Rather like the tiger, Shere Khan, of The Jungle Book, man has always had a love-hate relationship with fire. It serves to warm us, cook our food and allows us to manufacture things beyond our wildest imagination, but it can burn and hurt us too when it is not controlled. But is fire, itself, some sort of fire hazard, can you set fire on fire and make it even stronger?
Fire is not, in itself, flammable because by definition, it cannot be. Fire can heat the materials (fuels) around it and cause them to catch fire as well, but the fire itself cannot ignite.
However, there are many interesting properties of fire and flames, and it can help to be more familiar with them in the interests of your safety. Here’s what you need to know.
Also read: What Makes Something Flammable?
Table of Contents
- What Is Fire?
- What Is Flame?
- Is Fire Flammable?
- Chemistry of Fire
- What Is Conflagration?
- How Does Fire Interact With Ecology?
- How Did Humans Come To Control Fire?
What Is Fire?
Fire is the result of the “rapid oxidation” of any material in an exothermic reaction. It’s the heat and light that is produced as part of this reaction.
The heat of fire comes from the oxygen molecule, in the main, this uses a divalent bond to hold the two oxygen atoms together and this bond is particularly weak. When the atoms are separated and join with another substance, they form much stronger bonds, and this results in the release of heat and light.
What Is Flame?
A flame is not the only heat and light that is produced from a fire, it is, however, the only visible part of the fire.
Mainly, a flame will consist of carbon dioxide (CO2), oxygen (O2), nitrogen (N2), and water vapor. In some cases, if the fire is hot enough, it may also contain ionized gasses which are known as “plasma”.
Plasma is the fourth state of matter, beyond the three everybody knows about, (solid, liquid, and gas) and it has some fairly unique electronic properties.
The color of a flame depends on the material being burned and any impurities introduced in the process.
The heat of the flame will also vary based on the impurities and material burned though as we’ve already determined, the double bond in the oxygen molecule provides the majority of the heat, and thus, while flames can have different levels of heat, those that occur naturally tend to fall within a fairly similar range.
Also read: Does Fire Have Mass? What Does It Weigh?
Is Fire Flammable?
Fire cannot, by definition, be flammable.
Flammable refers to the fuel that enables the fire to burn.
As fire is a combination of heat and light, neither of these things can be used as fuel, and thus, they cannot burn, and fire is not flammable.
The fire can spread heat which can increase the rate of spread of the fire. This can create more fire, but the fire itself is not bunring.
Chemistry of Fire
Fire requires three things in order to get started and a fourth to continue.
To begin it must have heat, fuel, and oxygen.
The fuel must, using the heat, be raised above its “flashpoint” to begin the oxidation reaction.
Once the reaction begins, it must either have
a.) an external source of heat or
b.) release enough heat to sustain itself.
If the reaction does not have these things, it will cease and there will be no more fire.
When The Fire Reaction Fails To Self-Sustain
This is a common situation when something flammable is mixed with water.
For example, ethanol is flammable but in beer, it’s only about 5% of the volume, the rest is water.
It’s impossible to burn beer because though there is a fuel present and oxygen can be available, the water ensures that an external heat source cannot propagate the reaction and it also prevents the ethanol that does burn from releasing enough heat to other ethanol molecules to sustain the fire.
So, holding a lighter to the top of the beer might burn off a couple of ethanol molecules, but it will still be perfectly drinkable afterward.
This is also why we use water to extinguish many types of fire.
The Fire Tetrahedron
These four things need to start a fire: heat, fuel, oxygen, and “chain reaction” are often known as the “fire tetrahedron”.
In fact, there is another thing that must be present for fire to take place but which we take for granted in everyday life.
For example, in order for the fuel to burn in oxygen from the air – the oxygen must be acting under the influence of gravity, or it would just drift away.
Here, on planet Earth, there’s no way to switch off gravity (at least, not based on our current understanding of physics) and thus, it’s always present.
So, there’s no need to add “gravity” to make a “fire pentagram”.
Also, this is the reason that fires in space are not a huge concern, without gravity, any oxygen present simply floats off into space and the fire goes out.
To extinguish a fire, you need to remove one of the four (five) things that are essential for it to take place.
You can remove the heat (e.g. soak it in water), remove the fuel (e.g. switch off that gas), remove the oxygen (e.g. throw a fire blanket over the top) or prevent the chain reaction from continuing (e.g. douse it in Halon).
As we’ve already seen, you can’t remove gravity on Earth but if it were an option, that would work too.
What Is Conflagration?
Conflagration is the moment when fire becomes very dangerous, indeed, it threatens property or the lives of people or animals.
It may also be referred to as a “blaze”.
Conflagration can be started by fair means (such as the sun lensing through a discarded bottle top) or foul (such as when a lunatic pours gasoline on something and throws a match on top).
How Does Fire Interact With Ecology?
It is often assumed that fire is bad for nature but it’s more complicated than that and, in fact, many ecosystems depend on burning to thrive.
The wildfires in California, for example, may have serious implications for residents and possibly, the wider environment too, but they are fantastic news for the forest.
They clear out old dying wood and create fertilizer, in the form of ash, for new healthy plants to take their place.
Many forms of agriculture also depend on burning the fields after the harvest to enable the soil to be rejuvenated for the following growing season.
Does Fire Have A Fossil Record?
This is an awesome question, and the answer is “yes”.
Of course, individual tiny fires don’t leave fossils but when “wildfire” occurs as it did about 420 million years ago when plant life increased the oxygen levels on earth to greater than 13% in the air, huge areas burned.
This left a bunch of “charcoalified” plant fossils behind, and we’ve seen charcoal in the fossil record ever since, there was a recent spike in a wildfire about 7 million years ago when the grass became a substantive part of many of Earth’s ecosystems.
This too increased the oxygen content in the air and made fire much more likely.
How Did Humans Come To Control Fire?
With no written records, we have no idea how human beings learned to control fire, but we do know that it happened very early in our history.
In fact, there is evidence that humans were using fire to cook nearly 1 million years ago!
Scientists doubt, however, that we got proper control over the fire until about 400,000 years ago which is long before we learned to read and write.
One thing that might help quell concerns about environmental pollution is that the fossil record also shows that as man learned to harvest fire, humanity started to evolve biological resistance to pollution!
What Was The Main Use For Early Humans?
Early humans used fire to cook with but also to keep predators at bay during the night and, of course, in certain parts of the world, it was used to keep warm too.
The use of fire is found throughout nearly all human cultures by about 50-100,000 years ago.
There is also, sadly, evidence that man has long used fire to torture and kill with too and in more recent times the “iron boot” (the wearer is given iron boots which are filled with water or oil and then they are heated over a fire to deliver real agony to the wearer) was a popular way to treat someone’s enemies.
What Is The Main Use By Humans Today?
We still use fire in warfare today but the main use of fire in modern society is simply as a fuel, in many different processes and fashions.
In particular, fossil fuels are burned to release energy and while our dependence on these fuels is shrinking, we still use enough, for now, to continue to contribute to the climate crisis.