William Brangham:

Some U.S. industries where silica exposure occurs, like construction and fracking, are regulated by OSHA, the Occupational Safety and Health Administration.

That agency recognizes the threat and mandates exposure limits and safety precautions. But coal mining is covered by a different agency and has been an exception. That's now changing. In June, the federal Mine Safety and Health Association, or MSHA, proposed a rule to cut the exposure limit for silica dust in half for a work shift.

Christopher Williamson, Mine Safety and Health Association: This is my great-grandfather's hard hat that he wore when he was a coal miners.

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