The threat of a catastrophic explosion at a Garden Grove aerospace plastics plant has been eliminated, Orange County officials said on Sunday night, but tens of thousands of residents in the cities of Garden Grove and Westminster will spend a fourth day away from their homes as engineers work to safely vent a 34,000-gallon tank of methyl methacrylate.
A crack discovered in the tank earlier in the weekend appears to be relieving internal pressure faster than vapour can build up, eliminating the risk of a "BLEVE" — a boiling-liquid expanding-vapour explosion — that prompted an unusually wide-radius evacuation on Thursday. Orange County Fire Authority chief Brian Fennessy said a smaller leak, fire or localised explosion remained possible, and that emergency shelters in Los Alamitos and Westminster would stay open until the tank is fully drained.
Roughly 50,000 people remain under evacuation orders covering a quarter-mile radius around the GKN Aerospace facility, with a larger shelter-in-place zone extending further north and east. California Governor Gavin Newsom signed a state-of-emergency declaration on Saturday, freeing state matching funds for shelter operations and lost-wage assistance for affected workers. President Trump issued a federal emergency declaration the same day.
GKN Aerospace, which manufactures composite components for commercial and defence aviation, said it has hired specialist contractors from Texas to pump the remaining methyl methacrylate into mobile tankers and ship it off-site for processing. The company estimates that the venting and transfer operation will take 48 to 72 hours; air-quality monitors operated by the South Coast Air Quality Management District have so far detected only trace amounts of the chemical outside the immediate evacuation zone.
Methyl methacrylate is a colourless liquid used to make acrylic plastics and adhesives. It is highly flammable, with a flashpoint of around 10 degrees Celsius, and is classified as a respiratory and eye irritant; exposure at high concentrations can cause headaches, dizziness and central nervous system depression. The chemical is not classified as carcinogenic by the US Environmental Protection Agency, but public health officials have urged anyone with persistent symptoms after the evacuation began on Thursday to seek medical advice.
Orange County District Attorney Todd Spitzer announced on Sunday that his office had opened a parallel investigation into the cause of the leak, with a focus on whether GKN had complied with the state’s tank-integrity inspection regime. The facility was last inspected by Cal/OSHA in 2024; preliminary findings from that review have not been made public.
The Memorial Day disruption has rippled through the region. Disneyland in Anaheim, about 12 kilometres east of the GKN site, said its parks remained open but acknowledged a noticeable drop in attendance over the holiday weekend. Several school districts have cancelled the final week of classes for affected students and will offer make-up days in June.
County officials said they expect to issue the first partial re-entry permits on Tuesday morning, once the tank pressure has been confirmed below working thresholds and air monitors maintain clean readings for 24 consecutive hours. Residents have been told to expect a phased return, starting with the streets furthest from the plant.