EVACUATION ADVICE for workers in skyscrapers faces a major review as a result of lessons learned from the attack on the World Trade Center's (WTC) twin towers.
Most of those who died are thought to have been in the south tower - or WTC2 - which was the second to be hit. It was struck just above the 60th storey, 18 minutes after the north tower - WTC1- which was hit just above the 80th floor.
WTC2 collapsed less than an hour after being hit, killing thousands.
Normal emergency procedures for the WTC dictated that only people on the floor where a fire breaks out, along with those on the floors above and below, need to be evacuated.
Offices on other floors were expected to function normally with workers staying at their desks.
But in last week's scenario, keeping people at their desks was fatal, said Greenwich University safety engineering group director Professor Ed Gallea.
Office buildings are designed so that each floor is isolated from those above and below to prevent fires spreading. The World Trade Center towers would not have had enough stair capacity to accommodate a rapid total evacuation he said.
With a smaller fire, mitigating measures such as sprinkler systems would also have given people extra time to escape.
Collapse of the towers could not have been anticipated in the emergency plan, he said. If it had been, less emergency personnel would have been trapped in the collapse. As it was, 350 firefighters are thought to have been killed at the scene.
When the World Trade Center was bombed by terrorists in 1993, it took less than an hour to evacuate 40% of the occupants, three hours to evacuate 52% of the building and less than four hours to clear it completely.
Gallier said that the disaster would encourage the development of innovative evacuation procedures, perhaps including elevators that can be used in a fire.
He said that future skyscraper designers will have to take into account the human response to an aircraft collision.
Most who escaped from the towers disregarded orders to stay put. Some of those would have been in the building at the time of the 1993 bombing and this may have affected their response.
'We need to study what happened and see what we can learn from the structural, fire and human dynamics, ' said Gallea.