黑洞社区

The weeks after the tragedy seemed to confirm the gloomiest prophesies, as clients 鈥� particularly in the leisure sector 鈥� slashed their construction budgets, skyscraper proposals were thrown into doubt and the UK government ordered a full-scale review of security at public buildings.

Now, a year on, the doomsayers have been proved largely wrong. Gordon Masterton, director of consulting engineer Babtie, says: "Everyone still has images of 11 September in their mind's eye, but that shouldn't prevent people from investing in infrastructure for a peacetime environment."

It would seem he is right. A report on tall buildings by the House of Commons' urban affairs subcommittee, published this week, concludes: "Tall buildings are not inherently unsafe as places to live or work but there are areas in which further regulation could further promote safety." The committee calls for measures including minimum time periods for evacuation, regular re-inspection to update fire certificates and the licensing of occupiers.

In the City of London, the 37-storey Heron Tower has been approved and a many other tall buildings are expected to be proposed in the coming months. Peter Rees, planning officer for the Corporation of London, says: "We need to concentrate offices together. The alternative is to live in caves."

So what is the legacy of 11 September for tall buildings? The consensus seems to be that the most enduring impact of the terrorist attacks was psychological. "From an engineering point of view, there's no problem with tall buildings, but there are psychological problems with them," says Tom Foulkes, chief executive of the Institution of Civil Engineers. "In future, architects will need to think more about how people behave when they're stressed or in danger."

Jeff Cox, chairman of BRE's fire group, agrees 鈥揾e believes the attacks have left occupants of office towers in a state of latent paranoia. "Whenever there was a fire alarm in a tall building after the 11 September attacks, people were down the stairs like greased lightning,"

he says. And because these fears still persist, designers need to take them into account when designing tall structures.

A problem of perception
All kinds of panic measures were proposed in the immediate aftermath of the attack, including parachutes, giant helter-skelters and flying life-rafts to pluck stranded people from rooftops. Even engineers succumbed: last September, ICE president Mark Whitby called for "the equivalent of a Star Wars forcefield over our towns and cities that would prevent planes from entering".

A year on, designers and regulators have calmed down 鈥� Andrew Bennett MP, the chairman of the urban affairs subcommittee, merely points out that "improved evacuation procedures and safety regulation may help to ensure preparedness for any eventualities".

There鈥檚 no engineering problem with tall buildings, but there are psychological problems with them

Tom Foulkes, Institution of Civil Engineers

At the same time, engineers and architects have embarked on a campaign to reassure the public that tall buildings are safe. Bill Baker, a Chicago-based structural engineer with US architect Skidmore Owings & Merrill, points out that out of 30,400 people who died in building fires in the USA between 1991 and 1998, only 340 were in buildings more than seven storeys tall, and just one was in an office building. He concludes: "You're much more likely to die in your home than in your office."

Nevertheless, 11 September has had an impact on architects' prestige designs. On the day the twin towers fell, Baker had a meeting scheduled to discuss a plan to build the world's tallest tower in Chicago. After the attack, its 520 m was scaled down to 343 m. In October, the proposed design of Renzo Piano's "shard of glass" tower in Southwark, south London, was reviewed to take account of the risk of attack by aeroplanes. And in the same month, Birmingham's Holloway Circus Tower, designed by Ian Simpson Architects, which was set to become the UK's second-tallest residential block at 192 m, was reduced to 121 m because the Civil Aviation Authority feared it could be a target.

Faced with such decisions, the design community quickly suggested ways of making towers more resilient. In the UK, the Tall 黑洞社区s Working Group, comprising leading structural and fire engineers from around the world, was convened. In July, it published recommendations including wider escape routes and better management strategies to handle an emergency.

The government is now considering adopting the tall building group's recommendations as part of the 黑洞社区 Regulations. However, fire engineer Peter Bressington, a director at Arup, does not believe any action is likely. "I don't think there'll be any changes to the regulations," he says. "There could be changes to performance criteria 鈥� for example, people should be able to evacuate the building in a certain number of minutes. My own feeling is that the government will just set guidelines; it won't be prescriptive."

With improvements to building design under active consideration, consultants are now calling for greater emphasis on safety in masterplanning. In the hours after the World Trade Centre disaster, there were scenes of chaos in lower Manhattan as the emergency services struggled to co-ordinate their rescue. "There are amazing issues in the background that it's not polite to talk about," says Frank Duffy, founder of space planner DEGW. "It seems to me there was staggering incompetence in the evacuation. What happens when you have thousands of people pouring out of a building needs some empirical investigation."

As a result, issues such as where evacuees should congregate, pedestrian flow and rescue service access are rising up the agenda. Lawrence Ng, an associate principal at US designer Cesar Pelli & Associates, says: "In commercial masterplanning projects, safety, security and evacuation procedures are the foremost consideration."

The biggest driver of safety improvements could be the insurance industry. Insurers lost between 拢25bn and 拢50bn in the World Trade Centre attacks, and insurance premiums for builders and occupiers have increased as a direct result. The loss of life in the twin towers' upper floors has led to insurers charging higher premiums to high-level occupiers. Moreover, the cost of insuring a large building against total destruction has increased drastically. And for contractors, increasing levels of personal injury litigation have made the cost of employer liability insurance skyrocket.

Despite this, clients have bounced back since the dark days of last autumn. Airports operator BAA suffered from the dramatic fall in air travel after 11 September. In November last year, it cut its 2002/3 capital budget from 拢450m to 拢300m, deferring a number of projects such as Gatwick's Pier 6. But its spend has been revised back up to 拢410m, largely on the back of increased security measures, such as bombproof partitions and X-ray screening facilities. Confidence in the long-term growth of air travel has returned and BAA's 10-year spending plans have increased from 拢6.1bn last summer to 拢8.1bn.

Other clients followed a similar dip鈥搑ecovery pattern. Arup director Peter Bressington says reassuring clients is vital: "Over time, the anxiety dies down and the main thing that helps it is giving clients information about safety."