Dioxins are highly toxic and ubiquitous compounds that are unintentional by-products of several chemical processes on earth. According to the earth pollutant terminology, they are next to the nuclear catastrophes. It is because of their concerns over adverse health effects, a number of countries have introduced stringent emission standards.
“Burning vinyl is the most serious source of dioxin in the environment – whether from trash incinerator, house fires or chemical spills”, -- Eric Coppolino, writing for Planet Waves FM – Chiron Return.
”There are no coincidences in the universe, only convergences of Will, intent, and Experience” – Neale Donald Walsch
The official 'excuse' is that the cars got to 130 degrees and were a threat of exploding. Without having any of the on-the-ground facts, it's hard to assess whether this is true or not. Was it over-reaction? I don't know. I just know burning vinyl chloride is the last resort. They dug pits to drain the VC into them and once that was completed, they lit it on fire. Certainly, digging the ditches took time. So, your scenario sounds plausible. Why not pump the VC in a series of container trucks while isolating and mitigating the fire? Was there a lack of backup? Personnel? Procedure?