I'll be collecting all the updates I've found on social media here. The warehouse used to be the Ames Factory (I think they made shovels there), but for years has been a dump for things that Dupont can't legally get rid of. The state doesn't know what was in there, but there is possibilities of any number of these products being stored there - PVC, Nylon, Carbon black, Titanium dioxide, Fiberglass, Maleic Anhydride TLV 0.1 ppm, Formaldehyde, PTFE (Teflon), Styrene, Acrylonitrile, Polybutylene Terephthalate, and/or Acrylic Sheet all of which are not good things when burned.
Edit: Update from Reddit "There is also an underground storage tank from when it was ames that is full of trichloroethyene, lead, ethylbenzene, and toluene that is leaking. The fire suppression system for the warehouse failed last winter because one of the pipes froze and busted. They never had it fixed."