The Science of Fire

By Jack Scott

It is often argued that fire is one of the (if not THE) greatest and most influential discoveries of Mankind. Without the ability to summon and control the fickle nature of fire, our species, society, and surroundings would be unimaginably alien to what we perceive today. Over time, Man's experiences and relationship with fire have developed to the point where, despite making numerous appearances in many of history's milestones, in our current day to day lives we now rarely interact with this once essential element (in the Ancient Greek sense of the word). One could argue that thousands of years of manipulation and understanding has allowed our society to control and exploit the useful aspects of fire as well as providing safer substitutes to use in our everyday lives.

But, how much more has our knowledge grown since the times when this natural phenomenon would have been explained by fire-spirits and magic? We can all recognise the external characteristics of fire; we know that it produces light, that it burns most materials, and that it is useful for toasting marshmallows. We may also understand that in order to create fire, the components heat, fuel, and oxygen must be brought together in the correct mixture. But apart from that, could you now, categorically and simply explain what fire exactly is? "Well, it's a chemical reaction isn't it...?" was about as far as I got.

With a bit of further investigation, I was able to elaborate on my rather weak initial description. These were my findings. Fire is the visible effect of the process of combustion – a special type of chemical reaction. It occurs between oxygen in the air and some sort of fuel. The fuel must be heated to its ignition temperature for combustion to occur. The reaction will keep going as long as there is enough heat, fuel and oxygen - which is known as the fire triangle.

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Fuels can be solids, liquids or gases. During the chemical reaction that produces fire, fuel is heated to such an extent that (if not already a gas) it releases gases from its surface. When these gases are hot enough, the molecules in the gases break apart and fragments of molecules rejoin with oxygen from the air to make new product molecules – water molecules (H2O) and carbon dioxide molecules (CO2) (and other products if burning is not complete).

In the case of troll bogeys, the sneezes of Southern Wood Trolls contain a mixture of hydrocarbons, which have a melting point usually within a few degrees of human body temperature, which is approximately 37 °C.(2) This low melting point means that troll mucus has a much lower ignition temperature than similar forms of snot. However, it is flammable only when heated to liquid, then the fumes will light, not the liquid itself, so a wick material like leaves, bark, or small twigs is needed to light petroleum jelly bogeys.

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The heat generated by the reaction is what sustains the fire. The heat of the flame will keep remaining fuel at ignition temperature. The flame ignites gases being emitted, and the fire spreads. As long as there is enough fuel and oxygen, the fire keeps burning.

Fuel + oxygen (from the air) = combustion products (mainly CO2 + O2) + heat energy.

The mesmerising flicker of flames often masks the truly astounding science which most of us see but fail to comprehend. Once you are able to understand the intricate reactions taking place at a molecular level, the science of fire becomes a mind-boggling phenomenon - one that we now take for granted. With an increasing amount of detachment between our highly developed species and this ancient metamorphosing element, are we heading towards a time when we forget to acknowledge the unequivocal role that fire played in the history of our planet?


(1) http://www.sciencelearn.org.nz/Contexts/Fire/Science-Ideas-and-Concepts/What-is-fire
(2) www.vaseline.com