Garden Grove Chemical Tank Emergency — Methyl Methacrylate Leak Forces Mass Evacuation

The Garden Grove Unified School District said nine schools no longer within the evacuation zone are reopening Tuesday. Twelve campuses that closed Friday in the response remain closed through the final day of the school year, Wednesday, May 27. Check the district for your campus.

Officials cautioned that the worst-case explosion being off the table does not mean the response is over. A smaller explosion, fire, or leak from the tank remains possible as crews continue to monitor the site, and the remaining evacuation zone stays in effect.

The Orange County Fire Authority said the threat of a BLEVE — a boiling-liquid expanding-vapor explosion — is no longer a possibility at the compromised tank. The crack in the tank allowed pressure to release, and the temperature has been confirmed to be decreasing, which officials described as a turning point in the response.

At about 6 p.m. PDT Monday, officials announced the mandatory evacuation zone is being reduced by about 65%. Roughly 34,000 residents can return home, while about 16,000 remain under evacuation in a smaller zone bounded by Orangewood Avenue (north), Dale Street (east), Knott Street (west), and Garden Grove Boulevard (south). Confirm your address with the City of Garden Grove before returning.

Disneyland Resort said it remained open and was not affected by the leak at this time. The Anaheim park is about five miles from the facility and outside the evacuation zone.

Governor Newsom and three members of Congress — Rep. Derek Tran and Sens. Adam Schiff and Alex Padilla — appealed to the federal government for a disaster declaration to bring additional resources to the response.

Four of five evacuation shelters were reported full on Sunday morning, with Los Amigos High School (16566 Newhope St) the only one with remaining capacity. Availability changes quickly — confirm with the American Red Cross before traveling.

The interim fire chief said a crew mission on Saturday spotted a crack in the tank, which officials described as a step in the right direction because it could allow pressure to relieve more gradually. Officials cautioned that conditions were still developing.

The EPA administrator said the most likely scenario now appeared to be a low-volume release that local authorities could monitor, neutralize, and contain — a more contained outcome than the explosion officials had warned about earlier.

A law firm filed a proposed class-action lawsuit against GKN Aerospace on behalf of two residents within the evacuation zone, seeking class-action status. The filing reflects early legal activity tied to the incident; nothing on this page is legal advice.

Emergency officials said Saturday evening that air monitoring had detected no contaminants so far. The EPA deployed stationary air monitors around the facility, and the South Coast AQMD ran a mobile monitoring van along the evacuation-zone perimeter.

Authorities released a map estimating damage if the tank explodes: severe damage within roughly 1,100 feet, moderate damage within about 0.3 miles, and light damage within about 0.4 miles of the tank.

According to a report on the South Coast AQMD website, GKN Aerospace settled with the district in January 2025 for about $909,936 over permit, record-keeping, and nitrogen-oxide emissions violations. The company manufactures landing gear, jet engines, and other aircraft components.

The Orange County district attorney's office opened an anonymous tip hotline and online form seeking information about the circumstances leading up to the release, including the facility's operations and the maintenance of the tanks and systems involved.

Fire officials said an on-site sprinkler system, supplemented by unmanned ground units adding water, had held the tank's temperature at about 90°F after an overnight rise from about 77°F. Crews were checking the temperature roughly every 10 minutes.

Governor Gavin Newsom declared a state of emergency for Orange County as crews worked to keep the tank from leaking or exploding. Officials had warned the tank could crack and spill thousands of gallons or enter thermal runaway, with other nearby tanks within the potential blast radius.

The Orange County registrar said the in-person voting center and ballot drop site planned at the Garden Grove Sports & Recreation Center would be closed until further notice, as the building was being used as an evacuation center.

Caltrans closed the Beach Boulevard, Knott Avenue, and Valley View Street off-ramps from the 22 Freeway until further notice because of the chemical response. Check Caltrans QuickMap for current conditions.

The U.S. EPA describes methyl methacrylate as a flammable liquid that evaporates easily and can linger near the ground as a vapor. At high levels, inhalation can cause coughing, wheezing, and chest tightness, along with nausea, dizziness, and skin irritation. The county health officer noted a released vapor could carry a fruity smell. Follow official guidance and seek care for symptoms.

At a Friday news conference, Orange County Fire Authority Division Chief Craig Covey said the damaged tank was expected to either leak or enter thermal runaway and explode, describing the situation as unprecedented. Officials ordered residents out of parts of six cities until the tank could be secured.

The Garden Grove Unified School District closed 15 campuses in response to the chemical response, and schools near the zone canceled outdoor activities. Check the district for current closure and reopening status.

With a faulty valve leaving no safe way to relieve the tank, officials reissued and expanded the evacuation to roughly 40,000 people across six Orange County cities — Garden Grove, Cypress, Stanton, Anaheim, Buena Park, and Westminster — including the Little Saigon community.

An initial evacuation order — covering the area north of Garden Grove Boulevard, east of Monarch Street, south of Orangewood Avenue, and west of Beach Boulevard — was issued and then lifted later that evening as the first leak appeared controlled.

The Orange County Fire Authority was alerted at about 3:40 p.m. to vapor escaping an overheating tank of methyl methacrylate (MMA) at a GKN Aerospace facility on Western Avenue. Reports describe roughly 7,000 gallons of MMA within a 34,000-gallon tank.