In 1948, two major plants called Donora, Pa., home, Donora Zinc Works and the American Steel and Wire Company. Some residents were uneasy about them even before that October, when toxic smog enshrouded the town for almost five days.
Although haze was not uncommon to the area, this was different because of a temperature inversion that trapped the air in the valley. Before rain helped dispel the smog on Halloween, 20 people had died and as many as 7,000 more were sickened. Lawsuits were filed against the plants, but they never claimed responsibility. They did, however, pay out settlements to victims.
The federal government didn’t really get involved with the incident, experts say. But the Donora Smog did help inspire the clean air movement, which eventually saw the passage of the Clean Air Act.