Evacuation orders were lifted for roughly two-thirds of the 50,000 residents displaced by an overheating chemical tank at a Garden Grove aerospace plant Monday night, as authorities said the risk of a catastrophic explosion had passed. The announcement capped a six-day emergency at the GKN Aerospace facility that had forced the largest evacuation in Orange County in recent memory over Memorial Day weekend.
The crisis began Thursday when the storage tank, containing 6,000 to 7,000 gallons of methyl methacrylate, overheated. Firefighters repeatedly sprayed the tank with water to cool the chemical inside, but valves on the tank were broken or gummed up, preventing crews from removing the chemical or relieving pressure, officials said.
A breakthrough came Sunday when a crack developed in the tank, allowing pressure to escape. Orange County Fire Authority division chief Craig Covey said a team evaluating the tank overnight concluded the interior temperature had dropped and pressure had been released. “This is incredibly positive news,” Covey said. The tank’s temperature, which had reached 100 degrees Fahrenheit on Sunday — a 10-degree increase from Saturday — fell to 93 degrees Monday, Covey said. The information from Covey was first reported by the Associated Press.
Democratic state Sen. Tom Umberg said the temperature had been 100 degrees Sunday. On Monday, Covey said the temperature had fallen to 93 degrees.
Covey announced Monday night that the evacuation area had been greatly reduced and that many of the evacuees could return home. The remaining evacuation zone remained in place because officials said some risk to public safety persisted, including a possible fire, spill, or small explosion.
Methyl methacrylate is a flammable, colorless liquid used in the production of resins, plastics, and plastic dentures. It is regulated by the federal government. According to the Environmental Protection Agency, it can irritate the lungs, eyes, and skin, and in high doses can cause reduced lung function, dizziness, and memory problems. Prolonged exposure can cause serious respiratory problems or loss of consciousness.
Air monitoring over the evacuation area detected no hazardous chemical levels, and Orange County’s top health officer, Dr. Regina Chinsio-Kwong, said people outside the evacuation zone need not worry about health impacts. “Tests have found that air pollution in the evacuation zone is within normal limits,” she said.
The facility specializes in producing aircraft transparency systems, including cockpit windows, canopies, and windshields. British company GKN Aerospace apologized Monday for the “ongoing disruption this incident is causing,” saying in a statement that its specialists and the fire authority had removed external insulation material from the tank to help cool its contents.
Several evacuation shelters were opened over the holiday weekend. The evacuation zone was west of Anaheim and did not include Disneyland’s two theme parks, which were never under evacuation orders.
If the tank’s temperature had climbed high enough to convert the methyl methacrylate from a liquid to a gas, pressure would have built, increasing the risk of an explosion that could have ignited other tanks and released hazardous vapors over a wider area, officials said.