"There was a big column of brownish smoke coming up ... probably 200 feet in the air," Benicia Fire Marshal Ray Iverson said. "Smoke and vapor."
Iverson said the incident was reported at 8:51 p.m. He said the byproduct, which he identified as petroleum coke, mixed with steam, creating the cloud.
A similar incident occurred at the refinery Thursday morning, slightly injuring several employees. None had to be hospitalized and they all returned to work afterward, refinery spokeswoman Susan Fisher-Jones said.
Iverson said it does not appear anyone was seriously injured in Thursday night's incident but said one worker was being medically evaluated at the scene.
He said it is not yet clear whether the accidents are related but said it does not appear they happened in the same area of the refinery.
Thursday night's incident prompted a two-alarm response from the Benicia Fire Department. No shelter-in-place order was issued for the surrounding area, and the all-clear signal has been given, Iverson said. Refinery officials could not immediately be reached for comment tonight.
Fisher-Jones said that the morning's incident was reported at 10:10 a.m. She said there was a leak in a unit involving a byproduct that is eventually made into charcoal briquets.
Employees were asked to shelter in place until the all-clear signal was sounded at about 11:45 a.m., said Alysia Porter, a staff assistant at the refinery.
Fisher-Jones said the morning leak did not have any adverse impacts on the surrounding community.