The Three Modes of Measurement

For people just entering the field (or maybe even just curious), there are three principle factors that a fire investigator must consider when attempting to determine the origin and cause of a wildland fire.

Number One: Fuel

Fire requires four elements to continue combustion: Heat, Fuel, Oxygen, and a Chemical Chain Reaction. The main reason that wildland fires get to the point of being uncontrollable is due to the amount of fuel present. In a well forested area, the trees (fuel) are typically found close together, which increases the rate of radiant heat being transmitted. In a short brush area, the brush (fuel) is smaller, less dense, and typically found in further proximity. The less dense material will burn quicker; however, is less likely to spread due to the distance of other nearby fuel sources.

Number Two: Wind

When a fire investigator has to determine the path most likely taken by a fire, wind is a very concerning issue. This comes in two forms, intensity and direction. Of course, the more intense the wind, the more oxygen it is providing the emanating fire, and the more quickly it transfers the radiant heat and subsequent embers. With direction, the probability of fire travelling with the wind is much greater than it transferring to directions not being pushed by the wind. Key concepts with this are microclimatology and wind drafting.

Number Three: Elevation

Elevation again brings up the concept of radiant heat. The universal understanding that every wildland fire investigator has is that fire can burn quicker uphill than it can downhill; take the example of lighting a match. A match is lit and held upwards, the flame burns straight up. A match is lit and held sideways, the flame burns straight up and sideways towards the stick. A match is lit and held downwards, the flame burns straight up towards the stick. The same principles are taken towards a fire burning on a hill, the flames will move quicker upwards and sideways than they will downwards (assuming the fuel is even throughout the hill). This is not to say that flames can't spread downhill, because they can, the radiant heat is just alot weaker, and the fuel must combust and falldown in order to ignite the lower portions.