A sulfur tank exploded Friday at the Tesoro refinery in Wilmington, sending a chemical cloud into the air and causing a fire, authorities said. No injuries were reported.
There was no immediate word on the cause of the blast, which occurred at about 1 p.m.
"We are currently conducting air quality monitoring around the site," company spokesman Destin Singleton said. "At this time we have not detected any harmful levels of toxins."
Everyone at the scene near the 23200 block of South Alameda Street was accounted for, Singleton said.
The Los Angeles County Fire Department sent in a hazardous materials team.
No evacuations were ordered but the Sheriff's Department urged people within a quarter-mile of the scene to stay indoors, and Alameda Street was closed between 223rd Street and Sepulveda Boulevard.
The 930-acre refinery near the Port of Long Beach is located in both Wilmington and Carson. It is the largest refinery on the West Coast and produces gasoline, jet fuel, diesel and other fuels, according to Tesoro.
An Associated Press report was used in this story.