[hankw]

Well, here is a question. How much explosive (take your pick) do you estimate [edited: we are not giving estimates for blowing up one floor of a building]? I know it was a steel frame because some columns stuck up out of the rubble. I could use this estimate to see how off i am and then try to match the difference with visual clues from the video. At least i can learn something from this exercise by explaining the descrepencies.

Thanks
Hank

[hmx9123]

First, we are not going to answer questions about how much explosive is needed to blow up a steel framed building.  That is going a bit too far.

When i refer to high temperature, i really mean the explosive had a high melting point. RDX melts at 205C and HMX melts at 285C. They can withstand the temperature of fire without premature detonation or failing. Add fire proofing and they can withstand hotter temperatures. This is why i don't think any other explosive was used in the building collapse.

As Borek noted, this makes no sense.  There is no melting going on.  No one spread gasoline throughout the building, lit it, and then blew the building up.  Unless you're trying to figure out some whacked out theory on the WTC explosion, you're very confused.

Borek, it's not the brisance that is the thing with concrete, it's just that concrete is a very strange material.  It has a high compressive strength, but a low refraction strength, so it can shatter, but only for less brisant explosives.  The brisant ones pass a shockwave through the material too quickly to have the rarefraction shatter it.  Yes, HMX or RDX will break concrete, but not nearly as effectilvely as TNT.  It doesn't have to do with the explosive being 'too good' or turning things to dust.  Mining is done with ANFO because it's cheap, not because of brisance.  Anyway, that's about as much as I want to say on that topic.

If you want to continue going on about the cloud, that's fine, but don't trust internet sources.  They are generally full of crap.  Look for a real book, either on Amazon or at a library.

[hankw]

hmx9123,

I sincerely apologize. I did not mean to turn this thread into a personality thing. As you can guess, i am a newbie to science and don't know a whole lot about explosives. I consulted the forums because the problem i am working on is starting to go beyond my capabilities. Maybe i cannot solve this problem, or it will get too hard. Learning that a problem cannot be solved is part of the learning experience. This is the first reverse engineering exercise i have done. If it deadends, no biggie.

Anyways i appreciate the help that has been given so far. I will take it from here. I have determined that i need to calculate the following items in order to infer the quantity of explosives. Any additions you can suggest?

Calculate:
-Volume of gas produced by explosives (calculated)
-Volume of the produced gas heated up by explosives (calculated)
-Volume of the original floor air heated up by explosives (working on)
-Volume of air produced by explosion detonation velocity (?) (not calculted yet- is this a real volume contributor? how do i measure?)

I have found from the internet a demolition that gives details on quantity of explosives used. I will use this data to estimate how much explosive might be used to collapse a certain floor area. This way i can check my estimates to see how far off they are and maybe search out other factors that might account for the volume descrepency. I guess in a sense i am creating a model of the demolition?

http://www.controlled-demolition.com/default.asp?reqLocId=7&reqItemId=20030225133807

To clarify my comments about HMX being "too good" and "dust". In my internet search i have read things similar to the following: "The reason [another "slow" explosive called ANFO is] used in mining [versus RDX or HMX] is because it has a slower reaction rate, producing gas and shockwaves that shove rather than shatter." I believe this is corroborated by the Cooper book you suggested earlier.

Hank

[Borek]

It is my feeling that we have told you several times between lines that your approach (while interesting as an idea) leads nowhere due to number of factors that can't be properly accounted for.

Look at the pictures shown on the page you have just quoted.

The only dust clouds produced by the explosives are small grey spots on the second picture (counting from the left). Everything else is just a dust produced by falling inside walls blown away from the inside of the building during collapse and it has nothing to do with the amount of explosives. It is probably much better correlated with the building cubature.

Tha bulding was told to be about 2.2 mil square feet, assuming 9 feet for a level gives total cubature of about 6*10⁵ m³ (which is probably underestimated). 2700 pounds of explosives (assuming 1 m³ of gases per kg of explosives) gives about 1300 cubic metres of gases. It is about 2‰ only, orders below precision of your measurements and calculations.

Let me put this straight this time: your approach leads nowhere.

[hmx9123]

"The reason [another "slow" explosive called ANFO is] used in mining [versus RDX or HMX] is because it has a slower reaction rate, producing gas and shockwaves that shove rather than shatter." I believe this is corroborated by the Cooper book you suggested earlier.

This is essentially correct, as brisance is shattering power, and it is measured in detonation velocity.  However, in concrete, higher velocity explosives don't give as good of breakup.  It's weird.  Rocks, I'm not for sure about; I do know that even if ANFO is wanted for its slower V_det it's definitely wanted for its price.

The problem with trying to figure out heated gas, etc., is that you are pushing all that air in the building out of the way, and that compresses it.  Personally, I think it's a fairly complicated fluid dynamics problem with the gaseous friction of the compressed air on the undisturbed air, etc.  Regardless of what the equation is, you'd be much better off starting with something like cuprous acetlyide, where you know that no gasses are produced, so you don't have to worry about that, and then figure out how much air is moved from the explosion.  It is a very complicated issue.

Another book to check out is: Numerical Modelling of Explosions or something to that effect.  It's on Amazon, too.  You need to really be up on your math to understand that, though, as it's mostly calculus.  However, it does go into detail on what you're talking about.  I read through it, found out it wasn't what I was looking for, and never purchased it.  The Cooper book is enough for me.  Buy books.  Seriously, it's the only way you're going to be satisfied with the answer.

[hankw]

Borek,

I understand what you are saying. I would not pursue this if i was not confident that the air volume from explosives could be measured. Even if i am wrong, I am learning substantial things in Chemistry. Thank you! Learning was the object tackling this problem, not to get a definitive answer. I hope this helps your understanding.


hmx9123,

Thanks for the book suggestion. I may learn some things eventhough i may not be able to follow all the math.

Since my last post i have learned how to calculate bursting pressure for explosives. Basically, you use a combination of temperature, detonation velocity, and the gammas for gases and water. One then can calculate pressure at a distance and then infer air volume. Not all of this is clear to me yet at this point. Let me ask, does  this bursting pressure create its own air volume or is it just a combination of factors 1 and 2 below? That i am not too sure about.

-Volume of gas produced by explosives (calculated)
-Volume of the produced gas heated up by explosives (calculated)
-Volume of the original floor air heated up by explosives (working on)
-Volume of air produced by explosion detonation velocity/ bursting pressure (working on)

I realize that i am starting to get into some hevy-duty theromodynamics. But hey, it is a fun ride! I'm learning fast!

Thanks
Hank

[hmx9123]

If you're talking about what I think you're talking about, then it's just 1 and 2.  Again, this is getting away from my area of expertise--it's more engineering and physics.

I have one other suggestion, too, and that is not to use the building for your first calculation.  Even if the dust from the building gave you air volume, which is doesn't, you would still have a lot of complicating factors to work through.  My suggestion is to get a video filmed in slow motion of a high explosive going off on a desert floor somewhere that you can see the shockwave.  There is a great picture of it on the video 'Kaboom!' (available from PBS) and there used to be some from the New Mexico Energetic Materials Research and Testing Center (http://www.emrtc.nmt.edu/).  This would simplify your problem, as you can see a hemispherical shockwave and accurately calculate the volume based on that to validate your more complicated calculations.  Then move on to the building.  It's like your a beginning mountain climber and you want to tackle K2 your first day out.  Slow down a bit.

[hankw]

hmx9123,

You are one step ahead of me! I just changed the problem to only concentrate on the air volume an explosion produces. Since the demolition problem was growing in complexity i chopped it down.

For the modeling, it seems one wants to calculate an initial sphere of heat, volume, and pressure at the time of the reaction, and then extend that sphere outwards to find air volume. Most of this problem is defintely physics, but i needed the chemistry help to get where i am. I learned some practical things about explosives from you folks. I appreciate it!

Hank

[hmx9123]

Good luck and let us know how things turn out!

[AndersHoveland]

https://sites.google.com/site/ecpreparation/dntz

here is a site about explosive chemistry, with a hefty dose of advanced chemistry  

...or even a whole forum for those so inclined:
http://energetic.proboards.com/index.cgi?