Jed Carlson / jcarlson@superiortelegram.com A Gold Cross Ambulance speeds past the road block on Hill Ave as a different ambulance speeds away from the scene after an explosion at Husky Energy in Superior on Thursday morning.
SUPERIOR, Wis. (AP) — A tank containing crude oil or asphalt exploded at a large refinery in Wisconsin on Thursday, injuring several people and prompting fire officials to urge people living near the still-burning plant to evacuate their homes.

No fatalities have been reported, but at least 11 people were being treated at hospitals in Superior, where the blast happened, and nearby Duluth, Minnesota.

The explosion at the Husky Energy oil refinery happened at about 10 a.m., Superior Fire Chief Steve Panger told The Associated Press.

Panger said the fire was out by 11:20 a.m., but Superior police later tweeted that the fire had reignited and urged residents living within a one-mile radius of the refinery to leave. Police blocked roads around the refinery in Superior, which is home to about 27,000 people and borders Minnesota to the north and the tip of Lake Superior.

A second wave of employees and contractors were rapidly leaving the scene after 12:30 p.m. as a series of seven or eight more explosions occurred at 12:40 p.m., according to the Superior Telegram.

Essentia Health spokeswoman Maureen Talarico said five people injured in the explosion are being treated at St. Mary’s Medical Center, a Level II trauma center in Duluth. She said emergency room physicians described those patients as awake and alert. Another five are being treated at St. Mary’s Hospital in Superior, Talarico said. She said the extent of injuries is unknown.

In Duluth, St. Luke’s Hospital was treating one person and did not expect to receive any more, spokeswoman Jessica Stauber said. She did not have a condition for that person.

Panger said a small tank containing either crude oil or asphalt exploded in the refinery. A contractor who was inside the building told WDIO television that the explosion sounded like “a sonic boom” and that it happened when crews were working on shutting the plant down for repairs.

No damage estimate was available.

State Rep. Rick Milroy issued a statement that today’s “disaster at the refinery in Superior has left everyone with a deep sense of worry and heavy hearts for all of the workers and families involved. Like most Superiorites, I have a lot close friends who work at the pant. Injuries have been reported, but thank God that no fatalities have been reported. I ask that everyone keep all of the workers, first responders, and their families in their prayers as they secure the facility and get the injured medical attention.”

In 2015 the federal Occupational Safety and Health Administration fined Calumet $21,000 over emergency response and flammable liquids violations. Those violations were marked as settled and the problems solved by the end of that year.

It was the only OSHA enforcement action taken against the refinery in the past 20 years, according to a search of the agency’s database.

In 2012 and 2013 there were four reports of hydrogen sulfide releases due to power outages, according to the National Response Center.

The refinery has not been fined over hazardous waste since 1999, according to the Environmental Protection Agency

The refinery’s most recent Risk Management Plan was submitted in 2012 and states: “In the unlikely event of a catastrophic release, the refinery, working in conjunction with local emergency management staff, is well prepared to respond and mitigate adverse consequences to the community or the environment.”

Calgary-Alberta-based Husky Energy refinery bought the refinery from Indianapolis-based Calumet Specialty Products Partners last year for over $490 million. It’s Wisconsin’s only refinery, and it produces gasoline, asphalt and other products.

The refinery, which dates back to the early 1950s, has a processing capacity of around 50,000 barrels per day and a storage capacity of 3.6 million barrels of crude and products. It processes both heavy crude from the Canadian tar sands in Alberta and lighter North Dakota Bakken crude.

Photo credit: Jed Carlson, Superior Telegram