Björkman became a formal critic of the “Progressive Collapse” or “Piledriver” theory promoted by Dr. Zdenek Bazant, a consultant for the National Institute of Science and Technology (NIST) in its work on 9-11. The Piledriver Theory basically says that prolonged heating weakened the support columns of a single floor which caused the upper section to crush what was below it in a chain-reaction all the way to the bottom.
"I explained on my website that you cannot destroy a building by dropping the top on the bottom; you have to destroy it from the bottom,” Björkman said. “Then a lot of people criticized that and said, ‘But Dr. Bazant says the opposite, and he has written all these papers,’ so of course I looked at these papers, and said, ‘This Bazant is nonsense.’ But others said, 'But he’s peer-reviewed. It has been published in a scientific journal—the Journal of Engineering Mechanics.’”