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Why Does Fire Turn Blue?

Flames and fire are often described with the term “red hot.” However, if youʻve ever built a campfire or cooked on a gas stove, you may have noticed that not all fire is actually red. Have you ever wondered why?

Fire turns blue when it becomes hotter. A fire occurs when a fuel source combines with oxygen and is exposed to enough heat to ignite. Blue flames contain the most oxygen, and gases, such as oxygen, burn at hotter temperatures than other fuels, such as wood. 

This article will discuss several topics related to this question, including what fire actually is, how fires start and keep burning, and why flames are different colors. I will also explain how to safely build a fire so you can see the process and check out the colors for yourself.

Why Fire Turns Blue

Fires burn because of a chemical reaction between oxygen and a fuel source. The color of the fire changes depending on how hot the fire is burning. Blue flames come when the fire gets hotter.

But what actually is a fire, and how does it burn hot enough to turn blue?

What Actually Is a Fire Anyway

Fire is caused by a chemical process known as combustion. Combustion occurs when oxygen and a fuel source react together to release gases into the air. Those gases are what makeup smoke. If a heat source is then introduced to the reaction, a fire will ignite.

A flame is the visible result of that combustion. Examining a flame, you can see the different colors of the fire, ranging from blue to red to orange. What causes this variation in color?

Why Does a Fire Turn Different Colors

The colors of fire are visible due to a scientific process called blackbody radiation. The simple explanation of this process is that a hot object will also give off light. That light is what we see as color when we look at the flame. 

The hotter the fire gets, the larger the frequency of the light released. Red light has a smaller frequency, so it is visible when the fire is “cooler,” while blue light is a larger frequency and visible as the fire gets hotter.

The blue flame occurs when the fire combustion is total. When this happens, there is so much oxygen present that the other fuel is all consumed. Oxygen and other gases burn hotter than fuel, such as wood or paper, resulting in a blue fire color.

Where the flame is not as hot, the fuel is not completely consumed, and soot particles are present. These soot particles give off light that is typically visible as an orange or red color. 

Another Reason Fire Can Turn Blue

While the color of the fire is usually related to temperature, there is another possible explanation as well. Some chemical compounds give off a blue color when burned. The presence of these in a fire can also cause the flames to turn blue while they are burning. Compounds containing copper, for example, give off blue flames when burned.

How Does a Fire Start

In order to ignite properly, a fire requires three things:

  •  Flammable material. This is any material that will catch fire easily. Paper, cardboard, and wood are good examples.
  • Oxygen. The air contains 21% oxygen, enough to fuel a fire. 
  • A heat source. Oxygen and fuel react together, but they need a heat source to spark them into an actual fire. 

What Keeps the Fire Burning

Typically, the initial heat source that ignites the fire is temporary. For example, a match or a lighter is used. 

In order for the fire to keep burning, it must become itʻs own heat source. As the fuel burns, it gives off both light and heat. The light, as I already discussed, is what gives the flames their visible color. The heat is used by us to cook our food or warm our hands but also by the fire to keep the combustion reaction going.

The fire produces its own heat, but remember, fuel and oxygen are also needed. In order to keep burning, the fire needs more fuel and a flow of oxygen. Removing any of the three elements will cause the fire to go out. 

Here is a video that explains what fire is and how it burns:

(47) What Is Fire? – YouTube

Building Your Own Fire

Now that you know how a fire starts and why it changes colors, maybe you would like to see it for yourself. To build your own fire, you will need:

  • A safe location. Indoors, a fireplace or wood stove, for example. Outdoors, in a fire ring or a fire pit, such as this one, available on Amazon.
  • Tinder. This is paper or something else that ignites easily.
  • Matches or a lighter
  • Kindling. These are twigs, dry leaves, or small pieces of wood.
  • Larger pieces of dry wood
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10/03/2023 03:49 pm GMT

How To Start Your Own Fire

  1. Gather your materials.
  2. Arrange the wood, kindling, and tinder. Here is a video that explains several ways to do it:
  1. Light your fire. 
  2. Keep feeding the fire with larger pieces of wood as needed.

Fire Safety Tips

Wherever you are building your fire, it is important to always remember that fire can be dangerous. Follow these tips to help you enjoy your fire safely. 

Chose a Safe Location

Whether you are building a fire in your backyard or while camping, it is important that you chose the right location for your fire. 

If a fire pit or fire ring is available, always use that. If not, ask what the rules are for where fires are allowed and how big they can be. Make sure any flammable objects, such as trees, brush, tents, or other gear, are at least fifteen feet away from your fire.

Have Water Available

Always make sure you have access to enough water to put out your fire. Whether it is a hose in your backyard or a full bucket on a campout, having water nearby is essential.

Check Weather Conditions

Be aware of the weather conditions before starting a fire. If it is very dry and windy, a fire could easily spread out of control. Many locations will ban fires in conditions like this. 

Donʻt Use Accelerants

Never use accelerants, such as gasoline, to help start your fire. These substances are highly flammable, and they can be very dangerous.

Put Your Fire Out

Never leave your fire unattended. When you are finished with your fire, put it out completely. Douse it with water until the remnants are cool to the touch. Coals that are still warm can flare up again if the wind kicks up, so make sure the fire is completely out. 

Final Thoughts

Despite the common practice of calling fires “red hot,” a fire that turns blue is actually hotter than a red fire. Because of the process of blackbody radiation, the color of the fire is determined by its temperature. 

The amount of oxygen available to a fire is the key factor in determining how hot it will burn. High levels of oxygen result in a hotter fire, causing the blue colored flames. 

If you are careful and can find the right location, building your own fire can be an enjoyable activity. Not to mention, now you will be able to answer if someone asks why some of the flames are blue.


  • Alanna Greene

    Alanna is an avid traveler who lives in Michigan. In addition to writing for Temperature Master, he also sells crafts on Etsy and takes long walks through the forests near her home.