Speaker 1: Get smarter in sixty seconds with brain Stuff from how
Speaker 1: stuffworks dot com. Hi, I'm Marshall Brain. Let's say that
Speaker 1: you have a nice fire going and it's burned down
Speaker 1: to the point where what you see is a collection
Speaker 1: known as hot glowing embers. The fires still producing a
Speaker 1: lot of heat, but it's producing no smoke at all.
Speaker 1: You might have gotten to this point either by starting
Speaker 1: with logs in a fireplace or by starting with charcoal
Speaker 1: and a barbecue grill. If you now toss a piece
Speaker 1: of wood or even a sheet of paper onto this fire,
Speaker 1: what you'll notice is that the new fuel produces a
Speaker 1: lot of smoke as it heats up, and then all
Speaker 1: of a sudden, often with a small pop, it bursts
Speaker 1: into flame and the smoke disappears. If you have a
Speaker 1: fireplace or a wood stove, or if you've been around
Speaker 1: a lot of campfires, this little scene is very familiar
Speaker 1: to you. It tells you a lot about smoke. So
Speaker 1: let's ask the obvious question, what exactly is smoke? There
Speaker 1: are four things that you find in any piece of wood, water, ash, carbon,
Speaker 1: and volatile organic compounds. Water is water. Freshly cut wood
Speaker 1: contains a lot of water. Sometimes more than half of
Speaker 1: its weight is water. Seasoned would or would that's been
Speaker 1: allowed to sit for a year or two, or kiln.
Speaker 1: Dried wood contains a lot less water, but it still
Speaker 1: contains some ash. Is the non burnable minerals in a
Speaker 1: tree's cells, like calcium, potassium, magnesium, whatever. Volatile organic compounds
Speaker 1: are chemicals that evaporate when you heat wood. When the
Speaker 1: tree was alive, it contains sap and a wide variety
Speaker 1: of volatile hydrocarbons in itsells. A compound is volatile if
Speaker 1: it evaporates when heated. These compounds are all combustible. Gasoline
Speaker 1: and alcohol are, after all, hydrocarbons, so the volatile hydrocarbons
Speaker 1: in wood burn the same way. When you put a
Speaker 1: fresh piece of wood or a piece of paper on
Speaker 1: a hot fire, the smoke you see is those volatile
Speaker 1: hydrocarbons evaporating from the wood. They start vaporizing at a
Speaker 1: temperature of about three degrees fahrenheit. If the temperature gets
Speaker 1: high enough, these compounds burst into flame. Once they start burning,
Speaker 1: there is no smoke because the hydrocarbons are turned into
Speaker 1: carbon dioxide and water, both invisible when they burn. So
Speaker 1: what is smoke it is all the volatile organic compounds
Speaker 1: evaporating from wood, but not ignited by a flame. Do
Speaker 1: you have any ideas or suggestions for this podcast? If so,
Speaker 1: please send me an email at podcast at how stuff
Speaker 1: works dot com. For more on this and thousands of
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