Fireline Construction

In fire suppression, constructing a fireline cuts off the supply of fuels.  The objective is to remove or to reduce the flammable materials that allow the fire to build up in intensity or continue to spread.  The success of initial attack is often very dependent on how skillfully the line is located and constructed so that the fire cannot cross it. 

The factors to consider when deciding how and where to construct a fireline are:  type and amount of available fuel, topography, and weather conditions. 

There are several ways a fire can cross a constructed fireline.  Radiant and convective heat may ignite fuels outside the line if it is too narrow and does not have adequate overhead clearance.  Convection may also cause spot fires across the line.  If the line is not deep enough, a fire may cross the line by burning through organic materials and duff.   

Sparks and embers may blow across the fireline in high wind.  Embers and sparks may also roll across fireline when the fire is burning on a slope.  A fireline that is constructed to overcome this hazard requires a cup- or V-trench to catch rolling embers and sparks.  This type of line is sometimes referred to as an underslung fireline. 

Burning snags next to the line become a problem if they fall across the fireline.  In addition, winds can cause sparks from these snags to be carried a distance across firelines. 

Unburned fuels next to the line become drier and more available as a result of radiated and convective heat. 

Fireproofing 

Large amounts of fuel must be available before aerial spotting and crowning can occur on a fire.  Fire danger must also be "high" or "extreme" before spotting or crowning occurs.  Wind also plays an important part in spotting and crowning. 

Three methods used to prevent spotting and crowning are: 

1. Burning out areas of unburned fuel.  Time of day, temperature, relative humidity, fuel moisture, slope, wind and weather forecasts should be considered prior to burnout.  This is a method that is basic to good line building procedure. 

2. Clearing brush and limbing of trees close to the fireline.  This prevents fire from climbing to the tree canopy or jumping the line. 

3. Fire proofing available fuels.  This entails a combination of previously mentioned procedures such as limbing, scattering heavy fuel concentrations, and using retardants and water on available fuels.  

Blackline 

Another facet of fireline construction is the blackline concept.  This is true both for suppressing wildfires and in controlling prescribed fires. A fireline must encircle the entire fire before it is contained.  Because firelines are built in a rather straight line to reduce the chances of the fire crossing the line and to use natural barriers and fuel breaks, there are often areas of unburned fuel between the fire's edge and the constructed line.  These fuels should be burned out as soon as possible.  By doing this, we have a black (burned out) line next to the fireline, therefore, a safe line.  The fire is less likely to jump the wider line and it is a safe area that firefighters can retreat into if the fire becomes more intense and life threatening.  Also, little or no mop-up is needed. 

Standards to make the fireline area as safe and secure as possible are: 

• Areas of heavy fuel should be avoided if possible.

• Logs and chunks should be turned parallel with the fall line of the slope to prevent their rolling downhill.  (As the fuel burns out, this becomes a problem on steeper slopes.)

• All snags, burning or unburned, which are close to the constructed line should be plowed around the distance out that the snag is tall or felled as soon as possible.  Snags pose a safety problem to personnel and equipment as well as sparks across the fireline.

• Keep lines as straight as possible with no sharp turns.

• Utilize barriers where they exist.

• Anchor line to a safe place that is fireproof.