So, I was watching a Penn and Teller video about some of the conspiracy theories surrounding the events of September 11, 2001 (http://www.youtube.com/watch?v=kcrF346sS_I) and got me thinking again about some of the ideas surround the collapse of the World Trade Center.
One argument I have heard that claims to be evidence that the WTC was a controlled demolition and not the result of fire is that jet fuel and office supplies do not burn hot enough to melt steel. It occurred to me yesterday that there are some things fairly fundamentally wrong with that line of conjecture.
First, there is a difference between energy required to start combustion and energy released by combustion, so unless we're clear on that difference it's hard to say what the "temperature" of a burning material actually is.
Second, the burning "temperature" is not really relevant to the discussion. The only things that matter are the energy density and the energy dissipation rate. If the energy density is high enough and the energy is contained in the system rather than leaking out of the system, the burning "temperature" (which is too ill defined to be at all meaningful to the discussion) makes no difference at all.
So, just because whatever was burning couldn't melt steel instantly has no bearing on whether enough energy could build up inside a steel structure to at least soften it to the point of collapse. I'm not a structural engineer, so I'm not going to make any suggestions about how plausible that theory is.
That said, that the scrap was sold and shipped to China as quickly as possible, rather than allowing a team of engineers to publicly examine the wreckage in an attempt to determine exactly what happened and allow future building designs to take it into account is at best suspicious and practically criminally negligent.
This still comes back to WTC-7, the third office tower that collapsed that day. Sustaining only secondary fires and indirect damage, it too collapsed. From what I stated above, it may be possible for such fires to bring down a building, except that it has never happened before or since. Even fires such as this and these didn't bring down the entire building.