In this second of a four-part series, you will learn the importance of the fuel component in prescribed fire.
A common science experiment in grade school is to light a candle, place a glass jar over the candle, and watch the flame go out as the oxygen is consumed. This demonstrates the fire triangle of heat, oxygen, and fuel (Figure 1). A prescribed fire is a working example of the principles of the fire triangle.
In conducting a prescribed fire, you are either working to move a fire across the land or working to extinguish a fire. In either case, good fire lines are critical for containing the fire within a specific area (Figure 2). Fire lines remove the fuel side of the triangle. Without the fuel, there is no heat and the fire goes out.
A number of factors play a role in the ignition of a prescribed fire and how well it may carry. This makes the fuels component of a prescribed fire the most difficult issue to deal with. It is critical to know your fuels, the number of days since a rain event, the duration and amount of rain of the event, and the relative humidity and wind. Anyone conducting a prescribed fire should be aware of these factors prior to conducting a prescribed burn.
The way a fire burns depends on a number of characteristics of the fuel. An often forgotten component is the predominant species of the fuel. Not all grasses burn the same; neither do all hardwood leaves or even pine needles. For example, leaves in an upland hardwood stand tend to curl on the ground and retain moisture. This can make it difficult to sustain a fire. Most fires of this fuel type are low intensity and slow to spread. In a mature pine plantation, the pine needle layer is matted and mostly flat, with the exception of the top layer. Due to rosin in pine needles, the needles will ignite with little heat and carry fires of greater intensity.
Along with species of the fuel, fuel type, fuel volume, fuel arrangement, fuel shape, fuel size, and fuel moisture content make up the major components of fuel and how it burns. For detailed explanations of each of these components and how they relate to fire behavior, visit the link below to access the second article of this prescribed fire series.
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