Why do some things such as a snailshell (or human skin!) burn but not catch fire while others sustain fire?

WATER, and skin does catch fire, if the heat applied is sufficient enough, it will ignite the fat layer beneath, wheras snailshel is made from calcium carbonate plus, and will only char and blacken.


regards LF

Why do some things such as a snailshell (or human skin!) burn but not catch fire while others sustain fire?
The quick answer is the the ratio of water to flammable material in the sample.
Reply:It depends on the availability of fuel for the fire. Snailshells don't have a fuel source which is quickly available for fire. Skin can burn, but it doesn't have much that will burn that quickly (normally carbon -based chemicals of certain types), so it doesn't catch alight. Also, skin has a lot of water in it, so it's harder to burn.
Reply:Good question. I think it depends how combustible the material being scorched or burnt is.
Reply:It depends on whether the combustion is sufficiently exothermic, that is produces more heat than it absorbs. A chemical reaction (like combustion) is self sustaining if it releases enough energy to keep itself going. If not, it dies down unless you keep putting energy into it.

pine