c. Meteorological Effects. Meteorological conditions will greatly influence fallout, particularly local fallout. Atmospheric winds are able to distribute fallout over large areas. For example, as a result of a surface burst of a 15 Mt thermonuclear device at Bikini Atoll on March 1, 1954, a roughly cigar-shaped area of the Pacific extending over 500 km downwind and varying in width to a maximum of 100 km was severely contaminated. Snow and rain, especially if they come from considerable heights, will accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radioactive cloud, limited areas of heavy contamination may be formed.
Roaring sounds of nuclear explosion
In Nagasaki and Hiroshima, the blast of the nuclear detonation sounded like a roar.
“At that moment, he heard a loud roar in the sky, and as he looked up, “wondering if it had in fact been the enemy, a blinding flash of light filled the sky and my body was showered in a wave of intense heat” [3]
Patricia Ondrovic, an emergency medical technician was working in front of WTC 6 evacuating the injured from the WTC towers when she was warned to move away from the towers as soon as possible. A few minutes later as she was running away from the complex, she heard a rumbling roaring sound. Soon after the South Tower collapsed.
KT: What did you do when the South Tower started coming down?
PO: I didn’t know what was happening, but there was a loud “roar” — lots of crashing sounds. I was attempting to put my stretcher back into the vehicle. [4]
The roaring sounds can distinctly be heard in the audio recording below in the 9/11 Eyewitness video.
Blast winds
The front of the blast wave can be many overpressures in magnitude and can damage the lungs, stomach, intestines and eardrums and cause internal hemorrhaging. However direct blast is not considered a primary cause of injuries that are treated in hospital because those close enough to suffer serious blast injury will die from initial thermal radiation (the first emission of thermal radiation from the fireball), or they will be crushed to death by overpressure. The greatest number of blast injuries are from falling buildings and flying debris such as glass [2] Some people resembled pincushions from the number of glass debris stuck in them [11].
Glass
Lots of glass flying around and broken windows are features of explosive events, and in nuclear explosions, the damage to windows is extensive. Blast winds can turn glass into missiles that injure people in the vicinity of an explosion.
“People with gruesome wounds were filing into the shelter one after another. They were horribly burned, covered with glass splinters like pin cushions” (America’s Reaction to the Atomic Bombings of Hiroshima and Nagasaki [11])
Hiroshima: “The explosion created a supersonic shock wave which was responsible for destroying most of the buildings in the blast zone. Fully half of the bomb’s released energy was released in the form of this wind, which spread out at 440 meters per second (1600 km/hr or 1000 miles/hr; the speed of sound is 330 meters per second). It not only knocked things down, it also filled the air with debris. The section of concrete wall below has numerous glass shards embedded in it, even though it was 2200 meters (one and a half miles) from the hypocenter, and sheltered from the blast by a low hill.” [27]
Glass shards embedded in this concrete wall (Hiroshima Atomic Museum) [27]
There is evidence of terrifically strong winds in the WTC area shortly after the collapse of the South Tower (the first tower to collapse). A car door ripped from its hinges by the blast winds struck Ondrovic as she was running away from the towers.
PO: I remember parts flying off — I think I got hit with a car door. I remember they were also on fire, but I don’t specifically recall the movie type fireball, but there was a loud bang as the door flew off the one car I was running past. [4]
Check the map to see the distance Vesey Street is from WTC 2 (South Tower). Vesey Street is a block away from the South Tower. Even at this distance from the tower, hurricane-force blast winds were in evidence, flinging objects around.
Map of WTC area [4]
It is typical of nuclear explosions that windows are shattered in buildings far from the explosion.
“Less than 10 percent of the buildings in the city survived without any damage, and the blast wave shattered glass in suburbs twelve miles away.” The Atomic Bombing of Hiroshima [29].
Windows of hundreds of buildings 400 feet away from the Twin Towers were shattered by the blast waves [28].
Widespread window damage though little structural damage in these buildings. Picture [28].
One person’s account of being caught in the explosion of the Hiroshima bomb. Her clothes were blown off and a glass splinter flew into her neck.
“Suddenly, a strong flash of light startled me-and then another .. To my surprise I discovered that I was completely naked .. All over the right side of my body I was cut and bleeding. A large splinter was protruding from a mangled wound in my thigh .. Embedded in my neck was a sizable fragment of glass which I matter-of-factly dislodged, and with the detachment of one stunned and shocked I studied it and my blood-stained hand.” America’s Reaction to the Atomic Bombings [11].
In nuclear explosions, the blast winds are so strong they can pick up people from the ground and turn them into projectiles and cause translational injuries as a result.
“The blast wave followed almost instantly for those close-in, often knocking them from their feet. Those that were indoors were usually spared the flash burns, but flying glass from broken windows filled most rooms, and all but the very strongest structures collapsed. One boy was blown through the windows of his house and across the street ..” (Atomic Bombing of Hiroshima) [29]
The blast effects were attenuated in the case of the WTC because the bombing happened within the walls of the towers. The towers’ walls acted as a shield and had a containing effect on the explosion and blast effects.
The blast blew out the windows of this firetruck but otherwise did little damage to it. More photos here.
Shattered windows but no other visible damage to the truck’s body. Picture [30]
Some other evidence of the blast winds that were present after the nuclear explosions in the Twin Towers.
- Thick dust clouds spewed from towers in all directions, at around 50 feet/second.
- Solid objects were thrown ahead of the dust — a feature of explosive demolition.
- The steel was thoroughly cleansed of its spray-on insulation [by the blast winds].
- Some pieces of the perimeter wall were thrown laterally 500 feet.
- Aluminum cladding was blown 500 feet in all directions.
From: WTC 9/11 Untold Story: The World Trade Center Demolition [28].
Ground Zero
At the hypocenter of a nuclear blast, there is total devastation. People disappear as if into thin air, and everything that used to exist becomes smouldering piles of black char. There are striking similarities between the scenes at Ground Zero of Hiroshima and Nagasaki and the Ground Zero of 9/11.
In the Hiroshima atomic bombing, everything in the hypocenter instantly vaporized.
“Then 8:15 am struck on the clock, and the sky over Hiroshima became illuminated with a flash brighter and more powerful than the sun. A wave of heat swept through the city and back again. The beautiful day, in an instant, became a nightmare. Any object within a two kilometer distance from the hypocenter suffered significant burn damage, and those located near the hypocenter were instantaneously vaporized. The Shima hospital, the hypocenter of the atomic bomb was vaporized, along with all her patients.” America’s Reaction to the Atomic Bombing [3].
Photos of Ground Zero of Hiroshima and Nagasaki:
Hiroshima before bombing:
A model of Hiroshima before the bombing. Hiroshima Atomic Bomb Museum [27].
Hiroshima after the bombing:
Ground Zero. Hiroshima after nuclear devastation [27].
Hiroshima aftermath. From tamilnation.org: Hiroshima & Nagasaki – the Worst Terror Attack in History The Record Speaks… [31]
Hiroshima in ruins [33]
Hiroshima: buildings leveled. Pic [34].
Hiroshima at Ground Zero. Pic [33].
Ground Zero: WTC. Pic [32].
Devastation at Ground Zero [32]
Ground Zero: WTC. Pic [32].
Ground Zero: WTC. Pic [32].
Ground Zero: WTC. Pic [32].
Ground Zero: WTC. Pic [32].
The Pile at Ground Zero. Pic [32].
Ground Zero Chernobyl disaster. Pic [35].
Chernobyl reactor after the accident.
Chernobyl
Mushroom Cloud [37]
Mushroom clouds are usually associated with nuclear explosions although they can occur with any large explosions such as volcanic eruptions.
Mushroom clouds appear with surface bursts or above-surface bursts.
When a nuclear bomb is detonated, a fireball forms. Like a hot-air balloon this fireball will rise and while it does so it sucks up air into it. The air produces air currents, called afterwinds. Inside the head of the cloud, the afterwinds have a toroidal motion. If the burst is close enough to the ground, the afterwinds will draw up dirt and debris up and these form the stem of the mushroom cloud.
Sometimes there is a donut ring around the stem of the mushroom cloud. These are vapor rings formed by the cooling of air from blast waves causing a sudden drop in surrounding air temperature.
In the Nagasaki bombing, a correspondent who accompanied one of the three aircraft on the bombing run, desribed the bomb producing a “pillar of purple fire”. From the top of this pillar, “came a giant mushroom that increased the height of the pillar by 45,000 feet”.
The heads of these mushrooms contain radioactive particles. These clouds eventually disperse in the wind and the radioactive particles deposit on the ground as nuclear fallout.
Measurements
Seismic shock
Patricia Ondrovic reports the ground shaking in addition to hearing the roaring sounds.
There are many other reports of ground shaking here [26]:
Michael Beehler — Firefighter (F.D.N.Y.) [Ladder 110] I was by I guess the outer part of the building and I just remember feeling the building starting to shake and this tremendous tremendous like roar …
Jody Bell — E.M.T. (E.M.S.) I lost track of time. You start to hear this rumble. You hear this rumble. Everything is shaking.
Nicholas Borrillo — Firefighter (F.D.N.Y.) on 23rd floor of North Tower:
Then we heard a rumble. We heard it and we felt the whole building shake. It was like being on a train, being in an earthquake …
The Richter readings of the seismic shock of the collapses are 2.1 for the South Tower (the first tower to collapse) and 2.3 for the North Tower (the first tower to be struck by a plane). [8] This is comparable to a small earthquake or tremor. Because one or more of the nuclear devices were detonated above the ground, this may have reduced the amplitude of the shock wave due to the lack of coupling to the ground. Additionally the force of the blast was directed upwards away from the ground.
With a directional blast, the energy is directed away from the ground, upwards into the building…ejecting matter in a “mushroom” at the top…the majority of the energy is absorbed by the potential energy of the falling material…practically in mid-air, thus, as Lerner-Lam describes, avoiding the coupling to the ground and would result in a very low seismic event. Such an event would be masked by the collapsing material. [7]
Other means may have been employed to reduce the coupling to the ground:
A further “shock absorption” could arise by locating the device on the back of a large truck…the recoil would be dampened by the suspension and tires, if you include pistons, the recoil could be further dampened and again masked within the collapse.. [7]
The seismic pattern has the fingerprint of a nuclear explosion [5].
All nuclear explosions have unique seismic signatures that are hard to disguise as earthquakes. They are short, sharp tremors that reveal the massive power and speed of the explosion. [5]
In the two seismic recordings below [5], there are striking similarities.
Onset of P waves from a Soviet underground nuclear test monitored at a relay station in England.
Seismic signature from the North Tower nuclear explosion.
Nuclear explosions are distinguished by having big P (compressional) waves and small S (shear) waves.[14] The seismic record below [15] shows the difference between an explosion and an earthquake. The P waves are more distinct from the S waves in a nuclear explosion. The P waves in the earthquake seismic record are less indistinguishable from the S waves and occur more regularly. The S waves in the earthquake record are prominent.
The pattern of seismic activity in the nuclear explosion shown above shows the Analysis of the recordings shown above reveal the following characteristics. There is minimal seismic activity prior to a big signal which occurs at the initiation of explosion. After the huge spiking, there is a ‘tail’ – a series of smaller spikes (S waves) that persist for some time before petering out.
Here is the record of an Indian nuclear test. [15] P waves are prominent. Like the nuclear explosion seismic pattern shown above, there is minimal seismic activity before the appearance of large P waves. These waves become smaller before trailing off.
Looking at the seismic record of WTC 2 below, recorded at a monitoring center 35 km north of the WTC, there is a similar pattern of seismic activity: low-amplitude peaks followed by a large spike. There are some differences however. In the case of the Twin Towers, at least two nuclear detonations occurred in each tower at close time intervals to each other. Hence the P waves will be more dense and there will be a double peaking. This is indeed what we see in the seismic record. Low amplitude waves (with a few small peaks) suddenly turning into a giant spike followed by another large spike and then the signal becomes smaller, trailing off in a ‘tail’. The double peaking is due to the overlap of the seismic signals from each nuclear explosion. The number of small peaks ahead of the big spikes in the WTC records are due to explosions that occurred before the nuclear detonations.
Seismic record of the South Tower [13]
Seismic record of the North Tower [13]
According to authorities, the recordings are ‘unexplained’. There was no significant earth-shaking when the airplanes impacted the buildings some 80+ storeys above ground level and as expected, spikes are absent at those points, but when the towers collapse, spikes appear. The reasons that the spikes are unusual are because they do not match the energy release from the alleged gravitational collapse and because they occur before the debris had a chance to hit the ground.
Much of the tower’s debris had turned into dust by the time it had hit the ground and so would have left much smaller seismic disturbances than the ones actually recorded (2.3 and 2.1 on the Richter scale).
“Only a small fraction of the energy from the collapsing towers was converted into ground motion” [8]
“Evidently, the energy source that shook the ground beneath the towers was many times more powerful than the total potential energy released by the falling mass of the huge towers.” [8]
Not only was there an energy mismatch but also a time mismatch [8].
“The Palisades seismic record shows that — as the collapses began — a huge seismic “spike” [actually a series of huge spikes] marked the moment the greatest energy went into the ground. The strongest jolts were all registered at the beginning of the collapses, well before the falling debris struck the earth.” [8]
A nuclear detonation is described as a sharp spike of short duration says seismologist Thorne Lay of California at Santa Cruz. The ‘unexplained’ spikes in the WTC 1 and WTC 2 record which occur at the beginning of the collapses are twenty times the amplitude of the other seismic waves recorded during the buildings’ fall. Seismologist Lerner-Lam says a 10-fold increase reflects a 100-fold increase in energy release [8]. Based on this the energy release during the collapse of the towers suddenly increased 4,000-fold at some point after the towers had started to break up.
The seismic recordings are evidence of nuclear explosions at the towers. If the nuclear devices had been coupled to the bedrock beneath the WTC towers, the seismic spikes would have been even larger .
Audio wave record
The audio wave evidence supports the seismic evidence.
VIDEO: 911 Eyewitness – Sound analysis shows explosives Dailymotion
‘9/11 Eyewitness video – sound analysis shows explosives prior to the collapse’ by Rick Siegel [9]. Full DVD is available from 911eyewitness.com
In this video of the North Tower collapse [9], the audio wave is juxtaposed against the sound recording. Audio wave spikes start to appear 17 seconds before the start of the fall of the tower (-17 seconds) and each spike is accompanied by a roaring boom sound (Ondrovic also heard a roaring sound when she the towers started to collapse – the characteristic roaring sound of a nuclear explosion). There are four spikes before the building starts to collapse:
- -17 seconds = medium to large spike
- -13.4 seconds = small spike
- -7.4 seconds = medium spike
- -3.5 seconds = medium spike
- 0 second = start of cascade
- +2 seconds = very large spike (first nuclear detonation)
- +10 seconds = very large spike (second nuclear detonation)
- +14 seconds = very large spike (Mach effect [13] of reflected wave, no accompanying boom sound) (MACHSTEM video)
After four of these small and medium-sized spikes, the collapse begins (at 0 seconds). Two seconds into the collapse, there is a huge spike. This appears simultaneously with the formation of mushroom clouds and pyroclastic flows that shoot up and out and then cascade down, with much ejection of material (at 45 degree angles).
A second giant spike appears at the 10 second mark and this coincides with a brightening of the screen and further acceleration of the energy of the collapse. The steel spire in the foreground of this video: Tower1_dust_cloud_afterglow [17] turns into a spray of dust at this point.
VIDEO: Tower1_dust_cloud_afterglow Dailymotion
Another 9/11 Eyewitness video of the audio wave for the North Tower [20]:
VIDEO: 911 Eyewitness video of the audio wave for the North Tower Dailymotion
Additional explosions
In this GIF image [16], you can see a smoke plume at the base of the Twin Towers. It was broadcast only on CNN. After it was broadcast once it was never shown again [24].
GIF [16] of explosion plume arising to one side of the base of the Twin Towers.
The South Tower has not exploded yet. There is some confusion about when the plume occurred. CNN told AFP investigative reporter Bollyn that the plume occurred immediately after the South Tower was hit by a plane [21]. The South Tower was struck at 9.02 am . However other visual depictions show the plume cloud appearing just before or at the same time the South Tower collapses (at 9.55 am)
The German Engineer’s site has photos that show the plume clearly. The caption “New explosion in World Trade Center” probably refers to the explosion(s) seen with the collapse of the South Tower. As can be seen in the screen shot of the CNN broadcast, the smoke plume is of great size and spreading out covering most of the buildings in that area. That is what we saw in other videos and photos of the WTC 2 collapse. No such smoke plume filled the space between the towers and other buildings when FL 175 struck WTC 2, so the plume shown in the CNN video that appears to the left of the screen occurred at the time of the WTC 2 collapse, not when it was hit by a plane. Besides only one tower appears in the screen shot on the right with the smoke plumes. In the middle photo, there are two distinct smoke plumes, one that is whiter and more dense and is located lower, and another that is longer, gray in color and is located posteriorly to the lower one.
German Engineers Help the USA: WTC 6 explodes [22]
The researcher in this video [24] investigates the plume in more detail.
VIDEO: 9/11 Ground Zero Part 2 Dailymotion
In this 9/11 Eyewitness video [24], a plume arises at the foot of the North Tower simultaneously as the North Tower begins to collapse. The perpetrators synchronized the detonation of preplanted explosives in WTC towers 3, 4, 5, and 6 with the detonation of the bombs in the Twin Towers to make it appear as if their destruction was the sole result of collateral damage from the collapses of the Twin Towers.
VIDEO: 911 Eyewitness – Witnesses reported rumbling and dust clouds before collapse Dailymotion [24]
Aerial view of Ground Zero. WTC 6 is in the top right corner. Photo [18].
Map of the WTC [18]. Note the position of WTC 6 relative to WTC 1 and 2 and the Hudson River.
Every building with a WTC prefix was completely destroyed or extensively damaged [18]. In this aerial shot you can see the cratered WTC 6 building in the top right hand corner of Ground Zero.
WTC 6 was extensively damaged in the WTC disaster. Aerial photography shows a huge crater in the center of the building with smaller holes surrounding this cratered section.
Aerial view of the partially destroyed WTC 6. To the left of it are the remains of WTC 1. [18]
If this building had been destroyed by a thermonuclear device, the device had a very low yield, lower than the yield of the thermonuclear bombs used in the Twin Towers. The perpetrators favored the use of nuclear devices to destroy the buildings because of their compact nature and the characteristics of their explosive effects. These detonation of just one or two of these devices produce a total effect that more closely mimics a tidal wave of destruction emanating from the one cause (universal weakening of the building supports). Conventional ordnance could have been used instead of nuclear devices but their use poses great logistical problems. Conventional ordnance was used in a supporting role.
The timing of the destruction of WTC 6 was intended to coincide with the destruction of South Tower to make it appear as if the collapse of the South Tower caused the damage to WTC 6. The perps had to place ordnance in the WTC 6 themselves as there was no guarantee that WTC 6 would be significantly damaged in the WTC 2 collapse. This is why an ordnance plume appears at the foot of the Twin Towers even before the South Tower begins to collapse and why the seismic record shows spikes before the collapse starts.
The other 3 early spikes and booms that occur before WTC 2 starts to collapse are evidence that multiple explosions occurred before its collapse. These could have been further detonations of WTC 6 or detonations of the other towers in the complex (WTC 3, 4, and 5). WTC 7 collapsed about 5 hours after the Twin Towers, and was intact until then. These buildings were extensively damaged in the WTC disaster [18].
In this aerial shot, the ruins of WTC 4 (bottom left), WTC 5 (bottom right), and WTC 6 (top right) can be seen [18]. Only the north wing of WTC 4 remains.
The map shows the location of the seven WTC towers. From this map it can be seen that most of WTC 4 was destroyed except for its north wing. [18]
WTC 1, 2 and 7 completely collapsed in this disaster. WTC 3 (the Marriott Hotel) was destroyed except for three floors. WTC 4 was all destroyed except for one wing (North wing), WTC 5 was extensively damaged, and the middle of WTC 6 was gouged out.
WTC 3 (Marriott Hotel) [19]
The aim of the perpetrators was to destroy all 7 towers and to make it appear as if the plane crashes had set of a sequence of events that resulted in their destruction. WTC 3, 4, 5, 6 were clandestinely destroyed by pre-planted ordnance devices which were set to detonate at the same time the Twin Towers collapsed. It appears the timing was slightly off as videos capture a smoke plume rising to the left of the Twin Towers before the demolition cascade of the South Tower even begins, and the sound recordings and seismic records confirm the occurrence of four explosions before the South Tower starts to collapse.
There is also visual evidence that these towers were exploded. In the aerial shots of WTC 6, there is a pattern of ‘holes’ that suggest explosions took place. Most explosives cause a spherical pattern of destruction around the center of explosion, and these spheres of destruction appear as circles and craters in aerial views. In the aerial views of the WTC 6 shown below, the circles that appear are well-defined.
WTC 6 ‘holes’ . Photo [18]
Similarly, the round punched-out areas in this aerial photo of WTC 5 are consistent with the detonation of explosives. It is extremely unlikely that falling debris punched out circular holes in the buildings.
WTC 5 ‘holes’. Photo [18]
The remains of WTC 6 (top left) and WTC 5 (bottom right of the picture). [25]
Aerial view of the damage to WTC 6. [25]
Eyewitness accounts of “basement” explosions
Because of the proximity of the Twin Towers to WTC 6 and the fact that they shared the same foundations (Bathtub and basement level floors) meant that the firefighters and other personnel in the South Tower who were in the basement or lower levels of the South Tower experienced the effects of that explosion (and the explosions of the other towers – WTC 3, 4, and 5).
There are many first-hand eyewitness accounts of ‘basement’ explosions occurring before the towers started to collapse.
Blast
Noise – roar
Seismic spikes
Expulsion of tower debris
– tridents thrown
Glass shattered in windows of buildings far from site
People covered in dust – pix – dust like snow – very thick
Paucity of the debris pile – low height
Dustification
Before and after pictures of Hiroshima/Nagasaki and WTC area – completeness of destruction
Pyroclastic flow
Mushroom cloud
Metal particles/dust – chemical analysis of dust, ablated steel, spire turns into dust, metal press
Lack of body parts – compare with IRA bombings
Cratering
Concaving – MMR
Body parts were small fragments scattered far
Measurement of effects
Winds – blew cloud of dust far and fast – pix of clouds and people running away from them
Thermal radiation
Light
Glow, bright light – show all the videos that show this light
Heat
“The numerous small fires that erupted simultaneously all around the city” (Bombing of Hiroshima) [29]
Incendiary Effects
Molten steel in basement – continuing niuclear reactions? Unexploded fission material
Toasted cars
Trees and leaves – picture
Twisted tridents
Meteorites
Soot
Lack of large-sized debris
Sulphurization of steel/brown rusty steel
Measurement of effects
Radiation Effects
EMP pulse
Fallout cloud
Radioactivity detected post 9/11 – 80 unexpected hot spots including over Israeli embassy
Radiation – summary of medical effects
Radiation hotspots
The Hill (Fresh Kills) – toxic, radioactive, bubbling
The Pile – fluorescent, blue glow
Cancers
Containment of radioactivity – extensive washing that started the same afternoon, removal of steel
Measurement of Effects
Radionuclides
(1) Heat. Within less than a millionth of a second of the detonation of a nuclear weapon, the extremely hot weapon residues radiate great amounts of energy. This leads to the formation of a hot and highly luminous, spherical mass of air and gaseous residue which is the fireball. The heat radiated from the fireball contributes to the overall damage caused by a nuclear burst by igniting combustibles and thus starting fires in buildings and forests. These fires may spread rapidly among the debris produced by the blast. In addition, this intense heat can burn exposed personnel at great distances from ground zero where the effects of blast and initial nuclear radiation become insignificant. The degree of injury from thermal radiation becomes more marked with the in- creasing size of the weapon. The degree of injury from thermal radiation is also affected by weather and terrain. During periods of limited visibility, the heat effect will be reduced significantly. Additionally, since thermal radiation is primarily a line-of-sight phenomena, terrain masking can help reduce its effects (figure 29-3).
Thermal
(2) Light . The fireball formed at the instant of a nuclear detonation is a source of extremely bright light. To an observer, 135 miles away from the explosion, the fireball of a 1-megaton weapon would appear to be many times more brilliant than the Sun at noon. The surface temperatures of the fireball, upon which the brightness depends, do not vary greatly with the size of the weapon. Consequently, the brightness of the fireball is roughly the same, regardless of the weapon yield. This light can cause injuries to personnel in the form of temporary or permanent blindness. Temporary blindness from a burst during daylight should be of very short duration and is not an important consideration for anyone other than aircrew members. At night, this loss of vision will last for longer periods because the eyes have been adapted to the dark. However, recovery should be complete within 15 minutes. The light flash can cause permanent injury to the eyes due to burns within the eye, but this is only likely to occur in personnel who happen to be looking directly at the fireball at the instant of explosion (figure 29-4).
Light from blast can be seen very far away, especially at night.
c. Nuclear Radiation :
(1) Initial nuclear radiation is the radiation emitted in the first minute after detonation. For practical purposes, it consists primarily of neutrons and gamma rays. Both of these types of radiation, although different in character, can travel considerable distances through the air and can produce harmful effects in humans. Gamma rays are invisible rays similar to X rays. These penetrating rays interact with the human body and cause damage to tissues and the blood-forming cells. The effects of neutrons on the body resemble those of gamma rays. They are highly penetrating and are easily absorbed by human tissue. Neutron radiation can penetrate several inches of tissue. The neutron radiation produces extensive tissue damage within the body. The major problem in protecting against the effects of initial radiation is that a person may have received a lethal or incapacitating dose of radiation before taking any protective action (figure 29-5).
Initial radiation
(2) Residual nuclear radiation is that which lasts after the first minute and consists primarily of fallout and neutron-induced radiation.
(a) The primary hazard of residual radiation results from the creation of fallout. Fallout is produced when material from the Earth is drawn into the fireball, vaporized, combined with radioactive material, and condensed to particles which then fall back to the Earth. The larger particles fall back immediately in the vicinity of ground zero. The smaller particles are carried by the winds until they gradually settle on the Earth’s surface. The contaminated areas created by fallout may be very small or may extend over many thousands of square miles. The dose rate may vary from an insignificant level to an extremely dangerous one for all personnel not taking protective measures.
(b) A secondary hazard which may arise is the neutron-induced radioactivity on the Earth’s surface in the immediate vicinity of ground zero. The intensity and extent of the induced radiation field depend on the type of soil in the area around ground zero, the height of the burst, and the type and yield of the weapon. The only significant source of residual radiation from an airburst weapon is induced activity in the soil of a limited circular pattern directly beneath the point of burst (figure 29-6).
Residual radiation
29-3. Types of Nuclear Bursts. Nuclear bursts may be classified into three types according to the height of burst-airbursts, surface bursts, and subsurface bursts (figure 29-7).
a. Airburst . The detonation of a nuclear weapon at such a height that the fireball does not touch the surface of the Earth is called an airburst. Blast, thermal radiation, and initial radiation effects are increased in a low airburst. Fallout of radioactive material from an airburst is not of survival significance unless rain or snow falls through the radioactive cloud and brings the material to Earth. Neutrons from the detonation will cause induced radiation in the soil around ground zero. Except for very high airbursts, neutron-induced radiation in the area of ground zero will be of concern to survivors who are required to go into or across the area. Radiological monitoring will be required as units pass through such an area so that hazardous levels of radiation can be detected and avoided, if possible.
b. Surface Burst . The detonation of a nuclear weapon at such a height that the fireball touches the surface of the Earth or water is called a surface burst. Blast, thermal radiation, and initial nuclear radiation are not as widespread as from an airburst. Induced radiation is present but will be masked by residual radiation from fallout. The fallout produced by a surface burst is by far its most dangerous effect because the burst picks up a great deal more debris and radioactivates this debris; and, depending on the prevailing winds, the fallout covers thousands of square miles with high levels of radioactivity.
Types of blasts
c. Subsurface Burst . The detonation of a nuclear weapon so that the center of the fireball is beneath the surface of the Earth or water is called a subsurface burst. If a fireball of this type breaks through the surface, fallout will be produced. Thermal radiation will not be a significant hazard since it will be almost completely absorbed by the soil. Blast effects will also be significantly reduced. Shock waves passing through the ground or water will extend for a limited distance. The range of the initial nuclear radiation will be considerably less than from either of the other two types of bursts because this will also be absorbed to a great extent by the soil. However, extremely hazardous residual radiation will occur in and around any crater. If the fireball does break the surface, shock waves will pass through the ground and craters may result due to settling.
29-4. Injuries . The explosion of a nuclear bomb can cause three types of injures-blast, thermal radiation and nuclear radiation. Many survivors receive a combination of two or all three of the above injuries. For example, an unprotected person could be killed by a piece of debris, could be burned to death, or could be killed by initial nuclear radiation if the person is within a few thousand yards from the center of the blast.
a. Blast Injuries . Direct blast can cause damage to lungs, stomach, intestines, and eardrums, or can cause internal hemorrhaging. However, the direct blast is not considered a primary cause of injury because those close enough to suffer serious injury from the direct blast will probably die as a result of initial thermal radiation, or they will be crushed to death. The greatest number of blast injuries are received as an indirect result of the blast from falling buildings, flying objects, and shattered glass.
b. Thermal Radiation Injuries. Burns are classified in degrees according to the depth to which the tissues are injured. In first-degree burns, the skin is reddened as in sunburn. In second-degree burns, the skin is blistered as from contact with boiling water or hot metal. In third-degree burns, the skin is destroyed or charred and the injury extends through the outer skin to deeper tissues. The degree of burn received from thermal radiation depends upon weather conditions, distance from the explosion, and available protection. Many thermal casualties are compounded by nuclear radiation and indirect blast injury. This makes it difficult to attribute casualties to thermal radiation alone.
c. Nuclear Radiation Injuries. The injurious effects of nuclear radiation from a nuclear explosion represent a new threat which is completely absent in conventional explosions. This does not infer that this source of injury is the most important in a nuclear explosion. Rays from radioactive material are not as great a hazard as people fear. The amount of danger from fallout depends upon where and how the nuclear bomb explodes and how well the person is protected. The greatest danger from residual radiation (fallout) comes from exposure for a long period of time to radioactive particles which are nearby, or from dust settling on the body or clothing. Since fallout (like X rays) can destroy living tissue, particularly in the blood-forming system, the exposure of persons working in a radioactive or “hot” area must be controlled so as not to exceed a safe limit. Although a person can become seriously ill and even die from breathing radioactive dust, there is less danger from this than when the whole body is exposed to fallout. Remember, all types of radiation are dangerous (nuclear, thermal, X ray, or even that from an infrared lamp).
Types of bursts [REF=http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html. Nuclear Weapon Archive, Effects of Explosions]
It might seem logical that the most destructive way of using a nuclear weapon would be to explode it right in the middle of its target – i.e. ground level. But for most uses this is not true. Generally nuclear weapons are designed to explode above the ground – as air bursts (the point directly below the burst point is called the hypocenter). Surface (and sub-surface) bursts can be used for special purposes.
5.4.1 Air Bursts
When an explosion occurs it sends out a shock wave like an expanding soap bubble. If the explosion occurs above the ground the bubble expands and when it reaches the ground it is reflected – i.e. the shock front bounces off the ground to form a second shock wave travelling behind the first. This second shock wave travels faster than the first, or direct, shock wave since it is travelling through air already moving at high speed due to the passage of the direct wave. The reflected shock wave tends to overtake the direct shock wave and when it does they combine to form a single reinforced wave.
This is called the Mach Effect, and produces a skirt around the base of the shock wave bubble where the two shock waves have combined. This skirt sweeps outward as an expanding circle along the ground with an amplified effect compared to the single shock wave produced by a ground burst.
The higher the burst altitude, the weaker the shock wave is when it first reaches the ground. On the other hand, the shock wave will also affect a larger area. Air bursts therefore reduce the peak intensity of the shock wave, but increase the area over which the blast is felt. For a given explosion yield, and a given blast pressure, there is a unique burst altitude at which the area subjected to that pressure is maximized. This is called the optimum burst height for that yield and pressure.
All targets have some level of vulnerability to blast effects. When some threshold of blast pressure is reached the target is completely destroyed. Subjecting the target to pressures higher than that accomplishes nothing. By selecting an appropriate burst height, an air burst can destroy a much larger area for most targets than can surface bursts.
The Mach Effect enhances shock waves with pressures below 50 psi. At or above this pressure the effect provides very little enhancement, so air bursts have little advantage if very high blast pressures are desired.
An additional effect of air bursts is that thermal radiation is also distributed in a more damaging fashion. Since the fireball is formed above the earth, the radiation arrives at a steeper angle and is less likely to be blocked by intervening obstacles and low altitude haze.
5.4.2 Surface Bursts
Surface bursts are useful if local fallout is desired, or if the blast is intended to destroy a buried or very hard structure like a missile silo or a dam. Shock waves are transmitted through the soil more effectively if the bomb is exploded in immediate contact with it, so ground bursts would be used for destroying buried command centers and the like. Some targets, like earth-fill dams, require actual cratering to be destroyed and would be ground burst targets.
5.4.3 Sub-Surface Bursts
Exploding a bomb below ground level can be even more effective for producing craters and destroying buried structures. It can also eliminate thermal radiation and reduce the range of blast effects substantially. The problem, of course is getting the bomb underground. Earth-penetrating bombs have been developed that can punch over one hundred feet into the earth.
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The first energy to escape from the bomb are gamma rays. A significant number of these rays will escape the bomb casing and tampers and escape into the outside world where they strike and ionize air molecules causing chemical reactions that form a ‘smog’ around the bomb. The smog is composed of ozone, nitric and nitrous oxides. These chemicals impart a brown color to the smog.
Incendiary effects
Incendiary effects refers to the occurrence of fires after the explosion. These fires are the result of thermal radiation and blast.
Hiroshima: ‘Those closest to the explosion died instantly, their bodies turned to black char. Nearby birds burst into flames in mid-air, and dry, combustible materials such as paper instantly ignited as far away as 6,400 feet from ground zero.’
[REF=http://www.mbe.doe.gov/me70/manhattan/hiroshima.htm]
The fireball incinerated matter in its radius. Two-thirds of the Twin Towers was reduced to dust. [REF] 11oo people have not been identified as yet. There are no body parts, not a fingernail, not a bone fragment, a tooth to show these people existed. [REF]
Like the people at the hypocenter of the Hiroshima detonation, these people simply vanished.
The paucity of debris was staggering. In an earthquake-type of pancake-collapse (gravity collapse), you expect to find debris of crushed furniture. However this fireman had this to say about the amount of identifiable debris.
Firefighter Joe Casaliggi: “You have two 110-story office buildings. You don’t find a desk, you don’t find a chair, you don’t find a telephone, a computer. The biggest piece of a telephone I found was half of the keypad, and it was about this big.”
http://911research.wtc7.net/reviews/911mysteries/index.html
An EMT, Patricia Ondrovic, who helped in recovery detail after the WTC attacks, had this to say about what she found:
PO: I never came across any personal effects. The things I did find were charred, burnt, rubble covered in soot. I guess that’s the needle in the haystack [the ATM card]. REF=http://killtown.blogspot.com/2006/02/911-rescuer-saw-explosions-inside-wtc.html
Melted bottles at Hiroshima [REF=http://www.richard-seaman.com/Travel/Japan/Hiroshima/AtomicBombMuseum/individualArtifacts/]
“The heat of the blast, estimated at 3000 to 4000 degrees celcius (5500 to 7000 degrees fahrenheit) immediately below the explosion, was sufficient to melt glass bottles such as these, which were 900 meters away.
The bomb was designed to explode in the air, 600 meters (2000 feet) above the ground, in order to maximize the destructive effect.
The fireball which resulted reached a diameter of 300 meters (1000 feet).” [REF=http://www.richard-seaman.com/Travel/Japan/Hiroshima/AtomicBombMuseum/individualArtifacts/]
The only filing cabinet found
The only filing cabinet found in the WTC debris despite the fact that the WTC would have contained hundreds of filing cabinets. This filing cabinet is a twisted burned piece of wreckage.
‘Another object looks like just a crumpled, twisted chunk of metal — but it’s one of the few recognizable objects found in the debris at Ground Zero. With a 110-story building collapsing on itself in a matter of seconds, pretty much everything was pulverized beyond recognition. This basketball-sized lump’s identity was given away when money fell out of it. It was once a filing cabinet at a Ben & Jerry’s ice cream shop in the World Trade Center.’ http://www.pittsburghlive.com/x/pittsburghtrib/s_247740.html
WTC ‘meteorite’
A meteorite-like object that actually consists of a few floors of a WTC tower compressed together during the collapse (nuclear detonation). Furniture, twisted metal, pipes, cords and even papers with legible type are fused together. [REF=http://www.amny.com/entertainment/news/am-wtcrelics-pg2006,0,6613706.photogallery?index=57] Only something that is a source of tremendous heat can create something like this.
[REF=http://www.amny.com/entertainment/news/am-wtcrelics-pg2006,0,6613706.photogallery?index=35]
Metal was deformed by the blast and thermal energy of the nuclear explosion. The only thing powerful enough to bend these huge beams of steel in a split second is nuclear energy.
These bent pieces of metal are ‘tridents’. These were at the base of the center and formed the structural part of the ground level exterior arches of the twin towers. Three of these relics that are preserved in a display kept at a hangar of Kennedy International Airport weigh over 30 tons. [REF=http://www.amny.com/entertainment/news/am-wtcrelics-pg2006,0,6613706.photogallery?index=57]
This is a collection of the metal pieces that were warped in the WTC attack. Notice the resemblance to the bent pieces of metal in the Nagasaki Atomic Bomb Museum shown below.
Twisted beams of steel from the WTC attack. These are stored at the hangar with other relics from 9/11.
Angle iron from a factory. Part of Mitsubishi Nagasaki Arms Factory Mori-machi Plant located about 1.3 kilometers from the hypocenter
[REF=http://www1.city.nagasaki.nagasaki.jp/na-b…seum/m2-7e.html
The Nagasaki Atomic Bomb Museum]
Cars in the vicinity of the WTC were toasted. The parts of the cars facing the WTC were affected whereas the parts not facing were unaffected. Like the human body, thermal radiation of nuclear detonations does not penetrate objects. [ REF=http://www.answers.com/radiation%20poisoning]
Thermal radiation from a nuclear explosion ignited upholstery and caused fire to spread in this car at the Nevada test site. [REF=http://www.nukefix.org/weapon.html. Nukefix – Blast Effects]
Car ignited at the Nevada test site
Cars on fire. Look at all the paper that escaped damage. Paper and powder effect.
Blast effects
Radiation Effects
[REF=http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html. Nuclear Weapon Archive, Effects of nuclear weapons]
The first energy to escape from the bomb are the gamma rays produced by the nuclear reactions. They have energies in the MeV range, and a significant number of them penetrate through the tampers and bomb casing and escape into the outside world at the speed of light. The gamma rays strike and ionize the surrounding air molecules, causing chemical reactions that form a dense layer of “smog” tens of meters deep around the bomb. This smog is composed primarily of ozone, and nitric and nitrous oxides.
X-rays, particularly the ones at the upper end of the energy range, have substantial penetrating power and can travel significant distances through matter at the speed of light before being absorbed. Atoms become excited when they absorb x-rays, and after a time they re-emit part of the energy as a new lower energy x-ray. By a chain of emissions and absorptions, the x-rays carry energy out of the hot center of the bomb, a process called radiative transport. Since each absorption/re-emission event takes a certain amount of time, and the direction of re-emission is random (as likely back toward the center of the bomb as away from it), the net rate of radiative transport is considerably slower than the speed of light. It is however initially much faster than the expansion of the plasma (ionized gas) making up the fireball or the velocity of the neutrons.
5.3.2 Ionizing Radiation Physics
There are four types of ionizing radiation produced by nuclear explosions that can cause significant injury: neutrons, gamma rays, beta particles, and alpha particles. Gamma rays are energetic (short wavelength) photons (as are X-rays), beta particles are energetic (fast moving) electrons, and alpha particles are energetic helium nuclei. Neutrons are damaging whether they are energetic or not, although the faster they are, the worse their effects.
They all share the same basic mechanism for causing injury though: the creation of chemically reactive compounds called “free radicals” that disrupt the normal chemistry of living cells. These radicals are produced when the energetic radiation strikes a molecule in the living issue, and breaks it into ionized (electrically charged) fragments. Fast neutrons can do this also, but all neutrons can also transmute ordinary atoms into radioactive isotopes, creating even more ionizing radiation in the body.
The different types of radiation present different risks however. Neutrons and gamma rays are very penetrating types of radiation. They are the hardest to stop with shielding. They can travel through hundreds of meters of air and the walls of ordinary houses. They can thus deliver deadly radiation doses even if an organism is not in immediate contact with the source. Beta particles are less penetrating, they can travel through several meters of air, but not walls, and can cause serious injury to organisms that are near to the source. Alpha particles have a range of only a few centimeters in air, and cannot even penetrate skin. Alphas can only cause injury if the emitting isotope is ingested.
The shielding effect of various materials to radiation is usually expressed in half-value thickness, or tenth-value thickness: in other words, the thickness of material required to reduce the intensity of radiation by one-half or one-tenth. Successive layers of shielding each reduce the intensity by the same proportion, so three tenth-value thickness reduce the intensity to one-thousandth (a tenth-value thickness is about 3.3 half-value thicknesses). Some example tenth-value thicknesses for gamma rays are: steel 8.4-11 cm, concrete 28-41 cm, earth 41-61 cm, water 61-100 cm, and wood 100-160 cm. The thickness ranges indicate the varying shielding effect for different gamma ray energies.
Even light clothing provides substantial shielding to beta rays.
5.3.2.1 Sources of Radiation
5.3.2.1.1 Prompt Radiation
Radiation is produced directly by the nuclear reactions that generate the explosion, and by the decay of radioactive products left over (either fission debris, or induced radioactivity from captured neutrons).
The explosion itself emits a very brief burst (about 100 nanoseconds) of gamma rays and neutrons, before the bomb has blown itself apart. The intensity of these emissions depends very heavily on the type of weapon and the specific design. In most designs the initial gamma ray burst is almost entirely absorbed by the bomb (tamper, casing, explosives, etc.) so it contributes little to the radiation hazard. The neutrons, being more penetrating, may escape. Both fission and fusion reactions produce neutrons. Fusion produces many more of them per kiloton of yield, and they are generally more energetic than fission neutrons. Some weapons (neutron bombs) are designed specifically to emit as much energy in the form as neutrons as possible. In heavily tamped fission bombs few if any neutrons escape. It is estimated that no significant neutron exposure occurred from Fat Man, and only 2% of the total radiation dose from Little Boy was due to neutrons.
The neutron burst itself can be a significant source of radiation, depending on weapon design. As the neutrons travel through the air they are slowed by collisions with air atoms, and are eventually captured. Even this process of neutron attenuation generates hazardous radiation. Part of the kinetic energy lost by fast neutrons as they slow is converted into gamma rays, some with very high energies (for the 14.1 MeV fusion neutrons). The duration of production for these neutron scattering gammas is about 10 microseconds. The capture of neutrons by nitrogen-14 also produces gammas, a process completed by 100 milliseconds.
Immediately after the explosion, there are substantial amounts of fission products with very short half-lifes (milliseconds to minutes). The decay of these isotopes generate correspondingly intense gamma radiation that is emitted directly from the fireball. This process is essentially complete within 10 seconds.
The relative importance of these gamma ray sources depends on the size of the explosion. Small explosions (20 kt, say) can generate up to 25% of the gamma dose from the direct gammas and neutron reactions. For large explosions (1 Mt) this contribution is essentially zero. In all cases, the bulk of the gammas are produced by the rapid decay of radioactive debris.
5.3.2.1.2 Delayed Radiation
Radioactive decay is the sole source of beta and alpha particles. They are also emitted during the immediate decay mentioned above of course, but their range is too short to make any prompt radiation contribution. Betas and alphas become important when fallout begins settling out. Gammas remain very important at this stage as well.
Fallout is a complex mixture of different radioactive isotopes, the composition of which continually changes as each isotope decays into other isotopes. Many isotopes make significant contributions to the overall radiation level. Radiation from short lived isotopes dominates initially, and the general trend is for the intensity to continually decline as they disappear. Over time the longer lived isotopes become increasingly important, and a small number of isotopes emerge as particular long-term hazards.
Radioactive isotopes are usually measured in terms of curies. A curie is the quantity of radioactive material that undergoes 3.7×10^10 decays/sec (equal to 1 g of radium-226). More recently the SI unit bequerel has become common in scientific literature, one bequerel is 1 decay/sec . The fission of 57 grams of material produces 3×10^23 atoms of fission products (two for each atom of fissionable material). One minute after the explosion this mass is undergoing decays at a rate of 10^21 disintegrations/sec (3×10^10 curies). It is estimated that if these products were spread over 1 km^2, then at a height of 1 m above the ground one hour after the explosion the radiation intensity would be 7500 rads/hr.
Isotopes of special importance include iodine-131, strontium-90 and 89, and cesium-137. This is due to both their relative abundance in fallout, and to their special biological affinity. Isotopes that are readily absorbed by the body, and concentrated and stored in particular tissues can cause harm out of proportion to their abundance.
Iodine-131 is a beta and gamma emitter with a half-life of 8.07 days (specific activity 124,000 curies/g) Its decay energy is 970 KeV; usually divided between 606 KeV beta, 364 KeV gamma. Due to its short half-life it is most dangerous in the weeks immediately after the explosion, but hazardous amounts can persist for a few months. It constitutes some 2% of fission-produced isotopes – 1.6×10^5 curies/kt. Iodine is readily absorbed by the body and concentrated in one small gland, the thyroid.
Strontium-90 is a beta emitter (546 KeV, no gammas) with a half-life of 28.1 years (specific activity 141 curies/g), Sr-89 is a beta emitter (1.463 MeV, gammas very rarely) with a half-life of 52 days (specific activity 28,200 Ci/g). Each of these isotopes constitutes about 3% of total fission isotopes: 190 curies of Sr-90 and 3.8×10^4 curies of Sr-89 per kiloton. Due to their chemical resemblance to calcium these isotopes are absorbed fairly well, and stored in bones. Sr-89 is an important hazard for a year or two after an explosion, but Sr-90 remains a hazard for centuries. Actually most of the injury from Sr-90 is due to its daughter isotope yttrium-90. Y-90 has a half-life of only 64.2 hours, so it decays as fast as it is formed, and emits 2.27 MeV beta particles.
Cesium-137 is a beta and gamma emitter with a half-life of 30.0 years (specific activity 87 Ci/g). Its decay energy is 1.176 MeV; usually divided by 514 KeV beta, 662 KeV gamma. It comprises some 3-3.5% of total fission products – 200 curies/kt. It is the primary long-term gamma emitter hazard from fallout, and remains a hazard for centuries.
Although not important for acute radiation effects, the isotopes carbon-14 and tritium are also of interest because of possible genetic injury. These are not direct fission products. They are produced by the interaction of fission and fusion neutrons with the atmosphere and, in the case of tritium, as a direct product of fusion reactions. Most of the tritium generated by fusion is consumed in the explosion but significant amounts survive. Tritium is also formed by the capture of fast neutrons by nitrogen atoms in the air: N-14 + n -> T + C-12. Carbon-14 in also formed by neutron-nitrogen reactions: N-14 + n -> C-14 + p. Tritium is a very weak beta emitter (18.6 KeV, no gamma) with a half-life of 12.3 years (9700 Ci/g).
Carbon-14 is also a weak beta emitter (156 KeV, no gamma), with a half-life of 5730 years (4.46 Ci/g). Atmospheric testing during the fifties and early sixties produced about 3.4 g of C-14 per kiloton (15.2 curies) for a total release of 1.75 tonnes (7.75×10^6 curies). For comparison, only about 1.2 tonnes of C-14 naturally exists, divided between the atmosphere (1 tonne) and living matter (0.2 tonne). Another 50-80 tonnes is dissolved in the oceans. Due to carbon exchange between the atmosphere and oceans, the half-life of C-14 residing in the atmosphere is only about 6 years. By now the atmospheric concentration has returned to within 1% or so of normal. High levels of C-14 remain in organic material formed during the sixties (in wood, say, or DNA).
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Flash of the nuclear detonation
“Then 8:15 am struck on the clock, and the sky over Hiroshima became illuminated with a flash brighter and more powerful than the sun. ” [REF= America’s reaction]
“Suddenly, a strong flash of light startled me-and then another. . . . A profound weakness overcame me, so I stopped to regain my strength. To my surprise I discovered that I was completely naked. . . “[America’s reaction]
The next moment, “I was blinded for a moment by a piercing flash of bright light, and the air filled with yellow smoke like poison gas. Momentarily, it got so dark I couldn’t see anything. There was a loud, dull, thunderous noise. [America’s reaction]
“[T]here came a flash of light. I can’t describe what it was like. And then, I felt some hot mask attacking me all of a sudden.” [America’s reaction]
“My sister, nephew and I were playing inside the shelter when there was a sudden, brilliant flash of light. I remember nothing else.” [Ref= america’s reaction]
You can see the afteglow of nuclear detonation in this video of WTC 1 exploding. A strong light, more intense than sunlight bathes the video screen with its flash. It lasts more than 10 seconds and happens halfway through the collapse. At the same time, the steel spire that sat atop the WTC evaporates into a trail of steel dust in the foreground. This was the moment when the nuclear device in the tower was detonated. There was a sudden acceleration of energy of the collapse at the time. At the end of the video you can see a distinct white-colored mushroom cloud.
http://www.911research.com/wtc/evidence/videos/docs/tower1_dust_cloud_afterglow.mpg
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Demolition experts destroy the foundations and the bottom parts of any steel support columns in the core as a first step when they do an “implosion-type” or straight-down demolition. The aim is get the debris to fall downwards onto the building’s footprint by getting the building to collapse inwards on itself.
The principles used on an implosion are basically the same whether it is a true implosion, or if the structure is simply going to be laid out. The principle tool in an implosion is gravity. The explosives are used to weaken and cause the supporting members of the structure to fail, thus allowing gravity to pull the structure down or over [12]
The explosions at the base of the skyscrapers were to ensure the building did not topple over. Since the perpetrators wanted the whole building to disintegrate and crumble from the top to the basement, they had to place the charges at the base of the building.
“The WTC towers had a 6-times carrying capacity compared to the mass of the building, the steel members of the outer walls about 3x and the core columns
about 3x. A tower could not fall all the way to the ground, unless all pillars are cut near the bedrock. If those pillars were cut eg. at half way, the tower might collapse (with sufficient charges) up to that spot and then it would certainly fall over. 200 meters worth of tower would remain standing, and neighbouring buildings would probably be damaged.” [6]
Once an abyss is created, it is much easier for the building to fall inwards on itself.
“As the abyss (20 meters) opens in the bottom of the central core, above it there will be fairly heavy
part of the building drawing towards the center and downwards.” [6]
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The Day America Was Punked 