Heat and pressure continued to build on Saturday in an unstable tank of toxic chemicals at a Southern California industrial site, the authorities said, 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, 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 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, 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.
Air monitoring teams from the E.P.A. and South Coast AQMD, a local air pollution agency, said Saturday night that they had not detected contaminants in communities surrounding the facilities.
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 blocked valves, Covey said.
That left emergency responders with no clear options to prevent the tank from failing.
By Saturday afternoon, Gov. Gavin Newsom of California had declared a state of emergency in response to the threat. Representative Derek Tran, a Democrat whose district encompasses Garden Grove, said in a news conference on Saturday that federal resources had also been mobilized to the area, with observers from the Environmental Protection Agency on site.
In the event of the tank exploding, the Orange County Fire Authority is anticipating a blast zone that would cause structural damage in a several-block radius around the site, as well as a trail of chemical fumes that could harm human health or spark flash fires. At further distances, the chemical trail would be detectable by odor, but would not pose any health risks, the OCFA division chief, Nick Freeman, said in a video posted to social media on Saturday afternoon.
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.
Cindy Tran, a Garden Grove councilwoman, said that city staff had established a 24-hour call line, sent out phone alerts in multiple languages and dispatched police officers door-to-door in the evacuation zone to ensure everybody was notified of the evacuation order. She said that special outreach efforts had been made toward the city’s Vietnamese refugee community.
But the evacuation was not total. Mr. Tran, the congressman, said that the Garden Grove Police Department had estimated that 15 percent of people in the area had refused to leave.
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.”
The weather in Orange County was warm and mild on Saturday. The winds were light to nonexistent in the morning, but a sea breeze was expected to pick up in the afternoon, as it usually does in this region.
The strength and direction of those winds may shape the aftermath if the tank explodes and toxic material is ejected into the air.
“The winds would be blowing from the southwest, so it would push things more to the northeast,” said Casey Oswant, a meteorologist with the National Weather Service office in San Diego.
GKN Aerospace, which owns the facility at the center of crisis, is a U.K.-based manufacturer of aircraft parts for both military and civilian use. It is one of many such plants across Southern California, which has long been a hub for aerospace companies.
Marianne Mulder, a spokeswoman for GKN Aerospace, said in a statement on Saturday morning that the company was working with emergency services and specialized hazardous material teams to resolve the situation as quickly and safely as possible.
“We sincerely apologize for the significant disruption to the many local residents and businesses who have had to be evacuated,” Ms. Mulder said.
Amy Graff, Rebecca Fairley Raney and Francis Mateo contributed reporting.
