Last Updated on November 14, 2023 by Grow with Bovees
There are multiple reasons and explanations for why there would be green and blue flames in wood fire wood other than the traditional orange-colored flame.
A fire burning with a blue flame usually indicates a temperature of around 2600-3000º F, this is a tad hotter than the usual orange flame or yellow flame.
One possible alternative for a blue fire, other than intensity and temperature, is that there may be an iron nail in the fire, if the nail is rusted, the oxidation on the nail could cause blue and violet hues in the flame.
A green flame most commonly means, there is something additional burning, alongside the wood. Sometimes it’s a chemical or a pesticide.
Today we will be exploring why your fire’s flames might turn green or blue from time to time and why this is the visible light spectrum.
We will be looking at the cause and source of the color, as well as if you should be worried about these color changes or not.
What Causes Blue Flames in a Wood Fire?
The most common alteration in color when burning a traditional wood fire is blue. Blue colors may be seen where the fire burns the most intensely, usually close to the wood, at the base of the flame.
When lighting a match, this can be seen clearly. The blue flame burns closest to the match’s head.
It is clear that the flame’s color, in this case, depends on the temperature. If you remember a laboratory Bunsen burner from science class, the flame is completely blue.
The reason for this is that the flame is burning at a much higher temperature and a much higher intensity than the normal orange or yellow flames.
The science behind this blue flame is quite easily explained. The blue color means that all the material or wood that is currently available is being burned, there are no new ignitions and therefore the orange and yellow flames will be less.
The carbon content in the wood is all in a state of combustion.
If the wood has been pressure treated with copper sulfate compounds, it will usually also burn in a blue color. Burning pressure treated wood, however, is highly dangerous and not recommended.
The smoke that is released from burning this type of wood can be very toxic to humans.
One other contributing factor to a blue-green color in opposition to a yellow color or orange color of flame, might be the type of wood that is being burned.
American Elm and White Elm, as well as Black Locust wood, are all capable of burning in a blueish color if dried and aged sufficiently.
Is Blue Flame Dangerous?
When normal firewood is being burned, and there is nothing else being burned in the fire, the common color for flames to be is orange, yellow and blue.
This is not at all harmful or dangerous and only means that all the wood fuel is being consumed, and hotter flames are being produced.
Having said that, if you are burning older pressure treated lumber or wood that has been chemically treated, the fumes released from this wood will be dangerous.
When burning scrap wood, this always needs to be taken into consideration. Here the chemicals in the wood will also create a blue flame.
Also, monitoring carbon monoxide levels because of the accelerated burning of carbon, especially indoors, is advisable. A carbon monoxide detector will solve this issue and deter any possible carbon monoxide poisoning.
What is the Reason Behind Green Flames When Burning Wood?
There are many alternative flame colors other than orange, or yellow-colored flame. Blue and blue-green flames are fairly common.
Similarly to the blue colored flame, when your fire burns green, there could be several contributing factors. Knowing whether these are cause for alarm or not is fairly important.
Green flame means – possible causes;
- Firewood with wood rot, or decaying wood.
- Wood that contains nails, particularly copper roofing nails.
- Wood that has been treated with pesticides which contains copper.
- Cedar wood.
The relationship between flame temperature and flame color does not apply in this case. A green flame is usually attributed to something external.
The change in color from the usual orange flame must come from something other than the wood itself or any other traditional fuel sources.
Wood flames that burn green, usually come from wood that has been treated with borax. Borax is a common additive of pesticides used to treat wood against termites and other insects and burns in a bright green color.
Another reason for this different-colored flame may be because there is copper residue in the wood or pieces of copper in the fire. Copper compounds create green flames.
Is Green Flame Dangerous?
A green flame is not considered as very dangerous.
But, there are several precautions that should be taken when a green flame is present. Cooking over a flame with a green color is definitely not recommended.
The cause of the change in color is likely to be caused by some chemical that should not be burned. These chemicals become airborne through smoke and will be absorbed by the food you are cooking over an open fire.
This can be detrimental to your health. The risk of developing copper toxicity, for instance, because of copper being burned in the fire is quite possible.
However, if your fire is outdoors or in an extremely well ventilated room, there should be nothing to worry about.
If you are not constantly breathing in the smoke from one of these fires, green flames will not cause harm to you.
What is the Correlation Between Temperature Change and Flame Color Change?
There are several reasons why a flame would take on a certain color, between orange, yellow and blue, the two deciding factors are the temperature and the fuel source that is feeding the fire.
Different materials produce characteristic colors that are different. Firstly, we shall explore how temperature has an effect on the color of your fire.
Recent scientific studies have found that the color spectrum of flames aligned to temperatures as follows:
- 980 – 1800° F – Red flame
- 2000 – 2200° F – Orange / Yellow flame
- 2400 – 2700° F – White flame
- 2600 – 3000° F – Blue flame
You can confirm these colors with a simple experiment.
Lighting a match and observing the layers of color will show you exactly what is stated above.
Looking at the color closest to the fuel source or, in this case, the head of the match, the color will be a white hue.
Further outwards to the center and tip of the flame, the color changes to an orange/dark yellow color and then finally, the flame burns red and with a visible glow. It is amazing that such a small flame can burn so hot.
Another very common color seen in a fire is blue.
Flames that burn from natural gas instead of firewood are usually blue.
This can be seen in the use of gas stoves and Bunsen burners, which usually produce a very hot flame. In the candle experiment, you will see a little blue mixed in with the white at the center of the flame.
Blue flames derived from burning natural gas take their color, because gases always burn hotter than wood or other organic fuel sources.
The difference in temperature is directly linked to a change in color in your flame, as the fire moves through the temperature levels as listed above.
However, the type of fuel used and the composition of that fuel chemistry can also play a role. Case in point, most hydrocarbon fuels or more commonly known as fossil fuels (i.e. natural gas and oil) burn with a blue color. Earth’s alkaline metals like Lithium will burn pink in color.
All things considered, these two basic colors (green or blue colors) in fire are nothing major to write home about. It is helpful however, to know why your fire is burning in these colors.
If you are not sure about the types of flame and reason behind them, it’s always better to be cautious. Doing adequate research and checking if your fuel source is safe should always be a priority before lighting up.