How to calculate the size of an explosion?

  1. I'm studying a photo of a jet crash and it's subsequent cloud plume. I'm calculating that the cloud is 1000 meters wide and 7-800 meters tall, with the altitude of the cloud hitting maybe 900-1000 meters.

    Is there anyway to determine if this cloud is too big to have been made by a 757 carrying approx. 9-10,000 gallons (not pounds) of jetfuel? If not, what amount of TNT might produce such a cloud?

    Any help at all would be appreciated. Thank you for your time.
  2. jcsd
  3. Astronuc

    Staff: Mentor

    Well the simplest way would be to calculate the volume of the vapor produced by vaporizing 10,000 gallons of jet fuel. Ignition (combustion) would probably increase that volume by about an order of magnitude, just by converting one molcule of dodecane (or naphthalene) to CO2 and H2O, even without the thermal energy released.
  4. Calculating explosion

    Thanks for responding, but have to tell you that I've got no idea how to do this. I'm not a student of physics, I just came on here figuring I'd ask people who knew more about these things than I did. Is there a layman's way to calculate this?

    Thanks for your time.
  5. russ_watters

    Staff: Mentor

    800 meters? No airplane crash or conventional bomb alone will produce a cloud 800 meters across.

    How high or far a continuous fire's smoke will go is mostly a matter of weather.
    Last edited: Aug 9, 2006
  6. FredGarvin

    FredGarvin 5,084
    Science Advisor

    Russ beat me to it. What was the weather like? What kind of winds were in the area? Convective currents could have carried to top of the plume to very high heights which has nothing to do with the source.
  7. Well, here's what I'm trying to determine. A photograph was taken of Flight 93's mushroom cloud, and you'll see it here:

    There seems to be some discussion about whether or not this image is real or a crock. As a professional image retoucher (Photoshop as a day job), I know that pasting in a cloud on a clear blue sky is virtually impossible to pull of seamlessly. However, I cannot inspect the master file so I have to ask questions based on other known quantities:

    1. The plane may have had approximately 10,000 gallons of fuel on board as it was a cross country flight, and it carried a capacity for 11,500 gallons.

    2. The point at which the photo was taken is a known, the crash site is a known, so the distance between the two is known. So by graphing out a pair of vectors originating from the camera, to the edges of the cloud (using the two barns on either side of the cloud as reference points,) the cloud seems to be about 600-800 meters wide, if you account for a little wind and intertia from the blast moving the cloud southeasterly by the time the photo was taken.

    (See the Google earth jpg here:

    So, I'm trying to determine if 10,000 gallons of jet fuel could blow up and form a cloud this big. I thought physicists might offer some sound ideas.

    By the way...would that be Fred Garvin....Male Prostitute?
  8. Bystander

    Bystander 4,077
    Science Advisor
    Homework Helper
    Gold Member

    If you'll notice the plume of hot air, 'bout 1/4 the width of the cloud rising vertically from the ground to the cloud, you'll deduce that not all the fuel went to producing black smoke --- there's a nice hot fire on the ground behind the trees.
  9. I'm not sure I'm following you. You can tell there's hot air rising from a fire onthe ground, behind the trees, from the shape of the bottom of the cloud?
  10. Bystander

    Bystander 4,077
    Science Advisor
    Homework Helper
    Gold Member

    The small white structure in the center of the picture --- there's a narrow plume of smoke directly above it --- that plume is just within the right-hand boundary of the hot air plume. The "notch" in the tree line above the white structure --- move to the high point on the left --- one cursor width to the left of that is the left hand boundary of the hot air plume. It remains at constant width all the way up and through the black cloud to the top of the picture.

    Is it a "large" cloud for 10k gal.? No.
  11. russ_watters

    Staff: Mentor

    Good enough.

    Sorry, Buckwheat Jones, we don't entertain conspiracy theory here.
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