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.
Beginning sometime on October 26, weather conditions in the valley brought a heavy fog into Donora. This fog appears to have trapped the airborne pollutants emitted from the zinc smelting plant and steel mills close to the ground, where they were inhaled by the local residents. Soon, a wave of calls came in to area hospitals and physicians. Dr. William Rongaus, the head of the local Board of Health, suggested that all residents with pre-existing respiratory problems leave town immediately. However, 11 people, all elderly and with heart problems or asthma, were already dead.
Most residents then attempted to evacuate, but the heavy smog and increased traffic made leaving difficult. Thousands flooded the hospitals when they experienced difficulty breathing. It was not until October 31 that Zinc Works shut down operations. Later that day, rain fell on Donora and dispersed the pollutants. By that time, another nine people had already perished.
The Donora smog disaster received national attention when it was reported by Walter Winchell on his radio show. In the aftermath, air pollution finally became a matter of public concern; the incident led to the passage of 1955 Clean Air Act. The Donora Zinc Works shuttered operations in 1957. Although the types of heavy visible pollutants responsible for the deaths in Donora have now been mostly outlawed and eliminated, invisible pollutants such as ozone remain a threat to people with chronic respiratory ailments.
Years later, a local high-school student’s research and activism led the Pennsylvania Historical and Museum Commission to place a commemorative plaque in Donora honoring the victims of the killer smog.