The concept of fire propagation is to give games the ability to have fire that actually acts like fire! When you light a flammable object with whatever you have be it a match or a flamethrower, it creates a small fire . As we all know , fires get bigger over time as more material catches fire. The fire will eventually get to a size where it can start burning other objects and the fire will spread. Some of these objects after they have burned out will look scorched and have a burnt look to them.