system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a firefighter lighting a backfire help stop a fire and how does that fire not go out of control?
gpt
When a home is on fire there are usually large sources of water nearby, like a fire hydrant, or the ability to call for tanker trucks for additional water.

Wildfires are not that way, remote often far from roads or too difficult to being large tanker trucks. So wild fires are rarely fought with water except in certain situations. With a wild fire you stop the fire by removing the fuel. Use workers with hand tools, bull dozers and other heavy equipment to clear the grass brush and trees.

Once you've created a fire break, and cleared as much brush as possible, a second back fire that's hopefully burning into the wind and not with the wind is set. By burning into the wind it's a smaller slower fire that burns all the fuel that the uncontrollable wildfire would want. So when the wild fire gets there all the fuel is already burnt and the main fire dies out.