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Unit 10: Fire Behavior Affects Fireline Tactics

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Management   ::   Control Lines   ::   Standards   ::   Attack Planning   ::  Planning  ::   Exercises

Planning

Planning control of wildfires must consider:

  1. Projected fire perimeter by time periods.
    • Rate of spread at various points
    • Spotting and crowning potential
  2. Degree of fire activity by time of day.
    • Diurnal weather changes
    • Fuel moisture conditions
  3. Hazards and limitations to control forces.
    • Hazardous fuels and terrain
    • Extreme or unusual fire behavior
    • Fireline intensity or flame length
  4. Other environmental and management factors.
    • Fire control policies
    • Resource management objectives

Now we'll move on to more aspects of planning attack and control of wildfires. Above we have outlined four primary considerations essential to the planning process:

  1. Where will the fire perimeter or projected perimeter be, by time periods. This can be estimated by determining probable rates of spread at various points and by anticipating fire spread due to spotting and crowning.
  2. What will be the degree of fire activity by time of day. Fire activity will change due to diurnal weather changes and fuel moisture changes. Certain times of day or night will be better than other times for various fire control activities.
  3. Identify the hazards to, and limitations of, control forces. This can vary by time of the day or night, but we are concerned with hazardous fuels and terrains, extreme or unusual fire behavior, and with fireline intensity or flame length.
  4. Assess and consider other environmental and management factors that may be unique to the fire area. These include agency and local fire control policies and resource management objectives.

We must try to relate each of these four primary considerations to the various planning activities.

Resistance to Control : The relative difficulty of constructing and holding a control line as affected by resistance to line construction and fire behavior.

One step in the planning process that we have not discussed is the evaluation of factors affecting fire control. This is the evaluation of all existing factors pertinent to probable future behavior of an ongoing fire, and of the potential ability of available forces to carry out control operations on a given time schedule. Note that the two primary considerations are probable fire behavior and ability of available forces to accomplish the job.

Fire planners have another term which they use in the planning of control. It is resistance to control. This refers to the relative difficulty of constructing and holding a control line, as affected by physical problems related to line construction and fire behavior. In resistance to control, the two primary considerations are fire behavior and the terrain and/or fuels which can make line construction difficult.

The next step in planning control is to determine line construction rates. These rates will depend on resistance to control and the type of forces available.

An important consideration can be the accomplishment of control actions on a given time schedule. This often requires that priorities of attack are set, and timing is right, to accomplish the various fireline activities.

Fire behavior predictions play an important part in the setting of priorities and in timing of fireline activities. Priorities must be given to fireline location, attack methods, and the distribution of forces. Timing can be important to determining control line standards, burning out and backfiring activities, and certain potentially hazardous situations. For example, certain times of day and the accompanying weather conditions might make one portion of the fire perimeter very hazardous, but several hours later it may be safe for personnel to work.

Proper timing, weather, and fuel moisture conditions are important to have a successful burning out or backfiring operation. We must have:

  1. Adequate fuel loadings
  2. Suitable fuel moistures
  3. Favorable winds and slope
  4. Tolerable flame lengths

Fireline Intensity (BTU/second foot) Flame Lengths (Feet) Fire suppression Interpretations
< 100 < 4 Fires can generally be attacked at the head or flanks by persons using hand tools. Handline should hold the fire.
100 - 500 4 - 8 Fires are too intense for direct attack on the head by persons using hand tools. Handline can not be relied on to hold fire. Equipment such as dozers, pumpers, and retardant aircraft can be effective. Fires are potentially dangerous to personnel and equipment.
500 - 1000 8 - 11 Fires may present serious control problems, i.e., torching, crowning, and spotting. Control efforts at the head will probably be ineffective.
> 1000 > 11 Crowning, spotting, and major fire runs are probable. Control efforts at head of fire are ineffective.

Next, we want to cover in more detail how fire behavior outputs are used in fire control planning. Two of the outputs are fireline intensity and flame length. Flame length is directly related to fireline intensity and is a more observable aspect of fire behavior. We noted earlier that these outputs are very important to determining standards for line construction and the success of various control forces. In the table above we have prepared a chart that can be used as a guide when planning attack methods on a fire. Four ranges of fireline intensity and average flame lengths are given in the left hand columns. Fire suppression interpretations of these ranges are given as guides for fire planning purposes. For example, a flame length of 4 feet produces approximately 100 BTUs per second per foot of fire front. Up to these intensities, fires can generally be attacked at the head or flanks by persons using hand tools.

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, November 11). Unit 10: Fire Behavior Affects Fireline Tactics. 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_10__Fire_Behavior_Affects_Fireline_Tactics_6.html. This work is licensed under a Creative Commons License Creative Commons License