The shocking collapse of the World Trade Center's twin towers on 11 September -- which left some 3,000 people dead in the ruins -- has raised questions about the future of tall buildings and prompted calls for rethinking the standards used in building skyscrapers.
Prague, 17 November 2001 (RFE/RL) -- For more than 40 centuries, Egypt's Great Pyramid of Cheops -- at 146 meters high -- held the title of the world's tallest man-made structure.
But since skyscrapers began dominating skylines in the 1800s, that distinction has changed hands many times in the drive to build taller and taller buildings.
The World Trade Center's north tower held the top spot for two years, until Chicago's Sears Tower surpassed it by 25 meters in 1974. The Sears Tower, at 442 meters, remains the tallest building in the U.S., but has since been eclipsed on the international level by Malaysia's twin Petronas towers, which hold the world title at 452 meters.
But following the tragic events of 11 September, the world is looking at skyscrapers in a different way. Is the era of tall buildings coming to an end?
Even before 11 September, some wondered if the days of a highly concentrated workforce -- as epitomized by skyscraper offices -- were numbered, at least in the West. Digital communications has made the workforce in many countries more mobile. They don't have to be in the same place to be connected.
Insurance is now another issue. Many owners of tall buildings in the U.S. are set to see their insurance premiums skyrocket when they come up for review in the new year -- and employee health coverage may also rise.
But others say the drive to build tall buildings -- as a symbolic expression of power or economic progress -- is likely to remain, especially outside the U.S. and Europe.
Paul Morrell is a senior partner at construction cost consultants Davis, Langdon and Everest. He is also on the board of the British Council for Offices.
Morrell was among those to deliver presentations to building industry experts meeting in London last week to discuss the future of tall buildings in the wake of the September tragedy. In an interview with RFE/RL, he says "we're still going to build tall," because skyscrapers meet specific needs.
"We need space for people to work, and we need cities to be dense to achieve two things. Firstly to bring people together so that they can work in a tight economic unit -- a so-called cluster, where a network of cooperating businesses comes together. For that you need density. [Also,] we need to reduce the [energy] use in transport, which means you put people together in a city, and there is far lower energy use in mass transit systems that bring people to those places of work. In the City of London [financial center], 95 percent of those who work there come by public transport. So we need [tall buildings] for that. And we need them to prevent land from being gobbled up and cities just sprawling out and using up their green belts. So these are real social and economic needs."
He says buildings higher than 50 stories do have specific problems. There's the wind load to contend with. Efficient people movement and safe evacuation routes are also tricky. And skyscrapers also take a long time to build -- often construction begins during a boom and ends during a recession.
"So we've got a series of things stacking up against super-tall buildings. And if you add to that a certain amount of fear, I think what will happen is that some buildings above 50 or 60 stories -- that might have got built because of pride or ego or the needs of a city to start a regeneration process -- those feelings might be overwhelmed by a new fear above 50 or 60 stories."
So are they safe? Morrell and other building experts say yes -- but not in exceptional circumstances like what happened to the World Trade Center.
"If someone aims a 200-ton airplane at you at 400 miles an hour loaded with fuel, you are not safe wherever you are. And this isn't about skyscrapers or tall buildings, it's about terrorism, it's about airplanes, it's about political and economic icons and so on, and it's not a specific skyscraper thing. And if we were to react only to the situation that existed in New York, then we could create new problems."
He says it would be too costly to turn tall buildings into the kind of fortresses they would need to be to withstand this kind of terrorist threat. Much better, he says, to spend money tackling the root causes of terrorism, or thwarting potential attacks at an earlier stage, like in airports.
Professor Wilem Frischmann is chairman of the Pell Frischmann Group of consulting engineers. He took part in an inquiry into the partial collapse of a tower block in London in the 1960s.
While the World Trade Center tragedy was an extreme scenario, he says there are valuable lessons to be learned from its collapse.
"The first thing is to look at existing or future buildings to ensure that if you've got one or two columns [where] one or two floor slabs collapse, you don't have the collapse of the whole building. The other problem that was noticed at the World Trade Center is that the fire protection of the steelwork might have been knocked away by the impact from the planes. Now I think one has to make sure that the fire protection cannot get knocked away and expose the steelwork to the fire that will soften it, and stop it carrying the load."
In other words, when the World Trade Center's fire protection peeled away, the cores were softened by the intense heat from the jet-fuel fire, and were no longer able to support the weight of the upper floors. When these began to crash, their accumulated weight forced everything underneath them, accordion-style, to the ground.
Frischmann also says fire escape routes must be protected with "proper material" like bricks and not plaster, which he says is common practice in the U.S. and U.K. Another issue is how to ensure a safe escape. Frischmann says bombings by Irish republican terrorists on mainland Britain prompted engineers there to build in such a way as to ensure that glass from upper stories does not fall onto people escaping at ground level. And if fire takes hold, he says so-called fireman's lifts are crucial for maximizing evacuations from upper floors.
"The idea is that the firemen's lifts have got a separate electricity supply to them, and the firemen completely use the lifts, and they enter it at the ground floor and go to the level to where the fire is and fight the fire. In New York, it appeared the firemen tried to walk up 60, 70 or 80 floors with all their equipment, which makes no sense. The other problem if you don't have firemen's lifts -- which is very serious -- is you don't know how handicapped people are going to escape. You have at least 10-15 percent of people who are older or slightly handicapped, and they can't escape 80 floors."
Morrell says separate facilities for firefighters are one possible way to improve safety. He says conference delegates also discussed a number of others, including making structures stronger to allow people more time to escape, fortifying and widening escape routes, and creating more backup power systems to kick in if the main one fails.
He says many delegates agreed it would help if conventions for escaping tall buildings were the same around the world.
But will any of this be implemented?
Since regulations vary around the world, Morrell says the only way to enforce upgraded safety standards would be to make them part of a statutory code in each country.
But he says this kind of "top-down" enforcement is not necessary. He believes industry bodies like the British Council for Offices and the U.S.-based Council on Tall Buildings and Urban Habitat -- one of the conference organizers -- can take the lead in establishing common standards and then encourage their application through their members. The Council on Tall Buildings has already set up a task force to review safety standards.
Morrell says improvements will mean higher costs for the industry. But he adds that this is unlikely to deter those who build "trophy" skyscrapers for personal, and not economic, reasons -- much like the Great Pyramid, built more than 4,500 years ago for King Cheops.