SALT LAKE CITY (AP) ¿ An explosion at a Utah oil refinery ¿ the second this year ¿ smashed windows, bent garage doors and peeled siding Wednesday from 10 nearby houses, officials said.

Federal investigators expressed alarm over the extent of damages caused by a refinery that has had a history of trouble dating to 2003.

The U.S. Chemical Safety Board was still investigating a January fire that burned for 11 hours when it dispatched a team to look at Wednesday's blast at Silver Eagle Refinery in Woods Cross, which is five miles north of Salt Lake City.

In all, 10 homes were damaged, said David McSwain, president of Silver Eagle, a company that operates its only oil refinery in Woods Cross.

A city building inspector condemned one house as structurally unsound after the blast shifted it off its foundation and knocked lose a roof truss, said Woods Cross Mayor Kent Parry. Officials feared the house could collapse in high winds.

The blast started in a vessel, called a diesel hydrotreater, that removes sulfur compounds from diesel fuel, said Donald Holmstrom, the Chemical Safety Board's investigations supervisor.

The refinery in Woods Cross had fires in 2003, 2005 and 2007, according to federal records. The board also was looking into an Oct. 21 fire at a nearby Tesoro Corp. refinery.

"We're concerned about the number of refinery accidents," said Daniel Horowitz, a spokesman for the board. "Counting this case, that's eight refinery cases open right now, with three in Salt Lake. It's a number we're concerned about."

The safety board, which is an investigative agency that has no regulatory or enforcement power, has faulted a decade of lax regulation by another federal agency, the Occupational Safety and Health Administration, for recent troubles among U.S. refineries.

OSHA has said it was catching up on refinery inspections. In a recent report, OSHA said that U.S. oil refineries have had more fatal or catastrophic releases of hazardous chemicals in the past 15 years than any other part of the chemical industry.

Silver Eagle executives said Wednesday that their safety record was "smack in the middle" of Utah's five refineries.

"I'll tell you we have spent a large amount a money on safety ... programs at the refinery," said McSwain.

Krege Christensen, a Silver Eagle vice president, said his company believed a utility outage Wednesday led to trouble at multiple refineries, but Rocky Mountain Power said it didn't cause the problem.

Utility spokesman Dave Eskelsen said the explosion at Silver Eagle briefly knocked out a 46,000-volt transmission line, leading to emergency measures at that refinery and two others.

Parry, the Woods Cross mayor, said the company has offered to put up displaced families in local hotels.

On Jan. 12, four people were seriously burned at Silver Eagle when a 440,000 gallon storage tank caught fire and burned for 11 hours. Federal investigators said the ignition source may have been a gas heater or a refrigerator's electric outlet in a utility shed about 160 feet from the tank.

The worst accident in recent years killed 15 workers at a BP PLC refinery in Texas City in 2005. On Friday, OSHA levied a record $87 million fine against the oil giant for that accident.

That refinery had gone without a comprehensive inspection for a decade, and OSHA did only a handful of such inspections during the same period for approximately 150 U.S. refineries, according to Holmstrom.

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