# Possible Use of Thermite to Melt Sections of WTC

Calculations on the Possible Use of Thermite

to Melt Sections of the WTC Core Columns

by D. P. Grimmer

Version 1.1, June 20th 2004

**Abstract**

Anomalies involving the collapse of WTC buildings on 9-11 are discussed from the perspective of possible controlled demolition implosion rather than of aircraft impact and fuel-fire damage. Considered is the possible use of thermite to melt sections of the columns of the WTC towers inner cores, thus aiding in their collapse. This paper will discuss the structure of the WTC core columns, and estimate the mass of metal to be melted; calculate the sensible and latent heat energy needed for melting this mass; discuss the nature and specific energies of the thermite reaction; estimate the mass and volume of thermite necessary to provide the energies for melting; and discuss the possible locations where such thermite could be placed to cause melting, both internal and external to a core column.

**Prologue**

The motivation for this paper was to apply physical and mathematical analysis to probably the most observed and least ephemeral 9-11 event: the collapses of the WTC towers. Uncounted millions have seen video footage of these collapses (and the later collapse of WTC-7). To an impartial observer, somehow unfamiliar with the 911 events, it would be difficult to distinguish between interspersed videos of the WTC collapses and those of controlled demolitions (particularly if the pre-collapse fire/smoke were digitally removed). In addition to the video evidence and eyewitness accounts of the many squib explosions associated with WTC events, the problem of the collapse of the central cores of the WTC towers remains. These cores were substantial structures unto themselves. They were probably capable of standing on their own (at least for a while), even if the outer tube walls and floors collapsed around them rings-around-a-tube style (assuming the “official? explanations of failed floor joist bolts are to be believed).

Thermite has been proposed as a chemical reactant that is capable of achieving the collapse of the central cores of the WTC towers. The thermite reaction produces great heat, capable of melting steel, and since it does not produce reactant gases, there would not be the high explosive signature of a massive shock wave. It is the rapid production and heating of gas reaction products that causes destructive shock waves from high explosives. The possible use of thermite was analyzed only because other researchers have proposed it and because the properties of the reaction are relatively easy to obtain. Undoubtedly, any number of heat producing, relatively non-explosive reactants that are more sophisticated and compact than thermite exist, but for the purposes of initial analysis, and determining the boundary conditions, it was felt that thermite was a reasonable first choice. Clearly the perpetrators of 911 did not want to leave the explosive signature of a controlled demolition.

The purpose of this paper was thus to put forth a quantitative analysis of various phenomena surrounding the WTC towers? collapses, in order to see what is possible. Because the government authorities have destroyed much of the forensic evidence at the WTC building collapse scene, calculations such those done in this paper must remain speculative. However, the strength of this paper is to show how scientific analysis and critical thinking can show what is possible ? or impossible. Whether or not conventional chemical reactants are sufficiently powerful to achieve column section melting, the outcome is equally valuable scientifically. This is the scientific process, to use quantitative analysis to discard the improbable theory: putting a number on observations makes a great difference (some might say __all__ the difference) in the process of determining what is reality and what is fairy tale.

Introduction

Of the events of 11 September ’01, perhaps the most dramatic were the collapses of the WTC towers. Re-played repeatedly on TV, the images of the collapsing towers and their pyroclastic clouds of debris are seared into our memories.

What immediately struck some observers, this author included, is how much these collapses resembled a controlled demolition. Indeed, this was the first reaction of V. Romero of New Mexico Tech, until he recanted days later [Ref. (1)]. There has been much discussion on the internet of the observed anomalies associated with the WTC building collapses (including the delayed collapse of the unstruck WTC7). Interesting sites can be found at __www.serendipity.li__, __www.americanfreepress.net __, __www.misternet.org__, __www.911-strike.com __, __www.plaguepuppy.net__, __www.whatreallyhappened.com __ and many others ( a google search is always useful).

One site deals directly with aircraft impact and fuel-fire physics [Ref. (2)]. The very anomalous case of the WTC7 building collapse was archived at Ref. (3); especially interesting are the observations by the inspection engineer at WTC7 of evidence for vaporized steel. As always, information about controversial events like 911 must be approached with some caution, and are not to be taken at face value. Careful analysis and appraisal is necessary. The internet has gained a reputation as a refuge of "conspiracy theorists," but recent events (e.g., the falsehoods told by US officials leading up to the Iraq war) have shown that "reputable" media are not to be trusted. They may themselves be regarded as purveyors of "official" conspiracy theories. This present paper hopes to achieve some level of objectivity about a very controversial subject.

(Occasionally, the media slips up. One noted instance is in the case of WTC7 where in a Sept. 2002 PBS documentary “Rebuilding America, A Year at Ground Zero,” Larry Silverstein, the leaseholder of the WTC complex, admitted that he and the NYFD made the decision to “pull? the badly damaged WTC7: i.e., to bring down the building in a controlled demolition [Ref. (14)]. To the author’s knowledge, the major media have yet to comment on Silverstein’s statement that directly refutes the FEMA report on the WTC7 collapse).

Total objectivity is of course impossible. Subjectively, for this author, several subevents of the WTC collapses stand out: the reported seismic spikes associated with the collapses; the observed near free-fall times of collapse; the pyroclastic clouds of debris; and the pools of molten steel found in the basement of the WTC tower complex, steel still warm weeks after 9-11. Analysis of the seismic spikes indicate that the seismic spikes correlate with the collapses themselves rather than any pre-collapse explosion [Ref. (4)].

Calculations done by the author correlated the collapse energies with the seismic signal of explosions at a quarry in the vicinity of the seismic observatory. These calculations indicate that the seismic spikes of the WTC events represent energies close to those of the collapses themselves (see Appendix A for these seismic energy correlation calculations). A sole video clip purported to show, by video image shaking, evidence of a pre-collapse WTC2 explosion is not conclusive. A video with shake-free periods for several minutes before and after collapse is not available. Therefore, wind flutter has not been disproved as a cause of camera shaking. A second video from another perspective is not available to show pre-collapse shaking temporally correlated with the first video. The existence of such a second video from an independent source would make such video evidence more credible [Ref. (5)]. From these observations, the author has concluded that there is no firm evidence of pre-collapse explosions that left seismic signatures.

[A brief note here about the mathematical notation used in this paper: subscripts, superscripts and exotic math symbols have not been used. Unlike most word processor programs, most email formats do not support these fonts. So, for example, ten to the nth power is denoted here by 10+n; the square root of N is SQRT(N); a quantity N with the exponent n (i.e., N to the nth power) is given by N exp(n); an so forth. This was done so individuals can communicate about this paper in any common email format].

The observed near free-fall times of the WTC towers (and WTC7) were a dramatic signature of a controlled demolition. (The articles at __http://members.fortunecity.com/911__ are a valuable resource for presenting and then challenging the "official" explanation for WTC collapses). Measured times are all around 10 seconds, which is close to calculated free-fall time, indicating the tower floors fell without much impediment. They essentially fell into air [Ref. (6)]. The theory put forth by T. Eagar of MIT and other "establishment" engineers is that while no steel members actually melted or failed, the floor assemblies, bolted at their joists to the outer walls and inner core structures, did fail [Ref. (7)]. The floor joists attachment bolts were weakened and gave way, twisting sideways and allowing the initial floor to "unzipper" itself all the way round and collapse to the floor below. The remaining floors then pancaked all the way down. Never mind that floor joist cross-members, placed to resist twisting, and additional support structures were not included in the MIT/FEMA/NOVA calculations and presentations (nor was the inner core collapse mechanism explained at all).

Consider the following: if the pancaking effect caused the total building failure, why is it that no video of either of the WTC collapses shows any sign of stutter between floor collapses, which should have been very apparent especially in the first few floors of collapse when the speed of gravitational collapse was small? Consider also that apologists for the official conspiracy theory propose that 30% of the gravitational collapse energy was necessary to create the pyroclastic cloud of debris: that is, in their own analysis, this energy came out of the gravitational energy. This means that the time of fall would have been slowed further than what was observed. When a body of mass m falls from a height h, acted upon by gravitational acceleration g, it converts its potential energy PE = m x g x h into kinetic energy KE = (1/2) x m x (v exp2). Here h = (1/2) x g x (t exp2), t = time of fall, and v =g x t, where v = velocity. Removal of 30% of the PE to pulverize concrete essentially reduces the amount of energy available from falling, effectively reducing the gravitational acceleration to something less than g.

Substituting, in the above equations we have (1.0 – 0.3) x PE = 0.7 x PE = m x g’ x h, where PE, m and h are as before and g’ = the effective gravitational acceleration. Hence, comparing terms for PE, g’ = 0.7 g. The time of collapse under g’ will also increase. If we let the effective collapse time be t’, then comparing terms for constant h, (1/2) x g x (t exp2) = (1/2) x g’ x (t’ exp2) =

(1/2) x 0.7g x (t’ exp2). Hence, (t exp2) = 0.7 x (t’ exp2), or (t/t’) = SQRT (0.7) = 0.837. Or, t’ = 1.195 t.

Now the observed time t = 10 seconds (a free fall time, the fastest possible time under g = 9.8 m/sec/sec = 32 ft/sec/sec = 32 ft/s exp2). For the cloud debris creation to absorb 30% of the gravitational energy, the observed time of fall would be 10s x 1.195, or almost 12 seconds. This long a collapse time was observed by no one. Clearly, there are serious flaws in the official explanation/conspiracy theory.

The implication from the above is that there were major energy sources other than gravitational involved in the WTC towers collapses. Certainly that is the conclusion of J. Hoffman in his thorough discussion of the north WTC tower dust cloud [Ref. (8)]. By calculating the major sources and sinks observed, particularly the sink of the pyroclastic cloud expansion, Hoffman establishes that a large amount of energy had to be available to drive that expansion, in a (minimum) range of 2,706,000 kWh to 11,724,000 kWh (see his Summary table). Hoffman does not propose an energy source to balance that sink. In Appendix B, an estimate, for discussion purposes only, of the amount of thermite-equivalent to provide this energy source is discussed. It is large, but physically possible.

A discussion of the melted steel found at the base of the WTC complex, not explained by any official, forms the bulk of the remainder of this paper. The following discussion explores the possibility of whether it is possible to get sufficient volume of a relatively slow-reacting chemical compound, like thermite, either on or inside the inner columns to melt a section of them or otherwise weaken them to allow for the inner core to collapse. As Mark Loizeaux of Controlled Demolition, Inc., commenting on the pools of molten steel he observed at the bases of the towers’ elevator shafts, said: "If I were to bring the towers down, I would put explosives in the basement to get the weight of the building to help collapse the structure" [Ref. (9)]. Controlled Demolition, Inc., incidentally was the company contracted to remove the debris from both the WTC and from the 1995 bombing of the Murrah building in OKC. Also, in the 15 December 03 edition of Sam Smith’s Progressive Review [Ref (15)] there is an excellent discussion of the collapse of the WTC buildings from the perspective of professional firefighters. Included is an excerpt of an article by Jim Malott, a San Francisco architect, in the Nov/Dec 2001 issue of Designer/ Builder magazine. Malott states regarding a WTC tower collapse: “The outside of the building did not fail, it did not get hot enough”It was the core that failed.”__ __

To summarize so far: the discussion in the text above and in Appendix A indicates that the energy of the seismic signal (best viewed as a semi-logarithmic plot) and the gravitational collapse are very close to being the same. This coupled with the fact that there is only one short video clip allegedly showing shaking before collapse of one of the towers leads an objective observer to conclude that there is no actual proof that the seismic "spike" signal is nothing more than building collapse. This is not to say that the seismic signal is 100% guaranteed to be non-explosion related, just that there is no firm evidence so far for the alleged massive explosion. That is, this is not an area on which to stake a lot of credence. The seismic event must be regarded as a "red herring" unless a second, longer video showing the same behavior appears.

The free-fall times and pools of molten steel are entirely different matters. They are a matter of public record, observed by many individuals. So we have evidence of molten steel in the basement; the FEMA report saying molten steel was not to blame, just weakened floor joist bolts; collapse times close to free fall; no real record of a massive explosion (although numerous claims of sounds of smaller explosions and observations of demolition squibs). The immediate conjecture supported by direct observation is the following: controlled demolition, characterized by a (relatively) non-explosive, huge energy release necessary to melt (some) steel. M. Rivero of whatreallyhappened.com and others have proposed the use of thermite, familiar to those of us who had the high school chemistry course with an impressive thermite demonstration. So the question arises: can one get enough thermite close enough to melt sections of the inner core columns, as part of a controlled demolition scenario? The following calculations in this paper indeed do show that it is possible (and I stress possible). Until simple chemical reactants like thermite can be discarded there is really no need to invoke the use of highly speculative and sophisticated devices like thermobaric bombs and scalar EM weapons.

Melting of WTC Inner Core Columns

Evidence of molten steel was found at the very base of the WTC towers, and is a matter of public record. This present study is by no means exhaustive. It is intended as a first attempt to test the possibility that the core columns could have been melted by a known chemical compound. Thermite was chosen as the reactive chemical compound because it is well understood, and is used commercially to weld steel parts (e.g. train rail sections in situ). Other more sophisticated chemical compounds with higher energy densities, by mass and/or volume, could be used in future calculations. Broad assumptions will be made, to get rough estimates of relevant parameters.

Structure of WTC Columns and Their Metal Mass

The best on-line discussion resource found for these calculations was at Ref. (10). According to this source the inner core consisted of from 44 to 47 box columns (the exact number and layout is not known; the architectural firm had not released the construction drawings). The dimensions of the columns reduced in size with increasing height, changing to I-beams above the 85th floor. The above website article assumes (generously) that each core box column has the following (average) X-section: 12"wide x 36"deep x 2? thick. ~~ ~~

If w = box column width, d = depth, and t = thickness, then the X-sectional steel area is given by

A = [d x t + (w-2 x t) x t] x 2. For d = 36", t = 2" and w = 12", then

A = [36" x 2" + (12"-2 x 2") x 2] x 2 = 176 in2 = 1.222 ft2.

Floor height was 12ft, so we choose for discussion sake, a 12′ high box column in these calculations. Note that multiple floors could have had thermite-type compounds placed there. Also, no more than a foot portion, rather than a full 12 ft of column would be necessary to collapse that floor. Also, complete melt of a column portion is not necessary to cause collapse. So, per floor, per column there is a steel volume V = 12′ x 1.222 ft2 = 14.67 ft3. Also, note that the internal X-sectional area of a box column is given by

Aint = [d-(2 x t)] x [w- (2 x t)], and the internal volume by Vint = 12′ x [d – (2 x t)] x [w – (2 x t)].

Here, Vint = 12′ x [36"-2 x 2"] x [12"- 2 x 2"]/(144 in2/ft2) = 12′ x 1.778 ft2 = 21.333 ft3.

The internal volumes will be re-examined later as a possible space to place the thermite.

The website also mentions that the largest box columns used at the core bases had the dimensions of 16" wide x 36" deep x 4" thick. It is not known where exactly the molten steel, that puddled in the WTC basement, originated in the towers. The melt could have occurred some what higher in the columns (where "average" box columns would have been), or at the base where the "largest" box columns were. Molten material would flow down the various WTC shafts to the lowest point possible, 6 stories (some 72′) below ground level. Applying the same formulae as above, we have for these "largest" columns, A= [36" x 4" + (16" – 2 x 4") x 4"] x 2 = 352 in2 = 2.444 ft2. Note that this happens to be twice the area as for the "average" box column assumed above. Again, for a 12′ column, V = 12′ x 2.444 ft2 = 29.328 ft3. Also, here, the internal volume is Vint = 12′ x [36′ – 2 x 4"] x [16′ -2 x 4"]/144" = 18.667 ft3.

In summary, we have for a 12 ft. high core box-column, for a

12" wide x 36"deep x 2" wall thickness (hereafter referred to as an "average" box column), that it has 14.67 ft3 = 0.415 m3 volume of steel, and 21.33 ft3 = 0.604 m3 of internal volume; and

16" wide x 36" deep x 4" wall thickness (hereafter referred to as a "largest" box column), that it has 29.328 ft3 = 0.832 m3 of steel and 18.667 ft3 = 0.529 m3 of internal volume.

Sensible and Latent Heat Energies Needed for Melting a Core Column Section

Knowing the volume of steel involved, we next turn our attention to calculating the energy needed to melt a core column section. We decided to use values for the element iron rather than steel for the following pragmatic reasons:

steel is mostly iron (Fe);

whatever steel is chosen, may be the wrong kind and would be contested: Fe is a given and known quantity, whereas there are many steels;

Fe values found were readily available and reasonably self-consistent;

except for stainless steels, the thermal properties of steel are relatively close to Fe, although the mechanical properties may certainly differ more.

For Fe we will use the following values:

Density = 7874 kg/m3

Melting point = 1811 K = 1538 C

Specific heat = 25.1J/mol K = 449 J/kg K = 0.449 kJ/kg K

Latent heart of fusion = 13,800 J/mol = 2.47 x 10+5 J/kg

Latent heat of evaporation = 347,000 J/mol = 6.21 x 10+3 kJ/kg

mol = gm mole equivalent = 0.0558 kg for Fe

For a 12 ft high core Fe column, we have

for the "average" box column, 0.415 m3 x 7874 kg/m3 = 3267.71 kg Fe; and

for the "largest" box column, 0.832 m3 x 7874 kg/m3 = 6551.17 kg Fe.

Taking 300 K as "ambient" temperature on 9-11, then the temperature difference up to the melting point of Fe is given by

1811 K – 300 K = 1511 K (give or take a few degrees K).

Hence, the energy needed to raise a 12 ft high Fe column to its melting point temperature is given by

for an "average" column, 3267.71 kg x 1511 K x 0.449 kJ/kg K = 2.22 x 10+6 kJ; and

for a "largest" column, 6551.17 kg x 1511 K x 0.449 kJ/kg K = 4.44 x 10+6 kJ.

To actually melt the Fe at 1511 K, we need to provide the latent heat of fusion:

for "average" column, 3267.71 kg x 2.47 x 10+2 kJ/kg = 8.07 x 10+5 kJ; and

for "largest" column, 6551.17 kg x 2.47 x 10+2 kJ/kg = 1.62 x 10+6 kJ.

Thus we see that the sensible heat energies involved are almost a factor of 3 times larger than the latent heats.

Hence, for the total amount of energy needed to melt a 12 ft high Fe column, we need:

for "average" box column, (2.22 + 0.81) x 10+6 kJ = 3.03 x 10+6 kJ; and

for "largest" box column, (4.44 + 1.62) x 10+6 kJ = 6.06 x 10+6kJ

Energies of the Thermite Reaction

An iron oxide/aluminum "thermite" mixture consists of 23.7% Al, 74.7% Fe2O3 by weight, in the reaction

Fe2O3 + 2 Al => Al2O3 + 2 Fe + 849 kJ/mol.

Thus, 849 kJ of energy are released for every g-mole-equivalent (mol) of Fe2O3 that reacts with 2 mol of Al.

For Al, with a density of 2.699 g/cm3, there are 26.98 g/mol.

For Fe2O3, with a density of 5.24 g/cm3, there are 159.70 g/mol.

So then, 159.70 g of Fe2O3 + 53.96 g of Al (213.66 g total) produces 849 kJ of energy, or 3.974 kJ/g = 3.974 x 10+3 kJ/kg (Note that this gives the proper % component mixtures by weight).

For an infinitesimally compacted powder mixture, this would occupy a volume of 159.70g x (cm3/5.24 g) + 53.96 g x (cm3/2.699 g) = (30.48 + 20.0) cm3 = 50.48 cm3.

A separate analysis of a CuO/Al thermite mixture (used to weld copper parts) indicates a powder packing fraction of 0.82 (82%) can be achieved. Let’s assume a powder packing fraction of 0.82. Hence, our Fe2O3/Al thermite mixture would occupy not 50.48 cm3, but 61.5 cm3.

Thus the physical density of our densely-packed Fe2O3/Al thermite mixture is

213.66 g/61.5 cm3 = 3.474 g/cm3 = 3.474 x 10+6 g/m3 = 3.474 x 10+3 kg/m3,

and our energy density (per volume) is given by

849 kJ/61.5 cm3 = 13.805 kJ/cm3 = 1.3805 x 10+7 kJ/m3.

Thus to melt a 12 ft high Fe column, we need

for an "average" column, (3.03 x 10+6 kJ)/(3.974 x 10+3 kJ/kg) = 0.7625 x 10+3 kg = 762.5 kg of thermite. This would occupy a volume of 762.5 kg/(3.474 x 10+3 kg/m3) = 0.219 m3. Note that this volume of thermite is less than the internal volume Vint calculated earlier, 0.604 m3. Actually, the internal volume of the "average" box column could be filled with 0.604 m3/0.219 m3 = 2.76 times more than needed to do the job. Alternatively, the column does not require as high a packing density ( i.e. <0.82) and yet be able to load a sufficient charge of thermite mixture to cause melting

for a "largest" column, (6.06 x10+6 kJ)/(3.974 x 10+3 kJ/kg) = 1524.9 kg thermite. This would occupy a volume of 1524.9 kg/(3.974 x 10+3 kg/m3) = 0.439 m3. Note that this volume of thermFite also is less than the earlier calculated Vint = 0.529, but would require a moderately high packing density, approximately > 0.82 x 0.439/0.529 = 0.68.

Other Locations Where Thermite Could Be Placed to Cause Core Box Column Melting

In the preceding section, the amount of thermite needed to cause melting was calculated, and compared to the internal volume available. Just as insulation in building walls is introduced by means of relatively small holes drilled through walls, so could thermite have been placed into the interiors of the core box columns. For the "average" columns this would certainly work, since there is ample volume to overcharge with a low packing density (>0.5). The "largest" columns could be filled in the same way, although some way to "settle" the compound powders might be necessary to achieve a packing density from a pour to be > 0.68.

Rather than fill the interior of a column with chemical compound, what if the thermite compound was applied to the outside of the column, under a layer of "fire-proofing" protective cladding/thermal insulation? How thick would an exterior layer need to be applied?

(a) For an "average" box column, if T is the thickness of the applied outside layer of thermite compound, it would have a X-sectional area given by

Acoat = [T x (d + 2 x T) + T x w] x 2, where d = 36" and w = 12" as before.

This can be rewritten as Acoat = 2 x [2 x Texp2 + T x (d + w)]

For a 12 ft = 3.658 m column, the volume of the coating of thickness T is given by

Vcoat = 2 x 3.658 x [2 x Texp2 + (d + w) x T] = 0.219 m3, or

2 x Texp2 + (d + w) x T = 0.219 m3/ (2 x 3.658 m) = 0.0299 m2, or

2 x Texp2 + (d + w) x T -0.0299 m2 = 0. This is in the form of a quadratic equation, where the solution is given by

T (in meters)= {-b + SQRT(bexp2 – 4 x a x c)}/2 x a, where here

a = 2, b = (d + w) = 12" + 36" = 48" = 1.219 m, and c = -0.0299 m2. Substituting,

T = {-1.219 + SQRT[(1.219)exp2 – 4 x 2 x (-0.0299)]}/(2 x 2). Simplifying,

T = {-1.219 + SQRT[1.486 + 0.2395]}/4 = {-1.219 + SQRT[1.725]}/4 =

= {-1.219 + 1.313}/4, or

T = 0.0236 m = 0.93", which is less than 1" of coating for the "average" column.

(This solution can be verified by substitution in the original equation for Vcoat).

(b) For a "largest" box column, here Vcoat = 0.439 m3 and (d + w) = 16"+36" = 1.321m.

So, 2 x Texp2 + 1.321 x T = 0.439m3/(2 x 3.658 m) = 0.0600, or

2 x Texp2 + 1.321 x T – 0.0600 = 0. So, using the quadratic solution again,

T = {-1.321 + SQRT[(1.321)exp2 – 4 x 2 x (-0.600)]}/(2 x 2). Simplifying,

T = {-1.321 + SQRT[1.745 + 0.48]}/4 = {-1.321 + SQRT[2.225]}/4 = {-1.321 + 1.492}/4, or

T = 0.04275 m = 1.683", which is less than 1-3/4" of coating for the largest column.

In short, if a coating slightly less than 2" thick of a thermite coating were applied to the outer surface of any box column, that is sufficient chemical compound to melt that column section. A protective, insulating and cosmetic/disguising layer (e.g. fiberglass/foam) 1" or less would also be helpful.

Conclusions

In this paper we have attempted to establish the amount of thermite that would be necessary to melt a box column at or near the base of the WTC towers’ cores, to see if the amount necessary was physically feasible, or would require an unrealistic amount sure to attract detection before its use. We have used thermal parameters for iron, and assumed thermite as the chemical compound. The analysis is thus imperfect, since the structural steel used may have slightly different properties, requiring more (or less) of the chemical compound. A different, more sophisticated compound may have required even less volume than has been calculated here.

Still the implications are clear: such a melting of a section of all the inner core box pillars is possible, using relatively simple technology. Such compounds could have been applied to the interior or the exterior of even the largest of these columns in a surreptitious manner, to accomplish the task of melting and collapse. The amount necessary for complete melting of a segment of even the largest box column was calculated, and found possible. Of course complete melting was not necessary to cause total failure: a lesser amount of a thermite-like compound could have been used to raise the temperature of the steel to a point where the columns would fail before melting, although some melting must have occurred to account for the steel pools.

It is pure speculation if, how, and when this was done. The columns would have been most easily filled during the initial construction phase, but this requires belief in a foresight and 30-40 year "master plan" that may be difficult for many to think possible. (Many buildings are constructed with ultimate demolition in the design, to make way for future construction in urban areas. Usually, the building design includes cavities for controlled demolition explosive placement. The non-availability of WTC tower blueprints makes it difficult to assess this possibility).

However, there have been undoubtedly a number of opportunities under the guise of maintenance: many stories exist about problems with the "insulation" adhering to the steel support structures of the WTC towers. Also, the first attack on the WTC towers in 1993, in the basement of the complex, offered an opportunity for access and "repair" to demolition experts and construction personnel. Thermite is a relatively safe compound, requiring high temperature to initiate reaction – a magnesium fuse is commonly used. We will probably never know exactly what sequence of events unfolded to culminate in the WTC collapses of 11 September 2001.

Acknowledgments

The author wishes to acknowledge discussions with A.K. Dewdney, J. King, J. Longspaugh, B. Mayeux, J. Russell, R. Stanley, S. Walker and other friends and associates of SPINE. Of course, the author takes full responsibility for the content of this work; any errors are his alone.

**Appendix A: WTC Seismic Energy Correlation Calculations**

F. Moscatelli of Swarthmore College has provided figures on the energy releases involved in the WTC tower collapses in an article by the BBC [Ref (11)]. The article reports the gravitational energy for both towers plus sundry other collapses as 6.8 x 10+11 J, +-25%. Hence, for one WTC tower, the gravitational energy involved can be approximated by