LOS ANGELES — The Sandy fire is burning near a toxic waste area in the Simi Valley where a partial nuclear meltdown once took place, sparking concerns about the potential for contaminants to be released should the area catch fire.

The Ventura County Fire Department announced Wednesday evening that air quality monitoring is being conducted around the fire’s perimeter because of the blaze’s proximity to the Santa Susana Field Laboratory. The 2,850-acre laboratory complex was formerly used for rocket engine testing and nuclear research and is currently undergoing a state-led environmental cleanup.

Fire Department spokesperson Andrew Dowd said monitoring had been “deployed to establish a background air quality, so that if the fire advances further into that sensitive area we would have a baseline to compare against.” He noted that the fire had not yet reached the field laboratory area and that crews were making strong progress containing the blaze.

The fire had burned 2,141 acres and was 30% contained as of 3:30 p.m. Thursday, at which time several evacuation orders and warnings were downgraded. By nightfall, containment had jumped to 40%.

“Today we’re experiencing lower winds and higher relative humidity, so we’re seeing reduced fire behavior,” said Dowd. “Because of that, the risk of the fire spreading in any direction is less than it was before.”

The field laboratory is currently in an evacuation warning zone to the east of the fire. The Department of Toxic Substances Control, which oversees environmental remediation of the site, said it is working closely with local and federal agencies to monitor the incident and potential impacts to communities near the laboratory site.

“To ensure we are aware of any off-site impacts, the emergency response team has deployed air monitors to support response efforts and safeguard public health,” the department said in a statement. Boeing, which owns the Santa Susana site, said it had evacuated all personnel and was working in coordination with local authorities and emergency responders to monitor fire conditions near the facility.

The Ventura County Fire Department noted in a Thursday evening statement that the laboratory is in a historically wildfire-prone area, but maintained that there is limited need for concern about the possible release of radiation.

“Radiation measurements collected as recently as 2025, along with modeling conducted following the 2018 Woolsey Fire, continue to indicate that the extremely low levels of residual radioactive material at the site pose no risk to public health, even in the event wildfire activity reaches the area,” the department stated.

The Woolsey fire originated at the Santa Susana Field Labratory and swept through a significant portion of the site. Health officials said, however, that there was no increased risk to the public beyond what is normal for wildfire smoke. Testing from the Department of Toxic Substances Control found no radiation levels above background and no hazardous compound levels other than those normally present after a wildfire.

However, a study published in 2021 found evidence of radioactive waste in a limited number of soil samples collected after the Woolsey fire.

Some people living near the laboratory have expressed unease at the Sandy fire’s proximity to the heavily contaminated site — especially given its toxic history.

During the 1950s and 1960s, workers would regularly burn toxic waste in open pits and cleaned engines with solvents that later contaminated the groundwater. In 1959, there was a partial meltdown of the core in one of the lab’s nuclear reactors that is considered among the worst nuclear accidents in U.S. history.

In 2005, Boeing agreed to pay $30 million to settle a lawsuit alleging that pollutants from the hilltop lab were responsible for a variety of cancers, autoimmune disorders and tumors afflicting nearby residents. A 2006 study found that radiation at the site may have contributed to hundreds of cases of cancer in the surrounding community.

Since then activists have continued to document cases of cancer found in residents living near the site.

©2026 Los Angeles Times. Visit at latimes.com. Distributed by Tribune Content Agency, LLC.