A train carrying toxic chemicals derailed in eastern Ohio, igniting a fire that covered the town of East Palestine in smoke. Fearful of a major explosion, the authorities carved out an evacuation zone and carried out a controlled release of toxic fumes to neutralize burning cargo inside some of the train cars. Residents feared for their health as concerns have mounted about the effect the derailment and the fire could have on the environment and the transportation network. Here's what we know: h