Fire burns at a temperature range of 400 to 9,000 degrees Fahrenheit depending on how much oxygen the fire contains and its source. You know how incredibly hot a fire can get, but what about cold? Can a fire become cold with time?

A fire doesn’t become cold as it burns, as the fire needs activation energy to break open oxygen-containing molecules. However, cold fires do exist. Cool flames burn below 752 degrees and require a specific chemical reaction to trigger. They don’t occur in the wild except during engine knocking.

If you still have a few lingering questions about fires burning cold, you won’t by the time you’re done reading. We’ll talk more about how long a fire can burn hot, what a cold fire is, and what one looks like, so make sure you don’t miss it! 

Does a Fire Become Cold When It Burns for a Prolonged Period?

What keeps a fire burning? If you look at the fire triangle, a fire needs heat, oxygen, and fuel. 

If a fire has those three things in abundance, it will continue to burn. Since time isn’t part of the fire triangle, it doesn’t configure into what keeps a fire going.

As we mentioned in the intro, a fire needs to continually break apart oxygen molecules to use the oxygen within and remain burning. This requires activation energy.

You may think this can make the fire burn out, but not exactly! Activation energy requires to the minimum amount of energy for a reaction to occur, so a fire uses only that much energy. 

Outdoors, a fire should have plenty of oxygen to sustain it. Winds and cold temperatures can reduce the heat from a fire but not altogether stop it. That’s why you see fires occur in freezing temperatures. 

The biggest risk would be a reduction in fuel source, but that depends on the original fuel source. Sometimes, a fire has plentiful fuel. 

Usually, a fire department steps in to stop a fire before it can burn unfettered for hours, but some fires have stood the test of time. 

They’re often cold seam fires. One occurred in Centralia, Pennsylvania, deep underground. The fire started in 1962 and persists to this day. Residents had to mostly clear out due to safety concerns, as the fire was never extinguished. 

Another fire is in Australia. Known as Burning Mountain, that fire might have started 6,000 years ago, making it the longest fire in history. 

Those two examples prove that it doesn’t matter what kinds of temperatures a region experiences–especially in Pennsylvania, which has all four seasons–a fire can burn if it has all the requirements of the fire triangle. It does not become colder as it burns, as the ingredients of the fire allow it to retain heat.

Does That Mean Cold Fire Doesn’t Exist?

Now, just because a burning fire won’t become cold doesn’t mean that cold fire as a concept doesn’t exist. It does indeed and is known as cold fire or cool flames. 

A cool flame never exceeds 752 degrees Fahrenheit or 400 degrees Celsius. 

Cool flames can be naturally-occurring but require a chemical reaction between air and fuel to activate. 

The non-vigorous reaction of a cool flame sets it apart from a traditional hot flame. Methane, waxes, acids, oils, aldehydes, alcohols, and hydrocarbons can all start cool flames. 

Less carbon dioxide, light, and heat come out of a cool flame, which explains why their temperature never gets overly hot. 

Why does a cool flame work the way it does? It all has to do with the fragment size of flame molecules when broken down. 

A hot flame will produce very tiny fragments. Those fragments attach to oxygen and lead to carbon dioxide production.

A cool flame has larger fragments that can extend combustion and don’t as easily produce carbon dioxide, light, and heat. 

Do you have a vehicle that uses an internal combustion engine? If so, has it ever experienced engine knock, which causes it to make noise when you ignite the engine? 

When an internal combustion engine and low-octane fuel mixes, the result is a cool flame. However, you don’t want a cool flame in this case, as it contributes to noisy and clunky combustion.

You can always try using an octane booster, but you might have to see a mechanic for engine knocking! 

What Does Cold Fire Look Like?

Cold fire has another nickname, and that’s invisible fire. That’s not only because the primary time when cool fire emerges is during engine knock but because by daylight, it’s very difficult to see cool flames.

When we say very difficult, we mean nearly impossible. Cool flames don’t produce as much light as a standard flame, so there’s less of it to go around in the first place. 

When you consider how bright daylight is, that only complicates matters.

In a dark environment, you have a better chance of seeing a cool flame in action, but even then, it’s tough to see. 

Despite the name, cool flames aren’t blue. If anything, the hottest flames burn blue and the coolest flames burn red. Thus, a cool flame might look red, but that depends on what goes into its making. 

Can Cold Fire Still Burn You?

You’ll recall that cold fires burn at up to 752 degrees. A cool flame can endure in colder temperatures than that too.

A flame must only reach temperatures of 118 degrees to cause a first-degree burn to human skin. If the flame temperature jumps to 131 degrees, it can cause a second-degree burn. 

In temperatures of 162 degrees, your skin would be destroyed.

So a cool flame burning lower than 752 degrees can cause catastrophic burns, and a cold fire burning at 752 degrees or over could be more injurious still.

A cool flame doesn’t have that name because it feels cool to the touch. It’s because, compared to a regular flame, a cool flame gives off less heat and light.

Don’t be mistaken! Cold fire is still fire and can burn you!  

Bottom Line

Fire can burn infinitely with enough oxygen, fuel, and heat. Even in cold temperatures, the fire can persist, and it doesn’t become cold.

Cool flames, which burn with less light and heat than traditional flames, do exist, but usually only in specific circumstances like in internal combustion engines. 

Despite the name, these flames burn at temperatures of 700+ degrees and can lead to serious injuries and burns if you’re directly exposed!