Investigators with the U.S. Chemical Safety Board are examining the potential causes of last week's fire at the Richmond refinery, a source for gasoline in the region.
Early this week, CSB investigator Don Holmstrom suggested an ignition source, likely from a nearby diesel engine, could have ignited a vapor cloud emanating from one of the Richmond units.
Dean Fryer, a spokesman for the California Occupational Safety and Health Administration, was quoted by the San Francisco Chronicle as saying that cause has been ruled out.
"Cal/OSHA has officially ruled out the fire truck as an ignition source," he said.
Investigators have focused on an 8-inch line that was identified as corroded during a November 2011 inspection.
The CSB last week said its investigators were at the refinery reviewing Chevron's documents and conducting witness interviews. Chevron and labor representatives are cooperating with the investigation.
The refinery shutdown caused retail gasoline prices to spike in California. Motor group AAA reports California drivers paid, on average, $4.11 for a gallon of regular unleaded Friday, compared with $3.98 last week. The national average is $3.71.