What to KnowA compromised chemical storage tank at Garden Grove’s GKN Aerospace facility is threatening to leak its toxic contents or explode in what authorities called an unprecedented emergency.The hazardous materials situation began Thursday night when firefighters responded to reports of a problem with the tank containing a flammable liquid called methyl methacrylate.About 50,000 people in the Orange County community were under evacuation orders, and Gov. Gavin Newsom declared a state of emergency.A potential crack was detected in the tank over the weekend, raising hopes that the pressure inside the tank might diminish. Crews were expected to conduct an “all-night mission” Sunday to evaluate if the threat of an explosion is eliminated.

Tens of thousands of residents remained under evacuation orders Monday as uncertainty surrounded the volatility of a chemical storage tank that was at risk of spilling its toxic contents or possibly exploding in Garden Grove. 

The chemical tank crisis that began Thursday stretched into a new week with authorities still searching for a resolution in what they described as a complex and unprecedented emergency. A potential crack discovered late Saturday in the GKN Aerospace storage tank appeared to offer a glimmer of hope in an days-long hazardous materials situation that has unsettled the Orange County community, where about 50,000 people remain under evacuation orders. 

A specialized team of experts ventured into the tank area late Saturday and found the potential crack. Authorities said there is nothing leaking from the tank.

“During that operation, our firefighters went in and were able to visualize the tank. What they found was a potential crack in the tank, which could potentially be relieving some of the pressure in there,” said TJ McGovern, interim fire chief for the Orange County Fire Authority.

The new information could change the “trajectory” and strategy for emergency crews, who said Friday that the most likely options were a spill or explosion. 

Crews were expected to conduct another operation Sunday night to evaluate if the threat of an explosion is eliminated.

“It’ll be an all-night mission in order to confirm that the pressure in the tank has been released and that the BLEVE threat is eliminated,” McGovern said in a video posted to the OCFA’s X account just after 8:30 p.m.

BLEVE stands for boiling liquid expanding vapor explosion. It describes the process when a liquid inside a container overheats; if the tank breaks, the pressure can drop quickly, causing the liquid to turn into an explosive vapor, according to the Center for Chemical Process Safety.

The hazardous materials situation began Thursday evening when firefighters responded to GKN Aerospace after reports of an overheating problem with a storage tank containing a flammable liquid called methyl methacrylate. That tank, located near two other tanks, began venting vapors and triggering a sprinkler system designed to spray water on the tank to cool the material inside.

It was not clear what caused the chemical tank to overheat.

Scenes from Garden Grove chemical tank emergency

After the first reports of a problem Thursday, firefighters began spraying the failing tank with water in an effort to cool the material inside. Conditions initially appeared to improve and the vapor leak was stopped, but the situation became more volatile due to a problem with the pressure-release valve on the tank, which still contained about 6,000 to 7,000 gallons of the toxic chemical.

The tank’s already high temperature continued to rise and evacuation orders were issued for 50,000 people as authorities warned around midday Friday the tank was likely to either spill its toxic contents or explode. At one point over the weekend, the temperatures reached at least 100 degrees, authorities said.

GKN Aerospace, a global supplier of vehicle and aircraft components, posted the following statement on its website Sunday.

The infrared technology from a drone gave a specialized hazmat team confirmation that there’s a potential crack in the tank. Hetty Chang reports for the NBC4 News at 8:30 p.m. on Sunday, May 24, 2026.

“We continue to monitor the condition of the affected material and are working round the clock to mitigate the risk of a leak. We are acutely aware of the uncertainty this incident is causing and sincerely apologize for the ongoing disruption to the local community.

“We are working closely with the Orange County Fire Authority, the EPA, OSHA, and all relevant federal, state and local agencies, and remain deeply grateful for the dedication and expertise of all the emergency services and agencies involved. Our priority remains the safe resolution of this incident, so that residents can return to their homes as quickly as possible. Please continue to follow all instructions issued by local authorities and emergency personnel at this time.”

For residents in the evacuation zone, the hazardous materials situation triggered an unsettling chain of events that continued to play out over the weekend. Evacuation shelters were at or near capacity and there was no immediate word on when resident will be allowed to return home.

Several schools in the area are closed until further notice.

OCFA Interim Chief TJ McGovern called Saturday night’s operation “positive” despite not meeting all objectives. Hetty Chang reports for the NBC4 News at 3 p.m. on Sunday, May 24, 2026.

Spill or explosion

OCFA said a spill of the chemical was preferable to best case to an explosion and possible plume of toxic material spreading over the area. 

In the event of a spill, emergency crews are working to execute a plan that would dam and contain the toxic chemical.

OCFA Division Chief Nick Freeman on Saturday released a map that detailed which communities could be impacted if the tank explodes, dividing the map into three circular damage zones and three oblong blast zones.

Alex RozierAlex Rozier

“This diagram shows you the evacuation zone that was carefully selected, taking into consideration the worst-case scenario,” Orange County Health Officer Regina Chinsio-Kwong said. “If you are not in the evacuation zone in red here, you do not need to worry. Just stay informed with any updates that you see. Now, if you remain in the evacuation zone, that’s where your risk increases.”

Potential blast zones

Inner-most circle: Freeman said this area would experience “severe structural damage and significant harm.”

Moderate blast damage: Those under this area would also experience structural damage and harm, but not as severely as areas in the inner-most circle.

Light blast damage: Structural damage would be limited but still possible.

Potential impact zones

Red zone: Freeman said this “indicates areas of flammability where we could have fire or flash fire zones.”

Orange zone: Homes and businesses in this area fall under an “immediate danger to life and health where it would cause injury if anybody inhales or is impacted by the product in question,” according to Freeman.

Yellow zone: This area is considered non-hazardous but is under what’s described as the odor threshold. “Product is a very low odor threshold and can be smelled very easily, so that’s why that representation is very large but again, it is non-hazardous at that level,” Freeman said.

About methyl methacrylate

Methyl methacrylate, a colorless, volatile, flammable liquid chemical used in the manufacture of resins and plastics, can irritate the skin, eyes and nose in humans.

The Environmental Protection Agency said respiratory symptoms can include chest tightness, dyspnea, coughing, wheezing, and reduced peak flow.

Neurological symptoms, including headache, lethargy, lightheadedness, and sensation of heaviness in arms and legs, have occurred in humans following acute exposure to the chemical, according to the agency.