A mushroom cloud is seen over western Texas after an explosion at a refinery.
A thunderous explosion rocked an oil refinery Monday, injuring four workers and shaking buildings miles away.
One employee was hospitalized for burns, while the others were treated and released, said Blake Lewis, a spokesman for refinery owner Alon USA.
All workers were accounted for about an hour after the explosion, he said. The refinery employs about 170 people.
Fires caused by the blast were under control but still burning in the afternoon, Lewis said. The Dallas-based company was waiting for access to the site to investigate the cause of the explosion.
The blast sent black smoke billowing into the sky, and forced the closure of schools and an interstate.
"It was extremely scary. You shook you were so scared," said Laura McEwen, the mayor's wife who lives about two miles from the refinery. "Our walls shook. It jolted your bed. It was like an earthquake."
John Moseley, managing editor of the Big Spring Herald whose downtown office is also about two miles from the refinery, said, "I thought it would knock the walls down."
Two elementary schools were evacuated, then classes were canceled at all nine campuses in the Big Spring school district, assistant superintendent Carie Dunnam said.
Classes also were canceled at Howard College, according to the two-year junior college's Web site.
The explosion forced open the doors of the school district's administration building about four miles from the plant, Dunnam said.
"Literally pieces of my ceiling came on top of my head," she said.
Bus routes were affected by road closures and that emergency officials were warning of the potential for more explosions, Dunnam said. Parents were asked to pick up their children, she said.
Interstate 20 was shut down near the plant, Big Spring police spokesman Roger Sweatt said.
"There's some fire and a whole bunch of smoke," Sweatt said.
Big Spring is about halfway between Dallas and El Paso.
The blast followed one the night before at an iron pipe factory in Utah that injured 11 workers, one critically.
The explosion occurred on the casting floor Sunday night after a frozen pipe leaked water onto calcium carbide, said John Balian, general manager at Pacific States Cast Iron Pipe Co.
The explosion in Springville was loud enough to be heard at the Utah County jail, more than 4 miles from the plant, sheriff's Sgt. Spencer Cannon said.