BEVERLY, Ohio – A powerful explosion yesterday at a coal-burning power plant in southeast Ohio killed a worker delivering liquid hydrogen and injured nine others, authorities said.

The delivery driver was unloading hydrogen into cylinders just outside the plant when something triggered the explosion. Plant officials weren’t sure whether the truck or hydrogen tubes exploded or what caused it, said Vikki Michalski, a spokeswoman for American Electric Power.

The blast blew out the windows of a nearby building.

“It was real strong,” said Doug Burke, who was operating a front-end loader at Reed Minerals, about a half-mile from the plant. “I felt it inside my loader, and I looked up and saw smoke and then fire, and then after that steam.”

“If you blinked your eyes you would have missed it,” he said.

Although hydrogen gas is highly explosive, it is used to cool steam generators at the plant because it has a high capacity for heat and it is more efficient than using air.

Hydrogen is delivered to the plant about once a week, Michalski said.

The Muskingum River Plant continued to produce electricity after the explosion although the unit near the blast was shut down.

AEP officials said they were investigating the cause. Federal safety officials also were at the plant, which is near the West Virginia border and about 100 miles southeast of Columbus.

Nine workers were treated at three hospitals in Marietta and Parkersburg, W.Va., for mostly cuts and bruises, authorities said. None of the injuries were life threatening, Michalski said.

One worker at the Parkersburg hospital had head trauma, a spokesman said.

Washington County Sheriff Larry Mincks said the delivery truck caught fire but was still in tact, and there was not major damage to the plant, where 210 people work.

Across the river from the plant, bystanders gathered at a park to look but all that was visible was a fire truck pouring water outside the plant walls.

There are just a handful of homes and businesses near the plant.

Columbus-based AEP, one of the nation’s largest power generators, has more than 5 million customers in 11 states.