The Monongahela River meanders from the West Virginia coal country to the middle of Pittsburgh, where it joins the Ohio and Allegheny rivers in a famous confluence called Three Rivers. Along the way the river curls around this hill and that, forming elbows and horseshoes that can make travel between towns along its banks long and lonely.

Along one of those curves, a large horseshoe about 30 miles southeast of Pittsburgh, lies a a town called Donora, an old mill town that would largely be forgotten now were it not for an unusually long patch of unlucky weather that led to the deaths of hundreds of people and ultimately prompted the creation of the Clean Air Act. For it was at that horseshoe curve that at the turn of the 20th century a wealthy Indiana industrialist, William H. Donner, had decided to build a series of zinc and steel plants to supply the growing needs of a flowering America.

The plants employed thousands of Donora residents, supplied steel and wiring for hundreds of buildings, bridges, and highways, and spewed untold tons of respiratory pollutants and irritants into the air. In the fall of 1948 Mr. Donner’s plants gave grave notice to the town that all was not well.

On Tuesday October 26, the air over Donora became foggy from cool air being trapped beneath warmer air above in what meteorologists term a temperature inversion. Normally inversions last less than a day, but this one lasted a devastating five days. Within two days the fog had turned into a stinging, yellowish-gray shroud so thick that many people couldn’t drive, couldn’t even walk without stumbling. “It was so bad,” said one resident, “that I’d accidentally step off the curb and turn my ankle because I couldn’t see my feet.”

On the worst day, Saturday the 30^th, volunteer firefighter Bill Schempp worked his way around town, feeling the way from house to house to deliver oxygen to residents with respiratory problems. Each visit lasted only a few minutes and happened the same way. Schempp placed a mask on someone struggling to breathe and turned the oxygen on for just a few seconds, what he called a “shot of oxygen.” Just as the person began to breathe more easily, Schempp then moved to the next house. The residents needed continuous oxygen but there simply weren’t enough oxygen tanks to go around. “These people were just desperate for air,” said historian Brian Charlton, curator of the Donora Smog Museum and active member of the Donora Historical Society.

So it was that Schempp, a man who had lived and worked with the people of Donora for years, who had fought fires, transported the sick and injured to local hospitals, and plucked frightened cats from raging storm drains, had to decide how much oxygen to give each resident. He had to say over and over, No, I’m sorry, as he shut off the oxygen and removed the mask. He had to listen to those desperately ill people plead with them, begging for their life, and then walk away knowing he might never see his friend alive again.

All told 20 people would die over that five-day period, at least 50 more the following month, and hundreds more over the following years. The event spurred an investigation by the Division of Industrial Hygiene, then part of the U.S. Department of Public Health and now part of the Environmental Protection Agency. After numerous states, including Pennsylvania, enacted their own clean air acts, the Government decided that clean air should be a national priority and in 1955 passed the first national air pollution law, initially called the Air Pollution Control Act of 1955 (public law 84–159), later renamed the Clean Air Act.

Today Donora residents maintain a sense of pride about the tragic events of that dark October 68 years ago. In a 2009 interview with NPR, long-time Donora resident Don Pavelko said, “We here in Donora say this episode was the beginning of the environmental movement. These folks gave their lives so we could have clean air.”