Normally, the cutter charges are high-explosives strapped to a metal wedge on the side of the beam.

Many scientists and engineers have looked at the way the WTC towers fell and remarked that it had the appearance of controlled demolition. The buildings collapsed symmetrically, and fell straight down. The speed of the fall indicated that the buildings were collapsing unimpeded. They must have had the “legs” simultaneously pulled out from under them, because a layered collapse from the top down would have taken several minutes, whereas the observed collapse took place in less than 20 seconds. But the conjecture has been that the cutter charges consisted not of explosives but of finely-powdered aluminum mixed with iron oxide, with added sulfur. This mixture contains both fuel and oxidant – it needs no air – and it burns hot enough to melt steel. The trade name for this product is “Thermate.”

In addition to the speed and symmetry of collapse, another anomaly in the WTC collapse was the violent explosions. Firemen reported earthshaking blasts from the basement before collapse, and the impact areas in the upper floorss of the buildings exploded just at the onset of collapse. Jet fuel burns but cannot explode.

In an article published this week in the journal Environmentalist, chemical engineer Kevin Ryan collects evidence from EPA documents that suggest there was both Thermate and high-explosives in the debris from the WTC collapse. Ryan was formerly employed by Environmental Health Labs, a division of Underwriters Labs, before he was fired for raising these and other questions.

Fires at the WTC site persisted for weeks after 9/11, despite firefighters’ use of water and chemical extinguishers to smother the flames. This suggests that it was a fuel-oxidant mixture that was burning. Pools of red-hot molten iron could not have been caused by burning jet fuel or building materials, because these burn at a much lower temperature than steel melts.

Ryan’s evidence consists in traces of 1,3-diphenylpropane as well as sulfur and particulate matter, reported by the EPA to have appeared in spikes continuing as late as March, 2002. Ryan believes that these came from brief, intense fires ignited by the molten steel when it came in contact with yet-unburned plastic building materials during the clean-up process.

Link to Journal article full text