You are viewing this page on, which is the backup mirror of .
The original page is at
Please link to the original page rather than this mirror page.
< ^ >
9 - 1 1 R e s e a r c h
New York City
collapsing buildings
other high-rise fires
other collapses
WTC 1, 2 collapses
design parameters
role of fires
fire severity
effects on steel
collapse features
explosive events
demolition squibs
frame shattering
concrete pulverization
dust volume
steel shredding
speed of fall
demolition proofs
speed of fall
volume of dust
breakup of top
collapse theories
column failure theory
truss theory
demolition theories
basement bombs
nuclear devices
directed energy
radiant projectiles
distributed explosives
Building 7 collapse
rate of fall
controlled demolition
WTC 6, 5 holes
assault location
Pentagon videos
impact damage
damage pattern
aircraft debris
jetliner approach
attack from the air
NORAD stand-down
flight mysteries
phone calls
suicide pilots
home run system
flight program
bumble planes
Flight 93 shoot-down
Won-Young Kim
follow-up attacks
minimized fatalities
maximized shock
Attack Scenario 404
official actions
evidence destruction
investigation prevention
9-11 anomalies
top anomalies
historical precedents
Site Guide
V 1.329
Copyright 2003-2010, site last updated:12/18/10
fair use notice

Background Attack Aftermath Evidence Misinformation Analysis Memorial

Concrete Pulverization

Twin Towers' Concrete Turned to Dust in Mid-Air

A striking feature of the Twin Towers' destruction was the pulverization of most of the concrete into gravel and dust before it hit the ground. This is evident from the explosive mushrooming of the towers into vast clouds of concrete as they fell, and from the fact that virtually no large pieces of concrete were found at Ground Zero, only twisted pieces of steel. 1   Estimates put the size of the particles, which also included gypsum and hydrocarbons, in the ten- to 100-micron range. 2  

Some idea of the volume of the dust clouds can be obtained by examining photographs taken shortly after each tower collapsed.

The researcher calling himself plaguepuppy articulated the thoroughness of the destruction and its incompatibility with the official explanation.

In trying to come to terms with what actually happened during the collapse of the World Trade Towers, the biggest and most obvious problem that I see is the source of the enormous amount of very fine dust that was generated during the collapses. Even early on, when the tops of the buildings have barely started to move, we see this characteristic fine dust (mixed with larger chunks of debris) being shot out very energetically from the building. During the first few seconds of a gravitational fall nothing is moving very fast, and yet from the outset what appears to be powdered concrete can be seem blowing out to the sides, growing to an immense dust cloud as the collapse progresses.

The floors themselves are quite robust. Each one is 39" thick; the top 4" is a poured concrete slab, with interlocking vertical steel trusses (or spandrel members) underneath. This steel would absorb a lot of kinetic energy by crumpling as one floor fell onto another, at most pulverizing a small amount of concrete where the narrow edges of the trusses strike the floor below. And yet we see a very fine dust being blown very energetically out to the sides as if the entire mass of concrete (about 400,000 cubic yards for the whole building) were being converted to dust. Remember too that the tower fell at almost the speed of a gravitational free-fall, meaning that little energy was expended doing anything other than accelerating the floor slabs.

Considering the amount of concrete in a single floor (~1 acre x 4") and the chemical bond energy to be overcome in order to reduce it to a fine powder, it appears that a very large energy input would be needed. The only source for this, excluding for now external inputs or explosives, is the gravitational potential energy of the building. Any extraction of this energy for the disaggregation of the concrete would decrease the amount available for conversion to kinetic energy, slowing the speed of the falls. Yet we know that the buildings actually fell in about 9 seconds*, only slightly less than an unimpeded free-fall from the same height. This means that very little of the gravitational energy can have gone toward pulverizing the concrete.

Even beyond the question of the energy needed, what possible mechanism exists for pulverizing these vast sheets of concrete? Remember that dust begins to appear in quantity in the very earliest stages of the collapses, when nothing is moving fast relative to anything else in the structure. How then is reinforced concrete turned into dust and ejected laterally from the building at high speed?

dust covers Manhattan street
Evidence indicates that the hundreds of thousands of tons of concrete in the Twin Towers was converted almost entirely to dust.

Both reports of workers at Ground Zero and photographs of the area attest to the thoroughness of the pulverization of the concrete and other non-metallic solids in the towers. 3   An examination of our extensive archives of images of Ground Zero and its immediate surroundings reveals no recognizable objects such as slabs of concrete, glass, doors, or office furniture. The identifiable constituents of the rubble can be classified into just five categories:

  • pieces of steel from the towers' skeletons
  • pieces of aluminum cladding from the towers' exteriors
  • unrecognizable pieces of metal
  • pieces of paper
  • dust
Despite the presence of 400,000 cubic yards of concrete in each tower, the photographs reveal almost no evidence of macroscopic pieces of its remains.

Pyroclastic Flows

Many observers have likened the Towers' destruction to volcanoes, noting that the Towers seemed to be transformed into columns of thick dust in the air. An article about seismic observations of events in New York City on 9/11/01, relates the observations of scientists Won-Young Kim, Lynn R. Sykes, J.H. Armitage:

The authors also noted that, as seen in television images, the fall of the towers was similar to a pyroclastic flow down a volcano, where hot dust and chunks of material descend at high temperatures. The collapse of the WTC generated such a flow, though without the high temperatures. 4  

* 15 seconds is a much more accurate estimate of total collapse time than 9 seconds. (See this time analysis of the North Tower collapse.) Yet the 9-second figure is widely repeated in the literature of both detractors and supporters of the official story.

1. Waste Industry, Others Help with Cleanup at World Trade Center Site,, 11/1/01 [cached]
2. World Trade Center Dust Analysis Offers Good News For New Yorkers,, 12/24/02 [cached]
3. Sifting Through the Dust at Ground Zero,, [cached]
4. Damage to Buildings Near World Trade Center Towers Caused by Falling Debris and Air Pressure Wave, Not Ground Shaking, Seismologists Report,, 11/16/01 [cached]

page last modified: 2006-12-18