An international materials technology conference in San Diego has been given a new explanation for the explosions heard within the Twin Towers just before their collapse.
The explosions could have been caused by a mixture of water from sprinkler systems and molten aluminium from melted aircraft hulls, and led to the buildings' collapse.
There have been widespread conspiracy theories that someone - take your pick who - had placed explosives in the buildings. The explosions had been taken by many to contradict theories that the collapse was caused by overheated steel beams.
Christian Simensen of SINTEF Materials and Chemistry believes it's overwhelmingly likely that the two aircraft were trapped inside an insulating layer of building debris within the skyscrapers.
If so, he says, it was the aircraft hulls rather than the buildings themselves that absorbed most of the heat from the burning aircraft fuel.
The heat melted the aluminium of the aircraft hulls, he says, which then flowed down through staircases and gaps in the floor. As it did, it would have encountered water - with devastating results.
"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," he says.
"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."
The official report on the causes of the collapse concluded that all three buildings - World Trade center 1,2 and 7 - was caused by heating and the 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.
"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."
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," says Simensen.
"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."