Oil industry documents filed with the federal government reveal that an accidental release of a lethal chemical used in 50 aging refineries across the country could prove devastating, with 16 million Americans living within range of toxic plumes that could spread for miles.

Los Angeles, Philadelphia, Minneapolis, New Orleans, and the stretch of Texas coastline known as "Refinery Row" are among the at-risk areas cited in the documents. Citing homeland security concerns, the government keeps the industry filings under close guard in Washington, D.C. They were reviewed as part of a joint investigation by ABC News and the Center for Public Integrity.