About 300 workers have returned to Martinez Refining Company after a leak ignited an explosion and subsequent fire Saturday afternoon, leading to a shelter-in-place order for neighboring communities.

As Contra Costa County Fire and Martinez Refining Company investigators sift through the damage, refinery workers have returned to their posts in an attempt to prevent further incidents, following numerous health advisories from Contra Costa Health Services department in recent days.

“I think some of the residents don’t understand that our workers are in there doing their best to prevent any further injuries and impacts to the surrounding community,” United Steelworkers Local 5 President Nick Plurkowski told Bay Area News Group.

Employees were forced to evacuate Saturday afternoon when an explosion shot flames hundreds of feet into the air. Four refinery workers received minor injuries during the incident and were transported to local hospitals, according to Martinez Refining Company Public Information Officer Brandon Matson.

Billowing, jet-black smoke over residential neighborhoods in Martinez, Pacheco and Clyde led to a shelter-in-place order Saturday evening from the Contra Costa Health Services department. The department lifted the shelter-in-place order around 9 p.m. Saturday night, but maintained a Level 2 public health advisory calling for sensitive populations to stay indoors.

The fire was mostly put out by 11 a.m. on Sunday, allowing refinery personnel to return to work in a limited capacity at designated safe areas of the refinery. Plurkowski said workers have been in the refinery since evacuations were lifted and are doing everything in their power to keep the affected communities and the refinery safe.

“It’s an oversimplification when I say this, but we’re scrambling around and seeing what we can do that’s still safe to do,” Plurkowski said. “The whole refinery is intertwined, and all the units affect the other units, so there’s stuff still going on.”

Gas prices ticked up slightly Monday, but one expert predicted a more significant spike due to the potential loss of the Martinez facility’s operations, which represent some 10 percent of the state’s refining capacity.

Martinez Refining Company will be required to launch a Root Cause Analysis to identify how the incident happened. Additionally, the refinery will be ordered to create and implement mitigation strategies to prevent future incidents, according to CCH.

When asked for an update on the incident and investigation, company spokesperson Matson told Bay Area News Group, “We will continue to provide updates on our social media and have nothing further to add at this time.”

Saturday’s incident adds a new chapter to the history of incidents at Martinez Refining Company in the past five years where hazardous materials were released to the public. On Nov. 24 and 25, 2022, the refinery accidentally released a powdery substance known as a “spent catalyst” that contained higher levels of heavy metals than normal. The Contra Costa County district attorney pursued legal action against Martinez Refining Company at the time for not notifying County health officials when the accident happened.

On July 11, 2023, the refinery unintentionally released petroleum coke dust, a byproduct of refining crude oil, for about one minute. The investigation that followed did not find soil contamination in the affected communities.

Neither of the incidents resulted in injuries.

Other refineries in the area have been plagued by problems, as well, including intermittent flaring reported Sunday at the Chevron Refinery in Richmond. In 2024, the Bay Area Air Quality Management District announced a $5 million penalty against Marathon Martinez Refinery for 59 air-quality violations from 2018 to 2022 — the second-largest fine the agency had ever assessed.

The repeated public health incidents at Martinez Refining Company and other refineries in the East Bay have exhausted the patience of many local residents, including a Martinez woman who asked to be identified as a “quite irritated resident.”

“By now, we’ve gotten used to this,” she said.