Fire extinguished at ND oil supply company

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Smoke rises from the site of a fire in an industrial area of Williston, N.D. on Tuesday, July 22, 2014. Authorities have set up an evacuation zone within a half-mile radius of Red River Supply, the site of the fire. No injuries were immediately reported. Red River Supply provides services to oil companies working in North Dakota's oil patch. (AP Photo/Josh Wood)

WILLISTON, N.D. (AP) — A once-massive blaze at an oil supply and logistics company that housed flammable chemicals in Williston, North Dakota, has been extinguished, according to the town's fire department.

Most firefighters returned from the facility belonging to Red River Supply late Tuesday, though one truck remained early Wednesday to monitor hot spots, said fire department shift captain Steven Kerzmann.

"The fire is out, but you've got some smoldering embers that might pop up here and there," he said.

The blaze, which started around midnight Monday in an industrial part of the western North Dakota oil patch town, grew so intense that it at one point sent fireballs hundreds of feet into the air. Kerzmann said early Wednesday that the department is not sure what caused the fire.

State records show several flammable chemicals were on the company's property. The company's website says it provides storage, blending and delivery of drilling fluids, among other things. It did not respond to a request for comment.

At a news conference about 15 hours after the blaze began, Williston Fire Chief Jason Catrambone said officials couldn't identify which specific chemicals had burned at the site.

The North Dakota Department of Health and other agencies are monitoring air quality near the site for any potential threat, according to agency spokesman Tim Wiedrich. Williston Mayor Howard Klug said a hazmat unit that monitored air quality Tuesday morning found nothing of concern.

A large plume of smoke rose above Williston on Tuesday. It prompted the Federal Aviation Administration to issue a six-hour temporary flight restriction that lasted until 2 p.m. for Williston's Sloulin Field International Airport, airport manager Steven Kjergaard said.

Roads were closed Tuesday near the site, including a stretch of State Highway 1804. Local law enforcement officers cordoned off a half-mile area around the site, diverting traffic.