Thousands of Southern California residents still could not return home Tuesday as crews worked to keep cooling a damaged tank containing a hazardous chemical at an aerospace plant, despite officials saying the risk of a catastrophic explosion had largely passed.
Officials began ordering residents of Garden Grove near Los Angeles to evacuate their homes on Thursday after the tank overheated. About 16,000 residents out of the 50,000 evacuees were still waiting for the all-clear.
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“It’s not over yet,” TJ McGovern, interim fire chief of the Orange County Fire Authority, said Monday. “We still have to mitigate a fire and very small explosion concern, and also a spill potential.”
The tank at GKN Aerospace Transparency Systems contains 6,000 to 7,000 gallons (22,700 to 26,500 liters) of methyl methacrylate, which is highly flammable. Exposure to the chemical can cause serious respiratory problems, neurological problems and irritation to the skin, eyes and throat, according to the federal Environmental Protection Agency.
An evaluation of the tank showed a reduction of pressure inside, thanks to a crack that was discovered Sunday. The tank’s interior had cooled to 93 degrees F (33.9 degrees C), the county's fire division chief Craig Covey said Monday, down from 100 degrees (37.7 degrees C) a day earlier.
Health officials have sought to reassure people who are returning to homes near the plant.
“There was no contamination. There were no fumes. There were not vapors that came from this incident,” Orange County Health Director Regina Chinsio-Kwong said at Monday's 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.”
Relief among residents
Kim Yen, a retiree who had to evacuate her home two blocks from the plant, said she’s ready to go back but wants to be sure it’s safe first.
“I am happy and many of us are happy but, still, we are still on our evacuation,” she said Monday.
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.
Yen added that she’s been worried about the emergency crews.
“They are really our heroes,” she said.
Environmental risks remain
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.
GKN is a British company that supplies aircraft manufacturers
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.
Aircraft manufacturing is vulnerable to supply chain disruptions
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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This story has been corrected to attribute a quote to TJ McGovern, interim fire chief of the Orange County Fire Authority, not to division chief Craig Covey.
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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.