Ohio Death Cloud

 A train derailed carrying uncured vinyl chloride. Because there were fires, there was a risk of explosion. The local government made the decision to vent the chemical cars, releasing the vinyl chloride into the environment. The land is now poisoned and the locals are in real danger of developing aggressive cancers. To illustrate how dangerous vinyl chloride is, when exposed to uncured vinyl chloride the typical reaction is to develop tissue cancers and die within a month. It is perhaps one of the deadliest things on earth.