Features of the crash and explosion described in eyewitness reports and in damage reports have been used to speculate that the jet crash was augmented with exposives, on the plane or on the ground.

Explosive Characteristcs

Those features described as indicating the presencd of explosives include:

A shockwave that was strong enough to knock people off their feet hundreds of feet from the center of the blast
The odor of cordite, an explosive compound
A bright silvery flash

Strong Shockwave

Several witnesses described a shockwave that knocked them to the ground, both inside and outside the building. Several described it as a concussion. The violence of such a high-speed crashe would seem to preclude the kind of pre-mixing of the fuel and air needed to support even a weak detonation. In the Twin Tower jet collisions, the columns of the curtain walls diced the fuel tanks in the wings, assuring fuel and air mixing about as optimally as could be imagined in a collision, and yet there were no reports of detonation shockwaves.

Cordite

Cordite is an explosive compound used in aircraft gun ammunition. Several witnesses with the benefit of military experience recognized the smell of this compound. Cordite N consists of three main explosive compounds: nitroguanidine, nitrocellulose, and nitroglycerin. It is cool-burning, and produces little smoke and no flash, but, like other explosives, produces a strong detonation wave.

Silvery Flash

Several witnesses described seeing a bright or silvery flash. This is also inconsistent with jet fuel combustion, which produces a fireball whose color is at brightest yellow, not white or silver. This flash must have been produced by some means other than a cordite explosion, whose detonation is notably free of a flash.

Crash Physics Questions

Assuming that the jetliner hit the Pentagon's west facade at the offically-reported 532 mph, it is possible to imagine chemical and mechanical processes that could account for the features suggestive of explosives. For example, it is possible that rapid oxidation of metals in the plane such as aluminum and magnesium, was responsible for the bright color of the flash. The grinding of the plane's metal by the high-speed impact might have powderized a significant quantity of such metals to produce a bright flash. The sixty-or-so tons of aluminum in a 757 represents a huge amount of energy -- perhaps more than that of the jet fuel -- if it can be brought into direct contact with an oxide such as silicon oxide, for example. Aluminum powder combined with silicon oxide powder is a form of thermite:

3SiO₂ + 4Al -> 3Si + 2Al₂O₃

It's possible to imagine that such reactions in which the reagants are brought into contact through conversion of the planes' kinetic energy to extremeley rapid grinding and mixing of the materials.

Might some of the plane's aluminum reacted through such contact with the silicon oxides in the 2-inch-thick blast resistant windows to create a flash and pressure wave way beyond with the combustion of jet fuel were able to produce?

Defensive Missile Strike

It is also possible that a surface-to-air missile, fired from within the Pentagon's perimeter, hit the plane coincident with its impact with the facade. The explosion of such a missile's warhead could create the flash and shockwave, and the missile's propellant could have the smell of cordite.

page last modified: 2010-05-09

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