Intact Pentagon Windows
Claim: Many of the Pentagon windows remained in one piece -- even those just above the point of impact from the Boeing 757 passenger plane. The animation on
www.pentagonstrike.co.uk claims the "intact windows" support the theory that "a missile" or "a craft much smaller than a 757" hit the Pentagon.
Fact: A number of windows near the impact area did indeed survive the initial concussion and ensuing explosions, because that's exactly what they were designed to do -- the windows in that section of the Pentagon are blast resistant.
The windows were installed just weeks earlier as part of a massive Pentagon modernization plan. The original windows were essentially standard commercial units from the early 1940s. The need for blast protection in the E and A rings -- the outermost and innermost rings, respectively -- became clear after the bombings of the Alfred P. Murrah Federal Building in Oklahoma City in 1995 and the embassies in Kenya and Tanzania in 1998.
In a rare stroke of good luck on September 11, Flight 77 struck Wedge 1, the first section of the building designated for renovation. The first phase was five days from completion when the plane hit, and 383 new-and-improved windows were already in place. Weighing approximately 1,600 pounds apiece, the new windows feature laminated glass, in which a thin polymer interlayer is sandwiched between two or more panes of glass. The effect is that the windows will crack but not shatter, much like a car windshield. Because the Pentagon was designated a National Historic Landmark in 1992, the new windows were required to match the exterior look of the originals, so it is impossible to tell the old from the new from the outside.
But installing new windows would not have made much of a difference without corresponding structural improvements in the building around them. As a result, the designers engineered a complicated reinforcement scheme with the steel beams built into the walls around the window frames and bolted to the concrete floors slabs. The structure behaves like a catcher's mitt, absorbing the force of an explosion and shielding the people inside the building.
"It would have be imprudent and sort of counterproductive to have a window that was stronger than the wall," says Ken Hays, executive vice president of Masonry Arts, the Bessemer, Alabama-based company that designed, manufactured, and installed the windows. "The wall should be stronger than the window glass. If the window construction is stronger than the wall, it would eject the window from the unit and now you've got a flying missile. You want to design your windows and structure so that they fail in a certain order."
Hays declined to discuss the levels of force the Pentagon windows are designed to withstand, as doing so could jeopardize the security of the building. However, he say, the windows performed to specifications. "I personally inspected those windows, and anywhere a windows was not actually hit by the fuselage of the aircraft, the best we were able to determine was that if there was a glass missing, it was because of the subsequent fire burned the glass out."
Bill Hopper, communications manager for the Pentagon Renovation and Construction Program, confirms this account.
The Pentagon Building Performance Report adds that the reinforcement around the windows kept the edifice surrounding the impact hole standing for 19 minutes. That was long enough to enable hundreds of Pentagon employees to exit the building before the damaged section of Ring E collapsed.
If the plane had hit an unrenovated section of the building, the damage would have been much more sever -- not only from the force of the blast, but also from fire. In Wedge 1, where a new high-tech sprinkler system had been installed during the renovation, the fires did not spread significantly and most were put out fairly quickly. When some fires spread to Wedge2, which did not have upgraded sprinkler system, they burned on and off for more than hours.
