Fire Question...

F

Frostyfingers

Joined
Aug 27, 2008
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I was building a fire in the wood stove a few minutes ago, and as I was breathing it to life, I began to wonder something:

If fire feeds on Oxygen, and I exhale Carbon Dioxide, how does blowing on the fire help the fire grow? Is there a high enough percentage of Oxygen of my breath to feed the fire?

My personal theory is that it is not the Oxygen in my breath, but the sudden influx of Oxygen after I quit blowing that causes the growth or increase in flames.

Bellows and other mechanical blowers, on the other hand, do NOT exhale CO2, and therefore they consistently feed the flame, and thus work better than a person blowing by mouth.

Maybe there's a scientist here who can help me out...What's the deal? Is my theory correct? :confused:


Note: A Scottish friend of the family showed us all a trick he used as a child to "blow" on a woodstove fire. It is this: hold a piece of newspaper over the door, leaving a 2-3" gap at the bottom of the door. The updraft of the heat inside the stove will cause a vacuum, and a constant inflow of Oxygen rich air. You can really get the fire roaring this way, but it only works in a woodstove.
 
Your exhaled breath still contains nearly as much oxygen as when you inhaled it, I'm not sure of the exact figure.

I used to use the newspaper trick getting an open coal fire started - basically getting the wood kindling to blaze fiercely to light the coal. I actually got the idea because I saw it done in a film - "Whistle Down The Wind", IIRC. I've also used a square of tinplate with a handle on.
 
IIRC from my cpr training I believe that exhaled air is 17% oxygen versus 23% percent in normal air. Correct me if this is wrong though
 
A.W.U.K. said:
Your exhaled breath still contains nearly as much oxygen as when you inhaled it, I'm not sure of the exact figure.

Hmmm...Interesting. I have always been under the impression that one's lungs removed a large part of the Oxygen, but I guess I was wrong.

And yeah, I guess CPR wouldn't work if there wasn't some Oxygen in the air you exhale.
Click to expand...
 
Yes, that is the reason. Your body does make an exchange for CO2, but the amount used for each breath is negligible. Even if you were breathing out straight CO2 it would probably work though because the air swirling around it would carry oxygen in. Air is 75% Nitrogen and only 21% Oxygen to begin with.
 
Thanks for the interesting thoughts.

I never really thought about this. but it is cool.
 
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