For the third time in the last six months, local air regulators and Contra Costa County health officials are looking into a problem at Chevron's Richmond refinery.
Large flames and black smoke shot out of the facility for three hours on Saturday morning after one of the refinery's hydrocracking units, which helps turn gas-oil into gasoline, failed.
"The refinery lost one of its hydrocrackers and sent a lot of fuel to the flares," said Randy Sawyer, Contra Costa's chief environmental health and hazardous materials officer.
That "upset" built up pressure inside the unit, leading to "some intermittent flaring," Chevron spokeswoman Leah Casey said.
The Bay Area Air Quality Management District is investigating and could penalize Chevron if it violated air regulations.
Initially, the county did not plan on asking Chevron for a 72-hour report on the incident because it was not expected to have a health impact on the community, Sawyer said Tuesday morning.