How Smoke Works

When you put a fresh piece of wood on a hot fire, volatile organic carbons in the wood evaporate, creating smoke. Learn more about smoke in this Brainstuff podcast.

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Episode Transcript

Speaker 1 (00:00):
Get smarter in sixty seconds with brain Stuff from how
stuffworks dot com. Hi, I'm Marshall Brain. Let's say that
you have a nice fire going and it's burned down
to the point where what you see is a collection
known as hot glowing embers. The fires still producing a
lot of heat, but it's producing no smoke at all.

(00:21):
You might have gotten to this point either by starting
with logs in a fireplace or by starting with charcoal
and a barbecue grill. If you now toss a piece
of wood or even a sheet of paper onto this fire,
what you'll notice is that the new fuel produces a
lot of smoke as it heats up, and then all
of a sudden, often with a small pop, it bursts

(00:44):
into flame and the smoke disappears. If you have a
fireplace or a wood stove, or if you've been around
a lot of campfires, this little scene is very familiar
to you. It tells you a lot about smoke. So
let's ask the obvious question, what exactly is smoke? There
are four things that you find in any piece of wood, water, ash, carbon,

(01:06):
and volatile organic compounds. Water is water. Freshly cut wood
contains a lot of water. Sometimes more than half of
its weight is water. Seasoned would or would that's been
allowed to sit for a year or two, or kiln.
Dried wood contains a lot less water, but it still
contains some ash. Is the non burnable minerals in a

(01:29):
tree's cells, like calcium, potassium, magnesium, whatever. Volatile organic compounds
are chemicals that evaporate when you heat wood. When the
tree was alive, it contains sap and a wide variety
of volatile hydrocarbons in itsells. A compound is volatile if
it evaporates when heated. These compounds are all combustible. Gasoline

(01:53):
and alcohol are, after all, hydrocarbons, so the volatile hydrocarbons
in wood burn the same way. When you put a
fresh piece of wood or a piece of paper on
a hot fire, the smoke you see is those volatile
hydrocarbons evaporating from the wood. They start vaporizing at a
temperature of about three degrees fahrenheit. If the temperature gets

(02:16):
high enough, these compounds burst into flame. Once they start burning,
there is no smoke because the hydrocarbons are turned into
carbon dioxide and water, both invisible when they burn. So
what is smoke it is all the volatile organic compounds
evaporating from wood, but not ignited by a flame. Do

(02:38):
you have any ideas or suggestions for this podcast? If so,
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works dot com. For more on this and thousands of
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