From Ohio History Central
On July 8, 1986, fifteen cars of a forty-four-car CSX train derailed near Miamisburg, Ohio. Some of the cars that derailed contained phosphorus. When ignited, phosphorus releases poisonous gas. Shortly after the derailment, city officials ordered thousands of Miamisburg residents to evacuate their homes. The next day, officials allowed these people to return, only to have the phosphorus ignite. One Miamisburg resident described the resulting vapor cloud as "real heavy stuff, hugging right on the ground, like fog. People had their lights on, it was so dark." A second evacuation occurred, with approximately twenty thousand people seeking shelter at Dayton, Ohio, at the University of Dayton and the Dayton Convention Center. This was the largest evacuation to occur in Ohio's history. By July 10, all but two hundred families had returned home, as most of the phosphorous had burned. Over three hundred people sought treatment at area hospitals due to respiratory problems. More than one billion dollars in lawsuits resulted from this derailment.