There are four elements that make up our world; Air, Earth, Water, and Fire. Fire is an element of warmth, it is what we turn to when we get cold, when we need to cook, it is an element and concept that powers energy and engines.
It enabled mankind to rise up out of the Stone Age, and into homes, towns, and cities.
Fire is the element responsible for light and heat, even in the coldest places in the world, however it is powerful and destructive too. Fire is a commonplace today, and is something that we take for granted.
But, don’t you think it is strange how we never even ask the most basic questions about fire? Like, how hot is fire? Does anyone even know?
Well, to answer that for you, the temperature of fire can be anything from 400 °F all the way up to 9000 °F (Which is about 200 °C to 4980 °C).
The temperature of the fire can be influenced based on the oxygen content available to the fire, and the fuel source that allows it to turn. Then there are even cold fires, which will not burn you… bet you didn’t know about those, did you?
Fire is weird, wonderful, scary, and fascinating. Today we will look more into the science of fire and how it affects a wide range of temperatures, many of which you may encounter regularly and not even know about.
Fire- What actually is it?
Fire is what happens when there is an exothermic chemical reaction (this means that it exudes heat) in which one material is quickly oxidized, meaning that it loses electrons, in order to release heat, light, sometimes sounds, and chemical byproducts too.
However, remember that just because it looks like fire doesn’t mean that it is fire.
What we mean by this is… the sun. There is no oxygen on the sun, or on any star for that matter. While the process going on there might look like a ball of flames, it actually isn’t.
When it comes to the sun, what you are actually seeing is nuclear fusion of hydrogen into helium, and so on. It is not fire as we know it.
The fire we know requires oxygen, or it needs to have an oxidizing agent present, this doesn’t have to be oxygen itself, or even an oxygen compound, but there are also no alternative oxidizing agents on the sun.
Fire starts when any flammable, or combustible material is given a decent supply of oxygen (or an oxidizing agent) and enough heat, as well as potentially a spark or naked flame to allow it to burn.
Fire is also a chain reaction, so the act of a fire starting requires that the burning reaction be hot enough that it can sustain itself.
This means that fire is a combination of heat, fuel, oxygen, and a chain reaction that will allow it to continue like this without any additional effort. This is known as something called a “Fire Tetrahedron” which is a more complete version of the fire triangle.
If any of these elements are missing, you won’t get a fire. Although, in some rarer cases, you might also need a fifth element known as a ‘fire catalyst;. This is a substance that is not consumed, or used up in the process, but is essential for a fire to begin in the first place.
Now, there is one more important element that is essential for a vast majority of fires to start, but it tends to go completely unnoticed because it's as natural as the air we breathe and the ground we walk on. Gravity.
If you attempted to start a fire somewhere with no gravity, i.e. in the middle of space, then the oxygen around the fire would very quickly be exhausted, and it would not be replaced, as oxygen does not move under its own will, it moves under gravity.
This is a process known as ‘thermal convection’. Thus, the fire would quickly dissipate because it would have no oxygen, and it would become engrossed in its own byproducts and non-flammable gasses from the surrounding air.
This is why if you get into a spacecraft in the atmosphere it is a bit risky (thanks oxygen), but once in space the risks of a fire are incredibly miniscule.
Why does fire get hot?
This may seem like a pretty impossible question to answer, however, the reason that fire is hot is that there is just a lot of energy trapped inside the molecule of oxygen, or whatever the oxidizing agent is, and this is released during the fire reaction.
Now, time to get a bit science heavy. The double bond that binds two molecules of oxygen together is broken when it is on fire, and the oxygen then forms bonds with other compounds instead.
These bonds are much stronger than the ones that they replaced, and therefore they cause a release of energy.
Strangely, while the bond energies of the fuel in this reaction are not entirely irrelevant, the part they place is much smaller when it comes to the creation of heat in a fire, than the oxygen compound does.
When energy from these bonds is released, it is released as heat and light, and that is exactly what fire is.
Also, it is very important that you remember that a fire is much more than a flame.
The flame is simply the part of the fire that you can see, there may well be some other invisible elements to the fire, or they may simply be beyond the seeing power of our eyes. This is why you can get burned by standing too close to a fire, even if you do not touch it!
What is the temperature of fire?
So, that is what fire is, but now we want to know, how hot is it? Well, this is much harder to answer, unfortunately. This is not something that we can give to you as a short answer, so buckle up.
Really it depends on the fuel, different fuels will burn at different temperatures. So, we know that a wood fire can reach a temperature of around 2000 °F or 1093 °C, but that is no hard and fast rule, it can, but it doesn’t mean that it will.
Some types of wood will not reach 2000 °F when they burn because they just do not have the suitable chemical makeup for it, but ten others will have the chemical makeup to get even hotter.
A good example of this is burning a green wood Vs burning dry kindling. Green woods will burn at a much lower temperature than dry wood does.
Then there is also the factor or the oxygen, the flames' temperature will also vary depending on how much oxygen is available to the flame.
Now, think about propane, this is a very popular fuel that is used in so many things, from household BBQs to major industry operations. It has an extremely hot flame when it is burning in the air, it will reach around 3600 °F or 1982 °C.
Which is just a bit more than an average wood fire, don’t you think?
You might gasp at that, however it is absolutely pittance compared to how hot propane can burn if you give it extra oxygen. If you burn the propane in pure oxygen, the temperature will soar to around 5100 °F!
When you think about the vast difference there, it is a bit crazy, and all you needed to do was change the amount of oxygen available to your fire! It is still the exact same chemical reaction as you get when burning propane in the air.
This is not even the hottest though, there are still plenty of other fuels that can burn at much higher temperatures, especially in pure oxygen.
Where in the fire is the hottest part?
Yeah, yeah, yeah, we know. Heat rises… and you aren’t wrong there. But, remember the chemical reaction takes place in the most copious amounts at the base of the fire, and then it diffuses as it rises.
Think about it, this is why you can move your finger through the top of a candle flame (very fast) without burning yourself.
However, if you attempted to do the same at the wick (without getting molten wax all over you- which would also burn by the way), you would get a rather severe burn, even if you went even faster than before.
Do not put your hands in a fire though… Do not put your hands near fire, or in fire. It will burn you.
Flame color and heat
As long as you are in fairly normal conditions on planet Earth, you should be able to get a good guess at the approximate heat of a flame simply by its color.
You will typically find, as we have already spoken about, that the hottest color of any flame is at the base, and the coolest color at the top.
So, a red flame is often seen on the outermost edge of a majority of flames, and blue is often found at the base of the flame.
A red flame will typically be around 977 °F to 1832 °F/ 525 °C to 1000 °C.
An orange flame will typically be around 2012 °F to 2192 °F/ 1100 °C to 1200 °C.
A white flame is even hotter, and will typically be around 2372 °F to 2732 °F/ 1300 °C to 1500 °C.
Blue flames are the hottest of them all, and these can burn as hot as 5432 °F/ 3000 °C.
Thinking about this, you may start wondering how hot is the flame coming from your lighter when you light up a cigarette?
Well, this flame can reach up to around 3590.6 °F! This is why you will also often see a tint of blue in the flame of a butane lighter, and it’s also why it is super easy to burn yourself with a cigarette lighter too.
Never put your fingers, hands, or any other part of your body into a flame, if you want to be cool then do something that doesn’t involve the risks of burns or scarring.
Some real world examples of this are; a candle will typically burn white/ orange at its hottest point, a wood fire in a grate at home will burn red. A bonfire will drift between red and white, depending on the nature of the wood and the wind (wind means oxygen availability).
Bunsen burner flames fully open will typically be white or blue, a propane torch will have a blue flame at the hottest part.
Even a red flame is more than hot enough to inflict severe burns on any person. Knowing that a fire is often hotter than this is more useful for the sake of curiosity than as an additional safety measure. Nonetheless, it is still good to know.
What type of fire is the coldest?
So, what part of a fire is the coldest? Well, in theory, the coldest possible fire color would be black. This part is the fuel that is burning, but such a small amount of energy is being produced that there is no light being emitted and miniscule heat too.
Practically, we have no idea how a flame like this would be created, though. A majority of exothermic reactions tend to be rather violently exothermic, it is one of the many reasons why you can often get a bit of an explosion when a fire ignites.
There is no logical way we can think of to create a black flame. However, this is, without any doubt, theoretically a possibility, and therefore it is the coolest type of flame there is.
How is a fire put out?
Fires are put out by simply removing, or separating one of the plethora of essential components from the fire, be this heat, fuel, the oxidizer, or the chemical chain reaction.
You can remove the fuel, the oxygen, the flame, the gravity- well, maybe not the gravity, however we aren’t physicists, we will leave this debate to them- the chain reaction, or if one is involved, the catalyst.
There is a wide variety of ways that you can extinguish a fire, and what works with one fire won’t always work with another. You should only ever use the correct kind of material to tackle a fire, and if you do not know what material is suitable, do not tackle it.
Only ever tackle a fire if you believe and are confident that you will succeed in your efforts to do so.
If you are not confident in this, just call the fire department and move to a safe place, it is always better to be safe than sorry when it comes to fire, fire is very hot and very destructive. The fire department won’t be mad if you called.
Even if it is a little fire, it is their job to tackle a fire, and they are very good at it.
What is hotter; Fire or Lava?
It is possible that fire can be hotter than Lava, but it is not always hotter than lava. Lava is molten rock, which is expelled from an active volcano. This substance can get crazy hot, able to reach a maximum temperature of around 2200 °F, which is very, very hot.
Lava is therefore hotter than the wood fire in your living room, or hotter than the bonfire in your backyard. However, any fire hotter than 2200 degrees, can sometimes reach up to 5000 degrees, and that is nearly twice as hot as lava. It really depends on the fire.
So, while it is possible for fire to be hotter than lava, a majority of fires won’t be
Is it possible for it to be too cold for Fire?
While general knowledge may make you think that it is never too cold for a fire, it can be. When temperatures reach absolute zero, which is -459.67 °F, there is no energy present at all.
At this temperature, molecules do not even vibrate within their own space, so if you could make something this cold, you could prevent a fire.
If it were possible to create something this cold, you could easily prevent fires, however it would also be at the cost of preventing anything else, even your life. Nothing, absolutely nothing can live at temperatures of absolute zero either.
Practically though, it is impossible to create this temperature, and although we can get close to absolute zero, we can’t achieve it. And at any temperature above this, a fire is possible. It might be challenging, but it is possible.
So, in reality, no, it is never too close for a fire.
Can it ever be ‘cold’? Well, yes, however it depends on how you define the word ‘cold’. You don't find cold fire on earth much, because the earth is not actually that cold.
As we already know, as long as it is above absolute zero, you can start a fire, and even if your flame is only 50° hotter than the temperature that you started the fire at, then it will burn cold.
The easiest way that you could make a cold fire would be to head out into space (if you can actually do that) where you could easily create cold conditions. The hardest part of this is getting into outer space. However, you can still create cold fire without going into space.
The Last Flicker
Fire can be cold, hot, or even up to 9000 °F, It can’t burn at millions of degrees as that is a process which doesn’t involve any oxidation, yes, we are referring to the sun, and no that is not technically fire.
But the fire we know is still very hot and can burn rapidly in the right conditions, all it takes if a few ingredients, and it is flaming high.
You can get an idea on how hot a fire is just by looking at the color of the flame, be it black, red, orange, white, or blue. but as we have already said, nearly every fire will cause a burn, so just don’t touch it.