Authorities in Southern California have allowed some residents to return to their homes after temperatures decreased sufficiently in a compromised tank holding dangerous chemicals, reducing the threat of a major explosion.
Emergency management officials announced that the risk of a significant blast at the GKN Aerospace Transparency Systems facility in Garden Grove has been eliminated, though smaller explosion or fire hazards persist, according to Orange County Fire Authority division chief Craig Covey during a Monday briefing.
A nighttime assessment of the container holding 6,000 to 7,000 gallons (22,700 to 26,500 liters) of methyl methacrylate, a highly combustible substance, revealed decreased internal pressure due to a fracture found on Sunday. This development allowed approximately two-thirds of displaced residents — around 34,000 people — to return home, Covey explained.
“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.”
Evacuation directives for Garden Grove residents, located near Los Angeles, began on Thursday when the tank experienced overheating, eventually affecting roughly 50,000 people by the weekend.
Authorities worked to reduce the tank’s temperature to prevent toxic discharge or detonation. The container’s internal temperature dropped to 93 degrees F (33.9 degrees C) on Monday, down from 100 degrees (37.7 degrees C) the previous day, Covey reported.
Orange County Health Director Regina Chinsio-Kwong emphasized safety assurances for returning residents. The federal Environmental Protection Agency warns that methyl methacrylate exposure can lead to severe breathing difficulties, neurological complications, and irritation of skin, eyes, and throat.
“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.”
Andrew Whelton, a Purdue University engineering professor specializing in environmental contamination research, suggested the tank might eventually cool sufficiently for crews to safely stabilize and empty the remaining contents without creating sparks or ignition.
Whelton warned that explosion risks continue while the chemical remains heated and reactive. He indicated temperatures must decrease to ambient conditions — approximately 60 to 70 degrees Fahrenheit (15.6 to 21.1 degrees C) — before safety conditions improve significantly.
Rising internal tank temperatures caused methyl methacrylate — utilized in plastic manufacturing — to transform from liquid to vapor, increasing pressure and explosion potential, Whelton explained.
Portions of the methyl methacrylate may have already solidified into stable plastic resembling plexiglass, decreasing internal tank dangers, he noted.
Orange County Supervisor Janet Nguyen announced that the South Coast Air Quality Management District will conduct air monitoring for several months while the EPA examines sewer and storm drainage systems.
County health authorities indicated the chemical produces a distinctive odor that people can detect across wide areas without experiencing harm.
Officials have not specified what constitutes a catastrophic explosion but confirmed Monday that worst-case scenarios are no longer possible.
Kim Yen, a retired resident forced to evacuate her Garden Grove residence, said she has monitored news coverage closely and feels relieved learning the worst dangers have passed.
“I am happy and many of us are happy but, still, we are still on our evacuation,” she said.
Yen, whose home sits two blocks from the facility, expressed readiness to return while wanting safety confirmation first. She also voiced concern for emergency personnel.
“They are really our heroes,” Yen said.
A large Fountain Valley park, located southwest of Garden Grove, had a crowded parking lot Monday as displaced individuals sought temporary shelter or erected tents outside. Other visitors used the park for Memorial Day activities.
GKN Aerospace Transparency Systems, the plant’s owner, operates as a British corporation manufacturing cockpit windows, canopies, and windshields for military and commercial aviation.
Technical experts from GKN Aerospace and the Orange County Fire Authority stripped external insulation from the tank to assist cooling efforts, according to a Monday company statement.
“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 reports on its website employing approximately 16,000 workers across 32 production facilities in 12 countries, supplying technologies and components to major commercial and military aircraft manufacturers globally.
The facility’s reopening timeline remains undetermined.
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.
Interruptions at specialized aircraft component manufacturing sites create absorption difficulties for the global aerospace industry due to highly concentrated and already stressed supply chains, explained Richard Aboulafia, managing director of aerospace consulting firm AeroDynamic Advisory.
Aboulafia noted aerospace manufacturing differs from other industries because aircraft production volumes remain relatively limited, resulting in few suppliers for specialized components and systems.
“There’s just not a lot of margin in the system,” he said.
