The weeks after the tragedy seemed to confirm the gloomiest prophesies, as clients – particularly in the leisure sector – 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 –he 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 – 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’s 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 Buildings 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 Building 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 – 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 £25bn and £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 £450m to £300m, deferring a number of projects such as Gatwick's Pier 6. But its spend has been revised back up to £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 £6.1bn last summer to £8.1bn.
Other clients followed a similar dip–recovery 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."
What they said at the timeAll of us are doing a lot of soul searching. To me, things will change. Our codes will definitely change
Emmanuel Velivasakis, managing principal at New York structural engineer LZA technology If I was a prospective tenant or developer of a tall building, I’d be scared – tall buildings are clearly seen as targets. They’re trophy buildings – terrorists won’t go for low-rise buildings
Tony Arbour, head of the Greater London Authority’s planning committee Tall buildings have incredible safety records, but now is the time to think about further improvements to protect against such cataclysmic events
RIBA president Paul Hyett Discussions are being held right now in boardrooms about future projects
Richard Clare, EC Harris chairman People value the joy of living in towns and cities, but we’re seeing a new fear due to the ability of terrorists to cause damage to tall buildings. This will lead to fundamental changes
Lee Shostak, London spatial development planning committee The twin towers were the financial penis of America. They were a prime target
Will Alsop, Alsop Architects The full horror of it didn’t really dawn until the weekend. The bottom of the city is now cut off. Will large organisations always think of housing staff in tall landmark buildings? Probably not
Frank Duffy, architect and founder of space planner DEGW, which has offices in New York There are people in Europe that live around volcanoes. The idea that we are going to stop building tall buildings is ridiculous. The Pentagon was attacked by aeroplanes used as torpedoes
Ken Livingstone, London mayor
How the construction world reacted after the attacks11 September 2001
Two hijacked planes fly into the World Trade Centre’s twin towers, which collapse killing 2823 people. Within days, Amec and Bovis Lend Lease are appointed to oversee the salvage operation around the south tower. October
J Sainsbury cancels plans for two 40-storey towers in west London, saying they would be in “bad taste”. Prowting and Gleeson warn the City that the housing sector will suffer from a drop in consumer confidence in the British economy. A RICS survey shows that its members, too, are pessimistic about the outlook. November
More projects are cancelled. Airports operator BAA postpones £150m worth of work, and hotel group Accor freezes 20 projects worldwide. The Institution of Structural Engineers holds the first of a series of meetings to discuss the future of tall buildings. December
At the 21st Century Building Conference, Lord Foster defends the safety of tall buildings. January 2002
Bovis Lend Lease takes overall responsibility for the £1.2bn clean-up of ground zero. February
Government report highlights vulnerability of venues, including Wimbledon, Newcastle United’s St James’s Park and Durham Cathedral, to biological attack. March
A leaked report suggests that the World Trade Centre could have survived the attacks if their fire-control systems had survived the impact. April
BRE holds a three-day summit on terrorist threats to buildings, attended by delegates from Britain, Malaysia, Australia and the USA. May
A report on fire safety by Arup says building designers have not learned all the lessons from 11 September. July
The ISE publishes 20 recommendations aimed at protecting buildings against terrorist attacks. It focuses on structure, fire safety and evacuation. Six designs for the World Trade Centre site drawn up by Beyer Blinder Belle are unveiled in New York – to public disapproval. August
The Lower Manhattan Development Corporation launches an international competition to masterplan the World Trade Centre site. September
A report by the House of Commons’ urban affairs subcommittee concludes that tall buildings are not inherently unsafe, but recommends a range of safety improvements to improve occupants’ chances of survival in the event of an attack.