Five days after a train carrying vinyl chloride derailed and exploded near the Ohio-Pennsylvania border, crews ignited a controlled burn of toxic chemicals to prevent a much more dangerous explosion. Thousands in East Palestine, a town of about 5,000 people, evacuated, and officials warned the controlled burn would create a phosgene and hydrogen chloride plume across the region. Phosgene is a highly toxic gas that can cause vomiting and breathing trouble, and was used as a weapon in the first world war. Though no one died in the accident, the catastrophe serves as a wake-up call to the potential for...