Authorities are urgently trying to stop an overheated, pressured and bulging tank filled with a toxic chemical from exploding in Orange County, California -- and they are closely monitoring each aspect of the site of the spill at a manufacturing company, according to an internal briefing memo reviewed by ABC News.
In what is being called an "unprecedented" situation, tens of thousands of people in Southern California were told to leave their homes Friday, with officials issuing a dire warning that the chemical tank at an aerospace facility is in "crisis" and will either spill or explode.
California Gov. Gavin Newsom has issued a state of emergency in Orange County in response to the incident.
"The safety of Orange County residents is the top priority. We are mobilizing every state resource available to support local responders and make sure the community has what they need to stay safe," Newsom said in a statement Saturday.
Looming over the roughly 10-square-mile evacuation zone now are both concerns that either toxic fumes could waft through the neighborhood, or that a dangerous fireball could erupt, the memo said.
Mandatory evacuations have expanded for the estimated 50,000 residents in the densely populated area, the memo said. There are multiple public facilities nearby -- including schools, hospitals, nursing homes, fire and law enforcement stations -- critical infrastructure, and essential services, all currently subject to mandatory evacuation and ongoing response operations.
Multiple roads have also been closed off in the evacuation zone, changing transportation routes in the area. Evacuation centers have been established across Garden Grove, Cypress, Stanton City Hall, Anaheim, and Buena Park, the memo said.
Over a dozen schools have temporarily closed, and those adjacent to the evacuation area canceled outdoor activities "out of an abundance of caution," the Garden Grove Unified School District said.
Firefighters initially responded to a leak at the GKN Aerospace manufacturing company in Garden Grove on Thursday, for vapor releasing from a 34,000-gallon tank containing methyl methacrylate, which is used in plastic manufacturing, according to the Orange County Fire Authority.
Authorities first issued an evacuation order on Thursday, but that was later lifted when vapor conditions improved. However, the evacuation orders were reissued and expanded on Friday due to what police called an "unprecedented" event.
On Friday, the situation in the city, about 30 miles south of Los Angeles, had grown more dire, with officials warning that, though there was no active gas leak or plume, the tank was "actively in crisis" and unable to be secured.
Three tanks are affected at the GKN site, the memo said. Of most concern is Tank #1, which has the malfunctioning valve that, so far, is unable to be neutralized. That valve has seized due to the chemical reaction inside the container. Firefighters have been trying to get the temperature down and stable with water cooling.
Meanwhile, emergency responders on scene have been trying to troubleshoot Tank #2 -- which contains the same chemical as the other, compromised tank. Officials on scene have added a "neutralizer" to the methyl methacrylate in Tank #2 to prevent an even worse chain reaction. That tank appears to be structurally sound, the memo said.
Tank #4 is also structurally sound, however the status of what's inside it is "unknown."
Local fire and HAZMAT teams are on-site working to cool the 34,000-gallon industrial vessel and clean up, with investigation efforts underway, the memo said, with state emergency resources also partially activated. The EPA has also dispatched two on-scene coordinators to the facility.
The response remains active, and so far no injuries have been reported, the memo said.
At a press briefing, Friday, authorities laid out the urgency of the situation.
"There are literally two options left remaining: one, the tank fails and spills a total of about 6- to 7,000 gallons of very bad chemicals into the parking lot in that area. Or two, the tank goes into a thermal runaway and blows up, affecting the tanks that are around them that have fuel or the chemicals in them as well," Orange County Fire Authority Division Chief Craig Covey said in a video update Friday.
He added, "We are setting up these evacuations in preparation for these two options -- it fails or it blows up," he said.
On Friday evening, Covey said officials thought crews had successfully the lowered the temperature inside damaged tank with a curtain of water being directed at it. That is "buying us time to continue to sort out: How do we fix this?" Covey said in a video update.
However, in a follow-up video posted on Saturday, Covey said contrary to what officials first thought, the temperature in the tank had actually increased.
Covey has said crews are working around the clock to stave off the worst.
"It is not OK with me just to sit back and watch this thing blow up or fail," Covey said. "That is not acceptable to me."
Officials have said it is unclear when residents will be able to return to their homes.
"This is highly volatile, it's highly toxic, it's highly flammable," Covey said during an earlier press briefing, while urging people to evacuate. "This is not precautionary. This is gonna happen unless some brilliant guy behind me here figures out how we can mitigate this incident. This thing is gonna fail -- we don't know when."
Methyl methacrylate is an industrial chemical used in plastics and manufacturing and is primarily a respiratory irritant, authorities said. Around 7,000 gallons are estimated to be left in the tank that's in crisis, Covey said.
Short-term exposure to the chemical can cause skin and eye irritation, as well as breathing problems, according to the EPA.
Orange County Health Officer Regina Chinsio-Kwong said in a video update Friday evening that an explosion could cause the chemical to be released as a vapor, which, if inhaled, could cause "severe respiratory issues." Other symptoms include a sore throat, runny nose, itchy and burning eyes, and potentially nausea and headache, she said.
GKN Aerospace builds engines and landing gear for both commercial and military aircraft. ABC News has reached out for comment.
ABC News' Sasha Pezenik, Bonnie McLean, Josh Margolin, Jenna Harrison and Jack Moore contributed to this report.
