Investigators work to determine cause of blast at Wisconsin refinery

[April 27, 2018]  By Brendan O'Brien

MILWAUKEE, Wis. (Reuters) - Investigators on Friday searched for the cause of a blast at a Husky Energy refinery that injured at least 15 people and rocked a northern Wisconsin city, sending smoke billowing into the sky and prompting tens of thousands to evacuate.

A massive explosion shook Superior, Wisconsin, a city of about 27,000 people, at about 10 a.m. local time (1500 GMT) on Thursday, local authorities said.

At least 15 people were injured, local media reported, and at least 10 people - one seriously injured - were taken to area hospitals, said a spokeswoman for Essentia Health-St. Mary's Medical Center, which operates hospitals in Superior and nearby Duluth, Minnesota.

What ignited the blast was not clear. After an initial blaze was extinguished, a storage tank was punctured, and a second fire erupted, Husky Energy spokesman Mel Duvall said.

Another tank caught fire at 3:15 p.m., a local ABC affiliate reported, citing Douglas County authorities.

"The emergency situation at the Superior Refinery is now over, and our focus in the days ahead will turn to the investigation and understanding the root cause of the incident," Husky Energy said in a post on Twitter on Thursday night.

Thick black smoke billowed from the facility and hung over Superior throughout the day, forcing tens of thousands to flee homes and businesses. The evacuation order remained in effect late on Thursday, the Superior Police Department said on Twitter.

Friday classes were canceled in Superior and nearby Maple school districts.

There were no reports of fatalities, and all of the refinery's workers have been accounted for, Husky Energy's Duvall said.

Dark smoke rises from Husky Energy oil refinery following an explosion in Superior, Wisconsin, U.S., April 26, 2018. REUTERS/Robert King/Duluth News Tribune

Specialists from Williams Fire & Hazard Control of Port Arthur, Texas were hired by Husky Energy and were flying to the scene on Thursday to direct efforts to battle the blaze.

The refinery, which can process up to 38,000 barrels of oil a day, had additional workers on site preparing for a plant-wide overhaul, he said.

The U.S. Chemical Safety and Hazard Investigation Board has sent a four-person team to investigate. The non-regulatory federal agency investigates serious chemical accidents such as refinery fires.

Husky purchased the refinery from Calumet Specialty Products Partners LP last year, saying at the time that it intended to keep all of its workforce of 180. It produces asphalt, gasoline, diesel and heavy fuel oils, largely using heavy crude oil imported from Canada.

(Reporting by Brendan O'Brien in Milwaukee; Editing by Kenneth Maxwell and Adrian Croft)

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