Early Friday, an overheating tank filled with a toxic chemical at a Southern California industrial site took a turn for the worse.
Firefighters in Garden Grove, Calif., had responded on Thursday to the site, belonging to GKN Aerospace, where an industrial tank containing about 7,000 gallons of methyl methacrylate was becoming pressurized and releasing gas as it overheated. The tank was bulging dangerously, a sign that it could eventually explode.
They cooled the tank down with sprinklers. Residents who had evacuated their homes were allowed to return.
Methyl methacrylate, used to make plastics, has a low boiling point so it can easily overheat and turn to gas. Chemical plants typically have many fail safes for situations like this, experts said.
But when GKN Aerospace’s response team arrived to inject a neutralizing agent into the tank to reduce the liquid’s volatility, they learned that the tank’s valves were gummed up, making the interior inaccessible, said Craig Covey, an incident commander with the Orange County Fire Authority.
That left no clear options to prevent the tank from failing, Mr. Covey said.
It is possible that the tank could crack and allow the 7,000 gallons of liquid to pour out, he said. The fire department has made sand barriers to prevent the chemical from spilling into storm drains and river channels, he added.
“That’s the best-case scenario, believe it or not,” Mr. Covey said.
Worse, there could be a massive explosion that launches a fireball into the air, he said.
“If you’ve ever seen videos of tank cars on a railroad track blowing up — and that fireball it puts out — and it blows half the tank car half a mile down the train track, that’s the incident potential we are dealing with if this suffers a catastrophic failure,” Mr. Covey said.
He said that he was working with state and local officials, as well as experts across the country, to try to come up with a way to stop the tank from failing. The evacuation area was designed to be large because officials were not able to predict where a fireball from an explosion would land.
Methyl methacrylate is toxic when inhaled, and causes irritation to the respiratory system and potential damage to other organs. If the pressure keeps building inside the tank, the chemical inside eventually “could be shot outwards everywhere and then you have this cloud of toxin,” said Elias Picazo, a chemistry professor at the University of Southern California.
It is unclear why the liquid in the tank cannot be released in a controlled way to reduce pressure in the tank. It is possible that so much liquid has already vaporized inside that there is too much pressure to do that safely, said Faisal Khan, the head of the chemical engineering department at Texas A&M University.
The worst-case scenario, he said, would be a rupture of the tank that launches fire and debris into the air. Mr. Khan said that it would be similar to a car collision in which the gas from the vehicles vaporizes and causes a mushroom of destructive fire. In those cases, however, the fireball tends to stay close to the ground. Here, the fireball could fly upward and cause damage elsewhere, he said.
If about half of the material in the tank is released, the fireball from this explosion could be about the size of a house, Mr. Khan said.
Mr. Covey, the fire authority official, said on Friday evening that the tank temperature had stabilized, providing responders some more time to try to prevent an explosion.
He said that they were monitoring the temperature of the tank with a drone. If the tank reached a certain high temperature, he said, all staff would be removed from the area “to let the tank do what it’s going to do.”
Joseph E. Shepherd, a professor at the California Institute of Technology who studies chemical explosions, said that the 7,000 gallons of liquid could explode into a very large fire that would need special foams to extinguish. Worse, it could create a fireball that is blasted into the air.
“In an event, it’s not a good thing,” he said. “You could have a combustion event that could be pretty catastrophic.”
Soumya Karlamangla is a Times reporter who covers California. She is based in the Bay Area.
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