The fire broke out at 6:15 p.m., with flames visible at the top of two refinery stacks. Thick black smoke spewed from the Richmond plant, covering the city and San Pablo, about 10 miles northeast of San Francisco.
The fire was contained by 10:30 p.m., but it was not known when the flames would be extinguished, said Chevron spokeswoman Heather Kulp. Smoke continued to pour from the facility late Monday.
The blaze started at the refinery's No. 4 Crude Unit after an inspection crew discovered a diesel leak in a line in the unit, Nigel Hearne, manager of the refinery, told The San Francisco Chronicle. Shortly after the crew evacuated the area, the diesel ignited, Hearne said. One employee suffered a minor injury and was receiving first aid, Chevron officials said.
Residents of Richmond, San Pablo and the unincorporated community of North Richmond were advised by Contra Costa County health officials through automated calls to "shelter in place," meaning they should not only stay inside, but should also turn off heaters, air conditioners and fans, and to cover cracks around doors with tape or damp towels.
"Any kind of smoke can be toxic," said Randy Sawyer, the chief environmental and hazardous materials officer for the county's health services agency. "In this smoke, there can also be all kind of byproducts that can be toxic," he said.
The agency had four teams of inspectors in the field taking readings of the air quality, Sawyer said.
Daniela Rodriguez told the Contra Costa Times that she heard a "big boom" about the time the fire started. The 23-year-old resident said about an hour passed before she received a call to shelter in place.
"I was feeling kind of nauseous and light-headed (from the smell)," she told the newspaper.
Other area residents reported hearing explosions or loud blasts, though Chevron officials said they could not confirm the reports. Kaiser's Richmond Medical Center said several dozen people came to the emergency room complaining of shortness of breath, but none was seriously ill. To the south, Oakland police issued a community advisory suggesting that residents of the North Oakland Hills area close all windows and doors and turn off air conditioners.
Hearne said during an evening press conference that the company wanted to "apologize to the community for the fire and smoke this evening at the Richmond refinery."
The blaze also affected transit service, with the Bay Area Rapid Transit closing three stations near the refinery. Two of the three stations had been reopened, though there was no word when the third, the Richmond station, would be open again.
The Chevron Richmond Refinery is among the country's largest and most important refineries, processing up to 240,000 barrels of crude oil a day, according to the company's website.
The facility makes high-quality products that include gasoline, jet fuel, diesel fuel and lubricants, as well as chemicals used to manufacture many other useful products. It is the largest producer of base oils on the West Coast.
The Associated Press contributed to this report.