WEBVTT - How Smoke Works

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<v Speaker 1>Get smarter in sixty seconds with brain Stuff from how

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<v Speaker 1>stuffworks dot com. Hi, I'm Marshall Brain. Let's say that

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<v Speaker 1>you have a nice fire going and it's burned down

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<v Speaker 1>to the point where what you see is a collection

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<v Speaker 1>known as hot glowing embers. The fires still producing a

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<v Speaker 1>lot of heat, but it's producing no smoke at all.

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<v Speaker 1>You might have gotten to this point either by starting

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<v Speaker 1>with logs in a fireplace or by starting with charcoal

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<v Speaker 1>and a barbecue grill. If you now toss a piece

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<v Speaker 1>of wood or even a sheet of paper onto this fire,

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<v Speaker 1>what you'll notice is that the new fuel produces a

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<v Speaker 1>lot of smoke as it heats up, and then all

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<v Speaker 1>of a sudden, often with a small pop, it bursts

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<v Speaker 1>into flame and the smoke disappears. If you have a

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<v Speaker 1>fireplace or a wood stove, or if you've been around

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<v Speaker 1>a lot of campfires, this little scene is very familiar

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<v Speaker 1>to you. It tells you a lot about smoke. So

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<v Speaker 1>let's ask the obvious question, what exactly is smoke? There

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<v Speaker 1>are four things that you find in any piece of wood, water, ash, carbon,

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<v Speaker 1>and volatile organic compounds. Water is water. Freshly cut wood

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<v Speaker 1>contains a lot of water. Sometimes more than half of

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<v Speaker 1>its weight is water. Seasoned would or would that's been

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<v Speaker 1>allowed to sit for a year or two, or kiln.

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<v Speaker 1>Dried wood contains a lot less water, but it still

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<v Speaker 1>contains some ash. Is the non burnable minerals in a

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<v Speaker 1>tree's cells, like calcium, potassium, magnesium, whatever. Volatile organic compounds

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<v Speaker 1>are chemicals that evaporate when you heat wood. When the

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<v Speaker 1>tree was alive, it contains sap and a wide variety

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<v Speaker 1>of volatile hydrocarbons in itsells. A compound is volatile if

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<v Speaker 1>it evaporates when heated. These compounds are all combustible. Gasoline

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<v Speaker 1>and alcohol are, after all, hydrocarbons, so the volatile hydrocarbons

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<v Speaker 1>in wood burn the same way. When you put a

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<v Speaker 1>fresh piece of wood or a piece of paper on

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<v Speaker 1>a hot fire, the smoke you see is those volatile

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<v Speaker 1>hydrocarbons evaporating from the wood. They start vaporizing at a

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<v Speaker 1>temperature of about three degrees fahrenheit. If the temperature gets

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<v Speaker 1>high enough, these compounds burst into flame. Once they start burning,

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<v Speaker 1>there is no smoke because the hydrocarbons are turned into

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<v Speaker 1>carbon dioxide and water, both invisible when they burn. So

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<v Speaker 1>what is smoke it is all the volatile organic compounds

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<v Speaker 1>evaporating from wood, but not ignited by a flame. Do

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<v Speaker 1>you have any ideas or suggestions for this podcast? If so,

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<v Speaker 1>please send me an email at podcast at how stuff

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<v Speaker 1>works dot com. For more on this and thousands of

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<v Speaker 1>other topics, go to how stuff works dot com.