Officials lift evacuation orders for some California residents living near a damaged chemical tank

Emergency officials lifted an evacuation order for some of the people who live near a damaged tank containing a hazardous chemical in Southern California after temperatures inside the tank fell enough to eliminate the risk of a catastrophic explosion.

While there’s no longer a risk of a major explosion at the GKN Aerospace Transparency Systems plant in Garden Grove, there’s still a chance for a smaller blast or a fire, Orange County Fire Authority division chief Craig Covey said during a news conference on Monday.

An overnight evaluation of the tank containing 6,000 to 7,000 gallons (22,700 to 26,500 liters) of methyl methacrylate, which is highly flammable, showed a reduction of pressure inside the tank thanks to a crack that was discovered Sunday. About two-thirds — roughly 34,000 — of the evacuated residents can go home as a result, Covey said.

“It’s not over yet. We still have work to do,” Covey said. “We still have to mitigate a fire and very small explosion concern, and also a spill potential.”

Officials began ordering residents of Garden Grove, near Los Angeles, to evacuate their homes on Thursday after the tank overheated, and by the weekend about 50,000 residents had been told to leave.

Officials said they needed to cool the tank to prevent a toxic leak or explosion. The tank’s interior had cooled to 93 degrees F (33.9 degrees C), Covey said Monday, down from 100 degrees (37.7 degrees C) a day earlier.

Orange County Health Director Regina Chinsio-Kwong said she wanted to reassure everyone who is returning home that they can feel safe. Exposure to methyl methacrylate can cause serious respiratory problems, neurological problems and irritation to the skin, eyes and throat, according to the federal Environmental Protection Agency.

“There was no contamination. There were no fumes. There were not vapors that came from this incident,” she said at the news conference. “There was not a leak. So it should be, you should feel comfortable going home even if you’re across the street from that new zone line.”

The tank might eventually cool enough for crews to safely stabilize and drain the remaining material without triggering a spark or ignition, said Andrew Whelton, a Purdue University engineering professor who has studied environmental contamination.

Whelton cautioned there is still some risk of an explosion while the chemical inside the tank remains hot and reactive. He said temperatures need to fall closer to ambient levels — roughly 60 to 70 degrees Fahrenheit (15.6 to 21.1 degrees C) — before conditions are considered significantly safer.

As the interior temperature of the tank increased, methyl methacrylate — which is used to make plastics — converted from liquid to gas, ramping up the pressure and risk of explosion, Whelton said.

Some of the methyl methacrylate may already have hardened into a stable plastic similar to plexiglass, reducing the risk inside the tank, he said.

Orange County Supervisor Janet Nguyen said the South Coast Air Quality Management District will be monitoring the air for several months and the EPA will be checking the sewer and storm drains.

County health officials have said the chemical is easy to smell and people may notice it over a large area without being harmed.

Authorities have not defined what a catastrophic explosion might mean, but said Monday the worst-case scenario is off the table.

Kim Yen, a retiree who had to evacuate her Garden Grove home, said she has been closely following the news and is relieved to learn that the worst has passed.

“I am happy and many of us are happy but, still, we are still on our evacuation,” she said.

Yen, who lives two blocks from the plant, said she’s ready to return home but first wants to be sure it’s safe. And, she said, she’s been worried about the emergency crews.

“They are really our heroes,” Yen said.

The parking lot was full Monday at a large park in Fountain Valley, just southwest of Garden Grove, as people sought refuge in an ad hoc shelter there or pitched tents outside. Other people gathered in the park to enjoy Memorial Day.

GKN Aerospace Transparency Systems, which owns the plant, is a British company that makes cockpit windows, canopies and windshields for military and commercial aircraft.

GKN Aerospace technical specialists and the Orange County Fire Authority removed external insulation material from the tank to help cool its contents, according to a GKN Aerospace statement released Monday.

“We apologize for the ongoing disruption this incident is causing and our priority remains its safe resolution, so that residents can return to their homes as quickly as possible,” the statement said.

GKN Aerospace says on its website that it employs about 16,000 people across 32 manufacturing sites in 12 countries and supplies technologies and components used by major commercial and military aircraft manufacturers worldwide.

It remained unknown when the operation would reopen.

GKN Aerospace agreed in 2025 to pay state regulators more than $900,000 to settle violations involving recordkeeping, permitting issues and nitrogen oxide emissions, according to a report on the South Coast Air Quality Management District website.

Disruptions at facilities producing specialized aircraft components can be difficult for the global aerospace industry to absorb because supply chains are highly concentrated and already strained, said Richard Aboulafia, managing director of the aerospace consulting firm AeroDynamic Advisory.

Aboulafia said aerospace manufacturing differs from many other industries because aircraft production rates are relatively low, leaving only a small number of suppliers for many specialized parts and systems.

“There’s just not a lot of margin in the system,” he said.

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Willingham reported from Boston. Stengle reported from Dallas. Associated Press journalist Ethan Swope in Garden Grove, California, contributed to this report.