Under construction!
Post edited June 8th, 2012: References are now numbered; added reference [5]; added "Technical data" and "Observations in video [5]"
In this post, I will try to examine 9/11 truther claims that explosives may have been planted and used to demolish skyscrapers in New York by comparing the events there with what happens in real implosions using high explosives by building demolition experts. I will try to assess the minimum requirements to rig the towers (how much of explosives had to be used, how many charges, how large would those charges have to be, how much and what kind of work must be done beforehand to install these charges, etc.), and then see if the various claims and observations put forward in favour of explosives use can be explained this way at all, or would explain the events of 9/11 better than the commonly accepted theory of structural failure due to fires and plane impacts.
In particular, I want to assess if any truther theory exists, or is even possible, that would explain all their observations.
Some 9/11 truthers claim, or suggest, that explosives were, or may have been, used to bring down the twin towers, or building 7, or all. They base this claim on assertions like these:
- The collapses looked like explosive controlled demolitions
- Witnesses heard "explosions" at various times before the collapses, or even during
- Lots of concrete was pulverized in mid-air
- Large pieces of steel were ejected laterally at significant speeds
- There was not enough energy available to turn all of the buildings into fine rubble and dust, so additional energy must have come from explosives or other kinds of weapons
- Fires (and plane crashes) alone were not sufficient to cause collapse initiation
- The twin towers could not have collapsed all the way to the ground without the help of explosives below the fire/collapse initiation zones
- High-speed ejections of dust were observed below the collapse fronts at the twin towers
- Freefall acceleration of collapse is characteristic for CD
- Symmetry of collapse is characteristic for CD
Some references to real CDs of highrise buildings
Case study A) The Landmark Tower in Fort Worth, Tx, CDed in 2006:
References
[1] D.H. Griffin of Texas, Inc.: A talented team of demolition experts "blow down" Fort Worth's Landmark Tower. (PDF)
[2] D.H. Griffin of Texas, Inc.: Video and photos
[3] A fact sheet
[4] One of many youtube videos, that shows how loud the charges were.
[5] A video shot from 0.4 miles away (2000 feet, 650 meters), from location A in this Google Map
Some technical data from [3]
- Address: 200 West 7th Street, Fort Worth, TX 76102
- Roof height: 116 m / 380 ft
- floors above ground: 30
- Width: I estimate 90 feet for each face, perhaps slightly less
Observations in video [5]
23 floors plus mechanical penthouse are visible before collapse initiation, that's about 300 feet. First flash is seen at 1:10 minutes. Man comments on it at 1:11. First explosion is heard at 1:12 (as expected about 2 seconds later, as that is the time sound takes to travel 2000 feet). Explosions continue for 6 seconds, to 1:16. First visible movement at 1:12 (possibly already at the end of 1:11 already,but not sure). Building drops out of sight at 1:17 (after roughly 6 seconds). This corresponds to an average acceleration equivalent to 52% of g - but that is rough and dirty, error margin could easily be +/- 15 or 20%! Still, the Landmark Tower fall at significantly less than freefall!
What one can't fail to notice is that, at a distance of over 600 meters, or 5-6 city blocks, and amid the loud noise of 2 helicopters overhead, the many loud explosions are very clearly heard!
The building leans to the left (west) as it falls. I estimate that the roof has moved laterally as much as half the width of the building (ca. 45 feet / 15 meters) by the time it drops behind the overpass. This was by design - reference [1]: "The implosion was designed so that the building would fall into the two- level basement and into trenches dug on the north and west sides of the structure.". The Landmark Tower collapse was far from symmetric!
Some crude calculations
Potential energy (gravity)
I consider all estimates that follow to be conservative, that is, if I am wrong, the results would shift in a direction that is unfavourable to many truther standard arguments.
The Landmark, at about 115m high and 30m by 30m wide, had a volume of about 100,000m3. Elsewhere, I have argued with good reason that an office highrise would have 1/6 the average density of water, which would make it swim like a large steel ship, or 170kg/m3. So I estimate the total mass of the Landmark to be about m=17,000,000kg.
The height of the building was 115m, but its center of mass would be at most at 50% that height, more probably around 41% of 115m, or h=47m
Potential energy of the building, that was mostly released during the collapse, therefore is
E = m*h*g = 17,000,000kg * 47m * 9.8m/s2 = 7,830,200,000J, or rounded 7,830MJ
Chemical energy (explosives)
To bring down the Landmark, they used "only 364 pounds, consisting of 198 pounds of 60-percent nitroglycerine-based gel in 1-1/4 inch sticks, and 166 pounds of RDX (a C-4 derivative)" [1]. That's 53.9kg of pure nitroglycerine and 75kg of a C-4-like explosive.
According to Wikipedia, nitroglycerin has a molar mass of 227g/mol and a standard enthalpy of combustion of -1.529 MJ/mol. This translates into a chemical energy density of 1.529/0.227 MJ/kg = 6.7MJ/kg. 53.9kg of pure nitroglycerine thus have a chemical energy of 53.9kg * 6.7MJ/kg = 363MJ.
I have no direct reference on the enthalpy/energy density of C-4 or RDX at this moment, but read that it is about 1.125 to 1.25 times as "brisant" as nitroglycerine. An estimate of 7,6MJ/kg is thus not unreasonable (though probably too high; that's a conservative estimate with regard to truther claims). 75kg of this stuff would bring 75kg * 7,6MJ/kg = 570MJ to the demolition.
Total chemical energy of the explosives is about 363MJ + 570MJ = 933MJ.
(I assumed that a preparation with 60% nitroglycerine would have only 60% the energy of pure stuff; if I assume 100%, then the total chemical energy raises to about 1175MJ).
Comparison Potential vs. chemical energy (explosives)
The total energy available to cause all the destruction at the Landmark Tower demolition site was 7,830MJ (from gravity) + 933MJ(from explosives) = 8,763MJ.
Explosives provided 933/8763 = 11% (rounded) of the total energy, gravity 89%.
