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Could Deforistation lead to lack of ability to light fires?

  1. Dec 10, 2003 #1
    The rainforest produces a good amount of o2 (exactly how much I'm not sure), could deforistation of the rainforest lead to such a decrease of o2 in the air that fires wouldn't be able to light? About how much could the percent of o2 in the air vary before fires stopped being able to burn?
     
  2. jcsd
  3. Dec 11, 2003 #2
    Most oxygen in the air is produced by algae, not rainforests. If all of the oxygen production in the world was stopped, and the remaining oxygen was completely consumed, then sure forest fires wouldn't be able to light. But then again we'd all be dead. Trees included.
     
  4. Dec 11, 2003 #3

    ShawnD

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    Don't trees consume as much oxygen at night as they produce during the day? I heard something like that somewhere....might have been TV.
     
  5. Dec 11, 2003 #4
    Yes, algae produces about 70% of the worlds o2 and the rainforests produce about 20%. I'm not saying eliminating all the o2, but if let's say, the current amount of o2 in the air (about 21% or so, right?) was reduced to something like 19%, humans would, as a whole, be fine.

    Bassically what I'm asking is: what percent of the air does o2 need to make up for fires to burn?
     
  6. Dec 11, 2003 #5

    ShawnD

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    Depends entirely on air flow. If you have massive amounts of air flow, you can have a roaring fire with very low concentrations of O2. If you have poor air flow, higher concentration of O2 in the air is needed.
     
  7. Dec 11, 2003 #6
    what about in your house, with presumably no airflow or very little, perhaps that caused by central air, a fan or a draft.
     
  8. Dec 11, 2003 #7

    chroot

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    We need about 0.16 atmospheres partial pressure of oxygen to remain conscious.

    - Warren
     
  9. Dec 11, 2003 #8
    Care to put that in terms of percent, or does that bassically mean 16%?
     
  10. Dec 11, 2003 #9

    chroot

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    You can't just express it in percent -- it depends on the pressure. For example, at 1 atmosphere of total pressure, here on the surface of earth, I need a 16% fraction of 02 to stay conscious.

    If I dive to 33 feet in seawater, I am exposed to 2 atmospheres of pressure. There, I can survive with only an 8% fraction of 02.

    - Warren
     
  11. Dec 11, 2003 #10

    ShawnD

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    16% assuming that the air pressure is at 1 atm.
     
  12. Dec 11, 2003 #11
    Alright, I understand that, so bassically if all the rainforests were completely destroyed without any other loss of vegetation we could just remain concious
     
  13. Dec 11, 2003 #12

    chroot

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    Or we could pressurize our living environments.

    - Warren
     
  14. Dec 11, 2003 #13
    By doing what, living in underwater colonies, building domes around cities?

    Do you happen to know the atmospheres partial pressure needed to light a fire?
     
  15. Dec 11, 2003 #14

    chroot

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    Depends on the fuel.

    - Warren
     
  16. Dec 13, 2003 #15
    the fuel being oxygen in the air, or did you mean like wood/oil?
     
  17. Dec 13, 2003 #16

    chroot

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    The oxygen is (not suprisingly) the oxidizer. The fuel is the wood, oil, or other substance which is oxidized by the oxidizer.

    - Warren
     
  18. Dec 13, 2003 #17
    Well how much difference is there between different sources of feul, for instance, wood and oil.
     
  19. Dec 13, 2003 #18

    chroot

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    A huge difference.

    - Warren
     
  20. Dec 13, 2003 #19
    So how much atmospheres partial pressure do you need to sustain a wood fire and an oil fire?
     
  21. Dec 14, 2003 #20

    ShawnD

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    Why do you thik he would know that? It's not exactly common knowledge.
     
  22. Dec 14, 2003 #21

    russ_watters

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    I can't answer the question directly, but try THIS site for the opposite approach. At an altitude of about 5 miles, you're above 50% of the atmosphere so the pressure is half of what it is sea level. AFAIK, climbers in the Himalayas (sp) don't have problems lighting fires.
     
  23. Dec 14, 2003 #22
    Practically nothing discussed on this board is common knowledge. I just kinda figured how much o2 pressure you'd need to light a fire on wood would be relatively common knoweldge among people who talk about the ridiculously advanced things which are discussed on this board.
     
  24. Dec 14, 2003 #23
    Actually most of what is discussed here is common knowledge. It's mostly at the level of undergraduate science classes. Suplemented here and there with more expert opiniongs.

    How much O2 you need to light a fire is not common knowledge. Furthermore, your original question pertained to forest fires. Most of which, I believe, are triggered by lighting strikes. And I think a bolt of lighting could probably start a fire with very little oxygen. So as far as forest fires are concerned, I think the question isn't so much about starting the fire as it is sustaining it.

    It's further complicated by the fact that as oxygen is reduced, the fire doesn't just go out, it is slowed.

    Frankly, I think the lower limit of oxygen needed for wood to burn is quite less then that needed for aerobic organisms to breathe. Cut the oxygen level too low and you'll have a bunch of dead trees burning slowly.
     
  25. Dec 14, 2003 #24
    Mmm, I realize that, it just seems that if you understand all this stuff which is so far beyond what the average joe can even begin to imagine, that how much o2 you need to light a fire would be fairly common knoweldge, I guess I was wrong.

    I didn't say anything about forest fires, i referenced the rainforest as an o2 source, sorry if that somehow got misconstrued.

    So bassically we'd all be dead before lighting fires became a problem?
     
  26. Dec 14, 2003 #25
    That seems to contradict what chroot said, unless I misunderstood one or both of you, or my assumptions about mountain climbing are wrong.

    As understood:
    It's not disputed that tehre's approx 21% o2 in the air.

    Chroot said you need 16 atmosphere's partial pressure of o2 to stay concious.

    You're saying that there's 50% atmospheres partial pressure 5 miles up, which means that there's really only about 10.5% atmospheres partial pressure of o2.

    I know mountain climbers take o2 tanks with them, but i didn't think they are constantly using them, and I'm pretty sure I recently saw photos of everest climbers who were supposed to be about 16,000+ feet up with no o2 masks on doing work.


    So, where am I, you or chroot wrong?
     
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