Spreading fires
The rules are intentionally vague about how to spread fires, to let you set up your own house rules. The intent is simple: only the ‘leading edge’ (the direction the wind is blowing) spreads, usually one acre for each leading edge acre.
Below are some examples of how I usually spread fires. The ‘x’ acres are those where the fire spreads, the ‘?’ acres are acceptable if you want to do it a little differently.