The events of Sept. 11 are gnawing at the peace of mind of those who live and work in the upper strata of America's skylines.
Security experts advising on how to protect against further attacks on skyscrapers say that the most effective safety measures are already in place, or easily taken, in most buildings.
But entrepreneurs are offering a range of fancy new high-tech escape devices: low-altitude parachutes, levitating rescue platforms, and escape tubes that work like a huge playground slide.
One of the most exotic rescue technologies in the works is a levitating platform that can fly to any floor of a high-rise building and bring as many as10 people to safety. The plans, drawn up by David Metreveli, chief designer at DM AeroSafe Group based in Ashdod, Israel, have been developed into a working prototype called the Eagle vertical takeoff and landing aerial rescue platform.
Four ducted fans arranged on the corners elevate the Eagle alongside a building and can operate for five hours without refueling.
The pilot can change the pitch of the engines to drive the craft forward or negotiate a docking for rescue at high altitudes. There is space for 10 evacuees, each harnessed into chairs and protected from falling debris by a Kevlar cage.
Metreveli estimates that the mass-production unit cost of the platform will be under $500,000.
In the response to Sept.11, Precision Aerodynamics of Dunlap, Tenn., is offering an emergency parachute that functions from an altitude as low as 15 stories.
At $1,575, it's a pared-down version of a chute used by low-altitude skydivers who drop off skyscrapers and bridges for sport.
George Galloway, president and founder, says the company is developing a "panic version" that can be donned by the novice without any prior training. The danger is that jumpers risk colliding with the building or blowing closer to the flames.
As a lifelong skydiver, Mr. Galloway says his personal preference is to take to the air, emergency or none, but he adds: "If you can take the stairs, use the stairs. You're at the mercy of the wind. It's really a last resort only."
Another evacuation contraption called the Baker Life Chute has already been installed at several air-traffic control towers and high-rise buildings as tall as 18 stories. The user climbs feet first through a metal ring on the end of what looks like a long white stocking, and slides down to safety. The chute comes in a bundle that can be hitched to the roof and thrown over the side.
The manufacturer, Baker Safety Equipment, claims the chute is able to sustain a constant stream of up to 30 human beings.
Meanwhile, though, safety gurus are saying that in event of an emergency, old-fashioned, low-tech devices like fireproof concrete stairwells may be the best path to safety for dwellers on high.
Larry Z. Sherman, president of his own safety management firm in New Port Richey, Fla., says that in cases of earthquake or fire, the greatest danger is a reluctance of the workers to evacuate.
"When an alarm goes off," explains Sherman, "people ask questions. 'Is this real? Is this a false alarm?' There's a kind of herd instinct."
He explains that once the ear-shattering siren prompts people to flee, the sturdy stairwells in most high-rises will give safe passage to the ground, even if the intervening floors are engulfed in flame.
The walls of such buildings are generally thick enough to shelter human traffic from the fire. And if stairwell doors are normally kept closed, as they should be, the risk of a stairwell filling with smoke and turning into a fatal chimney is small.
Sherman says that the safest stairwells are constructed like independent towers and incorporated on the corners of the building. Open bridges jut out from the sides of the building itself to the towers to ensure a smokeproof escape.
However, Sherman says, "Not many buildings are built that way." The "skinny little tower" concept doesn't work well in hurricane zones, or for extremely tall buildings.
And most conventional stairwells are up to the job in any case.
What's needed is more evacuation drills, not new technology, Sherman says.
And some building managers may need to rethink their policies on evacuating buildings when the extent of an emergency is not clear.
On the morning of Sept. 11, for instance, some occupants of the World Trade Center's South Tower were reportedly told it was safe to stay put.
"It's not the design of the system," says Sherman, "It's the training of the people who are in it."