1 00:00:00,640 --> 00:00:03,720 Speaker 1: Get smarter in sixty seconds with brain Stuff from how 2 00:00:03,800 --> 00:00:08,000 Speaker 1: stuffworks dot com. Hi, I'm Marshall Brain. Let's say that 3 00:00:08,080 --> 00:00:10,960 Speaker 1: you have a nice fire going and it's burned down 4 00:00:11,000 --> 00:00:13,600 Speaker 1: to the point where what you see is a collection 5 00:00:13,720 --> 00:00:17,919 Speaker 1: known as hot glowing embers. The fires still producing a 6 00:00:17,960 --> 00:00:20,920 Speaker 1: lot of heat, but it's producing no smoke at all. 7 00:00:21,520 --> 00:00:24,160 Speaker 1: You might have gotten to this point either by starting 8 00:00:24,200 --> 00:00:27,360 Speaker 1: with logs in a fireplace or by starting with charcoal 9 00:00:27,360 --> 00:00:30,680 Speaker 1: and a barbecue grill. If you now toss a piece 10 00:00:30,680 --> 00:00:33,680 Speaker 1: of wood or even a sheet of paper onto this fire, 11 00:00:34,200 --> 00:00:37,840 Speaker 1: what you'll notice is that the new fuel produces a 12 00:00:37,880 --> 00:00:40,840 Speaker 1: lot of smoke as it heats up, and then all 13 00:00:40,880 --> 00:00:44,240 Speaker 1: of a sudden, often with a small pop, it bursts 14 00:00:44,240 --> 00:00:47,720 Speaker 1: into flame and the smoke disappears. If you have a 15 00:00:47,760 --> 00:00:50,760 Speaker 1: fireplace or a wood stove, or if you've been around 16 00:00:50,760 --> 00:00:54,120 Speaker 1: a lot of campfires, this little scene is very familiar 17 00:00:54,120 --> 00:00:56,840 Speaker 1: to you. It tells you a lot about smoke. So 18 00:00:56,920 --> 00:01:01,600 Speaker 1: let's ask the obvious question, what exactly is smoke? There 19 00:01:01,600 --> 00:01:06,640 Speaker 1: are four things that you find in any piece of wood, water, ash, carbon, 20 00:01:06,880 --> 00:01:12,440 Speaker 1: and volatile organic compounds. Water is water. Freshly cut wood 21 00:01:12,480 --> 00:01:15,440 Speaker 1: contains a lot of water. Sometimes more than half of 22 00:01:15,440 --> 00:01:18,920 Speaker 1: its weight is water. Seasoned would or would that's been 23 00:01:18,959 --> 00:01:21,759 Speaker 1: allowed to sit for a year or two, or kiln. 24 00:01:21,800 --> 00:01:25,160 Speaker 1: Dried wood contains a lot less water, but it still 25 00:01:25,200 --> 00:01:29,679 Speaker 1: contains some ash. Is the non burnable minerals in a 26 00:01:29,800 --> 00:01:36,240 Speaker 1: tree's cells, like calcium, potassium, magnesium, whatever. Volatile organic compounds 27 00:01:36,280 --> 00:01:40,039 Speaker 1: are chemicals that evaporate when you heat wood. When the 28 00:01:40,120 --> 00:01:43,560 Speaker 1: tree was alive, it contains sap and a wide variety 29 00:01:43,560 --> 00:01:48,440 Speaker 1: of volatile hydrocarbons in itsells. A compound is volatile if 30 00:01:48,480 --> 00:01:53,440 Speaker 1: it evaporates when heated. These compounds are all combustible. Gasoline 31 00:01:53,440 --> 00:01:58,120 Speaker 1: and alcohol are, after all, hydrocarbons, so the volatile hydrocarbons 32 00:01:58,160 --> 00:02:01,200 Speaker 1: in wood burn the same way. When you put a 33 00:02:01,240 --> 00:02:03,520 Speaker 1: fresh piece of wood or a piece of paper on 34 00:02:03,560 --> 00:02:07,320 Speaker 1: a hot fire, the smoke you see is those volatile 35 00:02:07,400 --> 00:02:12,000 Speaker 1: hydrocarbons evaporating from the wood. They start vaporizing at a 36 00:02:12,000 --> 00:02:16,240 Speaker 1: temperature of about three degrees fahrenheit. If the temperature gets 37 00:02:16,320 --> 00:02:21,200 Speaker 1: high enough, these compounds burst into flame. Once they start burning, 38 00:02:21,280 --> 00:02:24,600 Speaker 1: there is no smoke because the hydrocarbons are turned into 39 00:02:24,680 --> 00:02:29,040 Speaker 1: carbon dioxide and water, both invisible when they burn. So 40 00:02:29,200 --> 00:02:33,279 Speaker 1: what is smoke it is all the volatile organic compounds 41 00:02:33,360 --> 00:02:38,200 Speaker 1: evaporating from wood, but not ignited by a flame. Do 42 00:02:38,240 --> 00:02:41,760 Speaker 1: you have any ideas or suggestions for this podcast? If so, 43 00:02:41,919 --> 00:02:44,600 Speaker 1: please send me an email at podcast at how stuff 44 00:02:44,600 --> 00:02:47,360 Speaker 1: works dot com. For more on this and thousands of 45 00:02:47,360 --> 00:02:51,919 Speaker 1: other topics, go to how stuff works dot com.