Have you thought of building the entire haunt underwater in an Olympic sized swimming pool? It could be patrons have to snorkel or scuba throught the scenes. Just don't use anything made out of magnesium as it will burn even under water if heated up to about 1600 degrees. And these days all the damn kids are wearing portable oxy acetaline torches and shit, it is all a disaster waiting to happen. Or their cell phone battery could catch fire at any moment.
To be a bit serious, I think the FM doesn't get the occupancy realities of there will only be so many people per square foot. Like a clothing store being observed there might on a busy day be 50 people scattered through and racks of clothing are somewhat seperated from each other with the rules that isles have to be so wide. I think he has this picture of it being like a concert and all 10,000 people will be in there all at one time watching something for an hour.
So you have to play the Sesame Street game of some things are not like the other.
Any foam is bad. Hard coated or not. When exposed to heat it melts and any outside coating is irrelevent as the surface coat breaks when the foam mechanically moves due to heat. But, it is not an ignition source. None of these things are. Where are things that could prove to be a source of ignitions?
Another fabulous post from the U.S.Department of Wild Imaginings, now in spectaclar stereo, sponsored by the Adhesives and Sealants Council, suggesting ways to stick things together since the 1800s. Not fabulous in a gay way. Your results may vary. Illinois residents add 8% sales tax. These posts have been made by professional post makers, do not try this type of posting on your own without extensive training, lovely assistants and a trusty clown horn.