Exposure to methyl methacrylate, a highly flammable chemical used to make plastics, can cause serious respiratory and neurological problems.
GARDEN GROVE, Calif. — 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.
“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.”
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.
Exposure to methyl methacrylate — a highly flammable chemical used to make plastics — can cause serious respiratory problems, neurological problems and irritation to the skin, eyes and throat, according to the federal Environmental Protection Agency. The tank at the GKN Aerospace Transparency Systems plant contains 6,000 to 7,000 gallons of the chemical.
An evaluation of the tank showed a reduction of pressure inside, thanks to a crack that was discovered Sunday. The 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. The company said its technical specialists and the county fire authority have removed insulation from the tank to help cool it.
Health officials 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.”
The South Coast Air Quality Management District will monitor the air for several months and the EPA will be checking sewer and storm drains for spills, Orange County Supervisor Janet Nguyen said.
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
As the tank heated up, the chemical converted from liquid to gas, ramping up the pressure and explosion risk, said Andrew Whelton, a Purdue University engineering professor who has studied environmental contamination. Some of the methyl methacrylate may already have hardened into a stable plastic similar to plexiglass, reducing the danger, he said.
The tank could eventually cool enough for crews to safely stabilize and drain the remaining material without triggering a spark or ignition, Whelton said.
However, he said there is still the risk of an explosion while the chemical remains hot and reactive. Temperatures need to fall closer to 60 to 70 degrees Fahrenheit (15.6 to 21.1 degrees C) before conditions are considered significantly safer, he said.
GKN is a British company that supplies aircraft manufacturers
GKN Aerospace Transparency Systems makes cockpit windows, canopies and windshields for military and commercial aircraft. It employs about 16,000 people across 32 manufacturing sites in 12 countries, according to the company website.
“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 company said.
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.
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