For people avoiding caffeine, decaf coffee seems like a harmless option. But some health advocacy groups that argue otherwise are petitioning the US Food and Drug Administration to ban a key chemical involved in the decaffeination process due to cancer concerns. That chemical is methylene chloride, a colorless liquid that’s used in certain industrial processes, “including paint stripping, pharmaceutical manufacturing, paint remover manufacturing, and metal cleaning and degreasing,” according to the Occupational Safety and Health Administration. Methylene chloride has long been known to be a carcinogen, designated as such by the National Institutes of Health’s National Toxicology Program, the Environmental...