Wtc why collapse

Thermodynamically, the heat contained in a material is related to the temperature through the heat capacity and the density or mass. Temperature is defined as an intensive property, meaning that it does not vary with the quantity of material, while the heat is an extensive property, which does vary with the amount of material. One way to distinguish the two is to note that if a second log is added to the fireplace, the temperature does not double; it stays roughly the same, but the size of the fire or the length of time the fire burns, or a combination of the two, doubles.

Thus, the fact that there were 90, L of jet fuel on a few floors of the WTC does not mean that this was an unusually hot fire. The temperature of the fire at the WTC was not unusual, and it was most definitely not capable of melting steel.

In combustion science, there are three basic types of flames, namely, a jet burner, a pre-mixed flame, and a diffuse flame. A jet burner generally involves mixing the fuel and the oxidant in nearly stoichiometric proportions and igniting the mixture in a constant-volume chamber. Since the combustion products cannot expand in the constant-volume chamber, they exit the chamber as a very high velocity, fully combusted, jet. This is what occurs in a jet engine, and this is the flame type that generates the most intense heat.

In a pre-mixed flame, the same nearly stoichiometric mixture is ignited as it exits a nozzle, under constant pressure conditions. It does not attain the flame velocities of a jet burner. An oxyacetylene torch or a Bunsen burner is a pre-mixed flame. A fireplace flame is a diffuse flame burning in air, as was the WTC fire.

Diffuse flames generate the lowest heat intensities of the three flame types. If the fuel and the oxidant start at ambient temperature, a maximum flame temperature can be defined. This maximum flame temperature is reduced by two-thirds if air is used rather than pure oxygen. The reason is that every molecule of oxygen releases the heat of formation of a molecule of carbon monoxide and a molecule of water.

If pure oxygen is used, this heat only needs to heat two molecules carbon monoxide and water , while with air, these two molecules must be heated plus four molecules of nitrogen. Thus, burning hydrocarbons in air produces only one-third the temperature increase as burning in pure oxygen because three times as many molecules must be heated when air is used. But it is very difficult to reach this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio.

Typically, diffuse flames are fuel rich, meaning that the excess fuel molecules, which are unburned, must also be heated. This fuel-rich diffuse flame can drop the temperature by up to a factor of two again. Some reports suggest that the aluminum from the aircraft ignited, creating very high temperatures. While it is possible to ignite aluminum under special conditions, such conditions are not commonly attained in a hydrocarbon-based diffuse flame.

In addition, the flame would be white hot, like a giant sparkler. There was no evidence of such aluminum ignition, which would have been visible even through the dense soot. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel.

The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire.

The buckling is initially plastic but quickly leads to fracture in the plastic hinges. The part of building lying beneath is then impacted again by an even larger mass falling with a greater velocity, and the series of impacts and failures then proceeds all the way down stage 5. Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination.

Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards. Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete storey at the level of impact. Under these conditions, structural steel loses rigidity and strength. The resulting failure of the floor system at the site of impact sent the 30 to 25 floors above free-falling onto the 80 to 85 floor structure below.

Both towers collapsed shortly afterwards. World Trade Center 7 was a storey building in the complex, which was not directly hit by an aircraft, and also collapsed later that day. There are a number of reasons this building collapsed on the day, despite not being hit by planes, which have been described by investigators, scientists and experts since. NIST says that debris from the collapse of the North Tower ignited fires on at least 10 floors of World Trade Center 7, some of which burned out of control because the automatic sprinkler system for some floors had failed partly due to city water lines damaged by the collapse of the Twin Towers.

Heat from the fires then caused steel support beams to expand which led to several floors collapsing. These tests established burning histories, mass burning rates, and heat release rates.

NIST conducted a single workstation burn and a multiple workstation burn as a part of its investigation. Why did NIST only provide temperature data for one of these tests? Was the ventilation used in these tests representative of the ventilation that was present in the WTC towers on Sept. The principal quantity measured was the rate of heat release.

This quantity, combined with the ventilation, heat losses to walls, etc. In these tests, the window openings were close to the same size and layout as in the fire floors in the towers. There was no glass in the windows, replicating the broken windows seen in the photographs of the vicinity of the tower fires.

The report includes plots of the heat release rate and temperature histories in multiple locations for all of the tests. Why didn't NIST consider a "controlled demolition" hypothesis with matching computer modeling and explanation like it did for the "pancake theory" hypothesis? NIST conducted an extremely thorough three-year investigation that included consideration of a number of hypotheses for the collapses of the WTC towers. Some technical experts—including about 85 career NIST experts and leading experts from the private sector and academia—reviewed tens of thousands of documents, interviewed more than 1, people, reviewed 7, segments of video footage and 7, photographs, analyzed pieces of steel from the wreckage, performed laboratory tests, and created sophisticated computer simulations of the sequence of events that occurred from the moment the aircraft struck the towers until they began to collapse.

Based on its comprehensive investigation, NIST concluded that the WTC towers collapsed according to the scenario detailed in the response to Question NIST's findings do not support the "pancake theory" of collapse, which is premised on a progressive failure of the floor systems in the WTC towers the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel "trusses" integrated with a concrete slab; see diagram.

Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.

NIST's findings also do not support the "controlled demolition" theory since there is conclusive evidence that:. Video evidence also showed unambiguously that the collapse progressed from the top to the bottom, and there was no evidence collected by NIST or by the New York City Police Department, the Port Authority Police Department, or the Fire Department of New York of any blast or explosions in the region below the impact and fire floors as the top building sections including and above the 98th floor in WTC 1 and the 82nd floor in WTC 2 began their downward movement upon collapse initiation.

In summary, NIST found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives. NIST also did not find any evidence that missiles were fired at or hit the towers.

Instead, photographs and videos from several angles clearly show that the collapse initiated at the fire and impact floors and that the collapse progressed from the initiating floors downward until the dust clouds obscured the view. Was the steel tested for explosives or thermite residues? The responses to previous questions demonstrate why NIST concluded that there were no explosives or controlled demolition involved in the collapses of the WTC towers.

As for thermite a mixture of powdered or granular aluminum metal and powdered iron oxide that burns at extremely high temperatures when ignited , it burns slowly relative to explosive materials and would require several minutes in contact with a massive steel section to heat it to a temperature that would result in substantial weakening.

Therefore, while a thermite reaction can cut through large steel columns, many thousands of pounds of thermite would need to have been placed inconspicuously ahead of time, remotely ignited, and somehow held in direct contact with the surface of hundreds of massive structural components to weaken the building. This makes it an unlikely substance for achieving a controlled demolition.

The metal compounds also would have been present in the construction materials making up the WTC towers, and sulfur is present in the gypsum wallboard that was prevalent in the interior partitions. Why were two distinct spikes—one for each tower—seen in seismic records before the towers collapsed?

Isn't this indicative of an explosion occurring in each tower? The seismic spikes for the collapse of the WTC towers are the result of debris from the collapsing towers impacting the ground. The spikes began approximately 10 seconds after the times for the start of each building's collapse and continued for approximately 15 seconds. There were no seismic signals that occurred prior to the initiation of the collapse of either tower.

The seismic record contains no evidence that would indicate explosions occurring prior to the collapse of the towers. How could the WTC towers collapse in only 11 seconds WTC 1 and 9 seconds WTC 2 —speeds that approximate that of a ball dropped from similar height in a vacuum with no air resistance?

NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: 1 precise timing of the initiation of collapse from video evidence, and 2 ground motion seismic signals recorded at Palisades, N.

As documented in Section 6. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass. In other words, the momentum which equals mass times velocity of the 12 to 28 stories WTC 1 and WTC 2, respectively falling on the supporting structure below which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum so greatly exceeded the strength capacity of the structure below that it the structure below was unable to stop or even to slow the falling mass.

The downward momentum felt by each successive lower floor was even larger due to the increasing mass. From video evidence, significant portions of the cores of both buildings roughly 60 stories of WTC 1 and 40 stories of WTC 2 are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence due to obstruction of view caused by debris clouds are reliable indicators of the total time it took for each building to collapse completely.

Weren't the puffs of smoke that were seen, as the collapse of each WTC tower starts, evidence of controlled demolition explosions? As stated in Section 6. These puffs were observed at many locations as the towers collapsed. In all cases, they had the appearance of jets of gas being pushed from the building through windows or between columns on the mechanical floors.

Such jets are expected since the air inside the building is compressed as the tower falls and must flow somewhere as the pressure builds. It is significant that similar "puffs" were observed numerous times on the fire floors in both towers prior to their collapses, perhaps due to falling walls or portions of a floor.

These observations confirm that even minor overpressures were transmitted through the towers and forced smoke and debris from the building. Why does NIST state that a yellow stream of molten metal seen in some photographs pouring down the side of WTC2 was aluminum from the crashed plane, even though aluminum burns with a white glow?