The fire erupted when a vapor cloud ignited Aug. 6. The massive blaze endangered more than a dozen workers in the immediate vicinity, and the resulting thick, black smoke caused thousands to seek medical attention for related health issues. It was marked as one of the most serious U.S. refinery fires in recent years.
Federal investigators said an old and corroded pipe was the likely cause of the fire. According to the San Francisco Chronicle, workers complained to the state Division of Occupational Safety and Health about increased corrosion problems following a smaller fire at the plant a year ago.
"We're afraid something is going to fall through the cracks," one worker told Cal/OSHA safety inspector Carla Fritz in documents obtained by The Chronicle.
The 2011 fire took place during a scheduled maintenance shutdown and was quickly extinguished. Chevron says the corrosion related to that fire was unexpected, and that they found nothing unusual afterward.
Cal/OSHA said in a statement that a violation notice was not issued to Chevron over the 2011 fire "because the problem alleged and potential hazard had been already identified and corrected."
The Richmond refinery, located about 10 miles northeast of San Francisco, produces about 16 percent of California's daily gasoline supply. The fire is being blamed for a spike in local gas prices to nearly $5 a gallon for regular unleaded.
The Associated Press contributed to this report.