Orange County officials say a cooling system likely failed at a Garden Grove GKN Aerospace facility holding 7,000 gallons of methyl methacrylate, setting off a heat buildup that could have led to a BLEVE or toxic release. Evacuation orders were lifted by Tuesd
For the third morning in Orange County, the question wasn’t whether firefighters could stop a chemical fire.
It was whether the tank containing thousands of gallons of a highly reactive liquid would turn into something far worse—either a BLEVE, a nearly instantaneous explosive vapor transition, or a toxic release that could foul the air and waterways.
Last weekend, that worst-case outcome never arrived. But the near-miss has left investigators asking how a crisis described as a “boiling liquid expanding vapor explosion” could have started in the first place.
The chain of events. authorities now say. began when the cooling system meant to control the temperature inside a pressurized tank failed at the Garden Grove aerospace facility operated by GKN Aerospace. Orange County Fire Authority Interim Chief TJ McGovern said Tuesday that they suspect the system responsible for maintaining the tank’s temperature didn’t do its job—leading the product inside to heat up. off-gas through a relief valve. and set the response in motion.
“We don’t know why, but it stopped cooling,” McGovern said Tuesday. “So that’s what started this event. to where the product heated up and it off-gassed through the relief valve. and that’s how this whole response started. We’re just now being able to get to the tanks. so there’s definitely more to come of what caused it.”.
The tank held 7. 000 gallons of methyl methacrylate—known as MMA—and officials have warned that a runaway thermal reaction can escalate with terrifying speed. MMA is used to make products such as Plexiglass and other household items. Inhaling it can irritate the lungs and, at high levels, can cause severe respiratory distress and hospitalization. Long-term exposure has been linked to serious organ damage.
Fifty thousand people were forced to leave their homes in Orange County last weekend as the threat played out across the area. The Garden Grove facility sits next to an elementary school and a residential neighborhood. bringing the consequences of any chemical failure directly into schools and front yards.
Officials framed the firefighting challenge as a lose-lose scenario. If the heat continued, a BLEVE could have produced widespread damage and released toxic material into the air. If the situation shifted instead toward a spill, it raised fears of a chemical release into waterways and the ocean.
As the response progressed, competing claims about whether toxic vapors were released emerged inside the official picture. Fire officials referenced off-gassing of “fumes” and said on Friday that the tank was “no longer purging any kind of product.” But Orange County’s health officer. Dr. Regina Chinsio-Kwong, said on Monday that no fumes or vapors were issued during the incident. The U.S. Environmental Protection Agency said its air monitors had not detected toxic airborne chemicals. while environmental experts were skeptical that nothing toxic was released.
The science being discussed by experts helps explain why time mattered so much. When MMA is exposed to heat or light, it can start a chain reaction. Elaine Villanueva Bernal. a lecturer at Cal State Long Beach’s department of chemistry and biochemistry. said that as MMA solidifies. “it produces heat. ” and that heat “furthers the chain reaction. ” keeping it going “and going and going.”.
If the reaction gets out of control, experts say, it becomes a thermal runaway—one possible pathway to a BLEVE. The American Institute of Chemical Engineers’ Center for Chemical Process Safety describes a BLEVE as the rapid depressurization of a liquid that triggers an almost instantaneous transition from liquid to vapor. releasing energy and often accompanied by a large aerosol fireball.
While this incident played out in California over Memorial Day weekend, researchers have spent years warning about similar dynamics across the country and around the world.
A study published in the journal ACS Omega—citing information from the U.S. Chemical Safety and Hazard Investigation Board—found that nearly 15% of incidents in the United States involving uncontrolled chemical reactions between 1980 and 2001 were thermal runaway incidents involving rapid polymerization of a chemical. The study said such incidents have led to deaths globally. and that some experts believe the industry has struggled to improve safety.
Officials and researchers pointed to a wider record of consequences. In India in 2020. 12 people died and more than 580 were injured after a thermal runaway of styrene and release of styrene vapor occurred at the LG Polymers plant in the port city of Visakhapatnam. A committee appointed by India’s top environmental court blamed “gross human failure” and a lack of basic safety norms for the disaster. reported by the Associated Press. The ACS Omega study also referred to styrene-related runaways and said “Lessons have not been learned.”.
In 2012, one person died and 36 were injured in an explosion and chemical fire at a chemical plant in Himeji, Japan. That disaster followed “runaway polymerization of acrylic acid” in an intermediate storage tank. according to a study published in the journal Process Safety and Environmental Protection. citing information from the factory’s operator. Nippon Shokubai Co.
More recently, a study published in 2023 urged more attention to MMA. It said the correct choice of operating conditions can be “the first line of defense against thermal runaway events.” Without evaluating potential thermal hazards. implementing safe process designs and strengthening thermal safety. it warned that the “highly exothermic nature of the reaction may pose a severe threat to process safety as well as to industrial-scale equipment and to human lives.”.
A report from the U.S. Chemical Safety and Hazard Investigation Board issued in 2002 called for improved management of reactive hazards after two accidents in the 1990s in New Jersey—one of which killed five workers. The report concluded that “Reactive incidents are a significant chemical safety problem.”.
In Orange County, the moment investigators believe the tank began to slip toward catastrophe came in the temperature readings and physical changes crews could track.
Officials watched as the temperature gauge in the crippled tank rose from 77 degrees Fahrenheit on Friday, to 90 degrees on Saturday, and to at least 100 degrees on Sunday—the maximum reading on the gauge. At one point, the tank began to bulge.
For responders, the situation narrowed to a few options, and even the most direct intervention didn’t work. The easiest solution—pumping in a neutralizing agent to stop the reaction—failed. Elias Picazo. an assistant professor of chemistry at USC. said the neutralizing agent couldn’t be pumped in because the MMA in the valve had reacted and transformed from a liquid to a solid. clogging up the valve. That meant neither the neutralizing agent could be delivered nor could the toxic reactive fluid be drained out.
McGovern put it in plainer terms: crews could not “get anything into the compromised tank because, the theory is, the product was starting to solidify and it gummed up the dump valves.”
For that reason, firefighters focused on spraying cool water on the tank, hoping temperature control would prevent tragedy.
By Monday, the operation began to look like a turning point rather than a countdown. “In the end,” McGovern said, the cooling strategy appeared to have worked and the worst scenarios never materialized. He said officials confirmed a crack in the tank on Monday and that it was no longer pressurized—taking the concern of a BLEVE “off the table.”.
With the immediate explosion risk reduced, evacuation zones shrank.
The crack “allowed us to get more of our crews into the tank,” McGovern said. “They were able to start peeling back the external wall of the tank and move the insulation.”
From there, firefighters shifted their focus to better cooling and driving down the internal temperature. By Tuesday morning, the substance was hovering between 90 and 92 degrees Fahrenheit and water was still flowing.
Later Tuesday, crews began adjusting the cooling strategy again—starting with one of two water systems to see how the temperature responded. McGovern said firefighters would be looking for fluctuations and wanted the internal temperature to avoid rising once water flow was reduced.
“We’re looking for any fluctuations. What we do not want is the internal temperature to increase because we’re shutting down the water. We would really like it to decrease, but as long as it doesn’t move, we’re looking at the stability of the internal temperature.”
If the temperature stayed constant, crews planned to consider shutting down the secondary water supply. If temperatures didn’t fluctuate after that, he said it would indicate the fire problem—or a small explosion—had been mitigated.
By Tuesday night, all remaining evacuation orders were lifted. Authorities declared there was no remaining danger of an explosion, chemical leak or fire.
GKN Aerospace. based in Britain. makes landing gears. jet engines and other materials for commercial and military aircraft at its Garden Grove facility. The company did not respond to questions Tuesday. but earlier said. “we apologize for the ongoing disruption this incident is causing and our priority remains its safe resolution.”.
Orange County GKN Aerospace Garden Grove methyl methacrylate MMA thermal runaway BLEVE evacuation orders chemical safety TJ McGovern Regina Chinsio-Kwong