Nicely put Matt.

Another thing was that the steel used in building the towers was changed when they were about halfway complete. It was too expensive and the project was in danger of going bankrupt.

The policy in the US is and was not stay put. The policy in the US is if you are below the fire, you evacuate to ground level. If you are above the fire, you evacuate up away from the fire. Most high rise building are built with fire breaks every few floors (10 IIRC) to prevent the vertical spread of a fire. If you have to, evacuate all the way to the roof, and they may be able to air-lift you to safety.

Attempting to evacuate down to ground level through a major fire is likely to be suicidal.

Given the severity of the fire in the WTC towers, it is highly unlikely that anyone above the fires would have survived an attempt to evacuate downward.

The WTC towers failed because of a unique construction that has been used in no other high rise building and the fact that the building was under construction when the major lawsuits over asbestos were decided.

The WTC towers were built as square tubes with all the vertical support in the exterior walls and rigidity and lateral stability was dependent on the links between the exterior walls and the floor decks.

The tie points between the exterior structure and the floor decks are the weak point of the building. Sever even just a couple of consecutive floors from the exterior walls and the structure isn’t rigid enough to support it’s own weight.

The original design called for the links between the floors and the exterior walls to be protected from fire with an asbestos foam spray. (that would harden in place) They were forced by NYC building regulators and the asbestos lawsuits to switch to a less effective fire retardant part way up the building.

No other building in the US (IAFIK no other building int the world) has ever been built with the same type of structure as the WTC towers.

Note the “stay put” fire policy.

The same policy that killed so many at the WTC.

There is no rescue if you are out of reach of the Fire Brigade’s ladder or tower trucks.