UNIT I--THE FIRE ENVIRONMENT
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