I've got a proper "Foam Knife", but essentially, it's just a big electric carving knife.
What ever you do, don't use a "Hot knife", (normally used for cutting nylon climbing rope) I tried that once and didn't realise that it would cause the foam to emit Hydrogen Cyanide gas, and within seconds of touching the foam, all 3 guys in the workshop started to dry retch, and we had to evacuate the 'shop until it had dissipated.
I spoke to a fireman about it later and he said that most people who die in house fires die due to inhalation of gas from burning mattresses, furnitue etc, and not actual burns or smoke inhalation. Cheers, Terry.