Roughly 40,000 people in Garden Grove, a Los Angeles suburb, were evacuated on Friday after a chemical storage tank was determined to be at risk of failing and spilling thousands of gallons of toxic material or exploding.

The malfunctioning tank holds methyl methacrylate, a flammable and volatile chemical used in plastics manufacturing for aerospace applications, igniting widespread worries over potential toxic vapor release.

The situation broke out Thursday, when the tank at a manufacturing facility started displaying signs of instability. By Friday, an update increased fears of an explosion, Orange County Fire Authority interim Chief TJ McGovern said.

Firefighters were working to cool the tanks with a mechanical device operated from a safe distance, stabilizing the temperature and buying critical time, officials said.

“I know I keep talking about we were handed this situation where there’s only two things that can happen: it could crack and leak, or it could blow up. That’s not acceptable to us,” Craig Covey, division chief of the Orange County Fire Authority, said in a video posted on social media.

Covey added in a later video, “I have an entire team actively working locally, regionally, across the state, and across the country, to try to figure out how to fix this.”

He said he is working to “get all these brilliant minds together to put a plan together, so that we don’t let this blow up.”

Reuters contributed to this report. 

This story will be updated with additional details.