Heat and pressure continued to build overnight in an unstable tank of toxic chemicals at a Southern California industrial site, the authorities said on Saturday, meaning that the tank could be inching closer to a rupture or an explosion that could spew toxic materials into a Los Angeles-area suburb.
It is also possible, officials said, that the increase in temperature is occurring because the liquid inside the tank is solidifying. If so, and if the tank holds, that could make a rupture less likely.
Still, some 40,000 residents of towns surrounding the plant in Garden Grove remain evacuated to shelters outside the potential blast zone.
In an update posted to social media on Saturday morning, Craig Covey, an incident commander with the Orange County Fire Authority, said that external temperature readings of the tank, taken via drone, had initially given officials hope that efforts to cool and stabilize the tank were successful.
But the tank’s internal temperature gauge, which the team glimpsed overnight for the first time since Friday morning, showed otherwise. The temperature inside the tank had risen by an average of one degree per hour, to 90 from 77 degrees.
Mr. Covey said the officials were consulting experts around the country to identify solutions. But, for the moment, the authorities still have no clear options to prevent the 7,000-gallon tank from failing — either by rupturing and leaking toxic chemicals, or, in the worst case, exploding.
“Letting this thing just fail and blow up is unacceptable to us,” Mr. Covey said. “Our goal is to find something and not allow that to happen, not let it damage our community, not let it damage our environment.”
Mr. Covey said that it was possible the liquid, through a chemical reaction, was turning into a solid, and that officials hoped the tank would have enough capacity to handle the pressure as that transformation took place.
“Because of the heavy deluge of water and cooling it, we are allowing it to cool at a slower rate and reducing its overpressure,” he said. “It’s one of the thoughts. So like an ice cube that freezes from the outside in, this stuff cures, it heats up and cures, from the outside in.”
Still, Mr. Covey said, emergency responders continued to develop contingency plans in case their efforts didn’t prevent a leak or explosion. They’re working on a plan that would, if successful, redirect any leaking fluid into the ocean and away from storm drains or river channels.
Authorities discovered the internal temperature had increased through what Mr. Covey described as a daring overnight mission to remove the explosive potential from a second, larger tank of chemicals adjacent to the unstable tank. During their approach, members of that team were able to read the internal pressure gauge, Mr. Covey said.
The chemical inside the tank is methyl methacrylate, a toxic and volatile substance widely used in the manufacture of resins and acrylic plastics, most notably plexiglass. According to the Environmental Protection Agency, exposure to methyl methacrylate can irritate the eyes and skin and make it difficult to breathe, among other symptoms. Birth defects have appeared in animals exposed to the chemical.
Firefighters first responded to the site in Garden Grove on Thursday, using water to cool the tank down as pressure began to grow inside it. But an attempt soon after by the company that owns the site, GKN Aerospace, to add a neutralizing agent to stabilize the chemicals was thwarted by the tank’s malfunctioning valves, Mr. Covey said.
That left emergency responders with no clear options to prevent the tank from failing.
The threat of a major explosion, which could disperse the tank’s toxic contents over a broad area, prompted orders for the evacuation of about 40,000 people in Garden Grove, Calif., a sprawling suburb just a few miles from Disneyland at the heart of Southern California’s Vietnamese community.
On Friday morning, evacuees at a Red Cross shelter at a park in nearby Fountain Valley lined up to use power outlets and tended to their pets. They intermingled with the usual early crowd of joggers, dog-walkers and golfers. Children fed ducks on the banks of one of the park’s ponds.
The evacuees — who received the order to leave their homes through phone alerts, social media posts and messages blared on loudspeakers — had passed a rough night at the shelter.
Mark Olson, 62, said he received the evacuation order via loudspeaker at his home early Friday morning. He found his way to the Fountain Valley evacuation shelter, where he’d spent the previous night pacing around the perimeter, sleeping for only three hours. Others were awake, too, he said, sitting in their cots, looking at their phones and snagging valuable time with the few charging outlets that were available.
“The cots are nice, but not for a guy with a bad back,” he said.
Cora Amolenda, 77, of Cypress, evacuated yesterday and “slept soundly” in the Fountain Valley shelter, she said.
Ms. Amolenda, who worked night shifts as a nurse in hospitals, said she could sleep anywhere. She said the evacuation center was well run.
“We’re well taken care of,” she said. “I don’t know how long we’re going to be out. We have to take a shower, you know.”
Amy Graff, Rebecca Fairley Raney and Francis Mateo contributed reporting.
