WOODS CROSS — Hydrogen gas leaked from a pipe and made contact with a nearby heater, causing a refinery explosion that damaged at least a dozen homes here this week, according to early findings from investigators.

No injuries were reported as a result of the Silver Eagle Refinery, but Donald Holmstrom, the U.S. Chemical Safety Board's lead investigator, said five workers were inside the unit just minutes before the explosion Wednesday morning.

"There was a large fireball in the unit," Holmstrom told reporters Saturday afternoon. "The unit was immediately engulfed in flames that went as high as 100 feet in the air. We're extremely fortunate that no one was hurt."

The unit where the explosion occurred generally removes sulfur and wax-like material from diesel fuel, but Holmstrom said workers were performing a special operation to regenerate the reactor's catalyst and remove impurities Wednesday.

The pipe was carrying 630 pounds of pressurized hydrogen when it ruptured, the investigator said. The explosion sent hydrogen and "waves of pressure" at a subdivision to the east, damaging a dozen homes.

Holmstrom said investigators must still evaluate whether the pipe was suitable for the process or if there were welding problems or cracking.

The Chemical Safety Board will assess the refinery's safety practices and analyze studies done by the city, the refinery and developers before releasing the final results of the investigation sometime in the next year.

Holmstrom was already leading an investigation into an incident at the Silver Eagle Refinery that occurred in January. Of the 10 investigations handled by the board since 2007, three have been in the Salt Lake area, he said.

"The Chemical Safety Board is very concerned about the number of refinery incidents we're seeing," Holmstrom said.

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