Anyway, I will drop my beef on this issue to return to the topic at hand:
How to demolish WTC 1 & 2 with minimum chance of detection:
I would add the pyrotechnic agent ammonium perchlorate, NH4ClO4 (AP), to the thermal insulation/fire-protective coating used on the upper floors of WTC 1 & 2.
Ammonium perchlorate, NH4ClO4, is a colorless, odorless, compound that is stable at room temperature. However, when heated to above 300 °C, or subjected to friction or impact, it becomes violently reactive. In fact, ammonium perchlorate is a much-used ingredient in explosives, pyrothechnics and solid propellants such as those used in the space shuttle booster rockets.
The decomposition reactions of ammonium perchlorate are complex and variable: Cl2, HCl, NH3, N2O, NO, N2, H2O and O2 have been consistently observed as major products. The decomposition reaction is highly exothermic, releasing about 2 MJ/kg of heat energy, and is accompanied by the production of about 800 liters/kg of gases. The combustion of ammonium perchlorate in oxygen-rich atmospheres produces a diffusion flame at about 3200 °C
The decomposition of samples of pure ammonium perchlorate at 225 °C is 25 % complete after 4 hours. However, if the ammonium perchlorate is mixed with suitable metal oxide catalysts the decomposition is accelerated. Among the large number of metal oxides that have been investigated as AP decomposition catalysts, such as Al2O3, CaO, Fe2O3 and MnO2, manganese dioxide is found to be by far the most effective.
To complete the set-up of the Towers I would proceed as follows:
Ammonium perchlorate powder, probably containing manganese dioxide and other additives (e.g. Al, HMX, etc.), would be prepared and mixed with a polysulfide binding agent and one or more of the five spray-on fire resistive (thermal insulation) materials used in WTC 1 & 2. These materials are identified in NIST NCSTAR 1-6A as: (1) Blaze-shield Type D, (2) Blaze-shield Type DC/F, (3) Blaze-shield Type II, (4) Monokote MK-5, and (5) Vermiculite aggregate plaster. In order to determine where and when these material could have been applied to surfaces in the Twin Towers we need to consider the history of the “passive fire protection” practices employed by the New York Port Authority during and after the construction of the towers, starting in 1970 and ending in 2001.
On April 13, 1970, New York City issued a ban on the use of all sprayed on thermal insulations containing asbestos, the notorious fibrous silicate mineral that was a major component of Blaze-shield Type D. The use of asbestos-containing insulation was discontinued at this time at the 38th floor of WTC 1. In February 1975, a fire occurred in WTC 1 that affected floors 9 to 19 and led to a review of the adequacy of the existing thermal insulation in the entire WTC. The need to upgrade the passive fire protection in the Twin Towers was finally addressed in 1995 when, after yet another study, it was decided to apply a 1½ inch thickness of an asbestos-free spray-on mineral fiber fire protection material to selected steel surfaces. Thus, between 1995 and 2001, thermal protection was upgraded specifically on 18 floors in WTC 1, including floors 92 to 100 and 102; and on 13 floors in WTC 2 including floors 77, 78, 88, 89, 92 and 97. (See NIST NCSTAR 1-6A page xxxvii). This is when the AP-spiked insulation could have been substituted for the authentic material. Very few people would need to be "in the know". The guys doing the spraying could be quite unaware of what they were really doing!
A reasonable estimate of how much insulation was applied in the late 1990s would be be a thickness of 2 cm over an effective area of 2500 m2 or 50 m3 per floor. If we assume the material had a density of 400 kg/m3 there would have been 20 tonnes of thermal protection per floor.
It should be noted that the specific floor selection was made on the basis of the need to apply fire protection material to a particular area. Thus protection would have been sprayed on areas that were known to be vulnerable to fire damage. However, in my dastardly plan, the fire protector would be, in fact, a fire accelerant or pyrotechnic. Given the fact that upgrading of the passive fire protection of WTC 1 & 2 was an on-going project throughout the late 1990s, a deadly pyrotechnic coating could have been applied almost anywhere and at any time during this period. If we assume that the normal cement-based material was “spiked” with 25 wt.% of our pyrotechnic mixture, up to 5 tonnes of ammonium perchlorate could have been sprayed onto a designated floor. Furthermore, once applied to a particular floor, the coating would have remained undisturbed, unnoticed, and with no loss of potency, until it was triggered by the events of September 11th 2001.
After the aircraft hit the towers, and started jet fuel fires, the exothermic decomposition of an AP “spiked” coating, initiated at ~ 300 °C, would have had catastrophic consequences to the integrity of the buildings at or above the impact zones in each tower. The most detrimental consequences of the presence of kilogram quantities of the energy-rich oxidizing agent ammonium perchlorate would have been in fire-ravaged areas of WTC 1 & 2 where rapid “shock-heating” of floor assemblies would have lead to:
(i) Differential thermal expansion causing buckling or fracture of floor elements
(ii) Complete collapse of entire floor sections
(iii) Explosive spalling and “powderizing” of the concrete.
(iv) Melting of the corrugated steel floor pans
The Towers would have collapsed pretty much "as observed" leaving no residues, wiring, fuses, etc. NIST would have completed its study pretty much as it did, and no one would be any the wiser....