David, I find your work interesting but i have some doubts about your explanation which I will be…
simon thorneycroft

> the ‘squibs’ all appear to exit from window opening in the external walls.

See https://www.youtube.com/watch?v=zoAD8HlrLZg for an example of cutter charges at the corner of the building where there are no windows.

>Also, the pictures from ground Zero show external wall panels many stories high, and the images of the collapse show sections of wall that are also several floors high. If the tower was being explosively cut floor by floor I would not have expected this.

Some panels, but also individual wall units thrown independently of any peeling effect: http://www.youtube.com/watch?v=eHnLlwqiu0A

> … compressing the air so that it blew out as squibs.

There were many point-source squibs far below the collapse front of the building, some on floors where the windows were already blown out. Also, pancaking floors can’t account for the failure of the interior columns that were heavily connected and acted like a building within a building. If the floors had failed, we would be left with the core structure intact.

> Each floor that was released to fall would add to the energy in the system, meaning that the calculation should not be based on the idea of a closed system.

Starting with nothing but the potential energy of the building, breaking apart does not add energy. It consumes energy to break apart. Others have calculated that the level of decomposition of the concrete in the building required more energy than was available in the potential energy alone. (I don’t have a good reference for this statement off hand, but the calculation has been done.)

>Also, may I ask, there is video of steel frame building collapsing due to fire in Tehran and another in Sao Paolo. The one in Sao Paulo looks to fall at freefall — have you calculated if this tower falls at freefall acceleration?

The Plasco building in Tehran did not fall at freefall. I have no way to do a calibrated measurement on the building I Sao Paulo, which I believe was not a steel frame building.