Some Garden Grove residents return as tank cools

Officials lifted evacuation orders for about two-thirds of Garden Grove residents near a damaged chemical tank at the GKN Aerospace Transparency Systems plant after temperatures inside the tank dropped enough to remove the risk of a catastrophic explosion—thou

For many Garden Grove residents, Monday’s update didn’t sound like an all-clear so much as a pause—one that came with the kind of relief that lasts only as long as the next check.

Emergency officials lifted an evacuation order for some people living near a damaged tank containing methyl methacrylate at the GKN Aerospace Transparency Systems plant in Garden Grove, after temperatures inside the tank fell enough to eliminate the risk of a catastrophic explosion.

While officials said there’s no longer a risk of a major explosion, Orange County Fire Authority division chief Craig Covey said during a news conference on Monday that there is still a chance for a smaller blast or a fire.

“ 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.”

The overnight evaluation found a reduction of pressure inside the tank, thanks to a crack discovered Sunday. The tank holds between 6,000 and 7,000 gallons of methyl methacrylate—about 22,700 to 26,500 liters—an extremely flammable chemical.

As a result, about two-thirds of the evacuated residents—roughly 34,000 people—can go home, Covey said. Officials began ordering residents of Garden Grove to evacuate their homes on Thursday after the tank overheated. By the weekend, about 50,000 residents had been told to leave.

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

Orange County Health Director Regina Chinsio-Kwong used the news conference to focus on what residents feared most: whether any chemical exposure occurred.

“There was no contamination. There were no fumes. There were not vapors that came from that incident,” she said. “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.”

Environmental and safety risk remain
The immediate explosion danger has shifted, but the work ahead is still complex. Andrew Whelton. a Purdue University engineering professor who has studied environmental contamination. said crews likely need to stabilize and drain the remaining material only after the chemical cools enough to reduce ignition risk.

Whelton cautioned that some explosion risk can persist while the chemical 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 tank warmed, Whelton said, methyl methacrylate—used to make plastics—converted from liquid to gas, increasing pressure and raising the chance of an explosion.

He also said some of the methyl methacrylate may have hardened into a stable plastic similar to plexiglass, which could reduce risk inside the tank.

Even with residents returning, environmental checks are continuing. Orange County Supervisor Janet Nguyen said the South Coast Air Quality Management District will monitor the air for several months, and the EPA will check the sewer and storm drains.

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

Relief—tempered by uncertainty
Authorities have not defined what a catastrophic explosion might mean, but officials 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 following the latest updates closely and felt genuine relief hearing 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 lives two blocks from the plant. She said she’s ready to return home, but first wants to be sure it’s safe. She also said she has been worried about the crews working around the clock.

“They are really our heroes,” Yen said.

In Fountain Valley, just southwest of Garden Grove, a large park was full Monday. Some people sought refuge there in an ad hoc shelter or pitched tents outside, while others gathered to enjoy Memorial Day.

How the situation was managed
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 is a British company that makes cockpit windows, canopies and windshields for military and commercial aircraft. The company 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.

The plant is owned by GKN Aerospace Transparency Systems. 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.

A broader vulnerability for aerospace suppliers
The disruptions at facilities producing specialized aircraft components can ripple beyond the immediate area, Richard Aboulafia said. Aboulafia is the managing director of AeroDynamic Advisory, an aerospace consulting firm.

Aboulafia said aircraft manufacturing differs from many other industries because 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.

He added that supply chains for specialized components are highly concentrated and already strained, making it harder for the global aerospace industry to absorb disruptions.

For residents watching the temperature gauges and the shifting perimeter lines, the message Monday was clear: some homes are coming back into the map, but the response isn’t done—and neither is the risk that still depends on how quickly the tank continues to cool.

Garden Grove California evacuation chemical tank methyl methacrylate GKN Aerospace Transparency Systems Orange County Fire Authority Craig Covey Regina Chinsio-Kwong South Coast Air Quality Management District EPA