Understanding the Fire Triangle
Whether it is for camping, bushcraft practice, a survival situation, or just backyard socializing, lighting a fire can be difficult. As simple as fire starting may appear to be, there are many variables at play. With a better understanding of these variables, the process of starting a fire becomes less mysterious. One model that’s often used to understand the process is called the fire triangle.
This is the first in a two part article on the fire triangle and how we can use it to better understand what is happening when we attempt to light an open fire.
What is the Fire Triangle?
The fire triangle is a model used to represent the three main components that must be present to make and sustain a fire. These elements are heat, oxygen, and fuel. Why a triangle? There’s no real reason other than the fact that there are three elements and that can be represented graphically with a three-sided shape -- the triangle.
Heat: Spark, Ember, and Flame
Let’s say you have some dry wood sitting on the ground and exposed to the air. Why doesn’t it burst into flames spontaneously? The reason is we still need the third side of the fire triangle, heat, to jump-start the process we call fire.
Heat can be introduced into the triangle in a number of ways. It may be the ember from a bow drill, the spark from a ferrocerium rod, light from a magnifying glass, or the flame from a lighter or match.
Oxygen: The Gas Needed for Combustion
The next part of the triangle is oxygen. The air around us is made up of about 21% oxygen -- exactly what we need to create fire. At times we may encourage more air to enter the system by blowing on the fire, fanning it, or creating physical structures that promote air flow.
Technically, there are other gasses that can be used to sustain fire, but in the context of an outdoor fire, we can ignore these for the most part.
Fuel: Tinder, Kindling, and Firewood
The final element in the fire triangle is fuel. For an outdoor fire, this means tinder, kindling, and firewood.
Our initial fuel is known as tinder. Tinder is a fine, often fluffy material capable of taking a small amount of heat and turning it into flame. Some tinder materials contain flammable compounds while others have very small fibers that are easy to heat up. Tinders may be natural or some form of human-made tinder.
After the tinder, we make use of kindling — matchstick to marker sized sticks — and then work our way up to pieces that are larger still: firewood.
The Chain Reaction of Combustion
When heat is applied externally to a fuel such as wood, the cellulose in the wood begins to undergo a type of thermal decomposition called pyrolysis. As the chemical structure of the wood decomposes, certain gasses are released or volatilized.
These gasses react vigorously with the oxygen in the air in a process called combustion. This is another way of saying that we have lit the fuel on fire.
Combustion is an exothermic reaction, which means it gives off heat. Because it does so, it reinforces the continuation of the process. Provided that adequate fuel and oxygen continue to be provided, we have started a chain reaction.
The cycle repeats: preheating of the fuel, gasses being released, and those gasses reacting with oxygen. If everything goes according to plan, the chain reaction continues with larger and larger pieces of fuel putting off more and more heat. Eventually, we have a fire large enough to heat up and ignite fairly large pieces of wood.
With a hot bed of coals established, we can add fuel of almost any size. Why? Because the coals are putting off a tremendous amount of heat and will be capable of starting the process of pyrolysis, which sets the stage for more combustion.
How to Make use of The Fire Triangle
In part 2 of this series, we’ll take a look at how the fire triangle can be used to troubleshoot problems we often encounter when lighting a fire outdoors.
Resources
| Spark Sources | Flame Sources | Other Sources |
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| Natural Tinder | Human-made Tinder | Improvised Tinder |
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