World Trade Center

More than ten years after the fact, a scientists based at the Norwegian research institute SINTEF is proposing that a well-documented chemical reaction spelled the ultimate demise of the Twin Towers after the attacks of September 11, 2001. This isn’t another conspiracy theory, nor is it proven fact.

On September 11, 2001, the World Trade Center transformed from a pair of gleaming towers into a carcinogenic pile of smoldering rubble that's still killing people. Currently rising out of that rubble, though, is a complex with the most environmentally advanced technologies ever attempted at the scale.

Trapped on a high floor? Reach for today's featured Invention Award winner.

As the 9/11 inferno unfolded on television, one question kept dogging Kevin Stone: Why weren't the people trapped in the World Trade Center able to make their way to safety? "I said to myself, This is crazy," recalls Stone, an orthopedic surgeon and seasoned inventor in San Francisco. "There should be a better way to exit a skyscraper when something like this happens."

Trapped on a high floor? Reach for today's featured Invention Award winner.

As the 9/11 inferno unfolded on television, one question kept dogging Kevin Stone: Why weren't the people trapped in the World Trade Center able to make their way to safety? "I said to myself, This is crazy," recalls Stone, an orthopedic surgeon and seasoned inventor in San Francisco. "There should be a better way to exit a skyscraper when something like this happens."

Running up the center of the building is a fortresslike tower whose walls, made of two-to-three-foot-thick reinforced concrete and steel, will provide structural support for the building and fire protection for the infrastructure it contains: elevators, stairways and utilities such as the pipes that carry water to the sprinklers.

Primers on high-security building design warn against basement garages. It’s a lesson learned from bitter experience: the 1993 truck bomb that exploded below the World Trade Center, killing six. But parking is a key commercial asset, and a large underground facility is planned for the Freedom Tower. Designers promise that vehicles will be screened and that blast-resistant materials will be used.

If the World Trade Center attack had occurred at a busier time, it would have taken occupants four hours to get down the stairs—hours they didn’t have. The solution: emergency elevators. Surprising?

Immediately after 9/11, it looked like the age of the high-rise trophy building was over. But at the politically symbolic height of 1,776 feet (designated by master planner Daniel Libeskind), the World Trade Center's replacement will be among the three tallest buildings in the world upon its completion in 2008.

Few people on the floors above where the planes hit the twin towers survived, in part because the stairs, sheathed only in drywall, were severely damaged. In the Freedom Tower, stairs will be housed in concrete enclosures within the central core, creating what SOM architect Carl Galioto calls "a core within the core." The stairs will be pressurized to push out smoke.

The Freedom Tower’s designers had to contemplate the whole horsemen-of-the-apocalypse spectrum of possibilities: explosives big and small; fire; chemical, biological and nuclear attack. But the most obvious goal of the design team—headed by the architectural firm of Skidmore, Owings and Merrill—was to create a structure robust enough to avoid a reprise of the twin towers’ fate: catastrophic failure as the buildings buckled under their own weight, 110 stories pancaking down in 10 to 15 seconds.

Diagonal columns wrap around the Freedom Tower. Connected to the central core by the floors, they share the job of supporting the building’s weight.

A federal investigation of the World Trade Center disaster found that a key culprit in the buildings’ collapse was spray-on fireproofing. The planes’ impact dislodged this material from the towers’ steel columns and, unprotected from the searing heat, the columns buckled. Freedom Tower architects promise a better grade of fireproofing, but fire safety expert Glenn Corbett notes, “That’s like saying you’ll use a better grade of Dixie cup.”

Not in the plans: In Europe and Asia, builders use fire-resistant steel.

Up to 85 percent of injuries in bomb attacks are caused by flying glass—“knives and daggers,” in the words of blast engineer Tod Rittenhouse. But thanks to commercial pressure for views and a graceful exterior, the Freedom Tower’s skin will be mostly glass. Designers will use safety glass, but have not provided details. There are two ways to pacify glass: tinker with it chemically or keep it from traveling.

High manufacturing temperatures make blast-resistant glass strong but too heavy for an entire building. Laminated glass consists of glass layers sandwiched around plastic; upon breaking, glass fragments stick to the plastic. A futuristic solution&58; glass that’s been chemically treated so that it cracks from below the surface into sand-like grains, not shards.