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How Much Wood to Equal An Atomic Bomb?

Post in 'The Wood Shed' started by madrone, Dec 31, 2008.

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  1. madrone

    madrone Minister of Fire

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    http://everything2.com/e2node/How much firewood equals an atomic bomb?

    Link won't work correctly...here's the text:
    (Advice on linking anyone? I don't want to violate copyright...)

    "As some people have pointed out, news reports in this country often give areas in two main forms: football fields and New Jersey. And along the same lines, many energetic reactions (hurricanes, volcanoes, comets smashing into Jupiter are given in terms of atomic bomb yields. This is often given in terms of the bomb that destroyed Hiroshima, which is, of course, by today's standards, a rather small atomic bomb. But it is a good measurement anyway.

    What if instead of measuring the impact of a mass extinction event in terms of atom bombs, we measured something seemingly smaller and closer to home? This was the question that led me to ask: how much firewood would you need to burn, to equal the explosion of a smaller fission bomb? For entertainments sake, ask yourself this question, write down your answer. You might want to ask some other people and see what they answer. How much normal, innocent firewood (you probably have some lying around) would you need to burn to equal an event able to vaporize people and knock down buildings? It might seem, at first, to be an astronomical amount.

    But let us look at the chemistry, physics and arithmetic of it. Much of this math will be rough, but we are assuming some perfectly spherical cows. The explosion that destroyed Hiroshima was measured at 15,000 tons of TNT. TNT has a lot of explosive energy, but that energy is not on a scale different than the combustion of any other organic substance. TNT actually has, per gram, the same energy potential as any fat or oil. (It just explodes instead of combusts). Wood, of course, is not made of fat, it is mostly made of carbohydrate, which is in effect half oxidized already, meaning it has roughly half the energy of a fat. (Of course, wood can also include water and ash, but we are leaving those out of our calculations.) So to equal the explosive power of 15,000 tons of TNT, we would need about 30,000 tons of wood.

    How much is 30,000 tons of wood? In terms of volume, it could be a wide range, since wood varies widely in density. However, for the easy of computation, lets assume that wood is exactly the density of water. That means that 30,000 tons of wood would equal 30,000 cubic meters. To get the solution to that, you just take the cube root of 30,000, which turns out to be around 30 meters.

    This means that the pile of firewood needed to equal an atomic bomb yield that could destroy a major city would need to be around 100 feet on each side. This is much less massive than most people would guess.

    Some readers might be wondering, at this point, if I cheated in my figures. And in certain ways, I did: for one thing, the energy of combustion is not just in the wood, but in the air that it reacts with (how much air it would take to totally oxidize this pile is left as an exercise to the reader). And of course, you can't stack wood as a totally solid pile. Even if you had solid blocks of wood, the nature of combustion means that they need surface area exposed. In addition, some firewood might have much less than half the caloric energy of an oil, and some of it might be much less dense than water. And of course, all of it won't burn, even in a hot fire.

    Of course, the square-cube relation can overcome many of these objections. If we move that pile from 30 to 40 meters on a side, we have more than doubled its volume, and that is enough to make up for the shortcomings of our spherical cows.

    The real reason that this answer might seem counter-intuitive is just that the firewood, while it will release a lot of energy, will release it rather slowly. Even in a very fast fire, it would take minutes or hours instead of microseconds for the energy to be released, and it would mostly be released in the form of thermal disorder and infrared radiation, instead of in the form of a kinetic shock wave and very high intensity radiation. The natural world isn't less energetic than the technological world, just slower.

    Further variations upon this theme can be done at the leisure of the reader: figure out firewood for everything from the Tsar Bomba to the smallest tactical nuclear weapon, the Davy Crockett. What size nuclear weapon would you get if you lit the General Sherman redwood tree on fire. (Don't actually try to find out empirically). What fraction of the world's nuclear article could be found in the biological energy of a cubic kilometer of ocean. All of these are, if nothing else, a fun way to play around with math. "

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  2. LLigetfa

    LLigetfa Minister of Fire

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  3. karri0n

    karri0n New Member

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    It's because you can't uses spaces in a url or filename without delving into the realm of ASCII codes and such. people should just follow web standards in thier url's and it wouldnt be an issue. Not the board's fault, but the article author's website. If you really need to get there with a ling and can't copy/paste, replace every space with
  4. Kilted

    Kilted Member

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    Come to think of it. Considering how much heat I get out of one good size log in my woodstove I would not want all that energy released in a microsecond. That would probably leave a pretty good sized hole in the house.

    -- Brandy
  5. LLigetfa

    LLigetfa Minister of Fire

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    Actually it is cuz it strips out the ASCII codes. Lemme see if code tags will preserve them.
    Code:
    http://everything2.com/e2node/How much firewood equals an atomic bomb?
    {edit}nope - not even code tags... what a stupid, stupid board.
    what about pre tags?
    nope, I'll try hiding them in bold tags
    http://everything2.com/e2node/How%20much%20firewood%20equals%20an%20atomic%20bomb%3F
  6. roac

    roac New Member

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    Or just use this.

    http://tinyurl.com/8em43d
  7. LLigetfa

    LLigetfa Minister of Fire

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  8. Corey

    Corey Minister of Fire

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    Interesting reading and true - just off the top of my head, I would have suspected even bigger stack of firewood would have been required to generate the same energy. Though the really amazing part to me is not how much firewood was required, but what a minute trace amount of uranium was actually reacted.

    By most accounts, the Hiroshima bomb, "Little Boy" contained a 64 kg of uranium core, of which 0.7 kg underwent nuclear fission with a mass only 0.6 g actually transformed into energy (a single penny weighs a little over 2 grams!) . So burning 30,000 tons of firewood = 0.6 grams of matter transformed to energy through the old E=MC^2 equation. If we could just find an efficient M to E reactor, your yearly home heating needs could literally be met with the energy in a couple grains of salt!
  9. Adios Pantalones

    Adios Pantalones Minister of Fire

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    If you look for the classic grill lighting using pure oxygen- then it helps one to think about releasing energy quickly from something that normally burns slowly. TNT contains all of the oxygen required to combust the included carbon fuel, and it is in the same molecule as the carbon- and so it reacts very quickly.
  10. SaratogaJJ

    SaratogaJJ New Member

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    Interesting question, so I approached this from a slightly different angle, and got slightly different values.

    One kiloton of TNT is 4.184x10^12 Joules. (http://en.wikipedia.org/wiki/TNT_equivalent)

    Accordingly, the 15-kiloton Hiroshima bomb equals about 6.276 x 10^13 Joules of energy.

    Converted into BTU's, this equals approximately 59.5 billion BTU's.

    Utilizing red oak as a benchmark, which contains 24 million BTU's per cord, you would need approximately 2,478 cords of red oak to obtain the same amount of energy that is contained in a 15-kiloton atomic bomb.

    At 128 cubic feet per cord, 2,478 cords equals 317,184 cubic feet of wood. Converted into cubic meters, I get 8,981. This equals about 21 meters per side of the cube.

    Is there a discrepancy between our calculations? Or my interpretation of the data? The difference between a 21 meter cube and a 30 meter cube is pretty significant.
  11. Corey

    Corey Minister of Fire

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    Adios - you're right...it all has to do with the speed at which the energy is delivered...kind of like falling off a roof versus climbing down a ladder. Interesting you mention the TNT. Some old figures I have laying around : gasoline/air flame speed (which we usually think of as a pretty big 'BOOM') is about 0.34 meters per second....acetylene in pure oxygen can get up around 25 m/s...TNT detonation is about 7,000 meters per second!

    Saratoga - It seems the original article was using several basic assumptions and giving the "benefit of the doubt" or going conservatively larger on each one. Your route seems to be more direct, and assumes a fairly decent hardwood (oak).
  12. free75degrees

    free75degrees New Member

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    So I burn the equivalent of one nuclear bomb every 1500 years or so.
  13. madrone

    madrone Minister of Fire

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    Thanks guys, I learnted something.
  14. EatenByLimestone

    EatenByLimestone Minister of Fire

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    Now lets look at the yellowstone fires in 1988. "On the worst single day, August 20, 1988, tremendous winds pushed fire across more than 150,000 acres."

    "Ecosystemwide, about 1.2 million acres was scorched; 793,000 (about 36%) of the park's 2,221,800 acres were burned."



    http://www.yellowstoneparknet.com/history/fires.php


    How big of a pile of wood would 150,000 acres make?


    Matt
  15. SaratogaJJ

    SaratogaJJ New Member

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    Wow, lots of variables to consider there, so you would have to begin with lots of assumptions, or begin with more data points.

    How far apart are the trees spaced? How tall is the average tree? Are you assuming 150k acres of uniformly dense forest?
  16. EatenByLimestone

    EatenByLimestone Minister of Fire

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    When I saw the area in '97 there was mostly small pines with fairly close spacing. If that was the makeup of the mature forest pre fire I don't know. Anybody from Wyoming care to chime in?

    http://www.livingwilderness.com/landscape/fierytree.html

    The bottom of this picture looks like the trees are fairly close together.

    Tree types of the southern Rockies:

    http://home.earthlink.net/~swier/RkyMtnTrees.html

    Matt

    EDIT: Yellowstone had all types of topography. I doubt it was all uniform forest, but I doubt the fire lingered in the spots that were grassland or rocky.
  17. SaratogaJJ

    SaratogaJJ New Member

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    Essentially, I think the number you are looking for is a simple derivation from the base unit of "cords per acre."

    Typing in that phrase on Google yields a bunch of different results.

    I found a useful link to an older publication called "The Farm Woodlot: A Handbook of Forestry for the Farmer and Student of Agriculture," published in 1914.

    The estimates range from anywhere between 25 to 60 cords per acre in the New England states, up to nearly 300 to 600(!) cords per acre in Oregon.

    The Society of American Foresters cites a 2000 forest inventory in Vermont, in which they estimate commercial timberland yields about 26 cords per acre in the year 1997. (Interestingly, this is a substantial increase, from only 14.5 cords/acre in 1966.)

    So...the answer to your question, like so many things in life is, "it depends." Using that recent figure from Vermont, 150k acres would yield about 3.9 million cords.
  18. Der Fuirmeister

    Der Fuirmeister Member

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    One grain of salt..............never mind the green glow from the basement.
  19. MaineMike100

    MaineMike100 Member

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    Yes, but you get better "mileage" out of your wood with a gasifier. Those of us with older technology would go through one bomb about every 750 years.
  20. Beanscoot

    Beanscoot Member

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    "TNT actually has, per gram, the same energy potential as any fat or oil."

    Not so. As Adios pointed out, the TNT contains its own oxygen for combustion, whereas hydrocarbons like gasoline and diesel fuel have virtually none (ignoring modern "reformulated" gasoline). So just for approximation without getting into the molecular weights, assume TNT has about half the energy per pound as does petroleum. This is why Saratoga's calculations came up with a much smaller amount of wood.
  21. leaf4952

    leaf4952 Member

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    OMG !
    Shouldn't this be under the catagory of "The Green Room" under: alternative ?
    Whether it be functional ideas or pure conjecture ?
  22. leaf4952

    leaf4952 Member

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    YOU GUYS ARE WHACKED !
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