Laura Seitz, Deseret News
An explosion ignited a fire at the Holly Refinery Wednesday night in West Bountiful. No one was seriously injured.

WEST BOUNTIFUL — An explosion rocked one of the city's major refineries Wednesday night, but no workers were seriously injured.

Hydrofluoric acid likely caused the blast at the Holly refinery, 398 S. 800 West, just before 9 p.m., said South Davis Metro Fire Chief Jim Rampton.

"It was a pretty big fireball," Rampton said, though officials could not immediately say how much damage the flames caused.

Workers are at the facility 24 hours a day, but Rampton said he did not know how many people were inside at the time of the explosion. One worker received minor injuries when the force of the blast caused him to fall off a truck, officials said.

Police blocked off several blocks around the refinery, but no evacuations were ordered. Rampton said hydrofluoric acid could be dangerous in large quantities, but the flames helped mitigate the problem.

"One of the positive things was there was a fire with this," he said. "That does consume the poison that gets put out."

Rampton said there could be fumes produced by the fire, but tests of the air Wednesday night did not indicate a cause for concern.

By 9:15 p.m., the flames inside the facility had been knocked down. Refinery workers and firefighters remained on site, however, to monitor the situation.

There are five major refineries within the South Davis Metro Fire Agency's jurisdiction, and Rampton said both firefighters and refinery workers are given extensive training on how to handle such emergencies.

After the explosion, workers immediately shut down valves, blocking off chemicals that could have fueled the flames, Rampton said. Each refinery also has its own fire brigade.

"That's huge for us to be able to depend on those guys," Rampton said.

Last week, Holly Refining & Marketing Co. agreed to spend more than $17 million on upgraded pollution controls at the refinery, averting a federal lawsuit accusing the company of violating the Clean Air Act.

The U.S. Environmental Protection Agency, the U.S. Justice Department and the Utah Attorney General's Office had drafted a lawsuit accusing the company of violating the act by failing to control emissions of organic compounds such as carbon monoxide.

A subsidiary of Dallas-based Holly Corp., the refinery announced it will pay $120,000 in penalties as part of the settlement.