Cypress, California — Fifty thousand Southern California residents remain under evacuation orders Monday after emergency crews raced to prevent a tank holding a volatile industrial chemical from exploding at an aerospace facility in Garden Grove. Officials announced Monday morning that they believed they turned a corner but that a threat still remained.

The threat centered on a tank containing methyl methacrylate, or MMA, at a facility operated by GKN Aerospace. Officials worried the chemical could undergo a dangerous "thermal runaway" reaction, causing temperatures and pressure inside the tank to rise to potentially catastrophic levels.

Evacuees face hardship, uncertainty

Entire neighborhoods were evacuated over the Memorial Day weekend as authorities warned that, in the worst-case scenario, the tank could explode and trigger additional blasts in nearby containers.

For displaced residents, the uncertainty has become its own crisis.

"We don't know how much longer it'll be," said Jackie Urquiza, who evacuated with her 7-year-old son Kyle from their home about a block from the facility. "Now we need clothes, and we're going to run out of medication."

Urquiza said she had no idea dangerous chemicals were stored so close to her neighborhood.

"We absolutely did not know this was near our home at all," she said.

Urquiza told CBS News that she was awoken at 6 a.m. to sirens and first responders at her door.

"At that moment, you can't think very well and you just pack whatever you can, like medications or clothes, but you don't have enough time to pack what you really need because you can't think at the moment," she said. "You know, you're freaking out."

Urquiza told CBS News the situation has been hard. In addition to running out of clean clothes, Kyle's school has been closed, and as a single mom, she has had to call out from work.

"I'm trying not to spend right now because I've already called off for a whole week until we'll see what happens," she said. "So just taking it day by day."

Another evacuee, Andrea Luna, said she and her two children had spent multiple nights sleeping in a parking lot after leaving their home.

"Devastating, nerve-racking," Luna said of the ordeal. Asked what had been hardest, she told CBS News: "Not knowing. Like just stuck, like what to do next. We're just trying to get by."

Some residents fled so quickly they barely had time to gather belongings.

"I just noticed I'm not wearing shoes. We had to go," Pavel Ramirez-Tellez told CBS News. He evacuated wearing slippers.

One threat off the table

Officials said emergency crews made progress after specially trained hazardous materials teams entered the danger zone Sunday night to inspect the tank directly and found a crack that could have released pressure.

Orange County Fire Authority interim Chief TJ McGovern announced Monday that a Boiling Liquid Expanding Vapor Explosion, or BLEVE, was "off the table." McGovern had told CBS News that there still could be an explosion even if a BLEVE was ruled out.

Orange County Fire Authority incident commander Craig Covey said crews verified a crack in the tank, which had released pressure. The temperature also stabilized and had fallen from 100 degrees to 93 degrees as of Monday morning.

While pressure has been released, the risk of an explosion comes from the core that crews haven't been able to assess yet. 

"There could still always be an explosion and that'll be the next step we're going," McGovern said Sunday. "The explosion would come with increased temps in that substance in there. That's why the next thing we're going to work out is getting accurate readings of what the solution's doing as far as increasing temperatures."

Evacuation orders remained in effect.

GKN issues apology

In a statement, GKN Aerospace apologized for the disruption caused by the incident, saying it was "acutely aware of the uncertainty this incident is causing and sincerely apologise for the ongoing disruption to the local community."

The company has previously faced environmental enforcement actions. Public records show GKN paid nearly $1 million to settle environmental violations in 2021.

MMA is commonly used to make clear plastic and glass substitutes. When stable, it is harmless, but in this form "it does pose acute toxicity hazards," said Elias Picazo, an assistant professor of chemistry at the University of Southern California. "Inhaling the chemical can result in dizziness, nausea, and irritation of the respiratory tract."

Officials said air monitoring had not detected a toxic release into the surrounding community. The Environmental Protection Agency also said there was no evidence chemicals had leaked into the environment, despite the crack in the tank.

Officials said the cause of the tank failure remains under investigation. At least two class-action lawsuits related to the current incident have already been filed.

Unknown timeframe

Because of the danger, only small numbers of responders have been allowed inside the evacuation zone at any one time. McGovern told CBS News six personnel entered during one overnight operation, with emergency evacuation protocols prepared in case monitoring systems detected worsening conditions.

Officials are unable to say when it will be safe for people to return home. "The first thing is firefighter safety, public safety," McGovern said. "We have to do this very strategically."