NEW YORK: A US government report expressed surprise of how well the World Trade Center withstood the impact of the two hijacked airliners that crashed into its twin towers on Sept 11, The New York Times reported on Friday.

What caused the skyscrapers to fall were the ensuing fires that burned as hot as the energy generated by a nuclear power plant, the report found.

The blazes, which raged as hot as 1,090 degrees Celsius, crippled sprinkler systems, fireproofing and the water system that fed fire hoses in the skyscrapers, the Federal Emergency Management Agency and American Society of Civil Engineers said in a draft report on how two of the world’s tallest towers fell.

The report obtained by the Times before its planned release in April or May said the towers would probably have remained standing, barring an earthquake or windstorm, had it not been for the fires.

It also contradicted some assumptions made about the centre’s collapse, including those involving the fuel that filled the passenger jets.

On September 11, the planes were described as bombs that brought down the World Trade Center, but the federal report found that the fireballs that erupted after the two collisions burned off a third of the jets’ fuel but caused little structural damage.

The remaining fuel, however, soaked furniture and papers in the high rises and burned off in minutes, creating the inferno that caused the collapse.

In addition, the World Trade Center’s fire-suppression systems catastrophically failed September 11, the investigators who wrote the report said, concluding that the jets cut the vertical waterpipes for the sprinklers and fire hoses and might have shaken loose the fireproofing that covered the building’s steel columns.

Skyscrapers are designed to smother fires before they can cause the buildings to fall, but that is under normal conditions, and the terrorist attacks were anything but normal.

The investigators recommended a federal study into whether engineering practices and building codes should be changed in light of the failures six months ago.—dpa