Fuel Loads

Let’s talk about fuels and fuel loads today.

A wildfire’s potential to spread is based on the type and amount of fuel it has access to. Fuel can be pretty much anything: trees, underbrush, grassy fields, homes, etc. Fuel loads are the amount of flammable material surrounding the fire and are measured by the amount of fuel per unit area, usually in tons per acre.

Light fuel loads (above) will cause a fire to burn and spread slowly, with low intensity.

Heavy fuel loads (above) will make the fire burn more intensely, causing it to spread faster. The faster the fire heats up the materials around it, the quicker they will ignite.

Dryness of fuels can also affect a fire’s behavior: when fuel is very dry it is consumed much quicker.

There are a few fuel characteristics that decide how a fire is affected:

·         Size and shape

·         Arrangement

·         Moisture content

Flashy fuels, such as dry grass, pine needles, dry leaves, etc. burn faster than large logs or stumps. Different fuels take longer to ignite than others – ignition time is the ratio of the fuel’s total surface area to its volume. The smaller, flashy fuels, have surface areas that aren’t much larger than their volume – resulting in a quicker ignition. Whereas a tree’s surface area is much smaller than its volume, which means it will need more time to ignite.

The heat and smoke from a fire approaching the fuel causes the fuel’s moisture to evaporate - drying out the material faster. Oxygen can reach more spaced out fuels easier, and as a result they will burn faster than the tightly packed fuels. Tightly packed fuels absorb some of the fire’s heat because they retain more moisture than the loosely packed fuels.

If you would like to learn more about how wildfires are affected by fuels, topography and weather you can click here to read more.