The greatest trainwreck in Human History has happened in America.
A two mile long train carrying ;Vinyl chloride: A highly flammable colorless gas used when making plastic is a known carcinogenic. Once it is made into PVC pipe it is no longer toxic or deadly.

• Butyl acrylate: A flammable clear liquid used in making paints can cause irritation to the skin, eyes, and respiratory system.

• Ethylhexyl acrylate: A colorless liquid used in making paints and plastics can produce hazardous vapors under heat.

• Ethylene glycol monobutyl: A highly flammable colorless liquid used in making solvent is deemed as acutely toxic.

Additional materials that were involved in the fire included petrochemicals and semolina.

How long they will persist is the main factor.
I had a personal experience seeing a victim of vinyl chloride in Rochester NY 40 years ago. The only consciousness the grandmother had was of panic knowing something happened to her but could not escape. Her IQ seemed below 50. The exposure did come from a single rail car of the chemical behind her house. She was trapped in an eternal hell.

As fish birds and animals are dying in mass numbers the people were told they could return home.

Deliberate Burning this deadly chemical cocktail was a bad idea imo.