(CNN) \u2014 California officials have significantly scaled back evacuation orders Monday as the risk of a catastrophic tank explosion has been eliminated. But about 16,000 residents still remain displaced, Garden Grove Police Chief Amir El-Farra said, as crews continue to manage the threat of a smaller blast or toxic release.<\/p>\n
Until Monday evening\u2019s reduction, about 50,000 residents were asked to flee their homes as the temperature and pressure escalated inside a tank at GKN Aerospace in Garden Grove. The tank contains 7,000 gallons of a chemical called methyl methacrylate, or MMA, which is used to make plastics and can cause myriad health problems upon exposure.<\/p>\n
Crews worked overnight into Memorial Day to investigate a crack in the tank, which authorities had said might alleviate pressure and prevent a disaster known as a BLEVE, or boiling liquid expanding vapor explosion.<\/p>\n
Additionally, a deluge of cool water has doused the overheated tank for days, helping to bring down the temperature, officials said in an update Monday night. Runoff water from the site \u2013 millions of gallons \u2013 is being tested for any hazardous chemicals.<\/p>\n
The threat of a catastrophic explosion has since been eliminated, Orange County Fire Authority Interim Chief TJ McGovern said Monday.<\/p>\n
But \u201cwe still have threats that we\u2019re mitigating right now,\u201d McGovern said, including the \u201cpotential for an explosion that\u2019s not as bad as a BLEVE\u201d but still a risk to public safety, he said.<\/p>\n
A presidential emergency declaration has been signed for the situation, California Gov. Gavin Newsom announced Monday<\/a>.<\/p>\n A volatile situation<\/p>\n The tank contains MMA, a chemical that can cause skin and eye irritation as well as respiratory problems.<\/p>\n \u201cThere is still no chemical leak, as verified by continuous atmospheric monitoring,\u201d the Orange County Fire Authority said Monday.<\/p>\n Still, some residents have reported symptoms of exposure. And some schools have closed and switched to online learning as a precaution.<\/p>\n The tank started showing signs of trouble Thursday, when heat and pressure started building up.<\/p>\n When MMA overheats, it starts a chemical reaction that is difficult to control inside a large tank, said Elias Picazo, a chemistry professor at the University of Southern California.<\/p>\n Authorities are trying to keep the tank as cool as possible to keep the chemical reactions happening inside the tank stabilized, said Elaine Bernal, a chemistry lecturer at California State University, Long Beach.<\/p>\n Almost 800 state and local first responders have been deployed to respond, said Newsom, including toxicologists, hazmat teams and public health sheltering experts.<\/p>\n Temperature stabilized and falling<\/p>\n Methyl methacrylate\u2019s \u201chappy place\u201d is 50 degrees Fahrenheit, and an increase in temperature could cause a leak or explosion, Orange County Fire Authority Division Chief and Unified Incident Commander Craig Covey said.<\/p>\n The tank involved began to overheat after the refrigerating system used to keep it cool and stable stopped working, according to Covey.<\/p>\n \u201cOne of the valves in that system froze up, so (cool air) is no longer being circulated,\u201d Covey said Monday night. \u201cDue to that failure, the tank went into the heating up process because it wasn\u2019t continuing to be chilled.\u201d<\/p>\n Officials aren\u2019t sure exactly what temperature might cause the tank to ignite or explode, Orange County Fire Authority Captain Steve Concialdi said. They had no clue how hot it was inside the tank Sunday because the temperature gauge has already maxed out at 100 degrees.<\/p>\n By Monday morning, the temperature had stabilized and was falling, Covey said. \u201cIt is currently 93 degrees, down from 100 degrees. That is incredibly positive news as we turn the corner on this incident.\u201d<\/p>\n With the largest threat out of the way, \u201ccrews are actively working right now on the next steps,\u201d McGovern said. \u201cWe still have product in there. We can\u2019t physically see what the product is doing.\u201d<\/p>\n Based on the latest temperatures inside the tank, fire officials believe the chemical has started to gel or solidify \u2013 which is exactly what they want.<\/p>\n \u201cWe know that the product will solidify (from) liquid to a solid form \u2026 but we don\u2019t know how much of it has yet,\u201d McGovern said.<\/p>\n GKN apologized to evacuated residents<\/a> and businesses Sunday and said it\u2019s working with emergency services and hazardous materials teams \u201cto monitor the condition of the affected material and are working round the clock to mitigate the risk of a leak.\u201d<\/p>\n \u201cWe are acutely aware of the uncertainty this incident is causing and sincerely apologise for the ongoing disruption to the local community,\u201d the company said in a statement.<\/p>\n Theme parks such as Disneyland and Knott\u2019s Berry Farm are close to but not included in the evacuation zone.<\/p>\n \u201cAt this time, there is no impact to Disneyland Resort due to this situation and the resort remains open to guests,\u201d the park\u2019s website<\/a> said Monday. The park said it\u2019s monitoring the situation and working with local authorities.<\/p>\n Newsom issued a state of emergency<\/a> to support response operations. And Orange County District Attorney Todd Spitzer announced an anonymous tip line<\/a> and reporting form for anyone with information about the incident or what led to it.<\/p>\n He has also opened a criminal investigation into GKN Aerospace, DA spokesperson Kimberly Edds told CNN. The company has been ordered to preserve evidence, Edds added. When reached for comment, GKN Aerospace referred to its earlier statement<\/a>.<\/p>\n Residents sue tank owner<\/p>\n A couple who live in the evacuation zone filed a proposed class-action lawsuit against GKN Aerospace on Saturday, claiming the company negligently stored and handled MMA \u2013 leading to widespread disruptions for their community.<\/p>\n \u201cAside from just being evacuated, everything that they know and love is inside their home,\u201d said attorney Filippo Marchino, who\u2019s leading the class-action suit.<\/p>\n GKN Aerospace declined to comment on the litigation Sunday.<\/p>\n About 100 to 120 other residents have already expressed interest in joining the class-action case, Marchino said.<\/p>\n The lawsuit claims the company\u2019s handling of the chemical caused dangerous conditions by creating an ongoing risk of fire, explosion, toxic chemical exposure and environmental contamination that affected tens of thousands of residents, businesses and schools.<\/p>\n \u2018I forgot to close the window \u2026 and I regret it\u2019<\/p>\n Exposure to MMA can cause nausea, dizziness and \u201csignificant irritation\u201d to the lungs and nasal passages, Orange County Health Officer Dr. Regina Chinsio-Kwong said.<\/p>\n The chemical can produce a fruit-like scent, although smelling it does not mean you have experienced enough exposure to have symptoms, she said in another update.<\/p>\n Officials said the chemical has not been detected in the air, but some residents said they\u2019ve experienced symptoms.<\/p>\n \u201cI forgot to close the window during the Thursday night, and I regret it,\u201d said Stanton resident Van Ly, who evacuated Friday. \u201cMy throat and the inside of my nose feel sore, and my wife felt dizzy Friday night.\u201d<\/p>\n Air should be safe outside the evacuation zone, Chinsio-Kwong said, urging people to leave the affected area.<\/p>\n Evacuated residents flock to shelters<\/p>\n Some school districts in the evacuation zone announced they would move to online learning. Garden Grove Unified School District said its 13 affected schools would remain closed \u201cuntil further notice,\u201d and district trustee Walter Muneton said the schools would shift to virtual learning.<\/p>\n The Red Cross<\/a> opened a seventh shelter for evacuees Sunday as others in the area reached capacity for overnight stays.<\/p>\n