On May 21, 2026, a chemical leak occurred at a GKN Aerospace manufacturing facility in Garden Grove in Orange County, California, about southeast of Los Angeles. First responders with the Orange County Fire Authority (OCFA) determined that a chemical tank had begun to overheat and off-gas excess pressure. The tank contained approximately of methyl methacrylate (MMA), a flammable and volatile liquid chemical used in plastics manufacturing. Unable to chemically neutralize or drain its contents due to a faulty valve, authorities stated that the tank would either fail and spill liquid MMA into the surrounding area or experience a boiling liquid expanding vapor explosion (BLEVE), releasing toxic vapor over a wide area.
Due to the possibility of an explosion, mandatory evacuation orders were issued, affecting over 50,000 people in a which included parts of Garden Grove as well as the bordering Orange County cities of Anaheim, Buena Park, Cypress, Stanton, and Westminster. California governor Gavin Newsom declared a state of emergency in Orange County, and a Federal Emergency Declaration was signed by President Donald Trump.
On May 25, authorities discovered that a crack in the tank wall had relieved the excess pressure, and the evacuation orders were fully lifted the following day. An investigation conducted by the Orange County District Attorney's office concluded with no criminal charges. GKN Aerospace pledged $5 million in community donations, including $1 million to the American Red Cross, and announced a $100 million damages claims program for affected residents and businesses.
Background GKN Aerospace GKN Aerospace is a company based in the United Kingdom that manufactures commercial and military aircraft components. The company's in Garden Grove, California, has operated since 2004 and is involved in the production of military canopies, cockpit windows, and passenger windows. At the time of the chemical leak, the facility employed at least 540 people, according to a 2024 news release, and an expansion for a new production line was scheduled to be completed in January 2027. Garden Grove city officials issued a permit for a expansion of the facility on May 19, 2026, days before the incident. On its website, GKN Aerospace cited increasing demand for the F-35 fighter jet as the reason for expansion.
As early as 2018, GKN Aerospace faced penalties from the California Department of Industrial Relations after an inspection of the Garden Grove facility revealed the company did not maintain or inspect all active machinery on the site and improperly cooled and covered tanks. That same year, ten violations were found during Occupational Safety and Health Administration (OSHA) visits to the facility. In 2019, GKN Aerospace was fined $2,898 for unpaid civil penalties related to their failed safety inspections and poor maintenance. In 2021, GKN Aerospace paid $909,935 in a settlement with the South Coast Air Quality Management District for several environmental violations, including failing to keep emission records regarding volatile chemical compounds, operating equipment without a permit, and using toxic chemicals in plant operations. In 2022, OSHA fined GKN Aerospace an additional $420 over a safety issue at this facility. In March 2025, the company received notices to comply regarding operating records, registration of equipment, and an application for change in ownership of the facility.
Methyl methacrylate
Methyl methacrylate (MMA) is a chemical used in the manufacturing of plastics and resins. It is flammable and volatile, and short-term exposure can irritate the eyes, skin and lungs. MMA is a monomer that undergoes a polymerization reaction, which is exothermic, and the rate of polymerization increases as temperature increases; therefore, an uncontrolled self-polymerization can lead to thermal runaway. The increased temperature increases pressure, so a tank containing MMA that is actively polymerizing is an explosion risk.
MMA is a key ingredient in acrylic F-35 fighter jet canopies, for which the GKN Aerospace Garden Grove facility is a lead manufacturer. Two of the three chemical tanks at the facility were confirmed to contain MMA, including the damaged tank.
Incident
At approximately 3:22 p.m. PDT on May 21, 2026, the Orange County Fire Authority (OCFA) was alerted to a hazardous materials incident at the GKN Aerospace facility in Garden Grove. Upon arriving at the scene, the OCFA determined that a tank containing approximately of methyl methacrylate (MMA) had begun to off-gas vapor and bulge outwards. The off-gassing tank was one of three tanks at the GKN site, with a neighboring tank confirmed to also contain MMA. A problem with a valve in the tank's refrigeration system, which normally maintained the internal temperature at , caused the tank's contents to overheat and pressurize; the tank's pressure relief valve and sprinkler system activated automatically.
Authorities issued an evacuation order to local residents. As the temperature inside the tank continued to rise, firefighters cooled the overheating tank by spraying water with unmanned water hoses, allowing the relief valve to close and preventing further vapor release of the contents. The evacuation orders were lifted that night. GKN Aerospace's response team attempted to inject a chemically neutralizing agent into the tank to reduce the volatility of its contents. However, the tank's valves were "gummed up" due to the chemical reaction taking place inside, preventing the injection of the substance and leaving no clear options to prevent the tank's failure. Were the tank to explode, the toxic chemical would have been released as a vapor, distributing it over a wide area and posing a health risk to residents. Evacuation orders were reinstated and expanded the next day.
On the night of May 22, a team approached one of the two neighboring tanks in an attempt to chemically neutralize its contents and was able to read the internal temperature gauge on the overheating tank. The reading was , significantly higher than the reading that had been taken that morning before responders retreated. Firefighters had previously believed the temperature to be decreasing based on exterior temperature readings via drone. According to OCFA incident commander chief Craig Covey, the new assessment indicated an average increase of per hour on the afternoon of May 23. By May 24, the internal temperature had reached at least , the maximum temperature reading possible by the gauge.
The OCFA said teams were thinking "outside the box" and communicating with experts around the country to find ways to mitigate the crisis. In a press conference, Covey stated that, with the MMA unable to be neutralized or drained, the two outcomes possible were that the tank would fail and spill liquid MMA into the surrounding area, or that the contents would enter thermal runaway and experience a boiling liquid expanding vapor explosion (BLEVE). Responders constructed channels and holding areas to prevent liquid MMA flowing into storm drains, waterways or the ocean if the tank were to rupture.
Firefighters and hazardous materials experts conducted an overnight mission on May 23 to assess the integrity of the tank. The crew discovered a crack in the tank, through which no liquid was leaking, but were forced to retreat when alarm sounded. According to OCFA interim fire chief TJ McGovern, the crack was possibly relieving pressure inside the tank, potentially preventing the tank from exploding.
A second all-night operation was conducted the next day to determine whether the excess tank pressure had been relieved. The other neighboring tank containing MMA was successfully neutralized, and the third tank was assessed as structurally sound. Crews confirmed that the cracked tank's excess pressure was relieved, and they removed external insulation material to assist cooling efforts and allow for more accurate temperature readings. The internal temperature was recorded as a decrease to . On May 25, the OCFA confirmed that the threat of a BLEVE had been "eliminated", and authorities reduced the size of the evacuation zone while monitoring the possibility of a smaller explosion or leak. The following day, the OCFA stated that the risk of a chemical leak, explosion, and fire had been eliminated, and the evacuation order was fully lifted. No significant chemical spillage was reported. According to Garden Grove county officials, the OCFA incurred $2.8 million in expenses during the operation.
Responses
Evacuation The expanded mandatory evacuation orders issued on May 22 applied to roughly 50,000 people in a around the Garden Grove facility, including parts of the neighboring Orange County cities of Anaheim, Buena Park, Cypress, Stanton and Westminster. About 15% of residents refused to leave the evacuation zone, according to Garden Grove police chief Amir El-Farra. As Garden Grove includes part of the neighborhood of Little Saigon, local Vietnamese radio and television stations translated emergency updates for non-English-speaking residents.
Local authorities established evacuation centers at several community centers, schools, and parks, including Savanna High School, Mile Square Regional Park, Los Amigos High School, Ocean View High School, Golden West College, John F. Kennedy High School, and Los Alamitos High School. State-owned properties and fairgrounds in Orange County became available as evacuation centers, and evacuees with recreational vehicles were permitted to park at the OC Fair & Event Center in Costa Mesa. Several of these emergency shelters were managed by the American Red Cross. Airbnb.org, a non-profit company founded by Airbnb, partnered with 211 Orange to offer free emergency housing.
Several businesses provided free or discounted services for affected residents. Planet Fitness, 24 Hour Fitness, and LA Fitness locations in Orange County and portions of Southern Los Angeles County opened to evacuees regardless of membership, and Uber offered free transportation to evacuation sites. Various hotels in the surrounding area offered discounts for affected residents. The Elks Lodge in Garden Grove also provided shelter. U-Haul offered displaced residents 30-days free use of its self-storage units and portable storage containers. World Central Kitchen volunteered alongside local restaurants and food trucks to provide meals to evacuees.
Orange County supervisor Janet Nguyen assisted in opening more shelters for evacuees. Staff from the Orange County Registrar of Voters assisted evacuees at shelters with voting for the 2026 California primary elections. Orange County Sheriff's Department officers were sent to patrol the evacuated areas to deter looters.
Several schools districts either closed campuses or relocated classes to alternate physical sites or online, including the Garden Grove Unified School District, Magnolia School District, Savanna School District, and the Westminster School District. CR&R Environmental Services trash collection operations, which serve several cities, were delayed as its facilities were located in the evacuation zone.
The evacuation zone was reduced on May 25 after the OCFA eliminated the possibility of a boiling liquid expanding vapor explosion, allowing roughly 34,000 residents to return home, and it was fully lifted on May 26. California state government