What a useful discussion, guys!
Larak, you are undoubtedly correct about the fumes only being a hazard at actual burning temps, which I don't believe the hot knife approaches. Point taken. I would be concerned about the volatiles or anything that might be yielded by the melting it takes to actually break the substance apart and having them lodge in my alveoli. They may not be toxic per se, but they will occlude the surfaces where oxygenation of blood is meant to occur...at least, that's my story and I'm stickin' to it.
Same for the dust. Dust isn't necessarily perceptible, but that doesn't mean it isn't there. Tiny bits of the foam, a stable and robust compound, may also accumulate in the alveoli, and my guess is that they are going to be there long after my corpse begins to get soupy inside.
I am not an expert in these things, but my generalized learning suggests that our indoor environments are problematic enough without introducing more aerosols, volatiles, micro-particles, and other forms of foreign materials that our bodies must content with.
I would say, in closing, that neither coal dust nor sawdust are toxic (I think?), but they sure do a number on our lungs. In the case of foam, I have no idea what our immune systems might do to the little bits of whatever is left of the stuff when we cut it that gets into our lungs. I think I'll sleep better at night not knowing, but taking what I feel are sensible precautions.
