Is Charcoal Flammable?

This article will answer the following question: “Is Charcoal Flammable?”. We will explain how it is formed, how it becomes flammable, and discuss if its combustion produces flames or not.

Is Charcoal Flammable?

Yes, charcoal it’s flammable. At first, it may look that charcoal has already burned and wouldn’t be flammable, but charcoal is not exactly a byproduct of combustion. It still contains a lot of combustible material, and this is why we burn it to get energy.

What is charcoal?

Charcoal comes from wood or other sources of fuel like peat, coal, coconut shell, or petroleum.

Charcoal is a fuel that’s produced from other sources of fuel. Wood for example, even if it’s dried, has a lot of water within. But it’s not only in the form of liquid water, it is also dispersed in the wood structure, as we will see.

As a result of the chemical reactions that fuels go to turn into charcoal, the material gets lighter, darkness appears, it shrinks, and the heat that we got from burning it per weight increases.

It’s like we got a piece of wood, let it dry real hard, and create an amalgam of carbon that can burn more evenly.

Charcoal can be considered an impure form of graphitic carbon. It doesn’t mean that there are bad things mixed with it, it simply means that the charcoal structure is similar to graphite, but with other atoms bonded.

Charcoal types

Charcoal can be made from a lot of things and can have other functions than simply serving as fuel. We note:

  • Common charcoal. The ones we use to burn to get energy from.
  • Lump charcoal. Made from hardwood, it produces fewer ashes.
  • Japanese charcoal. It barely produces smell and smoke.
  • Pillow shaped briquettes. Made by compressing charcoal. It’s mixed with other flammable substances, binders, and additives.
  • Sawdust briquette charcoal. It’s also compressed, but without binders and additives. It’s used in barbecues because it produces a few odors, ashes, and smokes, but also a high heat that lasts for hours.
  • Sugar charcoal. Its matrix is sugar. Is made quite differently from the other types.

Charcoal production

There are many ways to produce charcoal. The general process consists in heat the matrix (eg., wood or coal) in the absence of low oxygen concentration. The chemical reaction is known as pyrolysis.

We will use wood as an example, but similar processes happen with any matrix.

Pyrolysis

Wood is composed of organic molecules of many kinds, mostly polysaccharides. These molecules form the structure of a tree. 

For example, trees have sucrose (C12H22O11) and cellulose (C6H10O5)n. In the first structure, one molecule has 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms. 

In the second, each molecule has the explicit number of atoms, but there’s also an “n”. This letter is a number, meaning that the compound is a polymer (a structure of C6H10O5 that repeats itself).

Adapted from: https://www.researchgate.net/figure/Putative-structure-of-charcoal-from-Verheijen-et-al-2010-showing-a-a-model-of-a_fig15_237077826 and https://en.wikipedia.org/wiki/Cellulose

Note that the proportion of hydrogen and oxygen is bigger than the carbon for cellulose. After the pyrolysis, this situation reverts. The charcoal structure has more carbon than oxygen and hydrogen.

This is the main reason why charcoal looks so dark, and why it presents higher flammability than the wood alone. It gets much similar to graphite, which is composed solely of carbon.

But at the same time, charcoal still has some hydrogen and oxygen bondings, and some of the previous carbon-carbon bondings are still there, so its “skeleton” remains.

When a plant realizes photosynthesis, it takes carbon dioxide (CO2) from the air and water (H2O), in the presence of light, to produce complex sugars of many kinds like sucrose and cellulose.

Carbon dioxide and water are used in many different proportions to create all carbon-based structures from plants. When pyrolysis happens, some of these structures are broken, and the oxygen and hydrogen generated bond to produce water once again.

Does charcoal burn with flame?

Yes, charcoal does produce flames.

As we saw in the previous topic, the charcoal structure is much more “clean” than wood, coal, and other solid fuels. It is mainly made of carbon and only a few carbon-hydrogen and carbon-oxygen connections remain.

Because of that, charcoal particle burns much more equally, evenly, and with fewer steps.

In common combustions, we normally see flames/fire after the combustion takes place. In charcoal, much fewer flames are visible.

But this doesn’t mean that charcoal doesn’t burn. In fact, 1kg of charcoal burns much more than 1kg of wood (generates more heat).

The fire, the yellow, red, and orange flames we see in some fires, are just one way in which the combustion reactions happen.

Charcoal burns more equally/ smoothly because its molecules are very much like each other, and because charcoal burns while solid. The carbon content in charcoal molecules gets reaped more evenly and slowly.

Combustions that generate bigger fire columns have much more complex reactions. Volatile organic compounds rise from the fuels, are heated, and then get shredded along the column. 

Once they reach the top of the fire, normally the red part, the temperature is higher, so the molecules eventually break until they form CO2. If the molecule is still too big to burn, smoke is generated.

Any smoke, carbon monoxide, graphite, and other byproducts different from carbon dioxide and water are products of incomplete combustion of the fuel.

Carbon monoxide is a nonrare byproduct of charcoal combustion. If a room where charcoal is being burned is not well ventilated or doesn’t have the required exhaustion, asphyxiation by carbon monoxide is certain.

Carbon monoxide is a colorless, odorless, tasteless, and non-irritating gas that can kill in low concentrations. It is a silent killer that has made many victims throughout history, including (possibly) Cleopatra and Princess Diana.

Can charcoal spontaneously combust?

A study published in 2004 evaluated the self-ignition capabilities of charcoal briquets. 

The study demonstrated that charcoal briquets of different sizes, formulations, moisture content, driedness, and age can’t ignite spontaneously in temperatures below at least 121ºC.

The research concluded that, under normal ambient conditions, charcoal can’t suffer spontaneous combustion.

But this doesn’t mean that charcoal can’t catch fire, only that it won’t do it without a source of ignition.

If charcoal is in an environment with low ventilation, a little heat and a source of flames, it might ignite. If for some reason the charcoal manages to unleash flammable vapors, there’s also a possibility of explosion.

Charcoal flashpoint

It’s hard to assess charcoal’s flashpoint because there are too many kinds of formulations, processes and different ingredients that can compose charcoal.

But there is also good news: charcoal flashpoint is considerably above the room temperature of any country unless there’s a source of heat closeby.

The flashpoint of charcoal lighter fluid is around 40ºC/104ºF. This means that the flashpoint of charcoal is considerably higher than this, otherwise, lighter fluid wouldn’t be required to help start charcoal combustion.

Conclusion

Charcoal is flammable. It can ignite and is used for this purpose all around the world. Charcoal presents fewer flames when burned than other fuels, and also generates fewer fumes, smoke, and other unwanted byproducts, but still unleashes carbon monoxide.

Frequently Asked Questions (FAQS): Is Charcoal Flammable?

Is charcoal toothpaste good?

The studies and trials regarding toothpaste products that have activated charcoal compounds as one of their ingredients are not definitive, but most of them indicated that they might do more bad than good. 

We can’t really be sure if it’s safe or effective, and much more research is needed on the long-term effects. It is not considered more effective than other products on the market.

Charcoal toothpaste is considered too abrasive for everyday use and may wear down our enamel. Could also cause tooth sensitivity.

Is charcoal a fossil fuel?

No, it’s not a fossil fuel. Charcoal is made from plants, especially trees (wood), but also peat, coal, coconut shell, or petroleum. Charcoal can be made from coal as well and, in that case, it’s a fossil fuel.

Coal was formed millions of years ago, much earlier than the dinosaurs. Thick layers of plants eventually settled and got covered by dirt and water, being compressed for millions of years.

Coal is considered a nonrenewable source of energy because it requires all those years to be formed, but charcoal and coal are made essentially from the same ingredients: plants.

is charcoal edible?

Activated charcoal is used as a food ingredient in the food industry, and in homes, since the last decade. It’s made normally from bamboo or coconut shell.

This charcoal form can be used as a food additive, it imparts a slightly smoky taste and provides a dark color for dishes

Citations

Bourke, J., Manley-Harris, M., Fushimi, C., Dowaki, K., Nunoura, T., & Antal, M. J. (2007). Do All Carbonized Charcoals Have the Same Chemical Structure? 2. A Model of the Chemical Structure of Carbonized Charcoal†. Industrial & Engineering Chemistry Research, 46(18), 5954–5967. doi:10.1021/ie070415u 

https://lebufes.com.br/wp-content/uploads/2020/07/Investigating-the-pyrolysis-temperature-to-define-the-use-of-charcoal.pdf
https://www.researchgate.net/publication/250275837_Size_Constraints_On_Self_Ignition_Of_Charcoal_Briquets
https://www.britannica.com/science/charcoal
https://www.fao.org/3/AD583E/ad583e00.pdf
https://en.wikipedia.org/wiki/Charcoal
https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Carbon
https://en.wikipedia.org/wiki/Pyrolysis

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