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Author Topic: Why do you need at least two pieces of wood to make a fire?  (Read 3211 times)

Offline CliffordK

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Sitting here by the fire...  which went out again.
Why does it take at least two pieces of wood to make/sustain a fire?
What do you get from that second piece of wood that you don't get from just one?

If the fire burns down to one piece remaining, despite a good roaring fire...  it inevitably goes out.  Or, with a campfire, one can usually put it out by knocking the pieces apart (of course, a good bucket of water is a good idea too).

I suppose a forest fire would be far more destructive if this wasn't the case.


 

Offline CZARCAR

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Why do you need at least two pieces of wood to make a fire?
« Reply #1 on: 03/12/2011 16:00:57 »
heat from lower piece ignites upper piece as  upper contains heat from the lower, what are u burning it in?
 

Offline Bored chemist

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Why do you need at least two pieces of wood to make a fire?
« Reply #2 on: 03/12/2011 18:54:52 »
You must really struggle with matches.
 

Offline Geezer

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Why do you need at least two pieces of wood to make a fire?
« Reply #3 on: 03/12/2011 22:14:31 »
I had a thought similar to BC's, which led me to suspect that it's something to do with mass, surface area and water content, or nothing to do with any of them (maybe it's about the oxygen supply.)

If you make a series of ever larger "matchsticks", do you get to a size where they won't stay lit?
 

Offline CliffordK

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Why do you need at least two pieces of wood to make a fire?
« Reply #4 on: 04/12/2011 08:06:28 »
heat from lower piece ignites upper piece as  upper contains heat from the lower, what are u burning it in?
Right now I'm using an classic open fireplace, although eventually I'll get a more efficient stove insert installed.  Now I'm burning fir & maple.

However, I've had similar observations outside with campfires, as well as viewing the aftermath of forest fires.

Generally if one has 2 pieces of wood in the fireplace, they'll be side-by-side, rather than stacked.   There seems to be an optimal gap of maybe ½" or so.

The match stick question is an interesting question.  The match stick will often burn out if held horizontally, but will burn up the stick if held vertically.  In the past, I've had troubles keeping a ¼" to ½" or so stick to sustain flames when pulled out of the fire, so perhaps size does matter.

A few thoughts I had.
  • I've heard that a fire essentially has to vaporize the wood before it oxidizes.  Perhaps it needs either a small piece, or the radiant heat of flames on 2 adjacent surfaces to keep it hot enough to vaporize the wood and to maintain the fire, especially with the heat sink bulk of a rather large piece.
  • One might get better drafting and air circulation with multiple pieces.  Often one finds that some air restriction causes faster flowing air that seems to be better for the fire.
  • Not all wood is created equal (more below)

Forest fires are a natural phenomenon.  Different species of trees may have adapted different strategies to deal with the fires.

In tall conifer stands, a fire can sweep through a forest, wiping out the undergrowth, but leaving many of the mature trees unharmed.

It is likely that trees like Cedars might burn more completely than trees like firs, even though the cedars are considered to be more of a slow growing secondary colonizer, and the firs are a primary colonizer. 

I've never seen green Balsa, but I've heard that Balsa is a primary colonizer, and I'd imagine that it would burn very rapidly.  Since it is a primary colonizer, perhaps part of its strategy would be to stoke the fires.
 

Offline Bored chemist

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Why do you need at least two pieces of wood to make a fire?
« Reply #5 on: 04/12/2011 11:05:20 »
Size definitley matters in this context. Sawdust in air can be explosively flammable.
 

Offline LetoII

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Why do you need at least two pieces of wood to make a fire?
« Reply #6 on: 04/12/2011 11:06:23 »
you dont, if you only have 1 piece break it in halve and you have 2, voila
 

Offline CZARCAR

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Why do you need at least two pieces of wood to make a fire?
« Reply #7 on: 04/12/2011 12:41:38 »
http://pook-natureoffire.blogspot.com/2010/11/air-buoyancy-is-main-factor.html   kinda inverse i wrote up, if legible
water boils @ 212*f, wood offgasses volatiles ~600*f, flame appears ~ 1300*f
Or & Wa are tough EPA states & may impose burning bans during weather inversions. Dunno wwhat firewood u have available locally but in Me softwood is considered too much hassle to deal with BUT softwood pellets have slightly more BTU/lb & balsa has most BTU/lb when pelletized.
Fireplace has too much draft which can result in heatloss for the house though FP inspired the invention of the wingback chair
 

Offline Geezer

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Why do you need at least two pieces of wood to make a fire?
« Reply #8 on: 04/12/2011 19:32:00 »
heat from lower piece ignites upper piece as  upper contains heat from the lower, what are u burning it in?
Right now I'm using an classic open fireplace, although eventually I'll get a more efficient stove insert installed.  Now I'm burning fir & maple.

However, I've had similar observations outside with campfires, as well as viewing the aftermath of forest fires.

Generally if one has 2 pieces of wood in the fireplace, they'll be side-by-side, rather than stacked.   There seems to be an optimal gap of maybe ½" or so.

The match stick question is an interesting question.  The match stick will often burn out if held horizontally, but will burn up the stick if held vertically.  In the past, I've had troubles keeping a ¼" to ½" or so stick to sustain flames when pulled out of the fire, so perhaps size does matter.

A few thoughts I had.
  • I've heard that a fire essentially has to vaporize the wood before it oxidizes.  Perhaps it needs either a small piece, or the radiant heat of flames on 2 adjacent surfaces to keep it hot enough to vaporize the wood and to maintain the fire, especially with the heat sink bulk of a rather large piece.
  • One might get better drafting and air circulation with multiple pieces.  Often one finds that some air restriction causes faster flowing air that seems to be better for the fire.
  • Not all wood is created equal (more below)

Forest fires are a natural phenomenon.  Different species of trees may have adapted different strategies to deal with the fires.

In tall conifer stands, a fire can sweep through a forest, wiping out the undergrowth, but leaving many of the mature trees unharmed.

It is likely that trees like Cedars might burn more completely than trees like firs, even though the cedars are considered to be more of a slow growing secondary colonizer, and the firs are a primary colonizer. 

I've never seen green Balsa, but I've heard that Balsa is a primary colonizer, and I'd imagine that it would burn very rapidly.  Since it is a primary colonizer, perhaps part of its strategy would be to stoke the fires.


Sounds like it's an oxygen supply thing. The separation creates a sort of venturi that increases the oxygen supply in that space.

If you stick a single log in a fire and blow air at it, I bet you can burn it to ash.

Don't try this at home, but, in olden times when we had open coal fires, to get it going we would cover the open space above the grate with an unfolded newspaper. That made the chimney much more effective at drawing air into the fire. People who had lots of money even had sheets of metal that could do the same thing a bit more safely.
 

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Why do you need at least two pieces of wood to make a fire?
« Reply #8 on: 04/12/2011 19:32:00 »

 

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