General Question

Sneki95's avatar

If there is an air bubble inside a wooden log, and the log gets on fire, would that air bubble make the log explode or snap?

Asked by Sneki95 (6997points) February 26th, 2017

It’s buggin’ me a bit now. Why do wooden logs explode when on fire sometimes? I was wondering that, and then I came up with a theory that there are air bubbles inside that…uh…create pressure or something that causes mini explosion.

Is that possible? If you have an air bubble in a wooden log, and the log gets on fire, could the heat make some pressure in the bubble and cause the log to explode (or simply snap real loud)?
How big would the bubble have to be? How high the pressure?

Can there even be an air bubble inside a wooden log?

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9 Answers

cazzie's avatar

when air is heated, it expands. Also, moisture. It’s why pop corn pops. It’s why wood snaps and crackles when it’s on fire. There is often sap or air trapped that heats and expands and so, wood cracks and pops when it’s on fire. Science is cool.

Sneki95's avatar

^ I thought so myself, but I wasn’t exactly certain if that is even possible. I knew that hot air expands, but I wasn’t sure if that is possible with wood.
I still wonder why and how did an air bubble form inside wood, and what does moisture have to do with it (the wood does burn faster if it’s dry, though. Is that it?)

Anyways, thanks for the info.

cazzie's avatar

Well, sap and such can collect in pockets. When this, basically water, solution expands, it creates quite the dramatic snap or pop. Other times, it might just wheeze out slowly, but if it is contained and the conditions are right, it will snap and make a loud pop.

cazzie's avatar

OH, and water is amazing in that it sort of defies the rules of physics in some cool but basic ways. But if you want to talk about that. it might be for a different thread.

zenvelo's avatar

It isn’t just wood that does this. I have seen it happen to rocks!

Granite can become waterlogged if soaked for really long times. Use a wet rock made of granite as part of a fire circle, and you may see it split in half if heated hot enough and long enough.

BellaB's avatar

Most often sap and moisture. It is one of the reasons people are careful to age/dry/season wood before using it. You want to prevent the popping/snapping if you can. It is not always safe.

Dutchess_III's avatar

When a log burns really hot sometimes pockets of super heated air are suddenly exposed, and hissing jets of flame shoot up. It’s pretty cool.

Sneki95's avatar

@Dutchess_III Yeah, it is, I just didn’t exactly know how does that happen.
@zenvelo Rocks can do that too? It’s kind of hard for me to imagine a rock snapping…
@BellaB I agree. Those explosions broke the glass in my fireplace a few times. Strong ish…

Dutchess_III's avatar

Oh sure the rocks crack. Check out any camp fire.

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