Jill Replogle

Drones are monitoring the temperature, but officials say they don't know how much advance warning they'll be able to give if the tank fails or how long residents might be out of their homes.

Governor Gavin Newsom has declared an emergency, and a fifth emergency shelter was opened Saturday evening for evacuees.

For NPR News, I'm Jill Replogle in Orange County.

The chemical in the tank is called methyl methacrylate, or MMA.

It's used in manufacturing plastics.

Exposure to MMA can cause skin and eye irritation and respiratory and nervous system problems.

Officials have been trying to cool the tank, holding thousands of gallons of the chemical.

They had made some progress, but warned Saturday that tank temperatures were again rising, increasing pressure in the tank.

If the tank explodes, it could cause a fireball and chemical fallout over the densely populated area.

If it cracks, the toxin could leak into storm drains and out to the ocean.

Officials say they are working around the clock to prevent both scenarios.

For NPR News, I'm Jill Replogle in Orange County.

Some 40,000 residents were told to evacuate early Friday when public safety officials determined the tank was likely to fail.

Officials say that could send some 7,000 gallons of its toxic contents spewing into the air or spilling out into the surrounding area.

But Craig Covey, division chief with the Orange County Fire Authority, says his team is working around the clock to prevent that.

The tank, which is owned by the company GKN Aerospace, is filled with a chemical known as MMA.

It can cause skin and eye irritation, respiratory problems, and can also affect the nervous system.

For NPR News, I'm Jill Replogle in Orange County.

Some 40,000 residents were told to evacuate early Friday when public safety officials determined the tank was likely to fail.

Officials say that could send some 7,000 gallons of its toxic contents spewing into the air or spilling out into the surrounding area.