Scientists have used a computer simulation of the 9/11 attacks on the World Trade Centre in New York to confirm findings about why the buildings collapsed.
A two-year study by Purdue University and the National Science Foundation shows that the initial impact of the aeroplanes stripped away fireproofing material, which allowed the supporting steel structures to weaken and then collapse.
The 3D animation has helped researched get to the bottom of why the towers collapse and demonstrates how engineers can better their structural designs in the future.
The computer animation shows an aeroplance hitting the north tower and follows its path through the building and out the other side.
It has shown that the explosion of the heavy fuel tank removed foreproofing insulation from support structures.
Since half the buildng's weight-bearing columns were in the cores of the towers, their loss meant the collapse from being exposed to fire was inevitable.