Dioxin is an example of why saying "10 train cars is fine" is an oversimplification, 10 train cars of dioxin is a problem even if it's spread out over a couple square miles.

Maybe 10 train cars of formaldehyde is fine, maybe not, but, this is something that should be assessed and not dismissed out of hand, even during discourse. Random internet commentators probably don't really know if it's fine. And despite the people on-site saying measurements are fine... animals are getting sick, which is the classic warning sign with chemical spills that things are not fine.

Although there is indeed dioxin formed during the combustion apparently. Bear in mind too that this isn't a controlled incinerator, there could be various things produced at different temps etc.

It wasn’t formaldehyde either.

Vinyl chloride will form some dioxin upon combustion.

When left to break down in the environment, after several days vinyl chloride will break down into a combination of formaldehyde and hydrochloric acid. The latter of which won't be harmful, but the former will be.

Vapor phase formaldehyde breaks down in the air within hours.[1]

It will also be destroyed in the soil by any number of mechanisms, with a half-life of about 14 days. [2]

[1] https://www.atsdr.cdc.gov/toxfaqs/tfacts111.pdf

[2] https://webwiser.nlm.nih.gov/substance?substanceId=1&identif...

I do not think combustion of vinyl chloride at atmospheric pressure is going to create much if any dioxin