Officials in Orange County warned a pressurized tank holding methyl methacrylate could either explode or leak as crews race to cool it after the tank began heating and bulging in Garden Grove. Experts say the real problem is that methyl methacrylate’s liquid m
When crews lowered the temperature of a chemical tank in Garden Grove late Friday night to around 61 degrees, it sounded like progress. It also wasn’t comfort.
Orange County Fire Authority division chief Craig Covey said Friday that the goal is 50 degrees. Dropping the heat further could give firefighters a chance to use approaches that don’t depend on a catastrophic explosion or a destructive leak. But officials also made clear that the tank still isn’t safe enough for people to go back.
Inside the pressurized tank is an estimated 7,000 gallons of methyl methacrylate, or MMA, stored in liquid form. The chemical is used to make plastics, including MMA’s final polymer, which can be described as durable, lightweight, and transparent.
“It’s durable, lightweight, transparent, so it could even be used as a substitute for glass,” Elias Picazo, an assistant professor of chemistry at USC, said, describing the end product.
What makes the situation so difficult is what’s happening before that plastic ever exists. The polymer itself isn’t toxic. But the liquid MMA predecessor—called a monomer—is. In air, MMA can harm people at high concentrations and through chronic or extended exposure.
“The other hazard is the explosion itself,” Picazo said. “And it sounds like it’s already the reaction has already initiated, and that’s where the worry comes in for the explosion.”
That worry isn’t just about a hot tank. It’s about how the chemistry behaves once heat takes hold.
In chemistry, Picazo explained, there are “thermal runaway reactions,” which are extremely hard to control. Covey said that if the temperature of the tank exceeds a certain threshold. “we know the tank is going into thermal runaway. and we’re going to pull everybody out of the area. make sure it’s safe. and let the tank do what it’s going to do.”.
The crisis began on Thursday in Garden Grove, when a tank containing MMA started to experience an increase in temperature. At one point, the tank began bulging. Covey said it “got to a point where it does what we call a BLEVE. ” explaining that BLEVE stands for a “boiling liquid expanding vapor explosion.”.
Officials have not said what caused the temperature to rise in the first place, but experts say something shouldn’t have allowed it to happen.
Some chemical reactions, Picazo said, can be initiated by heat. With MMA, heat can begin a reaction—and then the reaction releases even more heat.
“You can start to see the problem,” he said. “You have a reaction that is initiated by heat, but it also releases heat as it goes on, that then leads to the runaway, where it’s uncontrollable.”
He described it as a large-scale reaction that can generate a lot of heat quickly. And because the MMA is in a high-pressure tank, the conditions are especially dangerous.
“If you build too much heat or pressure, then you get the explosion,” Picazo said. “And the material is also highly flammable, in addition to being toxic, and so you can have, fumes of toxins, flames like literal fireballs, and the explosion itself.”
Covey described the worst-case scenario as an uncontrolled explosion. He compared the risk to tank cars on railroad tracks—specifically the fireballs and how far blast effects can travel.
“If you’ve ever seen videos of tank cars on a railroad track blowing up,” Covey said, “and that fireball it puts out, and it blows half the tank car a half a mile down the train track, that’s the incident potential we are dealing with if this suffers a catastrophic failure.”
There is another feared outcome too: a massive leak. Covey said such a leak would still pose serious environmental threat to streams. rivers. and the ocean. but it would also make the chemicals no longer at risk of exploding. In that scenario. teams in hazardous material suits would be able to enter and “neutralize and mitigate the vapors that will be coming off of that. ” Covey said.
For now, the central strategy has been keeping the tank cool—because cooling is what can slow or prevent the kind of runaway reaction that turns heat into its own fuel.
Crews were able to cool the tank with sprinklers on Thursday, leading officials to think the problem might be resolved. But conditions worsened Friday. Firefighters discovered they could not offload a neutralizing agent because valves were broken and gummed up.
The neutralizer itself was theoretically a clear fix. Picazo said MMA is an electrophile, meaning it “likes taking electrons,” and that if another molecule that is a nucleophile is added, it can quench and kill the reaction.
“[I]f you add another molecule that is a nucleophile that likes to give electrons, you can quench it, you can kill the reaction, you can stop the reactivity of whatever remains,” he said.
But the broken valves meant that planned intervention never reached the tank.
That reality shaped the response. On Friday. firefighters reissued evacuation orders and expanded the zone to include portions of the cities of Garden Grove. Anaheim. Buena Park. Cypress. Stanton and Westminster. They warned people they were told that the only two options ahead were either a massive leak or an explosion.
Instead of letting those options take over, crews kept buying time with cool sprinklers. Picazo said that is a viable approach—“just wait it out by keeping the tanks cool.” He explained that controlling the runaway reaction can slow the chemistry and help crews maintain the pressure.
Covey, in an update on Friday night, said that efforts to cool the tank by spraying it with water had been successful.
“Those efforts are succeeding and it’s giving us opportunity to reconsider engaging in close proximity to implement some of the concepts…to mitigate this thing,” he said.
Even as temperature dropped, officials were facing questions that don’t have easy answers. Picazo said they need to determine how much MMA remains in the tank “and how to quench whatever is remaining.”
One tank on Thursday did release vapor after the tank experienced an increase in temperature. By Friday afternoon, firefighters had cooled the tank enough that a valve on top of the tank was no longer purging chemical into the air.
If the temperature continues to equilibrate and the tank stops venting substances, one possibility is that the reaction could be over. But Picazo said the uncertainty cuts both ways.
“I wonder what would happen if they stopped trying to cool the tank, if it would start heating itself again,” he said. “Basically, I’m wondering if the reaction is over, or, or if upon stopping the cooling mechanism, if it would re-initiate itself.”
Another pressing question is why the valve clogged up in the first place—preventing neutralizer from being delivered. Picazo offered one possibility: the MMA could have already reacted inside the valve and shifted from a liquid state to a solid state.
“Maybe the material has already polymerized in that outlet,” he said. “And so you can can’t get anything in or out from it, because the monomer — which is a liquid — once it polymerizes, it becomes that plastic, glass-like material, and that’s solid, so nothing’s going to go in or out.”
Officials have called the Orange County situation unprecedented. Even so, experts say accidents do happen in a region dotted with chemical facilities, refineries and heavy industry.
One recent incident occurred in October at the Chevron oil refinery in El Segundo. A large fire broke out in a corner of the refinery where crude oil is turned to jet fuel. and officials reported it resulted in a violent blast that rattled homes up to one mile away. The details on the cause and the extent of environmental fallout have not been released.
In 2015, an Exxon Mobile refinery in Torrance suffered an explosion; no one was seriously hurt. The U.S. Chemical Safety Board said Exxon Mobile relied on outdated procedures and used equipment that was older than its safe operating life. It added that the explosion had the potential to be catastrophic because of the presence of a highly toxic chemical. hydrofluoric acid. on site. which can immediately penetrate the skin and destroy tissue.
Other incidents reach further back. The Bullock Texas State History Museum said one of the deadliest industrial accidents in U.S. history involved the ignition of highly flammable fertilizer aboard a cargo ship, the SS Grandcamp, in Texas in 1947. A fire aboard the ship ignited 2,300 tons of ammonium nitrate, killing an estimated 581 people and injuring thousands. The first explosion ignited a second explosion at a nearby Monsanto Chemical Co. plant and caused a fire on another ship, the SS Highflyer, which then exploded 16 hours later.
That disaster “brought about new regulations for the chemical manufacturing industry,” the museum said. The changes included requiring cool temperatures and special containers for shipping ammonium nitrate, and banning storage near other reactive materials.
In Orange County, firefighters are still working against the clock—keeping a tank cool enough to prevent the heat from turning into a runaway reaction.
By Friday night, the temperature had fallen to around 61 degrees, with 50 degrees listed as the goal. Covey said the cooling efforts were succeeding and giving crews a chance to reconsider steps they could take in closer proximity. But as officials continue to determine what remains inside the tank and whether the reaction is truly over. the evacuation zone stays in place. because the most dangerous part of the crisis isn’t just the chemical. It’s the chemistry when heat and pressure refuse to back down.
Orange County Garden Grove chemical tank methyl methacrylate MMA thermal runaway BLEVE evacuation Orange County Fire Authority Craig Covey