Methyl methacrylate, the highly flammable organic compound at the center of the chemical crisis in Garden Grove, Calif., is widely used to manufacture resins and acrylic plastics, such as Plexiglas.
In liquid form, it has an acrid, fruity odor; after production, it is found in products like advertising signs, light fixtures, plumbing and latex paint. The chemical is also used to make bone cement for orthopedic procedures, as well as dental crowns and fillings.
The Environmental Protection Agency warns that even short-term exposure can cause skin and eye irritation, alongside respiratory issues — including chest tightness, shortness of breath, coughing and wheezing. Inhalation has also been reported to cause neurological symptoms such as lethargy and lightheadedness.
Exposure most often occurs at manufacturing facilities, where workplace safety experts have developed guidelines to safeguard employees. The E.P.A. does not consider methyl methacrylate likely to be carcinogenic, but animals exposed to the chemical have shown fetal abnormalities.
Joseph Allen, a professor of environmental health at Harvard University, said the scale of the current crisis reminded him of the 2023 train derailment in East Palestine, Ohio, where similar toxic chemicals were released, causing widespread public health concerns.
As in that situation, the threat of combustion looms. Andrew J. Whelton, an environmental engineer at Purdue University, said an explosion would spread chemicals both vertically and horizontally, and that flying shrapnel from the tank would be an added concern. Because methyl methacrylate is so flammable, he is especially concerned with how fire would transform the compound, generating a complex host of new chemical byproducts and pollutants.
“An explosion does not render the chemicals inert — it greatly complicates the hazard and health risk,” he said.
Emily Baumgaertner Nunn is a national health reporter for The Times, focusing on public health issues that primarily affect vulnerable communities.
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