On October 30, 1948, killer smog hovering over Donora, Pennsylvania claims its first two victims. Over a five-day period, the smog killed about 20 people and made thousands more seriously ill.

Donora was a town of 14,000 people on the Monongahela River in a valley surrounded by hills. The town was home to steel mills and a zinc smelting plant that had released excessive amounts of sulphuric acid, carbon monoxide and other pollutants into the atmosphere for years prior to the disaster. During the 1920s, the owner of the zinc plant, Zinc Works, paid off local residents for damages caused by the pollution. Still, there was little or no regulation of the air pollution caused by the industries of Donora.

Source: history.com