The playful hot-air balloon is being harnessed for serious work: rescuing the victims of high-rise catastrophes.
When a cruel alchemy blew a crater in the basement of New York’s World Trade Center last February, the 110-story, 1,377-foot towers were plunged into blackness. To save themselves, tens of thousands of terrified workers, forced into smoky stairwells, had to grope their way down hundreds of steps they couldn’t see.
Engineer Sidney Conn says he has a better way. His hot-air balloon company is developing a new style of balloon, the Lifejack, for evacuating high-rise buildings.
Conn began designing his rescue device after the 1980 fire at the high-rise MGM Grand Hotel in Las Vegas that killed 85 people. I saw the problems with helicopters fighting turbulence and smoke as they tried to pull people off the roof, he says.
Although the Lifejack is based on the aeronautics of the typical sport balloon, it looks very different; it’s cube-shaped and rigid, not round and colorful. That shape lets it fit snugly against the wall of a burning skyscraper, while air jets on its bottom keep it from drifting. Although the deflated rescue balloon fits into the back of a pickup truck, once pressurized by its propane burner it stands 35 feet high, looking much like a giant outdoor elevator. But this elevator doesn’t only go up and down; it also moves sideways along the building. Projecting from the balloon’s bottom are two cables made of Kevlar, the wonder material in bulletproof vests. The cables hook up with two hydraulic winches on the ground that are positioned at an angle to the balloon. Fire fighters are able to direct the balloon to the left or right by remote control. When the balloon is moving straight up or down, the two cables are kept taut, providing added stability.
There’s no wicker gondola swaying gently below; instead an enclosed compartment at the bottom of the balloon allows a dozen evacuees to be hauled down, while a rigid exterior platform on top carries fire fighters up. And the balloon can climb up to 1,000 feet a minute--about 11 miles per hour. The Lifejack will fly faster than any helicopter pilot would dare when flying so close to buildings.
Conn says his biggest hurdle has been finding just the right space-age textile to use. He needs one that’s lightweight and abrasion- resistant; most important, though, it must be able to withstand not only a fire’s heat on the outside but the 600-degree temperature (hot enough to ignite paper) that will be generated on the inside. Normally a hot-air balloon flies because the heated air inside it is less dense than the surrounding, unheated air. To maintain this relationship during a fire, intense internal heat is needed to offset the outside air temperature, giving the balloon an enormous lift capability--about two metric tons-- enough, according to Conn, that if let loose, the balloon would take off like a rocket. That much power also provides the stability needed to counterbalance the strong buffeting common with high-rise fires.
Conn first looked at different blends of Kevlar as one possible fabric but rejected them because in time Kevlar falls apart in ultraviolet light. He has talked to Dow Chemical about a heat-reflecting fabric called PBZT that is being considered for use in the honeycomb flooring in space shuttles. It’s light and strong but also expensive. Another possibility Conn has looked into is a new fabric called PBI, made by the Hoechst Celanese Corporation and used in the protective coats fire fighters wear.
Otherwise all the wrinkles have been ironed out. Conn has already built a full-size prototype and hopes to have a working model by next summer. We’re not inventing anything that we haven’t used before, Conn points out. But will fire fighters want it? Even reaching a high-rise fire requires tremendous strength for any fire fighter because they’re wearing about 60 pounds of gear, says Douglas A. Brown, director of government relations for the International Association of Fire Chiefs, in Fairfax, Virginia. And fire fighters don’t use elevators, they use stairs. So I’d be receptive to another way of moving people, up as well as out. But of course, it still needs to be proven.