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Unit 1: The Environment

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Fire behavior, which is the subject of this course, can be defined as the manner in which fuels ignite, flames
develop, and fire spreads and exhibits other phenomena. Our analysis o£ what fire does recognizes the complexity of
the variable factors that influence it. Whether you are concerned with the suppression of wildfires, or you wish to
use fire as a management tool, a healthy respect for, and a basic understanding of, the natural forces or processes
related to fire are required. The safety and effectiveness of fire management operations usually are dependent on
sound judgments made on what the fire can and will do. Such judgments often are required of firefighters on the
fireline, as well as the fire overhead organization. Decisions made based on those judgments frequently reflect
success or failure in meeting management objectives, reasonable or excessive costs of suppression, low or high
accident rates, and reasonable or high losses to resources.
 
This unit is about the fire environment. You will be introduced to the most important variables that affect fire
behavior. You will see how the interactions of fire with its environment must influence our assessments of fire
behavior. This unit will also introduce you to mathematical fire models available to help us predict fire behavior.
 
Before starting the unit, be sure you have carefully read the instructions to students on page 1 of your workbook. On
page 2, you will find the unit objectives on which you will be tested at the end of this unit. Please study these
objectives; then, when you have finished, return to this text.
 
On page 3, figure 1 illustrates the three major components making up the fire environment. The current state of each
of the environmental components--fuels, topography, and weather or airmass--and their interactions with each other
and with fire itself, determine the characteristics and behavior of a fire at any given moment. Changes in fire
behavior in space and time occur in relation to changes in the environmental components.
 
Note the seven factors listed under fuels. At the head of the list is moisture content. One unit of this course will be
devoted just to fuel moisture content. Another unit will be devoted to fuel models, which will help you to analyze
the rest of the fuels factors and make some important estimations.
 
Under weather, windspeed and direction are our most critical factors. One unit has been devoted to winds and their
effects on fire behavior. A large part of this course concentrates on fire weather, as this is the most variable and most
difficult of the environmental components to predict.
 
Topography is the most constant of the three major components making up the fire environment. The most
important factor under topography is steepness of slope, since changes in slope have very direct and profound
effects on fire behavior. One unit of the course will discuss topography and how to measure slope.
 
Firefighters soon realize that fires seldom behave exactly the same way from time to time or place to place. This
complexity of variable factors indeed offers a challenge to any fireman and to his ability to predict what a fire will
do in the next 24 hours or after it has spread into new terrain.
 
Now let's briefly note how each o£ the three major components can change and influence fire behavior. Please turn
to page 4. Under Item A, note these changes that take place in time and in space: First, topography. With time, no
change. Terrain is generally constant. Regarding space, changes can be considerable, especially in mountainous
terrain.
 
Next, fuels: With time, fuel moisture changes on a short-time basis. Other changes occur due to man or nature. With
space, very significant changes occur due to region and site characteristics.
 
Last, weather: With time, temperature, relative humidity, and wind change almost continuously. In space, significant
changes occur with terrain and general weather patterns.
 
Let's go back to topography and point out just how it does affect the job of predicting fire behavior. We will see in
this course how topography directly modifies general weather patterns to produce local weather variations. Because
of these variations in weather, topography indirectly causes variations in fuel loadings and in local fuel moisture
conditions. As a result topography strongly affects the direction and rate of spread of fire.
Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, November 04). Unit 1: The Environment. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/Forest__Range__and_Wildlife_Sciences/Wildland_Fire_Management_and_Planning/Unit_1__The_Environment.html. This work is licensed under a Creative Commons License Creative Commons License