Toxic Chemical Leak Prompts Evacuation of 40,000 in Southern California

More than 40,000 people have been evacuated after a toxic chemical started to leak from a tank at an aerospace manufacturing facility in the US.

The tank in southern California contains an estimated 7,000 gallons of methyl methacrylate, a highly volatile and flammable substance used in the production of plastic.

The Orange County Fire Authority (OCFA) issued initial evacuation orders for the area surrounding the Garden Grove facility on Thursday afternoon, after reports of a tank temperature increase.

The evacuation zone has been expanded and the cause of the leak is being investigated.

OCFA officials say there are three tanks at the facility, one of which has a compromised cooling system.

In a press conference on Friday afternoon, OCFA Chief Craig Covey said there were two potential outcomes from the leak, the first being that the tank fails and spills "very bad chemicals" into the area surrounding the facility.

"Or two, the tank goes into a thermal runaway and blows up, affecting the tanks that are around it that have fuel or chemicals in them as well."

"This is not precautionary," he said. "This thing is going to fail, and we don't know when... We're doing our best to figure out when or how we can prevent it."

A hazmat team is working with experts to find a way to depressurise the affected tank and limit exposure.

The fire chief said that evacuation orders will remain in place as authorities try to mitigate the leak. He added that his team had been able to successfully prevent further temperature increases of the compromised tanks.

Evacuation centres have been set up by the OCFA, along with an information hotline.