Sunday, June 26, 2011

Chemical energy of the combustible office contents

The following is a first draft. I have not yet looked up the numbers in the NIST report, I only googled some numbers, and provide ballpark figures for others.

Each of the office buildings was packed with combustibles: paper, wooden furniture, plastics from computers, cables, carpets, etc. Even the bodies of the humans that died in the towers provided combustible material. There were basically two phases when a portion of all these combustibles burned:

  1. Open flames in office fire, after plane crash and before building collapse
  2. Smoldering underground fires after the collapse

The relevance of the first is to show how much heat was potentially available to heat up and thus damage the steel structure near the impact floors. The relevance of the second is to show why the debris could have burned for so long, created pockets of heat, even melt metals (other than steel, of course), etc. None of this will lead to exact conclusions. My goal is more to give 9/11 truthers a feel for the sheer (potential) magnitude of the fires. Because we again and again find the assertion that fires could not do much damage, and that explosives could do so much more.

First some links:

And some numbers (assumptions), gathered from the links

  • Combustibles per quare meter: 20kg/m2 (4 pounds per square foot, diveded by (0.3m/ft)2, multiplied with 0.45kg/lb. That is a very low value, compared to most office buildings, where a range from 45 to 20 lb/sft is often assumed, due to materials in partition walls and more furniture)
  • Office space total in twin towers (both combined): 400,000m2
  • Average energy density of office combustibles: 10MJ/kg (this is my own, very conservative, estimate; almost all organic materials rate higher; household waste rates around 8MJ/kg, but it contains a great deal of non-combustibles. The number for paper is about 15, plastics range from 20 to 40)

With these numbers as assumptions, we can derive the following through easy calculation:

  • Total mass of combustibles: 8,000,000kg (20kg/m2 * 400,000m2)
  • Mass of combustibles per floor: 37,000kg (8,000,000kg / 214 office floors; maybe there were some less, or slightly more. I rounded to the nearest 1000)
  • Total energy of combustibles: 80,000,000MJ (8,000,000kg * 10MJ/kg)
  • Energy per floor: 370,000MJ

The total energy (80,000GW, or 80TW) is roughly that of

  • 500,000 gallons of fuel, enough for my car to drive around the earth 700 times
  • 20 kilotons of TNT, pretty much equal to the release of the atomic bomb ("Fat Man") that destroyed Nagasaki to end WW2
  • the output of a large (1,000MW) block of a modern nuclear reactor in one day

I recall that the debris on Ground Zero burned for 99 day. That's 8.5 million seconds. So the average power was close to 10MW - 1% of a nuclear power plant, or just under the average for a large on-shore wind turbine. Enough to provide a town of 8,000 with electricity for housholds, industry and public infrastructure (in Germany; other countries may use more or less electricity per inhabitant).

Saturday, June 11, 2011

Controlled Demolition using Explosives: Some references

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:

  1. The collapses looked like explosive controlled demolitions
  2. Witnesses heard "explosions" at various times before the collapses, or even during
  3. Lots of concrete was pulverized in mid-air
  4. Large pieces of steel were ejected laterally at significant speeds
  5. 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
  6. Fires (and plane crashes) alone were not sufficient to cause collapse initiation
  7. The twin towers could not have collapsed all the way to the ground without the help of explosives below the fire/collapse initiation zones
  8. High-speed ejections of dust were observed below the collapse fronts at the twin towers
  9. Freefall acceleration of collapse is characteristic for CD
  10. 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%.

Monday, April 25, 2011

License Lookup for Professional Engineers in US states

Others:

Friday, September 10, 2010

Chemical energy of the jet fuel

Accoring to Wikipedia, which claims to quote NIST, either plane hitting the two WTC towers contained about 10,000 gallons of jet fuel, or 30,400kg:

According to the estimation in NIST's NCSTAR 1.5, page 58, AA11 carried 30,000kg of jet fuel, and UA175 carried 28,100 kg at the time of impact

http://en.wikipedia.org/wiki/American_Airlines_Flight_11
http://en.wikipedia.org/wiki/United_Airlines_Flight_175

Wikipedia further says about jet fuel:

Specific energy: >42.80 MJ/kg

So, AA11 carried with it fuel which, upon combustion, would this much energy as heat:
Efuel = 30,000kg * 42.8MJ/kg = 1.284 * 1012J

UA175 carried with it fuel which, upon combustion, would this much energy as heat:
Efuel = 28,100kg * 42.8MJ/kg = 1.203 * 1012J

At this time, I haven't found data about how much of that fuel burned outside of the towers and was not availabe to do damage inside.

In addition, each plane carried about 12,000kg of other combustibles (cargo, tires, mail, luggage, cabin materials). Humans are not included. "Other combustibles" generally having somewhere between 10 and 30 MJ/kg energy. For example: Paper about 15, many plastics 25-30. An assumption of 15MJ/kg seems not entirely unreasonable. So each plane put about 180GJ of chemical energy into the towers.

Kinetic energy of flight 175

The kinetic energy (KE) of a moving object is given by the formula

E = 1/2 m * v2

Where, in the case of flight UA 175:

  • m is the mass of the plane: That is, empty mass plus fuel load plus passengers, their baggage, and additional cargo. AA 11 was a Boeing 767-222, which has an operating emtpy weight of 80,130kg and a maximum take-off weight of 142,880kg. Maxium fuel capacity is 63.216l (see Specs at ZAP16.com). Maximum range is 7,300 km. Flight UA171 had 168 passenger seats, but only 56 passengers (33% capacity), plus 9 crew members. 65 people, weighing on average 70kg, have a mass of 4,550kg. For each, luggage, food, drinks and other supplies of 20kg may be added, or 1,300kg. It was scheduled to fly from Boston to Los Angeles, a distance of about 46% of its maximum range. Wikipedia, quoting NIST, states that it carried about 38,000l of fuel - about 60% of maximum fuel capacity, by the time of impact. Jet fuel has a specific weight of about 0.8 kg/l, so 38,000l fuel is about 30,000kg. The total mass of the plabe was thus at least:
    m = 80,130kg + (4,550+1,300)kg + 30,000kg = 115,980kg
    (empty weight + passengers + fuel)
  • v is the velocity of the plane at impact, which was estimated by NIST as 545mph or 243m/s

Using these estimates, the kinetic energy of flight AA11 works out as

Ekin = 1/2 * 115,980kg * (243m/s)2 = 3.42 * 109J

Kinetic energy of Flight 11

The kinetic energy (KE) of a moving object is given by the formula

E = 1/2 m * v2

Where, in the case of flight AA 11:

  • m is the mass of the plane: That is, empty mass plus fuel load plus passengers, their baggage, and additional cargo. AA 11 was a Boeing 767-223ER, which has an operating emtpy weight of 82,380kg and a maximum take-off weight of 179,170kg. Maxium fuel capacity is 90,770l (see Boeing technical specs). Maximum range is 12,195 km. Flight AA11 had 158 passenger seats, but only 81 passengers (51% capacity), plus 11 crew members. 92 passengers, weighing on average 70kg, have a mass of 6,440kg. For each, luggage, food, drinks and other supplies of 20kg may be added, or 1,840kg. It was scheduled to fly from Boston to Los Angeles, a distance of about 30% of its maximum range. Wikipedia, quoting NIST, states that it carried about 38,000l of fuel - about 42% of maximum fuel capacity, by the time of impact. Jet fuel has a specific weight of about 0.8 kg/l, so 38,000l fuel is about 30,000kg. The total mass of the plabe was thus at least:
    m = 82,380kg + (6,440+1,840)kg + 30,000kg = 120,660kg
    (empty weight + passengers + fuel)
  • v is the velocity of the plane at impact, which was estimated by NIST as 750km/h or 208m/s

Using these estimates, the kinetic energy of flight AA11 works out as

Ekin = 1/2 * 120,660kg * (208m/s)2 = 2.61 * 109J

There are, however, other numbers available for mass an velocity: NIST: 443mph = 198m/s, which would lower my estimate to 2.365 * 109J