How Hot is Fire? - The temperature of fire - FlameVenge
December 8, 2022

Fire is one of the hottest things in the universe. But how hot can fire be and can something even be hotter than fire? Let’s find out in this article.

So, How Hot is Fire?

There’s no singularity about the highest temperature fire can attain. But often, the fire temperature is between 400°F and 9000°F. 

This temperature variation depends on several factors. Some of them include the nature of the ignition source that fuels the fire, the amount of oxygen present, and which part of the flame you take your readings.

Let’s inspect those factors with the following sub-headings:

  • Nature of Ignition Source.

Different materials burn at different rates and produce different amounts of heat energy.

For instance, wood fire can be as hot or hotter than 2012°F, depending on the wood.

Dry wood, for example, burns more than green wood and gets hotter. Whereas, Pine wood is also known to generate more heat than other kinds of woods like Fir. And that’s for wood.

Propane can get as hot as 5108°F. A candle, which is another common ignition source, can reach a temperature of about 1800°F. And acetylene flame can be as hot as 5612°F.

The only thing hotter than this is the hottest fire ever produced. That flame was produced with a combination of ozone and dicyanoacetylene. In the end, it reached a temperature of 9014°F.

Then again, in 1951, Dr. A.V Grosse from the Temple University Research Institute produced a flame using fluorine as the oxidizer. In the end, the flame reached about 8000°F.

Besides that, some ignition sources produce so low a temperature that we call their resulting fire “cold flames.”

Some cold flames especially, the ones produced with a controlled air-fuel setting, burn as low as 248°F. This value is just a tad above the boiling point of water.

  • Amount of oxygen present.

In basic science, you can’t sustain fire without oxygen. The more oxygen is present, the more the fire burns and the hotter it gets.

Propane, for instance, burns in the air at about 3596°F. Air contains just 21% of oxygen. So, when propane is burnt in 100% oxygen alone, it gets as hot as 5108°F.

  • Parts of the flame measured.

A flame comprises different parts (or zones, as we call it). However, the number of zones you see depends on the flame in question.

But most flames have at least three zones. Namely, they are:

  1. the zone of unburnt vapor, which is the innermost layer–often dark and least hot because it’s where the fire burns the least.
  2. the luminous zone, which is the middle layer–often yellow and averagely hot because of partial combustion.
  3. the non-luminous zone, which is the outer layer–often blue and the hottest because it’s the region of complete combustion.

So, even if you have the hottest fire at your disposal, your readings could differ depending on which part of its flame you measured. And that makes another reason it’s hard to say precisely how hot fire can get.

How to Tell How Hot a Flame is From Its Color

Earlier, we noted that a flame has different color zones with different temperatures. However, some flames can come in colors we didn’t mention before.

An element called Potassium burns with a purple color, and there are more like that out there. Here, we’ll run you through some flame colors and how hot they can be:

  1. Red Fire – 1112°F – 1800°F
  2. Orange-yellow–2012°F
  3. White Flame–2400°F–2700°F
  4. Blue Flame–2600°F–5432°F

 What Makes Fire Hot?

How hot is the fire

Simply put, fire is hot because it expresses the heat energy stored in fuel or the ignition source. When it burns, the heat energy gets released suddenly.

In a more elaborate sense, fire is hot because the thermal energy stored in fuels and oxygen is released as the chemical bonds break and form. But for these bonds to break, they need starting energy, aka the activation energy.

In the science world, activation energy is the lowest energy needed for a reaction to take place. Since burning is essentially a combustion reaction, then it also needs starting energy to overcome the threshold of activation energy.

When it does, the double bonds in oxygen and other chemical bonds in the fuel get broken. Re-alignment and new bond formation occur between oxygen and the molecules of the fuel to form carbon (IV) oxide (or carbon (II) oxide if incomplete) and water.

As a backdrop, the products develop an enormous amount of heat energy greater than the starting energy. In most cases, this energy comes as light and thermal energy, aka heat.

The flame we see is the visible part of the fire and it contains hot gases. These hot gases are in an ionized state of matter called plasma and their reaction gives off light.

The heat is that part we feel. And there are other parts of the fire we can’t see.

Is There Anything Hotter Than Fire?

To answer this, we will need to inspect what fire means. So, bear with us a little for clarity.

Fire is the end-product of a combustion reaction that evolves heat and light. There are other by-products like gases and sound as well. But that definition sums fire up.

However, note one thing: that fire cannot happen in the absence of an oxidizer. In most cases, the oxidizer is oxygen or oxygen-containing substances. Although today, we now know of other non-oxygen oxidizers like fluorine.

Fire happens when:

  1. there is a flammable material that burns
  2. in the presence of an oxidizer, as explained earlier,
  3. with enough starting energy, which in most cases, is temperature,
  4. and hot enough to continue to self-sustain.

This is called the Fire Tetrahedron, as opposed to the common Fire triangle we often see in ads from fire departments.

Sometimes, even gravity can affect how fire burns, says NASA. And that’s why the risk of fire in space is lesser compared to earth.

From the foregoing definition, this means that not every hot thing is fire. The sun, for instance, is very hot, about 9914°F.

This heat energy is generated not from oxidation. Instead, that high temperature arises because of a high-energy nuclear reaction called fusion that happens inside the core of the sun.

Besides the sun, the following can be potentially hotter than even the hottest flame obtained from dicyanoacetylene:

  • A lightning bolt.

The outer surface of the sun reaches about 9914°F. A lightning bolt can be as hot as 50,000°F.

To put that into perspective, a lightning bolt can be 5 times hotter than the surface of the sun.

  • A nuclear bomb

A nuclear bomb can either be an atomic bomb or a fusion bomb like a hydrogen bomb. Both bombs produce an enormous amount of heat after detonation.

On average, an atomic bomb like the one in Hiroshima can reach a temperature of about 540, 000°F. 

Put that into perspective and you realize that a nuclear bomb blast is 300 times hotter than a cremating temperature.

This is even worse with hydrogen bombs that can be five times hotter than the sun’s core.

  • A supernova.

A supernova occurs when a star explodes. No, not stars as in celebrity, but star as in the one we find in the cosmos. For instance, our sun is also a star.

When stars explode, they generate millions of degrees Fahrenheit of heat on average. So, supernovas might be the hottest thing in the entire universe!

Lava Vs Fire: Which One is Hotter?

Lava simply means molten magma that reaches the earth’s surface. On average, this lava reaches about 2200°F.

As said earlier, some flames like the flame from acetylene and propane can easily clock 5000°F. Whereas, some flames like candle flame only reach about 1800°F.

That means lava is quite hotter than most flames, like wood flames and candle flames. However, it is not anywhere close to the temperature of the hottest kinds of fire.

So, yes, fire can indeed be hotter than lava. It only depends on the kind you’re comparing.

Final Recommendations.

So far, we noted that fire is hot because of the sudden release of energy in the bonds of oxygen and that of the fuel.

However, for fire to be classified, it needs a flammable material, an oxidizer, a starting temperature, and a self-sustaining temperature.

On earth, these factors are easy to come by, and that’s why we deal with fire often. In space, this is most unlikely.

As an earthling, here are a few tips that can help you keep fire out or extinguish it:

  1. Keep all flammables or combustibles from an ignition source.
  2. Avoid open flames at all costs.
  3. In case of fire, try separating one of the fire tetrahedrons (we discussed at length this in the article.)


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