Excerpt from a fascinating article at aerospaceweb.org:
... a number of factors explain why the Empire State Building suffered relatively minor damage while the twin towers were catastrophically destroyed. First, the energy of impact sustained by the buildings differed by orders of magnitude. The B-25 that struck the Empire State Building weighed approximately 21,500 lb (9,760 kg) and was traveling around 200 mph (320 km/h). The kinetic energy it created in the collision was about 30 million ft-lb (40 million Joules).
The twin towers of the World Trade Center, by comparison, were struck by Boeing 767 airliners traveling over twice as fast and weighing nearly 15 times as much as a B-25. The energy of impact for the two planes ranged from 2 billion ft-lb (2.6 billion Joules) to 3 billion ft-lb (4.1 billion Joules), some 60 to 100 times greater than that absorbed by the Empire State Building. This estimate is also conservative since it does not account for the energy released by the exploding jet fuel, which greatly exceeded the energy released by the much smaller B-25 fuel supply as well. The greater kinetic energy allowed the 767 aircraft to penetrate much further into the twin towers than the B-25 was able to do at the Empire State Building. Most of the B-25 impact was absorbed by the building's exterior wall leaving very little to damage the interior structure. The 767 impacts, however, not only produced gaping holes in the WTC exterior but also destroyed much of the structural core at the center of each tower. ...
Furthermore, the Empire State Building is a reinforced masonry structure in which the structural steel beams are encased within limestone walls or slabs of concrete 8 inches (20 cm) thick. This heavy mass provides exceptional fire protection that insulates the steel within from excessive heating. Many modern skyscrapers like the WTC towers have eliminated this extensive use of stone and concrete to reduce cost. The World Trade Center instead relied on lightweight spay-on coatings for insulation. This insulation was simply blown off the WTC structure by the 767 collisions exposing the steel beams and floor trusses to the raging fire.
The Empire State Building is also a heavily compartmented structure. Each floor is self contained with its own independent heating and cooling ducts, elevator and utility shafts are surrounded by thick masonry walls, fire partitions separate each floor and rooms within each floor, and the fireproof stairway prevents smoke from rising to upper stories. These features make it very difficult for fire to spread beyond a limited area. The World Trade Center instead offered vast open floor spaces that appealed to tenants but allowed fires to spread far more easily. Moreover, the fire suppression system in both towers lacked redundancy and the 767 collisions cut off the water supply to the sprinklers. For these reasons, the Empire State Building is still considered one of the world's safest skyscrapers in a fire.
I guess you could say---
Don't make them like they use to.
Posted by: Ron | 09/11/2008 at 08:18 AM