosion, investigators said it's too premature to tell if that will be the focus of investigation.

"We will be looking at the debris that was swung across the site and determine whether there were additional potential hazards that resulted from that," said Kulinowski.

Investigators say they have seen this before at a similar explosion that happened at Exxon Mobil's refinery in Torrance, California.  

The report says debris from the explosion flew about 200 feet, puncturing a hole in the side of a steel storage tank containing about 50,000 barrels of asphalt.  About 15,000 barrels of asphalt spilled into the refinery and ignited about two hours after the explosion, causing a large fire that sent a plume of smoke visible for miles.

The federal investigation continues.  The CSB said investigators continue to collect data and evidence from the site, and they will develop a root cause analysis based on evidence.  They said they are in the process of concluding their field phase.

The explosion forced tens of thousands of people in Superior and areas south of the city to evacuate for the night.  In an earnings report last month, Husky said the incident caused $27 million in damage and led to $53 million in expenses.

As for the next steps, right now, they say they are still in the beginning stages. They are wrapping up the field phase so they can start a thorough analysis. The goal is to wrap up the investigation within 18 months, that's because of the depth of investigation, the complexity of equipment testing, and some of the work has to be contracted out.

Wingard said they are also in process of analyzing air quality data, and determining if the evacuation zone that day was appropriate for the potential risks.

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