EXPLAINER: Toxic gases connected to Ohio train derailment


              FILE - A plume of smoke rises from a Norfolk Southern train that derailed Friday night in East Palestine, Ohio are still on fire at mid-day, Feb. 4, 2023. After toxic chemicals were released into the air from a wrecked train in Ohio, evacuated residents remain in the dark about what toxic substances are lingering in their vacated neighborhoods while they await approval to return home. (AP Photo/Gene J. Puskar, File)
            
              FILE - Ohio Gov. Mike DeWine points to a map of East Palestine, Ohio that indicates the area that has been evacuated as a result of Norfolk Southern train derailment, after touring the site, Feb. 6, 2023, in East Palestine, Ohio. After toxic chemicals were released into the air from a wrecked train in Ohio, evacuated residents remain in the dark about what toxic substances are lingering in their vacated neighborhoods while they await approval to return home. (AP Photo/Gene J. Puskar)
            
              FILE - A man takes photos as a black plume rises over East Palestine, Ohio, as a result of a controlled detonation of a portion of the derailed Norfolk Southern train, Feb. 6, 2023. After toxic chemicals were released into the air from a wrecked train in Ohio, evacuated residents remain in the dark about what toxic substances are lingering in their vacated neighborhoods while they await approval to return home. (AP Photo/Gene J. Puskar, File)