Forest Fires - An Overview
| FIRE PREVENTION | FIRE PREDICTION & ANALYSIS | FIRE SUPPRESSION ||
How Forest Fires Start
Forest fires always start by one of two ways - naturally caused or human
caused. Natural fires are generally started by lightning, with a very small
percentage started by spontaneous combustion of dry fuel such as sawdust and
leaves. On the other hand, human-caused fires can be due to any number of
reasons. Some classifications include smoking, recreation,
equipment, and miscellaneous. Human-caused fires constitute the greater
percentage of forest fires in our forests, but natural fires constitute the
great majority of the total area burned. This is because human-caused fires
are usually detected early in their duration, and therefore they are usually
contained easily. Natural fires, on the other hand, can burn for hours
before being detected by firefighting authorities.
How Forest Fires Burn
There are three elements that are required for a forest fire to burn: Heat,
Oxygen, and Fuel. This is the so-called "fire triangle". Without all three
of these elements, the fire will go out. Furthermore, the fire will spread
in the direction of the most abundant supply of the three elements, while
its rate of combustion is usually limited by one of the three elements. Once
the fire enters the combustion stage, there are three main types of
classifications for the fire. A smoldering fire is one that emits smoke but
no flame and is rarely self-sustained. A fire is classified as flaming
combustion when flames are present. Charcoal can be formed in the absence of
oxygen with this type of fire. Glowing combustion is a later stage of the
fire and is characterized by a slower rate of combustion and blue flame.
Forest fires can also be classified by what part of the forest they burn in:
It is not uncommon for two or three types of fires to occur simultaneously.
- Ground fires occur on the ground, often below the leaves.
- Surface Fires occur on the surface of the forest up to 1.3 meters high.
- Crown fires are the most dangerous fires and can spread the fastest.
They occur in the tops of the trees. They can be: (a) dependent upon
surface fires to burn the crowns, (b) active in which they occur at the
same rate as surface fires, or (c) the most destructive, independent, where
fire can "jump" from crown to crown.
Fighting Forest Fires
Perhaps the most overlooked aspect of fighting forest fires is
communication. It is vital that the proper authorities be notified as soon
as possible when a fire occurs. Obviously, a fire that is detected in its
early stages will be much easier to extinguish than a fire that has been
burning for some time but has only just been disovered because of lack of
communication. Once a fire has been detected, the fire fighters must be
transported to the fire and then apply suppression methods.
Transport and Suppression
One difficulty in fighting forest fires is transporting the firefighters to
the fire. Obviously, wildland fires often occur in rather rugged terrain, so
fire fighters often have to be transported in by air and then walk with
their equipment overland. Once crews are to the fire, the suppression method
they use depends on the type of fire.
- Ground fires are often best controlled by digging trenches in the soil
- Portable water backpacks and firebreaks are often the most effective
methods at controlling surface fires.
- Lastly, if a fire escalates to a crown fire, aerial support is used to
suppress the fire with fire retardant chemicals and/or water. However,
these fires are often very dangerous and human life always comes first
in fire fighting; sometimes these fires are just allowed to burn until
they run out of dry fuel.
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