A large part of Tesoro’s Martinez refinery shut down last December because someone accidentally pressed the wrong button.
The company spent the last few months working to ensure that its workers don’t inadvertently cause the facility’s main units to break down like they did Dec. 15 — an incident that will lead local air regulators to penalize the company.
Tesoro’s brief shutdown caused flaring and sent a large plume of black smoke into the air, prompting Contra Costa County officials to issue a health alert for several communities near the refinery.
Officials later disclosed that Tesoro mistakenly issued a test alert in the middle of the real emergency, leading to a delay of a public warning about the incident.
The company has now released the results of its investigation into why the refinery lost fuel gas used to power a boiler unit, halting the facility’s operations.
A button used for testing an electrical switch was accidentally pressed, cutting off fuel to the boiler unit, according to the root-cause analysis Tesoro filed with the county’s hazardous materials program earlier this month.
It’s unclear who pressed the button.
“There were staging and electrical crews working in the area during the time of the incident,” said James Jeter, an environmental health and safety manager at Tesoro, in the report. “In addition the area is congested and the button is at elbow height.”
Tesoro may not have known the button could disrupt operations.
“I think they didn’t realize if that button was pressed that it would shut down the whole system,” said Randy Sawyer, Contra Costa County’s chief environmental health and hazardous materials officer. “Someone could have been working around it, and they could have hit it with their elbow and not even realize they did it.”
A boiler that produces steam is located inside the refinery’s power plant. That plant connects to equipment throughout the facility.
When the button was pressed, power was shut off to a valve that controls how much gas is brought into the boiler unit. The boiler shut down, stopping steam from driving some of the refinery’s compressors and pumps, causing them to turn off.
The high pressure gas in those units then went to the facility’s vent system. Because the refinery wasn’t able to produce steam, instead of just flaring, Tesoro sent a large plume of smoke into the air.
“It was a vulnerable point,” said Eric Smith, associate director of the Tulane Energy Institute, who read the company’s report and specializes in oil and gas production.
Initially, Tesoro put a physical covering around the test button to make it harder for it to be accidentally pressed. In January, it removed the button entirely, said company spokeswoman Patty Deutsche in an email.
“No more possibility of human factors for that issue,” she said. “We took it one step further.”
The Bay Area Air Quality Management District is investigating the incident.
The agency issued a notice of violation for excessive smoke, according to district spokeswoman Kristine Roselius. When the district’s probe ends, it’s expected to decide what kind of fine Tesoro will face, Roselius said in an email.