40 000 ordered to evacuate after chemical tank failure risk in Garden Grove, California

U.S. Representative Derek Tran, whose district includes Garden Grove, said Orange County Fire Authority crews received reports of the leak at around 15:30 LT on May 21.

The leak involved methyl methacrylate, a volatile and flammable chemical, from a 129 000 L (34 000 gallons) storage tank at the GKN Aerospace facility. About 22 700 to 26 500 L (6 000 to 7 000 gallons) of the chemical reportedly remained in the tank when it began overheating and venting vapors.

Garden Grove first reported an evacuation order at 18:37 LT on May 21 for an area north of Garden Grove Boulevard, south of Orangewood Avenue, east of Monarch Avenue, and west of Beach Boulevard.

The city temporarily lifted residential evacuation orders at around 20:00 LT, leaving street closures in place, but reissued evacuation orders at around 06:30 LT on May 22 after damage to a valve on the tank created additional operational challenges and prevented complete mitigation.

At 13:00 LT on May 22, Garden Grove expanded the mandatory evacuation area to Valley View Street on the west, Ball Road on the north, Trask Avenue on the south, and Dale Street on the east, citing changing conditions while mitigation operations continued. The expanded zone included parts of Garden Grove, Anaheim, Cypress, Stanton, Buena Park, and Westminster, according to the Orange County Department of Education (OCDE).

Fire officials described two possible outcomes for the compromised tank — rupture and release of thousands of gallons of chemical, or a thermal runaway event causing a boiling liquid expanding vapor explosion affecting nearby tanks.

Officials said there was no active gas leak or chemical plume in the area at the time of the May 22 afternoon briefing, but evacuation orders remained in place because of the failure risk.

Firefighters used remotely operated water hoses to stabilize the tank temperature while authorities coordinated with technical experts on a longer-term mitigation plan.

OCDE reported closures, campus evacuations, relocations, and operational changes across multiple districts, including Garden Grove Unified, Magnolia, Savanna, Westminster, Cypress, Los Alamitos, and OCDE ACCESS sites.

NOAA’s CAMEO Chemicals database describes methyl methacrylate monomer as a clear, colorless, flammable liquid with vapors heavier than air that irritate the eyes and respiratory system. The chemical can polymerize exothermically if heated or contaminated, and polymerization inside a container can cause violent rupture.

Methyl methacrylate is a Class IB flammable liquid, with a flash point of 10°C (50°F), lower explosive limit of 1.7%, and upper explosive limit of 8.2%. The exposure routes include inhalation, ingestion, skin contact, and eye contact, with symptoms including irritation of the eyes, skin, nose, and throat, and dermatitis.

References:

¹ Chemical Spill Emergency – Garden Grove – City of Garden Grove – Accessed May 23, 2026

Teo Blašković

I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.

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