Early Friday, an overheating tank filled with a toxic chemical at an industrial site in Southern California took a turn for the worse.

Firefighters in Garden Grove, Calif., had initially responded on Thursday to the site, belonging to GKN Aerospace, where an industrial tank containing about 7,000 gallons of methyl methacrylate was becoming pressurized and releasing gas as it overheated. The tank was bulging dangerously, a sign that it could eventually explode.

The chemical inside the tank, methyl methacrylate, used to make plastics, has a low boiling point so it can easily overheat and turn to gas.

Firefighters worked to cool the tank down by constantly shooting water at its exterior. That allowed GKN Aerospace’s response team to get close enough to the tank to inject a neutralizing agent into the tank in an attempt to reduce the chemical’s volatility.

But when the team arrived, they found the tank’s valves were gummed up, making the interior inaccessible, said Craig Covey, an incident commander with the Orange County Fire Authority.

That left no clear options to prevent the tank from failing, Mr. Covey said.

It is possible that the tank could crack and allow the 7,000 gallons of liquid to pour out, he said. The fire department has made sand barriers to prevent the chemical from spilling into storm drains and river channels, he added.