Collapse of the North Tower of the World Trade Center

Crockett Grabbe © January 18, 2008

University of Iowa & SeaLane Consulting


Sequential photos of the first part of the collapse of the North Tower of the World Trade Center are examined for the causes and development. It initiates with a large explosion at the core of the tower at around the 94th floor, and is sequentially fed with at least 3 subsequent explosions a few floors below the progressing collapse which drive squibs [rapidly moving material] coming out of at least 2 faces of the tower. One of the squibs is seen to be composed primarily of a 30-foot or longer beam with tail material which breaks off at the wall and tumbles down. Also observed is a over 50-feet wide 6-story piece of the tower wall which was blown out away from the tower, as well as hundreds of pieces flying through the air, probably most of which came from the cladding on the tower's wall.

Observing the Collapse Sequence

The North Tower collapsed about 30 minutes after the South Tower did, which was about 1 hour and 42 minutes after it was hit by an airplane. It fell from the top down similar to the South Tower collapse, but the details of the collapse clearly differ from the South Tower. Let us look at a few views from some excellent photographs taken on the North Tower collapse by Richard Lethin.[1] He did not indicate the timing between the photographs, but from known fall rate of the tower a rough estimated is about 0.625 seconds.

In Figure 1 is the North Tower seconds before collapse, when fires are burning at the top of the tower from the plane collision just over 1.5 hours before. The fire unfortunately has trapped occupants on the 94th and higher floors. The dot just off the tower's lower right-hand side in Figure 1 is a person who has jumped from the high floors trapped by fire, possibly because of asphyxiation suffered from massive smoke and seriously limited oxygen availability.

Figure 1. The North Tower seconds before the initiation of collapse in which fires burning are confined to the top 17 floors.

Figure 2 shows an initiation of the collapse from another perspective-- the North direction -- very shortly after Figure 1. Flames at the base are emerging from the building in all visible directions, and smoke clouds are starting to rapidly develop.

Figure 2. Perspective of tower from North side at very initial start of collapse in the North Tower, with dust clouds starting to develop and flames at the edge of the building beginning to emerge outside the building.[2]

The closeup view from that same perspective 0.75 seconds later (Figure 3) shows the flames emerging from the buildings have erupted into huge fireballs, one almost 75 feet wide. The very quick development is explosive, and thick smoke clouds have developed masking the fireball.

Figure 3. View 0.75 secs later from North perspective in Figure 3, in which the emerging floors of flames have exploding into huge fireballs outside the tower, and smoke clouds have boomed to large size, covering part of the fireballs.[2]

Figure 4 is from the same perspective of Figure 1, shot very shortly after Figure 3 which shows a fireball and the building exploding at the top, with large dust clouds rapidly expanding around the tower. Several sudden-bright-lights like the ones in Figure 2 and 3 were seen as the building collapsed, all appearing explosively and short-lived. Notice also that the 360-foot television tower on the top center of the building is rapidly falling. This indicates there is a collapse of the building core, not just the side. In fact, the distance to the base of the antenna to the level of the fireballs is about 150 feet, while the distance from the core on the fireball level to the edge of the firballs is almost 150 feet. This strong suggests that both disturbances on coming from explosions in the center core of the building at the level at which the fireballs emerge.

About 10 floors below the dust clouds on the right-hand side is a squib [defined here as material ejected at very-large velocity in a horizontal direction] moving out from the side of the tower. This material is coming coming from inside the tower. There is a sizeable force sending that out at high velocity, through the windows or blown through the wall. Thus Figure 4 shows evidence of 2 separate types of explosive blasts -- one producing the fireballs outside the tower, and one lower down producing the squib ejecting from the tower.

Figure 4. The collapse in the North Tower from the perspective of Figure 1 which occurs shortly after Figure 3, which clearly shows rapidly expanding dust clouds, a sudden move of the top antenna based on the core, a flash of light on the right-side, and an injection of a squib out the tower on the right-hand side, rougly 10 floors below the dust cloud.[1]

Figures 2, 3 and 4 show in their clouds and fireballs huge forms of energy quickly arising. An ironclad principle of physics is the conservation of energy, so all that of that energy must arise from some source. Clearly it did not arise from the fires created by the plane impacts, because the fuel from the planes has long ago burned, and the remaining fires are fed by the flammable parts of the tower that remain. The only feasible source of that energy are explosions inside the tower.

Figure 5 is a view of the collapse about 2.5 seconds after Figure 4, where the falling dust clouds around the tower have fallen down to the level of the squib observed in the previous paragraph. Note that a new squib has been ejected on the right-hand side just over 10 floors below the dust cloud, whereas another squib has been ejected right from the center of the front face of the tower, just below the dust cloud. The latter ejection appears more developed, and would have appeared earlier than the one on the right-hand side.

Figure 5. Collapse about 2.5 seconds later, which shows 2 new squibs -- on the right face and the front face of the tower.[1]

Figure 6 shows the collapse about 1.25 seconds later in which the squib seen previously on the right-hand side has considerably expanded, and a new unusual squib on the right-hand side has appeared just below the dust cloud. Although the latter it is partially masked by dust that is coming from the cloud above, there is a clear almost-horizontal object going out about 30 feet from the tower. There is also a new squib coming head-on appearing on the face of the tower, about 10 floors below the descending dust cloud.

Figure 6. North Tower collapse just over 1 second later, in which a new squib with a 30-foot long beama has just been ejected on the right-hand side under the dust cloud.[1]

Figure 7 which shows the collapse about 0.6 seconds later reveals an astonishing development of that unusual squib. The squib below it is still there, and the dust cloud has descended more, but the right-side of that unusual squib is falling, whereas the left-hand side that is just against the tower has effectively not moved. That implies the squib is a solid object which is falling on one side, but the other side is stuck at the wall it blasted through. The object is a 30-feet metallic bar that has blown out the side, but has not come all the way, with one end being stuck in the window-wall it came out of. The fact that the other end is falling would mean that it is bending away from its tail that is still in the building.

Figure 7. North Tower collapse less than 2 second later, in which the right-hand side of the ejected solid squib is tumbling down due to gravity.

The photo of the collapse 0.6 seconds later shows the right-hand side continuing to fall, apparently criss-crossing with the less solid material of the lower squib. Then another 0.6 seconds later, the collapse is as shown in Figure 8. The downfalling solid squib has finally fallen down to a level that the force of gravitational pull on it can drag the bent tail out of the building. That shows the splintered tail that was stuck in the building. Note tremendous momentum would have to be applied to to the bar to drive it out of the tower. An important principle of physics is the conservation of momentum, which means that momentum had to have a source. The source was an explosion which impaled it against the wall of the tower.

Figure 8. Collapse less than 1 second later, in which the falling squib pulls it bent and splintered tail out of the building.[1]

Note also in Figure 8 the object emerging from the dust cloud on the left-hand side. This is a large object, and help in identifying it comes in the next next figure. In Figure 9 one can see it a bit more clearly in the collapse 0.6 seconds later. To identify it, notice the closely spaced black parallel stripes on it. These are identical to the parallel black stripes of cladding everywhere on the wall, so this is a big piece of the wall. Now notice the larger shaded lines the run perpendicular to the black stripes like those that cover the wall. One can readily identify these shaded lines as floors of stories of the tower. This piece of wall emerging from the descending cloud is a 6-story piece of the wall, covering just over 50 feet width for each floor. It is basically a 4,000 square feet section of the wall that has been blown away from it. Substantial energy would have been required to tear that away from the wall and blow it out.

Figure 9. The collapse less than 1 second later, in which the blown-out 6-story piece of the wall is falling on the left, the 30-feet steel beam slightly buckled at the front is falling the right, and 100s of other piecess of beams and other objects are emerging from the dust cloud in the collapse.[1]

Figure 9 also shows on the right-hand side how that 30-feet solid beam blown out the side has developed. Note that it has pulled away from its bent tail and the tail has separated into pieces, indicating it was probably badly splintered in that bending process. The 30-feet metal beam remains. Note its front end has been buckled, which would have happened as it hit the wall from coming out the building. This buckling of the steel beam against the wall would have required a sizeable force. Notice also there are hundreds of other beams and pieces of a smaller size evident in this photo. Considerably forces would have been required to break all these pieces apart. Conservation of energy says there was a source of that tremendous amount of energy for breaking all these pieces and propelling them away from the tower. The only feasible source of all that energy is an explosion or explosions.

Conclusions on the Collapse

The whole North Tower collapsed in just over 11 seconds. That is to be compared with a free-fall rate of 9.22 seconds, which is the time that it would have taken a brick down from the roof of the standing tower to hit the ground. Thus the whole structure that had been built into that tower resisting fall seemed to virtually all disappear at once. The figures show that explosions occurred at at least 4 separate locations. The 3 explosions below the plane impact zone (below the fires in Figure 1) generally occurred at times & locations to take out resistance ahead of the collapse. The 1 explosion at the level where the plane hit and fires existed hurled material on fire through the walls. When that material on fire hit the free atmosphere, the sudden infusion of fresh oxygen caused it to erupt into those bright-orange flames seen in Figures 2, 3, and 4. These 4 explosions provide the only feasible sources of the energy to produce the rapidly expanding clouds, the fireballs, and the broken flying pieces of the wall, and are the only feasibly sources of the momentum needed to ram material through the walls.

Fires cannot possibly cause all 287 columns of the North Tower to fail at once, which is precisely what happened with the fall. A hot raging fire might cause 2 or 3 columns to fail at once at its hottest, but under no circumstance could it be raging hot over all 41,000 square feet of cross-section of the tower to cause it to fall symmetrically like it did. The tower fell in many hundreds of pieces in a symmetrical fashion because explosives forces created the collapse.

This evidence clearly agrees with previous examinations which concluded the plane impacts and resulting fires could not have brought the North Tower down.[3],[4] It strongly disagrees with the National Institute of Standards & Technology [NIST] conclusions that the plane impacts were the cause of collapse.[5] NIST effectively engaged themselves in a tautological study: their investigations were confined to all aspects of the fires and the plane impacts that were assumed to have brought the towers down, and they worked on gathering evidence specifically in those areas, including all aspects of building suscepbilities that they might have created, to let them draw conclusions about how the fires & impacts brought the towers down. They have published 42 volumes on all aspects of the design of and fires in the towers, but none of them deals with the facts as laid out here or in the previous examinations cited. The volumes are scientifically flawed, and the scientific evidence is that their conclusions are in error.


[1] Excerpts from Richard Lethin photos, posted on the World-Wide Web at:

[2] Videos of sequences portion of the North Tower collapse were posted online in the 9-11 Research Project at: The photos in Figures 2 & 3 are specifically at:

[3] Stephen Jones, "Why Indeed Did the World Trade Center Buildings Completely Collapse?" Journal of 911 Studies, Volume 3, September, 2006, linked from journal index posted at

[4] Jim Hoffman, "The North Tower's Dust Cloud: Analysis of Energy Requirements for the Expansion of the Dust Cloud Following the Collapse of 1 World Trade Center, October 16, 2003, posted at

[5] NIST Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Reports of the National Construction Safety Team on the Collapses of the World Trade Center Towers , posted at