In 1975, the auto industry began to equip vehicles with catalytic converters to meet the emission limits of the Clean Air Act of 1970. Sitting unobtrusively between the engine and the muffler, the “cat” changes the noxious gases in automobile exhaust into harmless nitrogen, oxygen, carbon dioxide, and water. The result, according to the National Institutes of Occupational Health, was an 80 percent decline in the number of unintentional vehicle-related deaths caused by the most dangerous byproduct of combustion engines: carbon monoxide.