I did a Web chat yesterday on conspiracy theories. Topics included the September 11 attacks, the Kennedy assassination, the moon landing, the origin of AIDS, why Osama bin Laden is not wanted by the Federal Bureau of Investigation (FBI) for the September 11 attacks, the Illuminati, and other subjects. Check it out.

The mystery of why the 47-story World Trade Center (WTC) Building 7 collapsed at 5:21 pm on September 11, 2001, even though it had not been hit by an airplane, has been solved. The U.S. Department of Commerce’s National Institute for Science and Technology (NIST) investigated the collapse for three years, announcing its findings on August 21.

NIST says:

• Falling debris from the collapse of the north WTC tower at 10:28 am started fires on at least 10 floors of WTC 7.
• Fires burned out of control on six lower floors of WTC 7. Sprinklers there had no water because the collapse of the twin towers had damaged water mains.
• Heat from these fires caused a long floor girder on floor 13 to expand so much that its connection with an interior structural column failed.
• The displaced girder and other local fire damage caused floor 13 to collapse.
• This started a cascade of floor failures down to floor 5.
• The critical structural column now lacked any floor supports for nine stories of its length. It buckled, causing other structural columns to fail, setting off a progressive collapse that quickly engulfed the entire building.

NIST tested for a collapse caused by explosives, as conspiracy theorists have alleged, and ruled this out. It said the smallest blast capable of crippling the critical column would have produced a sound level of 130-140 decibels at a distance of at least 0.8 kilometers, if unobstructed by surrounding buildings. This is the comparable to the sound level produced by a gunshot blast or standing next to a jet engine, and more than 10 times louder than being in front of the speakers at a rock concert. But no blast sounds were heard on the audio tracks of video recordings of the collapse of WTC 7 or were reported by witnesses.

For details, see NIST’s August 21 press release, which includes links to supporting documents.