"Chevron understands the concerns neighbors felt this evening due to a loud noise from the Richmond Refinery as a result of steam pressure relief. We apologize for how this may have impacted your evening. There is no need to shelter in place," the tweet said.
Patricia Canessa, a Chevron spokeswoman, reiterated that apology to Butt.
"We posted something on Facebook and Twitter but recognize the concern," Canessa wrote in an email to the mayor. "I would be happy to discuss additional ways to address the community. We sincerely apologize for the inconvenience."
Later Friday morning, the company released more information.
"We want to assure our neighbors that Thursday night's noise did not pose any environmental or health risk to the community. This was not a planned event," Chevron said in a statement.
"Steam helps to power equipment and provides efficient heating during the refining process. In very rare instances, steam needs to be released to prevent over-pressuring of a system and this process may cause a loud noise. Our experts will investigate this incident so that we can learn from it and take appropriate action to prevent a similar event from occurring in the future," Chevron said.
Several Richmond residents said they could smell a gas odor, according to Butt.
The company says it does not believe its facility was the source of that smell, its representatives said.
Butt said the noise sounded like a very loud release of gas. He said refinery officials contacted the city's police department to explain the malfunction and emphasized that the release was not dangerous.
"There is no reliable method or system for notifying people about issues like this whether they're harmful or not" Butt said in an interview Friday morning.
"When people see fire and smoke and hear loud noises and they're coming from Chevron, people freak out," Butt said.
The refinery malfunction came two months after a large fire at scrap metal yard near the Port of Richmond released toxic smoke into air for some 11 hours.
That blaze at a Sims Metal Management facility prompted a set of alerts ordering residents to stay indoors and led to complaints from Butt and some city residents that information coming from Contra Costa County's community warning system was too slow and confusing. Sheriff's officials, who run the system, have said it worked as designed.
Thursday night's refinery incident was not as serious and did not prompt any alerts from the community warning system. But Mayor Butt says it's part of a pattern.
"Whether it's Chevron or whether it's Sims Metal or whether it's somebody else, people in the community are not getting information," Butt said.