Tens of thousands of Southern California residents have been evacuated after officials warned a leaking chemical tank holding a “highly flammable” substance at an aerospace facility would inevitably fail and potentially explode. 

The tank at GKN Aerospace is estimated to contain 7,000 gallons of methyl methacrylate, a “highly volatile” substance used in the production of plastics, according to Orange County Fire Authority Chief Craig Covey. It is not clear when the tank will fail, Covey said.

Methyl methacrylate is a flammable substance that generates its own heat. That means if it leaks into the atmosphere, any spark or flash could lead to an uncontrolled fire or explosion, said Elias Picazo, an associate professor of chemistry at the University of Southern California. At the moment, fire officials are working to keep the tank cooled.

Covey told CBS Los Angeles that this is “the most significantly dangerous event” he’s been a part of in his decades in fire service. 

“This is bad as I’ve ever seen,” he added. 

So far, no injuries or deaths have been reported. GKN Aerospace is in Garden Grove, a town about 38 miles south of Los Angeles. 

Health risks of methyl methacrylate 

Methyl methacrylate is a respiratory irritant, health experts told CBS Los Angeles. Exposure to the chemical can cause lung, skin and eye irritation, nausea and dizziness. 

Covey said there are “two options” right now. In one scenario, the tank could fail and spill thousands of gallons of “very bad chemicals into the parking lot and that area,” he said. 

Because the chemical is heavier than air, its vapor would settle and sink. Covey said crews have used sandbags to build containment barriers so that any spilled chemicals do not leak into storm drains or nearby waterways. 

In the second scenario, the tank could blow up, Covey said. This would send methyl methacrylate particles into the air. Covey said it’s unclear how widespread or dangerous such an explosion could be.  An uncontrolled explosion would also affect surrounding tanks, which hold chemicals and fuel. 

Efforts to keep the tank cool are continuing Saturday. Covey said he and other officials are also working to determine other options to safely end the incident. 

Covey said no particles that could compromise public health have entered the air as of Friday, and there is no active plume emitting from the tank. However, people have been advised to stay indoors.

Homes within a one-mile radius of the aerospace facility have been evacuated. There is no timeline for when the evacuation orders will be lifted. 

The cause of the leak remains under investigation.