Why Does Wood Pop?

Have you ever wondered why wood pops when it burns?

When burning wood, especially firewood, it is very common for wood to make a popping sound. Some say that this is air coming out from the wood while some say that this is made by strong fire.

Why does wood pop, as well as other curious things about firewood will be answered in this guide?

What makes that popping sound?

A quick answer to this question: the popping sound that you hear is due to the moisture, wood sap and other materials found in wood escaping as wood start to burn. This will be further explained later.

To find out what that distinct sound is, you need to learn about fire first. The fire comes from a chemical reaction between oxygen in the air and the source of fuel like wood or gasoline.

Most fuel sources don’t burst into flames spontaneously because these are surrounded by oxygen all the time. These fuel sources need to be heated to their ignition temperature for combustion to occur.

The ignition temperature of the wood

The ignition temperature of food is around 300º F. At this temperature heat starts to eat away the cellulose material found in wood. The decomposing material starts to take on different forms; this becomes volatile gasses, char, smoke, and ash.

Wood begins to burn when the volatile gasses have reached 500º F. This is the temperature at which the molecules break apart and then recombine with oxygen to create carbon dioxide and other products.

While this is happening, the carbon in the char mixes with oxygen at a slower pace. Doing so will create char or charcoal. Basically charcoal is wood that has been heated until the volatile gasses have been removed. This is a perfectly good explanation why charcoal burns with no smoke at all.

Popping wood explained

As you place a log of wood onto a campfire, it starts to burn. Tiny chambers filled with fluid like water and sap are found inside the wood. The wood body acts as a pot, heating and cooking the fluids inside the wood.

First, the fluids in the chambers start to boil and then begin to vaporize as steam. The steam gets trapped inside the chamber and this exerts pressure on the walls of the wood.

After a while, wood gives way and then the familiar snap, crackle, or pop is heard. This is steam released into the fire from a crevice. If you have used wet wood for firewood then you may have noticed that wood cracks, pops and snaps more than usual. This is because there is more moisture trapped in green wood than in dry wood.

Chemical explanation

The chemical reaction that occurs when wood is burning is called an oxidation reaction. The inner part of the wood is made from cellulose, which is a polymer made from chains of glucose (C6H12O6) molecules.

When this mixes with oxygen from the air, the reaction releases carbon dioxide and water vapor. Energy in the form of heat and light is also released.

Wood isn’t burning in this process but is actually sublimating or changing from solid to gas, and the gases produce the flames. If the temperature is not that high to ignite gases, these dissipate with unburnt wood particles as smoke.

Wood is filled with microscopic cells with walls made of cellulose. This is the substance that sublimates during combustion. When cellulose changes state and releases gas, this is trapped in the pores between cells.

As the temperature increases, the gas expands and puts pressure on the cell walls which are still waiting for sublimation. The gas expands and the weakened cellulose breaks the cell walls and lets the gas escape creating a burst or a pop.

And because the inner structures of wood are not uniform, combustion gases may collect in these voids and build up the pressure to cause a much larger explosion than a mere pop. This explosion may be so strong enough to hurl a large log a distance from the fire.

This is why is best to use a metal screen in front of your fireplace to protect your family and home. You must also consider burning only seasoned or dried wood instead of green wood.

Conclusion

Wood pops as it burns because of the release of gasses and other organic materials from the cavities of wood. You must keep a good distance from a bonfire, fireplace or wood-burning stoves and use only well-seasoned wood instead of green wood in your fireplace or stove.

  • January 5, 2019
  • DIY