If energetic nanocomposites were present at the WTC, the presence of 1,3-DPP might be explained through a mechanism of release from the silica microstructure by aqueous base. As noted above, the silyl aryl ether linkage of the composite is “thermally stable to ca. 550°C” but yet, the organic moieties “can be easily cleaved at room temperature with aqueous base for quantitative recovery.” The dust at GZ was known to be highly basic (Jenkins 2007), and combined with the large amount of water from fire-fighting efforts and rainfall, undoubtedly produced aqueous base throughout the pile.

It is important to understand that 1,3-DPP would not have been directly released from the silica microstructure via the route of aqueous base. It would have been the hydroxyl derivative, p-(3-phenylpropyl)phenol, abbreviated as HODPP, that was first released in this manner.

$$ \cong {\text{Si}} \hbox{-} {\text{O}} \hbox{-} {\text{DPP}} + {\text{ROH}} \to \cong {\text{Si}} \hbox{-} {\text{OR}} + {\text{HODPP}} . $$

But the pores of an energetic nanocomposite are also filled with a mixture of fine aluminum powder, and one or more finely dispersed metal oxides. Therefore, hydrogen gas could have evolved in the following way (as well as by several other reaction mechanisms in the high-temperature environment of GZ combustion).

$$ 2 {\text{Al }} + {\text{6H}}_{2} {\text{O}} \to {\text{2Al}}\left( {\text{OH}} \right)_{3} + {\text{3H}}_{ 2} . $$

Production of 1,3-DPP might then have followed from a metal oxide-catalyzed reaction of p-(3-phenylpropyl)phenol with hydrogen. A similar reduction of phenol to benzene, catalyzed by MoO 3 , has been reported (Woodward and Glover 1948).

$$ {\text{MoO}}_{ 3} + {\text{ H}}_{{ 2 }} \to {\text{ MoO}}_{ 2} + {\text{ H}}_{ 2} {\text{O,}} $$

$$ {\text{HODPP}} + {\text{ MoO}}_{ 2} \to {\text{1,3-DPP}} + {\text{ MoO}}_{ 3} . $$

Other pathways have been proposed for the release of 1,3-DPP, some without the need for preliminary reactions, but experiments are required to confirm these possibilities.

Based on currently released data, maximum detections for 1,3-DPP (at 290 Broadway, ~0.6 km from GZ) were measured on or about 5th, 13th, and 21st October. These last two dates are different from the dates suggesting violent, short-lived fires. That would be expected, of course, considering that 1,3-DPP would probably not survive such extreme fire events but would be converted into other products. In early October, however, full-scale clean-up operations had just begun at GZ, and 1,3-DPP might have been released at more locations in the pile, in some cases through physical or chemical means.

As for the effects of heat, the products of the pyrolysis of 1,3-DPP at 375°C are styrene and toluene, in equal amounts (Poutsma and Dyer 1982). This can occur directly in the dry composite (Kidder et al. 2005). Additionally, high temperature oxidation of toluene is known to produce benzene (Brezinsky et al. 1984).

The spikes in VOC detection could also be explained as a result of the rapid combustion of typical materials found within a building structure. If energetic nanocomposite materials, buried within the pile at GZ, were somehow ignited on specific dates (Table 1), violent, short-lived, and possibly explosive fires would result. Such fires would have quickly consumed all combustible materials nearby. The combustible materials available, after a month or two of smoldering fires in the pile, might have been more likely to be those that were less likely to have burned completely on earlier dates, like plastics. Later combustion of such plastic materials, in violent but short-lived fires, could explain the spikes in VOCs seen on those dates.

As for Cahill’s data, the presence of compounds of sulfur and silicon in the fine PM seems to fit well with this hypothesis. Sulfur is typically an ingredient of aluminothermic materials (e.g. thermate), and silica is often the structural base for energetic nanocomposites. Sulfur might have been released, along with very fine silicon compounds and other species related to energetic nanocomposites, through explosions, violent fires, or other physical disturbances in the pile at GZ.

Along these lines, it is noteworthy that the data from EPA and Cahill show that detection of aluminum, iron, and barium, all of which are common ingredients of thermate-like aluminothermic mixtures (Jones 2006), spiked on specific dates. Cahill’s data show a very noticeable simultaneous spike for aluminum and iron on 26th October. The EPA data show that, of the 28 days that aluminum was measured in air during 2001, the dates of maximum detection fall on the same dates as that of iron for the top 9 days in each case. Barium shares eight of these top nine daily maxima.

The metals mentioned by Cahill, for which the “anaerobic incineration” mechanism was proposed, might also be explained by further development of this hypothesis. For example, vanadium oxide has been used in energetic nanocomposites (Gash et al. 2000) and has been added to hybrid aerogels for the improvement of electrical conductivity, and to silica nanocomposites for the purpose of catalysis (Harreld et al. 1998; Luco et al. 1995). The EPA data show a maximum detection for vanadium on 19th December, the same date as EPA’s maximum detection of iron, and the date of the second highest detection of both barium and aluminum. The highest detection of barium occurred on 7th March, 2002.

Titanium and nickel, other metals detected in unusual quantities by Cahill, have been used in the production of energetic nanocomposites as well (Gash et al. 2003). Neither EPA nor Cahill reported specific measurements for titanium, but spikes in the detection of nickel are clear in the EPA data on 11th October, 19th December, and 7th March, 2002.

Further testing of this hypothesis, for the presence of energetic materials at GZ, might focus on dust samples. For example, if aluminothermic mixtures were ignited at the WTC, significant quantities of the oxidized aluminum would have been present in the air and dust. Because EPA and Cahill used elemental analyses only, the fraction of aluminum present as aluminum oxide was not identified. Unfortunately, air samples are not likely to be useful at this late date but specific measurement of aluminum oxide in dust samples can certainly be done. Such measurements may also help to explain other anomalies observed at the WTC, such as the plumes of white ash accompanying very bright flames at the South Tower just before its fall (Jones et al. 2008b). Other tests for the remnants of energetic nanocomposites in the WTC dust would be indicative as well.