Evacuations reduced in California chemical tank emergency after worst-case explosion risk eliminated

By Nina Giraldo, Taylor Romine, Emma Tucker, Alaa Elassar, Holly Yan, CNN

(CNN) — Officials racing to prevent an overheating chemical tank in California from exploding breathed a small sigh of relief Monday after confirming a crack in the structure had helped reduce pressure inside, eliminating the risk of a catastrophic blast and allowing tens of thousands of evacuated residents to return home.

But with a toxic leak or smaller explosion still possible, officials are asking 16,000 residents closest to the site in Orange County not to return home yet, as they continue to try to cool the tank’s internal temperature.

Authorities are expected to meet Tuesday to assess the situation after officials expanded their focus overnight on cooling efforts since finding pressure in the tank at GKN Aerospace in Garden Grove had been alleviated, preventing a disaster known as a BLEVE, or boiling liquid expanding vapor explosion.

Until evacuation orders were partially lifted Monday evening, about 50,000 residents were asked to flee their homes as the temperature and pressure escalated inside the tank containing 7,000 gallons of a chemical called methyl methacrylate, or MMA, which is used to make plastics and can cause myriad health problems upon exposure.

A deluge of cool water has doused the overheated tank for days, helping to bring down the temperature, officials said in an update Monday night. Runoff water from the site – millions of gallons – is being tested for any hazardous chemicals and so far, none have been detected, officials said.

To help with the cooling process, crews are removing insulation from the tank’s outer shell, Orange County Fire Authority Interim Chief TJ McGovern told CNN Monday night, adding authorities will be monitoring temperature data throughout the night.

While the threat of a catastrophic explosion has been eliminated, “we still have threats that we’re mitigating right now,” said McGovern earlier, including the “potential for an explosion that’s not as bad as a BLEVE” but still a risk to public safety, he said.

Meanwhile, a presidential emergency declaration has been signed for the situation, bolstering federal assistance, California Gov. Gavin Newsom announced Monday.

A volatile situation

The tank contains MMA, a chemical that can cause skin and eye irritation as well as respiratory problems.

“There is still no chemical leak, as verified by continuous atmospheric monitoring,” the Orange County Fire Authority said Monday.

Still, some residents have reported symptoms of exposure. And some schools have closed and switched to online learning as a precaution.

The tank started showing signs of trouble Thursday, when heat and pressure started building up.

When MMA overheats, it starts a chemical reaction that is difficult to control inside a large tank, said Elias Picazo, a chemistry professor at the University of Southern California.

Authorities are trying to keep the tank as cool as possible to keep the chemical reactions happening inside the tank stabilized, said Elaine Bernal, a chemistry lecturer at California State University, Long Beach.

Almost 800 state and local first responders have been deployed to respond, said Newsom, including toxicologists, hazmat teams and public health sheltering experts.

Temperature stabilized and falling

Methyl methacrylate’s “happy place” is 50 degrees Fahrenheit, and an increase in temperature could cause a leak or explosion, Orange County Fire Authority Division Chief and Unified Incident Commander Craig Covey said.

The tank involved began to overheat after the refrigerating system used to keep it cool and stable stopped working, according to Covey.

“One of the valves in that system froze up, so (cool air) is no longer being circulated,” Covey said Monday night. “Due to that failure, the tank went into the heating up process because it wasn’t continuing to be chilled.”

Officials aren’t sure exactly what temperature might cause the tank to ignite or explode, Orange County Fire Authority Captain Steve Concialdi said. They had no clue how hot it was inside the tank Sunday because the temperature gauge has already maxed out at 100 degrees.

By Monday morning, the temperature had stabilized and was falling, Covey said. “It is currently 93 degrees, down from 100 degrees. That is incredibly positive news as we turn the corner on this incident.”

Based on the latest temperatures inside the tank, fire officials believe the chemical has started to gel or solidify – which is exactly what they want.

“We know that the product will solidify (from) liquid to a solid form … but we don’t know how much of it has yet,” McGovern said.

GKN apologized to evacuated residents and businesses Sunday and said it’s working with emergency services and hazardous materials teams “to monitor the condition of the affected material and are working round the clock to mitigate the risk of a leak.”

“We are acutely aware of the uncertainty this incident is causing and sincerely apologise for the ongoing disruption to the local community,” the company said in a statement.

Theme parks such as Disneyland and Knott’s Berry Farm are close to but not included in the evacuation zone.

“At this time, there is no impact to Disneyland Resort due to this situation and the resort remains open to guests,” the park’s website said Monday. The park said it’s monitoring the situation and working with local authorities.

Newsom issued a state of emergency to support response operations. And Orange County District Attorney Todd Spitzer announced an anonymous tip line and reporting form for anyone with information about the incident or what led to it.

He has also opened a criminal investigation into GKN Aerospace, DA spokesperson Kimberly Edds told CNN. The company has been ordered to preserve evidence, Edds added. When reached for comment, GKN Aerospace referred to its earlier statement.

Residents sue tank owner

A couple who live in the evacuation zone filed a proposed class-action lawsuit against GKN Aerospace on Saturday, claiming the company negligently stored and handled MMA – leading to widespread disruptions for their community.

“Aside from just being evacuated, everything that they know and love is inside their home,” said attorney Filippo Marchino, who’s leading the class-action suit.

GKN Aerospace declined to comment on the litigation Sunday.

About 100 to 120 other residents have already expressed interest in joining the class-action case, Marchino said.

The lawsuit claims the company’s handling of the chemical caused dangerous conditions by creating an ongoing risk of fire, explosion, toxic chemical exposure and environmental contamination that affected tens of thousands of residents, businesses and schools.

‘I forgot to close the window … and I regret it’

Exposure to MMA can cause nausea, dizziness and “significant irritation” to the lungs and nasal passages, Orange County Health Officer Dr. Regina Chinsio-Kwong said.

The chemical can produce a fruit-like scent, although smelling it does not mean you have experienced enough exposure to have symptoms, she said in another update.

Officials said the chemical has not been detected in the air, but some residents said they’ve experienced symptoms.

“I forgot to close the window during the Thursday night, and I regret it,” said Stanton resident Van Ly, who evacuated Friday. “My throat and the inside of my nose feel sore, and my wife felt dizzy Friday night.”

Air should be safe outside the evacuation zone, Chinsio-Kwong said, urging people to leave the affected area.

Evacuated residents flock to shelters

As the evacuation zone decreased in size, school districts moved to open campuses where they could.

Garden Grove Unified School District said Monday nine schools that are no longer within the evacuation area will reopen Tuesday.

Three schools and district maintenance and transportation facilities are still within the evacuation zone and will remain closed, the district said.

All seven Red Cross shelters that had been set up in the area remained open Monday night, with officials saying they’d reassess capacity needs Tuesday.

Nearby hotels were also offering discounted rates over the holiday weekend.

Dawnedra Phillips, who lives in the evacuation zone, said she was taking warnings from officials seriously and staying at a shelter in Cypress.

“I’m waiting it out, ‘cause here we have our community and we’re supporting each other the best that we can with what we have going on right now,” Phillips told CNN affiliate KABC. “I don’t care how old you are, it’s going to harm you one way or another.”

Past inspection led to violation and settlement

GKN Aerospace says its Garden Grove location is the “world’s leading provider of military transparency systems and commercial aircraft transparencies.” Aircraft transparency systems include canopies, windshields and windows.

A November 2020 inspection led to a violation notice and GKN Aerospace paying a nearly $1 million settlement.

The inspection by the South Coast Air Quality Management District, or AQMD – a regional pollution control agency – determined the site failed to keep required records of its VOC emissions, which degrade air quality when released at harmful levels, the agency said.

Inspectors also found GKN Aerospace operated new equipment without securing a permit and used existing equipment that did not match the description in the permit, the agency said. GKN also modified permitted equipment without applying for a permit change, which is required by the agency.

The company received two orders to fix the issues — in December 2020 and February 2021 — but failed to comply, the agency said. It led to a notice of violation in April 2021 and a civil penalty of about $900,000 paid by GKN, the agency said.

Since the violation, the South Coast Air Quality Management District said it has been “working closely with GKN to help resolve these permitting issues.”

In March 2025, GKN received two more notices to comply, AQMD said. The notices requested operating records and applications for registering certain equipment and a change in facility ownership.

When reached for comment, GKN reiterated its earlier statement about working to resolve the current situation at the facility that led to evacuations but did not address any previous issues.

This story has been updated with additional information.

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CNN’s Hanna Park, Lauren Mascarenhas, Maria Prieto Aguilar, Amanda Musa, Karina Tsui, Rebekah Riess and Sarah Dewberry contributed to this report.