Jill Replicol

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.

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