Orange County leaders said the risk of a catastrophic explosion at a Garden Grove aerospace facility has largely been eliminated after firefighters sprayed more than 9 million gallons of water on a piping-hot methyl methacrylate tank. Tens of thousands of resi
When Orange County officials told residents they could go home, it wasn’t the end of the firefighting effort they were announcing—it was the moment they believed the worst-case scenario had moved out of reach.
Tuesday’s update came after six days of trying to prevent an overheating chemical tank at GKN Aerospace in Garden Grove from erupting into a giant fireball or spilling thousands of gallons of toxic substances. Local authorities lifted a large section of the evacuation zone around the facility and allowed tens of thousands of residents to return.
Firefighters had sprayed more than 9 million gallons of water onto a piping-hot tank of flammable methyl methacrylate (MMA). sharply reducing the vessel’s temperature. But the cooling didn’t happen without consequences. The tank cracked after high temperatures led to high pressure, and the crack acted as a relief valve.
Interim Orange County Fire Authority Chief TJ McGovern told residents at a Tuesday afternoon community meeting that evacuation zones could shrink again soon. He said crews had stopped spraying water onto the tank and were assessing whether the temperature had stabilized.
“Once we know that temperature is stabilized, we will be taking the fire risk off the table,” McGovern said. “If there’s no fire risk, our evacuation zones are going to shrink.”
Around 5 p.m., McGovern said officials were “hoping that we’re going to have a very positive outcome very soon.” He asked residents to keep their patience over the next few hours as crews worked to validate early signs that the tank’s temperature was stabilizing.
County health officials and fire officials have maintained that there were no vapors or chemical leaks during the six-day crisis. The U.S. Environmental Protection Agency said its air monitors around the facility had not detected methyl methacrylate or other toxic airborne chemicals. known as volatile organic compounds.
Environmental experts, however, have pushed back.
Andrew Whelton, a Purdue University professor who studies environmental disasters, said the tank’s damage made it hard to accept assurances that nothing came out. He compared the ruptured chemical tank to a soda can with a hole punched in it.
“I find it hard to believe you can heat up a tank with a [chemical] like methyl methacrylate, see that it clearly cracked under pressure and think that nothing came out it,” Whelton said. “That defies logic.”
Whelton said it was possible that the massive water spraying helped suppress much of the toxic vapors and the airborne risk. Earlier. fire officials said the tank of MMA was undergoing thermal runaway. a chain reaction that produces an uncontrollable spike in temperatures. They had said the situation was likely to end in an explosion or a chemical spill.
Even so, Whelton said an explosion was still possible.
While authorities emphasized that air monitoring had found no detectable MMA or other volatile organic compounds. they also prepared for the possibility of a spill. Sandbag barriers were set up to block chemical runoff into storm drains that lead to the ocean. The Orange County Fire Authority said it was also testing water that had been hosed onto the tank to make sure it didn’t contain elevated levels of contaminants.
The dispute isn’t just about what’s in the tank that cracked. Jane Williams. executive director of California Communities Against Toxics. warned that MMA is only one of the chemicals stored on the site and argued that the public has not received enough confidence about what else may have been released.
She pointed to the company’s disclosures in 2024 indicating that, in addition to MMA, it had released thousands of pounds of flammable chemicals, including methyl ethyl ketone and methanol n-butyl alcohol, according to records from the South Coast Air Quality Management District.
Williams also cited the company’s prior regulatory trouble. She said GKN Aerospace had previously been cited for failing to disclose flammable chemicals at other facilities. In 2007, the U.S. Environmental Protection Agency alleged the company stored about 8. 000 pounds of hydrofluoric acid and 34. 000 pounds of nitric acid at a Kent. Washington facility without reporting those stockpiles to the appropriate government agencies. A year earlier than that. she said. the company settled with the EPA over allegations that it improperly stored ignitable hazardous waste at a facility near San Diego.
“For me, this is not about MMA,” Williams said. “You have a company with a bunch of chemicals, and it lost containment, and it’s across from residences. I do not trust this company to disclose what else is on their site. I do not trust them with first responders. I do not trust them with my health.”
The moment residents returned to their neighborhoods hinged on a single question: whether the tank’s temperature has truly stabilized now that firefighters have stopped spraying water. McGovern made clear that the next step—shrinking evacuation zones further and removing fire risk—depends on the results of that continuing assessment.
For the people who lived through the six days of evacuation. the shift from danger to “largely eliminated” risk may feel like relief. But for others. the crack in the tank and the history Williams described keep the unease alive—an argument grounded not in speculation. but in the gap between what monitors recorded and what experts say is physically plausible after a tank breaks under pressure.
Orange County Garden Grove GKN Aerospace evacuation methyl methacrylate MMA environmental experts TJ McGovern EPA air monitors volatile organic compounds Purdue University California Communities Against Toxics chemical spill risk