Here's an interesting article from Popular Mechanics -
http://www.popularmechanics.com/science/defense/1227842.html?page=1&c=y
FROM THE MOMENT the first airplane crashed into the World Trade Center on the morning of September 11, 2001, the world has asked one simple and compelling question: How could it happen?
Three and a half years later, not everyone is convinced we know the truth. Go to Google.com, type in the search phrase "World Trade Center conspiracy" and you'll get links to an estimated 628,000 Web sites. More than 3000 books on 9/11 have been published; many of them reject the official consensus that hijackers associated with Osama bin Laden and Al Qaeda flew passenger planes into U.S. landmarks.
Healthy skepticism, it seems, has curdled into paranoia. Wild conspiracy tales are peddled daily on the Internet, talk radio and in other media. Blurry photos, quotes taken out of context and sketchy eyewitness accounts have inspired a slew of elaborate theories: The Pentagon was struck by a missile; the World Trade Center was razed by demolition-style bombs; Flight 93 was shot down by a mysterious white jet. As outlandish as these claims may sound, they are increasingly accepted abroad and among extremists here in the United States.
To investigate 16 of the most prevalent claims made by conspiracy theorists, POPULAR MECHANICS assembled a team of nine researchers and reporters who, together with PM editors, consulted more than 70 professionals in fields that form the core content of this magazine, including aviation, engineering and the military.
In the end, we were able to debunk each of these assertions with hard evidence and a healthy dose of common sense. We learned that a few theories are based on something as innocent as a reporting error on that chaotic day. Others are the byproducts of cynical imaginations that aim to inject suspicion and animosity into public debate. Only by confronting such poisonous claims with irrefutable facts can we understand what really happened on a day that is forever seared into world history.--THE EDITORS
Here's one of the myths they analyzed -
Puffs Of Dust
CLAIM: As each tower collapsed, clearly visible puffs of dust and debris were ejected from the sides of the buildings. An advertisement in The New York Times for the book Painful Questions: An Analysis Of The September 11th Attack made this claim: "The concrete clouds shooting out of the buildings are not possible from a mere collapse. They do occur from explosions." Numerous conspiracy theorists cite Van Romero, an explosives expert and vice president of the New Mexico Institute of Mining and Technology, who was quoted on 9/11 by the Albuquerque Journal as saying "there were some explosive devices inside the buildings that caused the towers to collapse." The article continues, "Romero said the collapse of the structures resembled those of controlled implosions used to demolish old structures."
FACT: Once each tower began to collapse, the weight of all the floors above the collapsed zone bore down with pulverizing force on the highest intact floor. Unable to absorb the massive energy, that floor would fail, transmitting the forces to the floor below, allowing the collapse to progress downward through the building in a chain reaction. Engineers call the process "pancaking," and it does not require an explosion to begin, according to David Biggs, a structural engineer at Ryan-Biggs Associates and a member of the American Society of Civil Engineers (ASCE) team that worked on the FEMA report.
Like all office buildings, the WTC towers contained a huge volume of air. As they pancaked, all that air--along with the concrete and other debris pulverized by the force of the collapse--was ejected with enormous energy. "When you have a significant portion of a floor collapsing, it's going to shoot air and concrete dust out the window," NIST lead investigator Shyam Sunder tells PM. Those clouds of dust may create the impression of a controlled demolition, Sunder adds, "but it is the floor pancaking that leads to that perception."
Demolition expert Romero regrets that his comments to the Albuquerque Journal became fodder for conspiracy theorists. "I was misquoted in saying that I thought it was explosives that brought down the building," he tells PM. "I only said that that's what it looked like."
Romero, who agrees with the scientific conclusion that fire triggered the collapses, demanded a retraction from the Journal. It was printed Sept. 22, 2001. "I felt like my scientific reputation was on the line." But emperors-clothes.com saw something else: "The paymaster of Romero's research institute is the Pentagon. Directly or indirectly, pressure was brought to bear, forcing Romero to retract his original statement." Romero responds: "Conspiracy theorists came out saying that the government got to me. That is the farthest thing from the truth. This has been an albatross around my neck for three years."