Your Campfire: An Owner's Manual


(Originally posted by ML on the Hoods Woods Forum, 03 December 2001; reproduced here with the author's permission)

At the risk of having my boss chain me to a rock while his pet eagle feasts on my liver, Your Humble Narrator and Obedient Servant has decided to shed a little light on a subject bound to warm the cockles of many Forum members’ hearts--namely, fire.

The ability to produce fire in the outdoors has long been the mark of the accomplished woodsman. Sometimes, producing a fire with a match is a struggle, yet fire is so important to most of us that many Forum members intentionally learn to produce fire by other means, ostensibly so they can be sure they can coax the familiar "rapid, persistent exothermic combination of oxygen with a combustible substance, releasing heat and light" even when there are no matches or Zippo lighters to be had.

Any schoolchild worth his junior fire-safety badge knows of the fire triad, the three conditions one needs for fire: fuel, oxygen, and ignition. But step back for a moment and think about the best way to turn your little flame into a big flame.

Take a section of 2x4, light a match, hold it to the end, and what happens? You’ve got an ignition source (an open flame), you’ve got fuel (the 2x4) and you’ve got oxygen. So why doesn’t that piece of construction scrap burst into flame?

Let’s quantify this. In order to make wood burn, you need to raise its temperature to a critical point. How hot? Well, at about 390 degrees Fahrenheit, wood dries out, and a slow pyrolsis takes place (the wood breaks down due to heat, but does not burn per se).

Between 390° F and 530° F, a piece of wood is reduced to charcoal, but without flame.

Between 530° F and 930° F, wood will be ignited by an open flame.

At about 1000° F, spontaneous ignition occurs.

So, in order to create a fire, our intrepid camper needs to raise the temperature of the wood in question to something hotter than 530° F.

The problem, here, is twofold: the size of the ignition flame, and the temperature and mass of the fuel wood (our 2x4). If you had a bigger flame, you could ignite a giant Sequoia (which is exactly what a forest fire does). Unwilling to drag a flame-thrower into the bush? Then you need to reduce the mass of the wood you are trying to ignite.

The 2x4 in our example isn’t burning directly; rather, the cellulose in the wood volatilizes into a combustible gas which mixes with oxygen to sustain the flame (most wood is about 50% cellulose, and cellulose volatilizes at about 650° F). Naturally, in lieu of the flamethrower (our friend Vector’s preferences excluded), most of us intuitively discover that smaller twigs ignite more readily than that 2x4, so we feed our fire with twigs to get it started.

This is the Eureka moment. A burning match can pretty easily raise a twig about the diameter of that match to the critical temperature. Grab a whole handful of those twigs though, compress them into a bundle, and you have effectively turned the twigs into a 2x4, and they suck up the heat generated by the match before it can raise the bundle of twigs to the critical 530° F-plus temperature. Not only does that bundle of twigs suck the heat into its greater mass before the temperature can rise, but should one ignite placing the twigs too close together also keeps the volatile gases from adequately mixing with the oxygen in the atmosphere--smothering the fire, or more correctly, making the mixture too rich to burn, just like an old carburetor with a stuck choke plate.

Igniting a twig about the diameter of a match allows you to ignite another, and another, and another, and the combined heat energy allows you to heat bigger pieces of wood to a critical temperature (the diameter of a pencil, say), and consequently those will let you ignite still bigger pieces until only an incipient hernia limits the size of the log you’re throwing on the fire.

And since it’s all about elevating the temperature of the fuel wood, here’s another Eureka moment: warm wood ignites better than frozen wood, because it takes less energy to raise it to the critical ignition temperature. (For each 10° C rise in starting temperature of the fuel wood, the activity of the molecules in the wood doubles, and it is that movement which ultimately provides the condition for combustion.) In practical terms, you’ll find that in very cold weather, if you move a stick of wood next to the fire to pre-warm it, it will burn sooner. This is especially noticeable when you’re burning wood in a cabin stove, and the wood is stored outside where it’s below freezing. Bring a few sticks in, set them near the stove, and you’ll notice a big difference.

Understand all this, and you’ll now have the third Eureka moment: This is why wet wood burns so poorly compared with dry firewood. We all know that water conducts heat about 200 times better than dry air, so wet wood simply absorbs a great deal of heat before it reaches a critical burning temperature.

So where does this ultimately take us? If you want to light a fire in a businesslike fashion, preparation is the key. Gather a lot of small, matchstick-diameter twigs (dry, of course), and make sure there is a fair amount of air-space between each twig (about three times the diameter of such small twigs is right to allow air circulation yet still close enough so that the flame from one twig heats another). How much? Mors Kochanski (see citation at the end of this long, boring screed) recommends the following rule: put the tips of your two thumbs together, then the tips of your middle fingers. That should describe a circle of about six or seven inches. Add material in cold or damp weather. Secure the same amount of small branches about pencil-size, and another bundle of material about as big around as a fat, Churchill cigar.

The number-one mistake I see repeatedly is not enough small material gathered at first. Getting ignition with matches is generally no problem, even for the neophyte. Transferring that initial flame to progressively larger fuel is the problem.

* * * * *

Let me tell a story exemplifying this. In the winter of 1997, I spent five days cross-country ski touring in California’s Sierra Nevada, between 8500 and 11,000 feet. On my last day out, I was skiing down a canyon to the roadhead, when I came to some small winter cabins. Two couples had been dropped off by snowmobile. It was just prior to nightfall, and I noticed a young woman outside of one of the cabins. She was highly agitated, in tears. I stopped to see what was wrong, and she told me, in a panic, that they had been trying to light a fire but had used all their matches and newspaper, and that the fire had gone out and they were worried about what to do.

I removed my skis and pack, and went into the cabin. They had plenty of wood, and a nice, airtight wood-burning stove. But they had no kindling to speak of, and their firewood had been out all winter, and was frozen by itself.

I had plenty of options. In my pack, I had an MSR gasoline stove with which I had been preparing my meals and melting snow for water. I had lots of matches. I had a lighter. I had a small solid-fuel Trioxane tab and a 35mm film can with Vasalined cotton balls in my survival kit. I had a metal match. I even had, in the pocket of my parka, my worst-case-scenario, get-out-of-jail-free, make-fire-anywhere-in-winter secret weapon: Four inches of common highway safety flare with the igniter head intact and the cut-off end sealed with wax.

But more important than any of that, I had knowledge and confidence.

I decided then and there to take them to school and make a fire with one match, and without any of the other aids. Producing a small hatchet from the legendarily voluminous, Norman Clyde-inspired ML pack, I went to work on one of their pieces of firewood, carefully splitting it into smaller and smaller pieces, following the guidelines given above. Since I had no twigs, I also produced some "feather sticks" or "fuzz sticks," as well as a sizable pile of wood shavings. As I worked on them, I shoved a good bunch of the small sticks into my jacket to pre-warm them. The whole thing took about half an hour, but, when it was done, with one match we had fire.

I will note that the cold stove, cold firewood, and cold stovepipe took another half-hour of careful attention to get drawing well, but after that, you could have forged steel in the flame. (Another aside: the coals in a really hot wood fire reach a temperature of about 2000° F, and even hotter if you force air into them--see Woodsmaster #9 for an example.)

Bidding adieu to the grateful four, I clipped back into my bindings and made my descent by headlight--it was quite dark now, and a good deal of the trail had iced over. Not deadly, by any means, but definitely an attention-focusing experience with a heavy pack. I was happy to see the truck after an hour, and even happier when not long after that I was sipping a cup of hot coffee and enjoying a scone at Schatt’s in Bishop.

* * * * *

Do you really need to know the exact combustion temperature of a piece of firewood in order to build an efficient fire? Absolutely not. Pre-lithic man built fire quite handily without any of this information. Of course, pre-lithic man didn’t know anything about Britney Spears or the Internet. Has the tradeoff been worth it? I’ll leave that for you to discuss over your next campfire.

--ML

03.xii.1

Forum members wishing more information are advised to read "Understanding Wood Fires" by Mors Kochanski, appearing in "Primitive Technology: A Book of Earth Skills," as well as Kochanski’s classic "Northern Bushcraft" (recently reissued as "Bushcraft : Outdoor Skills & Wilderness Survival").



Copyright © 2001 by Eric Stoskopf.
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