Monday, October 13, 2008
I was looking around on the internet last week for some basic information about the anatomy of a wildfire along with some definitions of some of the terminology that is commonly used by those who write about wildfires. I found this short reference on wildfires produced by the South Carolina Forestry Commission in 1994.
The graphic that I am including in this post is from the SC Forestry Commission, they are also the source for the terminology discussion below.
A wildfire is any outdoor fire (forest, brush, grass, etc) that is not controlled or supervised.
Fires need fuel, heat, and oxygen (aka the fire triangle) to burn. Structural fires are typically attacked with water to reduce heat or foam to take away the fires oxygen supply. Wildland fire fighters remove flammable materials from the path of the fire, attacking the fire's source of fuel.
A variety of tools are used to remove fuel from a strip of ground called a fire or fuel break. One tool that I have frequently seen referred to is called a backfire or drip torch that is used to widen firebreaks by burning out fuel between the firebreak and the oncoming fire.. It consists of fuel canister filled with a mixture of diesel and gasoline with a wick-like burner attached to the canister by a long tube. The fuel ignites as it passes the burning wick dropping on the ground to ignite leaves, pine needles, and other detritus on the ground.
The head (see graphic) is the fastest moving and most dangerous part of the fire. According to the SC Forestry Commission, "since this is the portion of the fire that causes the most damage, firefighters try to stop the head first." On large fast-moving fires, several firefighters may plow side by side to create a firebreak wide enough to stop the head.. After the wildland fire fighters have stopped the forward progress of the head they construct firebreaks around both flanks and the rear to contain the fire. The next step is to mop up the fire by putting out any remaining hot spots and/or other spot fires, and reinforce their firebreaks. A fire is not considered to be controlled until the mop-up phase is completed.
Addendum: I am adding this addendum a few hours later. I have already been on another web page from the State of Maryland where they say that "firefighters usually start building a fireline at the place where the fire originated and work along the sides of the blaze toward the burning front." Note the use of the term fireline, which they say "looks a lot like a trail or small road, is a strip of land cleared of flammable materials like plants and shrubs."
To this novice, a fireline seems to be synonymous with a fire or fuel break. Moreover the folk from Maryland seem to have different take on where the wildland fire fighters start to build a fireline or firebreak to work towards containing the fire. Perhaps the point is that the methods for fighting a particular fire including where firefighters start building a firebreak, if indeed they even do this first, will vary depending on the characteristics of the wildland fire itself. All I am aiming to do here and in later posts is to get a handle on some of the terminology used in fighting wildland fires and related issues and to offer this to you along with links for you to peruse at your leisure.