California chemical leak: What is methyl methacrylate, a deadly chemical that has forced 50,000 residents to evacuate and can damage eyes, skin and lungs?

California has declared a state of emergency as crews race against time to contain a toxic chemical leak at a manufacturing facility in Orange County. According to reports, a tank containing nearly 7,000 gallons of methyl methacrylate (MMA) began overheating at the GKN Aerospace facility in Garden Grove, releasing hazardous vapours into the air.

The incident forced nearly 50,000 residents to evacuate their homes as officials feared the unstable tank could rupture or explode. Many residents reportedly left in panic, worried that a major blast could occur if the chemical overheated further.

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What is methyl methacrylate?

Methyl methacrylate, commonly known as MMA, is a colourless industrial chemical used to make acrylic plastics, resins, paints, adhesives, coatings, aircraft windows and dental materials. It is widely used in manufacturing because it helps create lightweight and durable plastic products.

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The chemical has a strong fruity smell and evaporates quickly, meaning dangerous vapours can spread rapidly during leaks or industrial accidents. MMA is highly flammable, and its vapours can ignite if exposed to heat, sparks or flames.

Why is the chemical dangerous

In large storage tanks, MMA must be carefully stabilised and kept under controlled temperatures. If the chemical overheats, pressure inside the tank can rise rapidly, increasing the risk of fire or explosion.

Health agencies including the Centers for Disease Control and Prevention and the United States Environmental Protection Agency warn that MMA vapours can irritate the eyes, skin, nose and throat. Higher exposure levels may also cause headaches, nausea, dizziness, coughing and breathing difficulties.

Another major concern is something experts call “thermal runaway.” This happens when the chemical starts reacting with itself and producing heat. As the temperature rises, the reaction speeds up further, creating even more heat and pressure inside the tank.

If the process becomes uncontrollable, it can lead to rupture, fire or explosion. That is why emergency crews have been continuously cooling the damaged tank to prevent the situation from escalating.

Why were officials alarmed

Authorities feared not only a chemical leak but also the possibility of the tank exploding. Officials said the pressure relief valves on the tank had stopped functioning, raising concerns that pressure could continue building as the chemical changed from liquid into gas.

Reports said several tanks at the site had already been stabilised, but one unstable tank remained the primary concern. Because MMA vapours are flammable and hazardous, even a partial failure could endanger nearby neighbourhoods.

How crews responded

Firefighters used remotely operated water hoses to cool the tank and lower its temperature. Sandbag barriers were also placed around the facility to stop any chemical spill from reaching drains or waterways.

Hazardous-material experts were brought in to help manage the emergency and determine the safest long-term solution. Although the tank’s temperature later stabilised, officials continued evacuation orders as a precaution.

What residents were told

Residents living in evacuation zones were urged to leave immediately and avoid the area until authorities declared it safe. Officials warned that exposure to MMA vapours could lead to breathing problems, nausea and irritation.

Evacuation orders were issued across parts of Garden Grove, Anaheim, Stanton, Cypress, Buena Park and Westminster as crews continued monitoring the unstable chemical tank.