According to a theory advanced by a SINTEF materials scientist, a mixture of water from sprinkler systems and molten aluminium from melted aircraft hulls created explosions that led to the collapse of the Twin Towers in Manhattan.

Just before the two New York skyscrapers collapsed on Sept. 11, 2001, powerful explosions within the building could be heard, leading many people to believe that overheated steel beams in the building were not the cause of the collapse.

The explosions fed the conspiracy theories that someone had placed explosives inside the towers.

At an international materials technology conference in San Diego, the audience heard senior scientist Christian Simensen of SINTEF Materials and Chemistry present an alternative theory based on the physics of materials of what happened in the towers when they were attacked by the aircraft. The SINTEF researcher believes that his theory is much more likely to reflect the actual situation than the official explanation of the collapse.

In the wake of the conference Simensen had an article published in the journal Aluminium International Today, describing his theory.

Explosive meeting of molten aluminium and water

Simensen believes that it is overwhelmingly likely that the two aircraft were trapped inside an insulating layer of building debris within the skyscrapers. This leads him to believe that it was the aircraft hulls rather than the buildings themselves that absorbed most of the heat from the burning aircraft fuel.

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The SINTEF scientist believes that the heat melted the aluminium of the aircraft hulls, and the core of his theory is that molten aluminium then found its way downwards within the buildings through staircases and gaps in the floor -- and that the flowing aluminium underwent a chemical reaction with water from the sprinklers in the floors below.

"Both scientific experiments and 250 reported disasters suffered by the aluminium industry have shown that the combination of molten aluminium and water releases enormous explosions," says Simensen.

"Explosions demolished the towers"

Simensen continues: "I regard it as extremely likely that it was these explosions that made the skyscrapers collapse by tearing out part of the internal structure, and that this caused the uppermost floors of the buildings to fall and crush the lower parts. In other words, I believe that these were the explosions that were heard by people in the vicinity and that have since given life to the conspiracy theories that explosives had been placed in the skyscrapers."

Practical use

"Could your theory be used to protect human life and material values if other skyscrapers are ever hit by large aircraft?"

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"Yes, as a matter of fact it could. One lesson is that we could develop means of rapidly emptying sprinkler systems in the floors under the point of impact. Another possibility would be to fire in a rocket carrying a fire-retardant that would overlie the aircraft body and prevent the metal alloy from becoming overheated."

Day of unreality

It was in the morning New York time on September 11, 2001, when two Boeing 767 passenger planes flew into the World Trade Center's "Twin Towers" in Manhattan in New York. One hour later, WTC2 collapsed, followed after half an hour by WTC1.

Neighbouring buildings were bombarded by flying debris when the towers collapsed. The 47-storey skyscraper called 7 World Trade Center also caught fire and collapsed several hours later at 17.20.

30 tonnes of aluminium

The official report on the causes of the collapse of the three buildings was drawn up by a commission appointed by the federal government and has since been supported by other publications. The report came to the conclusion that the collapse was caused by heating and failure of structural steel beams in the centre of the buildings.

"I believe that it is overwhelmingly probable that the theories regarding the cause of the collapse of WTC1 and WTC2 are wrong, but that the report very likely came to the correct conclusion as regards WTC7," says Simensen.

"Why should we believe your alternative theory rather than the official explanation?"

"To put it as succinctly as possible: because the federal government commission did not take sufficiently into account the fact that the aircraft brought 30 tonnes of aluminium into each of the two towers."

The collision

"What sort of evidence do you have for the theory that you are putting forward?"

"I base my theory on comparisons I have made with parallel observable phenomena in the world of physics. Let us start with what I think must have happened when the planes struck the two towers. They came in at high speed and at a low angle. The only similar phenomenon that we have any knowledge of is meteors that hit the Earth. What we know is that these drag material with them on their way through the soil layer. The whole surface, including all its pores, is covered by the material that they carry along. The innermost layer melts and turns into a glass coating on the surface of the meteor."

"I believe that similarly, the aircraft must have been covered by fragments of internal walls, ceilings and floors that collapsed around them and that the planes carried along with them as they penetrated the buildings. Much of this material was plaster, a material with extremely poor heat conduction capacity. All this debris probably formed a shield that kept the heat close to the aircraft and protected the rest of the building."

The fire

"So you believe that it was the aircraft themselves that became superheated, rather than the buildings?

"Yes I do. The disintegrated aircraft probably came to a stop near the centre of the buildings. The materials along the track of the collision must also have burned. But the really hot zone was where the aircraft came to a stop. I believe that some of the aircraft's fuel tanks must have suffered major damage, but that most of them would have been cut in two when they met the steel beams in the buildings, and that the development of the fire was therefore fairly constant."

"I believe that the planes must have been lying in a sort of basin of material debris, with the floor of the basin two or three storeys below the one that they ploughed into. The entire internal basin must have been heated by the burning fuel. Outside of the basin, the temperature would have been much lower."

"The aluminium alloy of the aircraft hulls, which also contains magnesium, melts at a temperature of 660o C. Experience gained from the aluminium industry suggests that it may have taken between half and three-quarters of an hour to reach such a temperature. If molten aluminium is heated further to a temperature of 750o C, it becomes just as liquid as water. I presume that this is what happened within the Twin Towers, and that the molten aluminium then began to run down into the floors below."

The explosions

"What happened then?"

"All the floors in the Twin Towers were equipped with sprinkler systems. All the water above the hot aircraft bodies must have turned to steam. If my theory is correct, tonnes of aluminium ran down through the towers, where the smelt came into contact with a few hundred litres of water. From other disasters and experiments carried out by the aluminium industry, we know that reactions of this sort lead to violent explosions."

"The aluminium would immediately react with the water, with the result of a local rise on temperature of several hundred degrees, in addition to the explosions that were due to the fact that these reactions release hydrogen. Such reactions are particularly powerful when rust or other catalysts are present, which can raise the temperature to more than 1500o C."

"The aluminium industry has reported more than 250 aluminium-water explosions since 1980. Alcoa Aluminium carried out an experiment under controlled conditions, in which 20 kilos of aluminium smelt were allowed to react with 20 kilos of water, to which some rust was added. The explosion destroyed the entire laboratory and left a crater 30 metres in diameter."

"Many people in New York reported that they had heard explosions just before the buildings collapsed. Film taken of the buildings also showed explosions in the floor below the impacts. Given that the amount of aluminium involved was large in comparison with the quantity of water, and since rust was probably also present, I believe that it is highly likely that the building collapsed as a result of a series of extremely energy-rich aluminium-water explosions."

The collapse

"How could explosions in the centre of a building cause a whole tower to collapse?"

"Aluminium-water explosions are like dynamite explosions. They were probably powerful enough to blow out an entire section of each building. The top section would than fall down on top of the sections that remained below, and the sheer weight of the top floors would be enough to crush the lower part of the building."

The neighbouring building

"What happened in the case of the neighbouring WTC7 building?"

"WTC1 and WTC2 took huge amounts of aviation fuel, fragments of steel and, if my theory is correct, large quantities of molten aluminium when they collapsed. When these materials and everything else fell some three or four hundred metres to the ground, they were squeezed between the upper and lower sections of the towers. This led to the neighbouring buildings being bombarded by hot particles, fuel and probably also aluminium droplets. Both large and small clumps of particles have since been found embedded in the walls of these buildings."

"WTC7 may have taken more of these impacts than the other buildings. At any rate, the building caught fire, which got out of control. In this case, the structural steel may have reached a temperature of more than 1000o C, over seven hours, and the 13th floor collapsed in the course of a minute. In this case I do agree with the findings of the federal commission. Overheating of steel beams was probably the cause of the collapse."

The way ahead

"Would it be possible to perform scientific experiments that can support your theory?"

"It would certainly be possible to look specifically for solidified droplets of aluminium and aluminium oxide in the walls of the neighbouring buildings. Experiments could also be carried out to find out whether fuel tanks are cut cleanly when they plough through a network of steel beams at a speed of 800 kilometres an hour. We could also test on model scale whether an object that ploughs through a room at extremely high speed becomes covered in debris from collapsed walls, ceilings and floors."