The US has been hit by a wave of refinery explosions and fire in recent years, the latest at a Utah oil refinery on 4 November.
The industrys second explosion of the year at the Silver Eagle Refinery in Woods Cross damaged 10 homes after a blast in a diesel hydrotreater, which removes sulphur compounds from diesel fuel.
Federal investigators expressed alarm over the extent of damages caused by a refinery that has had a history of trouble dating to 2003.
The refinery in Woods Cross had fires in 2003, 2005 and 2007, according to federal records. The board also was looking into a 21 October fire at a nearby Tesoro refinery.
The US Chemical Safety Board was still investigating a January fire that burned for 11 hours when it dispatched a team to look at Silver Eagle Refinery.
Counting this case, that's eight refinery cases open right now, with three in Salt Lake. It's a number we're concerned about, Daniel Horowitz, a spokesman for the board, says.
The Occupational Safety and Health Administration (OSHA) is catching up on refinery inspections. In a recent report, OSHA said that US 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.
On 12 January 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 refinery in Texas City in 2005. In late October 2009 OSHA levied a record $87 million (58.6 million) fine against the oil giant for that accident.