Uploaded: Tuesday, Sept. 11, 2001, 4 p.m.

Stanford expert: Planes hit twin towers with A-bomb force

World Trade Center built to withstand airplane collision

by Jennifer Deitz Berry

The World Trade Center Towers were designed to withstand being hit by an airplane, according to Stanford University Professor Steven Block.

Block is a professor of applied physics and biological sciences and an expert on national security and terrorism. He spoke at a press conference this afternoon on Stanford campus.

According to Block's calculations, the energy generated by a fuel-laden Boeing 757 or 767 colliding into a World Trade Center tower is roughly equivalent to one-20th of the energy of the atomic bomb dropped on Hiroshima, Japan on Aug. 6, 1945.

"It's a staggering amount of energy," Block said. "Any aircraft is essentially a flying bomb."

According to Block, the World Trade Center twin towers were designed to withstand "enormous impacts," including being hit by a hurricane or an airplane.

Block said he doubted there were any structural flaws in the design of the twin towers. The plane could have inflicted major structural damage to the periphery of the towers, including passing through an entire floor or knocking out the steel girders on the outside, and still the towers would have remained standing.

What most likely caused the buildings to collapse was damage to the building's steel core, Block said, though acknowledging that his expertise does not extend to mechanical engineering.

Block said the explosion appeared to have "heated the core of the building to such a degree that it began to melt." When the melting steel core could no longer support the hundred or more floors above, the buildings collapsed.

Ignited fuel generated 90 percent of the energy in the explosion, Block said. A Boeing 767's fuel capacity is roughly 23,980 gallons, and a Boeing 757 carries roughly 11,466 gallons of fuel.

Block said it was a likely possibility that terrorists had intentionally taken over planes scheduled to travel across the country because they'd be carrying more fuel and would therefore cause more devastating explosions upon impact.