Ok, is it just me, or did anyone else recognize that it wasn't the airplane impacts that blew up the World Trade Center? To me, this is the most frightening part of this morning. I hope other people actually are catching this, but I haven't seen anyone say it yet, so I guess I will. I guess being an engineer may make one more conscious of these things...

If you watch the time sequence, you'll see that it happens like this:

- A plane hits tower #1, blowing a hole in it high up. The expected things then happen:

- The building stays up. A reinforced concrete building is *extremely* strong. Terrorists set off a large bomb *inside* that building without significant damage. Notice that neither plane impact does anything like break off a big hunk of building floors and send it crashing into the street. The WTC towers were specifically designed to survive a direct impact from a jumbo jet - which *both do*.

- The stories from the impact point up burn horribly. Note, fire moves upward, not downward.

- The second plane hits the second tower, lower and moving faster. It blows a bigger hole through it, showering debris on the street, but the building is clearly still standing and still looks quite solid.

- The second building begins burning, also from the impact point up.

- Perhaps a half hour later, the fire in the first building *goes out*. It is still smouldering and letting off black smoke, but there is no flame. Anyone who saw the documentary on that horrid skyscraper fire in Philadelphia that led to the codes requiring sprinklers on every floor knows why. There's no way to get fire apparatus into a skyscraper effectively, so it needs to be designed into the structure - which it is. The water flows from the roof reservoirs down. Sprinklers can kill incredible infernos, and that's what these do.

- The fire in the second building goes out.

- Then, later, the second building suddenly crumbles into dust, in a smooth wave running from the top of the building (above the burned part) down through all the stories at an equal speed. The debris falls primarily inward. The tower does not break off intact and collapse into other buildings. The bottom does not crumble before the top. The burned out section crumbles also. The crumbling comes from the top (above the damage). It moves at a uniform rate. All of the structural members are destroyed in a smooth pattern, so there is no remaining skeleton. The damage is uniform, symmetric, and total.

In summary, it looks exactly like a demolition - because that's what it is.

- The first tower collapses in a similar demolition wave.

There's no doubt that the planes hit the building and did a lot of damage. But look at the footage - those buildings were *demolished*. To demolish a building, you don't need all that much explosive but it needs to be placed in the correct places (in direct contact with the structural members) and ignited in a smooth, timed sequence. Someone had to have had a lot of access to all of both towers and a lot of time to do this.

This is pretty grim. The really dire part is - what were the planes for? If you're going to demolish the building, what's the point of the flashy display?

The way they're cutting the footage on the news now makes it look like the buildings crumbled soon after being hit by the planes, which is not true. They've also started slowing the clips from after the demolition explosion starts, so you don't see the top of the building go first - but those who taped it, go back and look at the early first-run clips.

If, in a few days, not one official has mentioned anything about the demolition part, I think we have a REALLY serious problem.