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Unit 10: Fire Behavior Affects Fireline Tactics

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

Standards For Control Line Construction

Once we have decided where control lines should be established, we need to determine just how they will be built to effectively stop the fire. We call these determinations the standards for control line construction. The graphic below illustrates chances for heat transfer across a control line. If we can anticipate how the heat transfer processes will threaten a control line, we can then establish standards to make the line more secure.

Heat transfer across a control line

Heat Transfer Related to Control Line Construction

Problems related to heat transfer which affect the standards for control line construction are:

  1. Radiation across control lines.
  2. Spotting across lines.
  3. Crowning originating from surface fire.
  4. Rolling firebrands.
  5. Fire creeping through subsurface organic fuels.

Blackline
The blackline concept in fireline construction

In this graphic we have illustrated the "black line concept." Many firefighters contend that the only safe fireline is a black line. The concept requires, for safety and security, that we burn out fuels remaining between the constructed line and the main fire to insure that the fireline is not threatened by active fire. This should be normal procedure in line construction.

Burning Out

For safety and security , we burn out fuels remaining between the constructed line and the main fire to insure that the fireline is not threatened. This should be normal procedure in line construction.

If you cannot get fuels to burn out, the usual practice is to cold trail inside the fireline, or to move the fireline to the fire perimeter. Remember, any fire burning inside a fireline remains a potential threat to that line.

Handline Construction

This graphic illustrates handline constructed in brush. Here we are concerned about how wide the fireline needs to be. If fuel concentrations are reduced near the line, the actual fireline to mineral soil can be relatively narrow, 1- to 3-feet wide. Reducing the amount of fuels near the line, thus reducing fire intensity, is a reasonable practice and is generally preferred to wide firelines cut to mineral soil. Line construction is generally easier, and less environmental damage is done to the site.

Handline

Rule of thumb : In low fuel types the vegetation should be cleared to 1 ½ times the height of the fuels, and a trench cut to mineral soil, usually much less in width.

Handline

Now let's consider some more fireline situations. In this figure we see a handline constructed through timber. The actual fireline to mineral soil can be relatively narrow if the adjacent areas are brushed out, trees limbed up, and surface fuels reduced. On the left, or inside the fireline, we scatter and reduce fuels for a reasonable distance to control fire intensity as it burns near the fireline or is burned out from the line. This can be done by removing unburned fuels from the inside and disposing of them outside the fireline. Note that it's advisable to leave enough light fuels inside the fireline to get a clean burn. The object is to keep burnout fire intensity low and to reduce the threat to a narrow fireline.

Handline

In this graphic we are dealing with a different threat to a fireline, that of rolling firebrands from slopes above, but inside the line. The steeper the slope, the greater the problem. Burning cones and chunks of logs easily respond to gravity and can scatter fire for considerable distance downslope. The yucca plant in the Southwest, which is round and burns off at the roots, has been known to scatter fire up to 1/4-mile downslope from the fire. So you see it's possible for the rear or flank of a fire on a slope to present greater control problems than the head.

What can we do about the problem of rolling firebrands? Well, firefighters have found that cup trenches are generally effective. The steeper the slope, the deeper the cup trench, It's still advisable to patrol these areas frequently, as some firebrands may evade capture.

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_4.html. This work is licensed under a Creative Commons License Creative Commons License