A cloud of flammable vapor emanated from a unit of Chevron's oil refinery in Richmond last week, sparking a blaze. The company and regional health officials said air quality was within federal safety limits, though several people in the area have sought medical treatment for health issues that could be related to the fire, the San Francisco Chronicle reports.
Don Holmstrom, an investigator with the U.S. Chemical Safety Board, said an ignition source, likely from a nearby diesel engine, ignited the vapor cloud, forcing Chevron to shut the unit down.
Investigators are focusing on an 8-inch line that was identified as corroded during a November 2011 inspection.
"This line was not replaced," Horowitz was quoted as saying. "We are very much interested in understanding the decision about why to keep this line in service -- I'm sure that everybody wishes that decision might have turned out differently."
The refinery produces gasoline and the shut down caused a regional spike in retail prices for motorists. AAA says San Francisco drivers paid around $4.19 for a gallon of regular unleaded gasoline Wednesday, up from $3.99 last week.
The Chronicle reports that investigators have limited access to the area because of structural safety concerns.