Douglas County officials posted an update saying the fire was extinguished but asking residents in the evacuation area to stay away from their homes for at least another two hours. The fire had poured thick clouds of noxious black smoke into the air after the explosion rocked the refinery. Schools and a hospital also were evacuated.

Authorities said a tank of crude oil or asphalt exploded about 10 a.m. at the Husky Energy oil refinery in Superior, a city of about 27,000 that shares a Lake Superior shipping port with nearby Duluth, Minnesota. That prompted them to order the evacuation of a 3-mile (5-kilometer) radius around the refinery, as well as a 10-mile (16 kilometer) corridor south of it where the smoke was heading.

It was unclear how many people evacuated, but Mayor Jim Paine said most of the city was being evacuated. The refinery is in an industrial area, but there's a residential neighborhood within a mile to the northeast. The corridor downwind to the south of the refinery is sparsely populated. Schools in Superior and nearby Maple, Wisconsin, canceled classes Friday as a precaution.

Hospital officials said only one of the injured was seriously hurt, with what was described as a blast injury. No deaths were reported, and officials said all workers had been accounted for.

Thick, black smoke poured from the refinery hours after the explosion. Refinery manager Kollin Schade said the smoke was from burning asphalt that was so hot that firefighters were unable to attack the fire to try to put it out. Emergency officials later said another tank had caught fire, too, though they didn't specify what was in it.

A four-person team from the U.S. Chemical Safety Board will investigate the blast. The board makes safety recommendations after serious chemical incidents.

The fire was put out about 11:20 a.m. but reignited, prompting police to urge residents living within an evacuation area to leave. Police blocked roads into the area around the refinery. Three schools and St. Mary's Hospital in Superior were evacuated as a precaution.

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.

Kara Tudor, 30, and Julia Johnson, 27, live about 2 miles from the refinery and were ordered to evacuate. They quickly scooped up their two dogs and three cats, grabbed their toothbrushes and drove to a friend's house in Duluth, where they were watching the news for updates.

Johnson, who was working from home at the time of the blast, said the windows shook.

"It felt like something had hit the house, like a vehicle or a branch from a tree. ... Our dogs started barking. It was a stressful moment," Johnson said.

Johnson also wondered if a plane had crashed and feared the house might collapse. Johnson looked around but didn't see anything — then a few moments later saw dense black smoke rising over the trees.

By lunchtime, they had to go. Tudor went home as the clouds in the sky were masked by thick, black smoke and the air smelled like burning tires.

"It was scary," Tudor said. "We threw our dogs in (Johnson's) car. I put the cats in my car ... we grabbed our toothbrushes and just left. ... We were mostly focused on the pets because it smelled like burning tires outside and we knew that wasn't a good smell."

Tudor, a scientist at a research company, said residents were not told much about the potential danger, what was in the smoke or why it was so black. But she said it was clear people should not have been breathing it in and she wondered how it will affect the water and air quality.

Oil smoke can contain a mix of noxious hydrocarbons and other chemicals with potential short- and long-term health effects.

National Weather Service radar showed the smoke plume extending south-southeast, taking it into sparsely populated areas. The weather service said winds were expected to weaken Thursday evening and eventually shift toward Lake Superior. It said the smoke probably would not affect Duluth, a city of about 87,000.

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

The refinery had been fined by federal officials several years ago under its previous owners. U.S. Department of Labor spokesman Scott Allen said the Occupational Safety and Health Administration fined Calumet Superior LLC $21,000 over emergency response and flammable liquids violations in 2015. The violations were settled and the problems resolved by the end of that year.

Allen said it was the only OSHA enforcement action taken against Calumet Superior LLC in the past 20 years. Calumet Superior operates as a subsidiary of Calumet Specialty Products Partners, which sold the plant to Husky Energy last year. 

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.

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