HOUSTON (Reuters) - The U.S. Chemical Safety Board said on Sunday it decided against investigating a deadly explosion on Friday at Valero Energy Corp's Texas City, Texas, refinery, saying there had been no release of hazardous chemicals.

"We're stretched very thin right now," said board spokesman Daniel Horowitz. "We have 15 open investigations, including eight at refineries. Although it was a very tragic accident, it did not appear to involve a release of hazardous chemicals or be a threat to the community."

One worker was killed and two injured in the explosion of a boiler that provides steam for refining petroleum at the 245,000 barrel per day refinery, located 50 miles southeast of Houston.

Tommy Manis, 40, of Alvin, Texas, was killed instantly in the blast by "blunt force trauma" to the head, according to the Galveston County medical examiner's office. Manis was one of a group of workers attempting to restart the boiler after it shut down earlier on Friday.

The refinery continued operating at planned rates through and after the explosion, Valero said on Saturday. The boiler is one of several providing steam to the refining process.

The U.S. Occupational Safety and Health Administration began an investigation of the explosion on Saturday.

Valero has called the incident a "failure" of the boiler, saying a company investigation was under way to determine exactly what happened and its causes.

Local media have reported Texas City residents up to a mile away felt shaking and heard a loud noise late Friday night when the accident occurred.

Friday's accident was the second fatality at the Valero Texas City refinery in 11 years.

(Reporting by Kristen Hays and Erwin Seba; Editing by Leslie Adler)