Workers Evacuated from Chevron's Richmond Refinery Over the Weekend

State workplace regulators launched an investigation Monday into a malfunction at Chevron's Richmond refinery over the weekend that led to the evacuation of crews doing maintenance work at the facility.

A Chevron spokeswoman said one of the refinery's process units experienced a problem Saturday morning.

"As part of the refinery's safety protocol non-operational workers were temporarily evacuated and agencies were notified," Chevron's Amy Mosley said.

The plant was later deemed safe and the workers returned, Mosley said.

The company has not responded to questions about the specifics of Saturday's problem, but in a brief filing with the Governor's Office of Emergency Services, the company said that a system that controls the release of gas "was overwhelmed" because of an "upstream plant upset."

Chevron's report to the state said that "non-critical workers" were evacuated and that on-site emergency medical personnel were called to assist workers. The company said the incident may have led to the release of at least 500 pounds of sulfur dioxide, a pollutant that can cause respiratory problems.

Refinery officials told local air regulators the plant had problems with hydrocarbons entering a sulfur recovery unit, according to Bay Area Air Quality Management District spokesman Ralph Borrmann.

The workers who had to leave the facility were contractors performing maintenance work, according to Randy Sawyer, Contra Costa County's chief environmental health and hazardous materials officer.

Sawyer said the contractors were doing work on the unit that malfunctioned. He said one of the workers experienced some sort of medical problem a couple hours after the initial episode and that the problem "seems to be unrelated" to the refinery incident.

Despite the fact that no refinery workers were seriously injured, California's Division of Occupational Safety and Health has launched a probe into the incident, according to agency spokesman Frank Polizzi.

The workers were employed by four different contractors: Contra Costa Electric, Harder Mechanical, BrandSafway and JT Thorpe, Polizzi said.

Bob Lilley, business development director at Contra Costa Electric, said he did not have information about the incident and it did not come up during a company meeting on Monday.

An employee who picked up the phone at Harder Mechanical said the company, due to a confidentiality agreement with Chevron, is not allowed to discuss work at the refinery.

Representatives for BrandSafway and JT Thorpe have yet to respond to requests for comment.

Two elected officials who represent the area of the refinery, Richmond Mayor Tom Butt and Contra Costa County Supervisor John Gioia, said they were not told about the incident.

"I'm surprised I was not made aware of this," Gioia  said in an email Monday.

In the last two years Chevron's Richmond refinery has experienced a spike in incidents in which the facility is forced to burn off excess gases because of operating problems.