GKN Aerospace officials and Orange County public-safety authorities said the immediate danger from a damaged chemical storage tank in Garden Grove had eased enough for many residents to return, after a weeklong response that began with heightened fears of a catastrophic explosion.
Authorities said the tank holding methyl methacrylate overheated last week at the Southern California aerospace plant, prompting evacuation orders affecting about 50,000 people. Officials later said monitoring had not detected hazardous chemical levels in the atmosphere, and they reported no injuries.
On Sunday, firefighters and emergency crews had been working to prevent escalation after the tank’s contents heated and pressure rose. The Orange County Fire Authority said the risk profile changed when officials identified a crack in the tank that helped relieve pressure.
Craig Covey, a division chief with the Orange County Fire Authority, said an overnight evaluation concluded that the temperature inside the tank had dropped and pressure had been released. Covey called the updated assessment “incredibly positive news,” describing the development as a key reason evacuation orders could be reduced.
Officials also described the tank as holding about 6,000 to 7,000 gallons (23,000 to 26,500 liters) of methyl methacrylate. They said vapors vented as the chemical warmed, but that monitoring continued to show no hazardous concentrations in the atmosphere.
Sen. Tom Umberg said the tank’s interior reached 100 degrees Fahrenheit (37.7 Celsius) on Sunday, after increasing by 10 degrees Fahrenheit from Saturday. On Monday, Covey said the temperature fell to 93 degrees F (33.9 degrees C), as crews continued their assessment and cooling efforts.
In addition to explosive risk, officials addressed other potential hazards they had been managing during the emergency, including possible fire, spill, or small explosion scenarios, even as they moved toward reducing the evacuation footprint. Covey said Monday night that the evacuation area had been greatly reduced and that many of the evacuees could return home.
Orange County’s top health officer, Dr. Regina Chinsio-Kwong, said the risk model driving the emergency also included the possibility that a tank failure could release chemical vapors that would be hazardous to inhale. Chinsio-Kwong said people outside the evacuation zone did not need to worry about health impacts, and officials reported that air pollution tests in the zone were within normal limits.
Officials said the immediate problem involved valves that were broken or “gummed up,” preventing crews from removing the chemical or relieving pressure. In Monday remarks, Covey focused on the changes that reduced the explosion likelihood, and the county’s public messaging reflected a transition from wide evacuation to returning residents.
The tank incident unfolded in a region near Anaheim, where Disneyland’s theme parks were not under evacuation orders. Meanwhile, GKN Aerospace issued an apology on Monday for disruption, and the company said specialists and the Orange County Fire Authority removed external insulation material from the tank to help cool its contents.