The Fire Environment

Firefighters recognize three components of the fire environment: weather, topography and fuel. These components affect the likelihood of a fire starting, the speed and direction at which a wildfire will travel, the intensity at which a wildfire burns and the ability to control and extinguish a wildfire. Although weather and topography cannot be changed, the fuels (or vegetation) can be modified. Consequently, many of our opportunities to reduce the wildfire threat lie in proper management and manipulation of wildland vegetation.

WEATHER: Dry, hot and windy weather increases the likelihood of a major wildfire. These conditions make ignition easier, help fuels burn more rapidly and increase fire intensity. High wind speeds, in particular, can transform a small, easily controllable, fire into a catastrophic event in a matter of minutes.

TOPOGRAPHY: Of topographic features, steepness of slope most influences fire behavior. As the steepness of a slope increases, the fire spreads more quickly. Other important topographic features include aspect (south and southwest slopes usually have mire fires) and steep, narrow drainage (chimneys), which can significantly increase the rate of fire spread.

FUEL: Fuel is required for any fire to burn. In regard to wildfire, fuels almost always consist of living vegetation (trees, shrubs, grass and wildflowers) and dead plant materials (dead trees, dried grass, fallen branches, pine needles etc.). Houses, when involved with a wildfire, can become a source of fuel. The amount, size, moisture content, arrangements and other fuel characteristics influence the ease of ignition, rate of fire spread, length of flames produced and other fire behavior.

THE HUMAN FACTOR: When people are living in high-hazard fire environments, the human-built environments becomes an important factor in predicting the loss of life and property. Untreated wood shake and shingle roofs, narrow roads, limited access, lack of fire-wise landscaping, inadequate water supplies and poorly planned subdivisions are examples of increased risk to people living with the threat of wildfire.