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The re-evaluation of high-rise buildings: the cost to civilisation

Every opinion has a function, and it did not take long for the shock and horror of last week's suicide attacks on New York to convert itself into an outpouring of opinion. This was reminiscent not of Pearl Harbour, as is claimed but, according to the historian Andrew Roberts, of the sinking of the Titanic.

The strength of his parallel - as opposed to the various others advanced in the wake of the event - is that it acknowledges, in addition to the tragic loss of human life, that this was not only a technological disaster but a disaster for technology. The drama may have shared some elements with earlier historical events - the blowing up of the battleship Maine that triggered the Spanish American War of 1898, or the Paris Concorde crash of 2000 - but it was no more the first war of the 21st century, as President George W Bush declared, than Chernobyl was the last war of the 20th century.

What we can see of Chernobyl, with the perspective of 15 years, is that it did lasting harm to the development of nuclear power, setting it back to an extent that may soon cause power shortages that a hastily resuscitated nuclear industry will be agonisingly slow to make good.

In the same way, setting aside (although this is all but impossible) the appalling human cost of the destruction of the two towers of the World Trade Center, the event will do lasting harm to the development of high-rise construction, which will, in turn, threaten the whole concept of high-density urbanisation.

It is this effect that is of particular interest to architects. Literally before the enormity of what had happened in New York had sunk in, commentators had already saddled this new steed - the vulnerability of any prominent tower building to a fuelled-up airliner flown into it at hundreds of miles an hour by a crew of suicidal hijackers - and galloped into print with demands for an end to all high-rise building.

As is well known, the 110-storey World Trade Center towers were designed long after the 1945 crash of a twin-engined aircraft into the Empire State building. Contemporary claims that Minoru Yamasaki's towers would withstand the impact of a Boeing 747 were prompted by memories of this event. But this time it was different. The eventuality of the napalm-like combination of 300 tonnes of airliner impacting one of the towers at high speed, with a full load of jet-fuel on board, was never taken into account.

As a result, while both towers remained standing, even after the full impact of the aircraft, neither could withstand the tremendous heat generated by the combustion of thousands of gallons of jet-fuel that softened their steel structure and led to their progressive collapse.

The argument that such a collapse could or should have been 'designed out' of the buildings by fire engineering is spurious. No fire engineer foresaw that huge quantities of jet-fuel might explode on contiguous upper floors; nor did the security review that followed the abortive 1993 terrorist bombing consider such an eventuality.

Terrorists had turned cars and lorries into bombs before, but no one considered that men with pocket knives could turn passenger-laden airliners into huge incendiary bombs and occupied office towers into death traps, until it actually happened.

Only in retrospect does the fact that each World Trade Center tower had 250 lifts but only three escape stairs for 25,000 people seem inadequate;

or the four hours it took to evacuate the building in 1993 seem alarming. Like the cathedrals of the middle ages, buildings like these were beyond criticism.They represented the highest achievement of a civilisation. One whose descent into barbarism has now begun.

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