How do backfires work?

Answer 1

In the fire triangle, heat, fuel and air (oxygen) form the basis for combustion. A backfire is sometimes set by firefighters working wild land fires to "burn back" an area of land from in front of a fire. The idea is to strip fuel from this area in front of the way the fire is moving. The hope is that this will deprive the fire of fuel and stop it from an uncontrolled advance. This may allow the fire to be contained and extinguished.

To set up for a backfire, a team (or several teams) of firefighters (with or without equipment support - like a bulldozer) spread out in front of an advancing blaze and cut a fire break. They do this by removing grass, brush, timber and any other fuel from a "line" and then spread out along it. Designated firefighters with ingition sources will move along the "inside" of the break (the side toward which the fire is coming from) and set the backfire. This fire is watched closely so it won't "jump" the break, and is tended so it burns back toward the oncoming blaze.

Timing is essential as wind is usually what is driving the main blaze forward. This means that the back fire won't be in a hurry to go the other way (against the breeze) and move back toward the main blaze. It does work, when executed properly in terrain that gives advantage to the firefighters. Note that as the main fire approaches and "eats the air around it" for oxygen, it may actually start "pulling air back" from where the firefighters stationed along their break are waiting to start the backburn or backfire. If timed correctly in good conditions, the backdraft can be employed to help the backfire move toward the main blaze.

A fire needs three things to burn: fuel, oxygen, and heat. Take away one of those three things and a fire goes out. A backfire is a fire set intentionally in the path of an approaching wildfire in a place where the backfire can easily be put out. The backfire consumes the fuel in its area and deprives the larger wildfire of the fuel; the wildfire cannot travel through the backburned area.

Backburns can also be used in an emergency situation by wildland firefighters to provide themselves with a safe place to go if they are unable to escape an incoming wildfire.