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Unit 1: The Changing Fire Environment

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Environment   ::   Heat Transfer   ::   Behavior   ::   Predictions   ::  Summary  ::   Exercises


Fire environment is the surrounding conditions, influences, and modifying forces that determine the behavior of fire. Prediction of fire behavior for safe and effective control and use of fire requires understanding of the interactions of fire with its environment.

The fire environment consists of three major components—topography, fuel, and air mass. From a fire standpoint, topography does not vary significantly with time, but does vary greatly in horizontal space. The fuel component varies in space and also in time; however, fuel characteristics, except for the moisture content of dead fuel, change slowly enough to be considered static for any one fire. The air mass is usually the most variable component, changing rapidly in both space and time.

The thermal energy responsible for most environmental interaction comes from the sun. Because the earth’s surface is not heated uniformly, temperature and air circulation patterns are set up that create large scale, local, and microscale climatic and weather patterns. The interaction of these patterns with other conditions determines the fire environment for a particular area.

Fire can be considered as a local heat source. As such, it influences and modifies the fire environment. Because a fire creates high temperatures, it can dominate sun-caused heat sources.

The extent of the environment of concern to fire behavior depends primarily on the size and characteristics of the fire. It ranges from a few feet to many miles horizontally and thousands of feet vertically. The vertical extent of the environment varies with fire intensity.

Most changes in fire behavior occur as the fire moves over the terrain and as time passes. But abrupt changes can occur when a fire moves vertically from one kind of environment to another, as when a surface fire in timber crowns.

Fire behavior is the interactions of the environmental components with each other and with the fire. The current state of each of these influences and their interactions determine the behavior of a fire at any moment.

Fire behavior is the result of complex interrelationships of aerodynamics, chemistry, thermodynamics, and combustion physics. Nevertheless, it is possible for firefighters to acquire sufficient skill in predicting fire behavior to allow safe and efficient control and use of fire. Development of this skill must come from experience, and from training in the fundamentals of fire behavior and the fire environment.

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, October 20). Unit 1: The Changing Fire Environment. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: This work is licensed under a Creative Commons License Creative Commons License