The processing and use of asbestos-containing diaphragms by the chlor-alkali industry poses an unreasonable risk to the health of workers, the US Environmental Protection Agency concludes in a draft risk evaluation. The assessment, released March 30, also finds unreasonable risks to workers and consumers who process or use asbestos-containing sheet gaskets, brake blocks, aftermarket automotive brakes and linings, and other vehicle friction products and gaskets.

The EPA did not evaluate the risks of so-called legacy uses of asbestos, despite a November 2019 court order to do so. Legacy uses are when a substance is no longer used in a particular product, but those products, such as insulation and construction materials, still exist in older buildings. Experts estimate that the biggest source of exposure to asbestos for firefighters, workers, and the general public is from such legacy products made in the 1970s and earlier.

In the 2019 ruling, the court directed the EPA to consider legacy uses as well as the disposal of asbestos-containing products that are currently found in older buildings. The EPA says that it will evaluate such risks in a supplemental evaluation, but it did not specify when.

Inhalation of chrysotile, the most commonly used form of asbestos and the only form evaluated by the EPA, is associated with lung cancer and mesothelioma, a cancer of the linings of the lungs and other organs. Chrysotile is imported into the US in raw form, exclusively for the chlor-alkali industry, according to the EPA. In 2018, the US imported 750 metric tons of the raw substance, the agency says.

The chlor-alkali industry uses asbestos in semipermeable diaphragms that separate the two compartments of an electrolytic cell. The diaphragm prevents sodium hydroxide from reacting with chlorine and allows the two chemicals to be separated for further processing. Some chlor-alkali facilities use polymer ion-exchange membranes, such as Nafion membranes, as alternatives to asbestos diaphragms. Those membranes contain per- and polyfluoroalkyl substances, which have their own risks to human health and the environment.

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