Fire in a multi-story building is a frightening scenario.

Escape via an emergency staircase is possible, at least as long as heat and smoke are kept out, but suffocation by smoke in particular causes many fatalities.

Trying to escape via the roof and wait for an emergency helicopter may be another option, but when a helicopter comes close, the rotor blades can act as a huge fan, kindling the fire. Fire Service ladders or sky-lifts also have their limitations - evacuating a large number of people in a short time is not possible.

The Ingström Escape Chute at the Helsinki airport air traffic control tower

A Twaron-reinforced alternative is the Ingström Escape Chute, marketed worldwide by Finnish company AB Mobiltex OY and capable of evacuating 30 people a minute.

It bears some resemblance to a giant nylon stocking - just many times longer.

It may have a length up to 150 metres, is incredibly strong and also heat resistant up to 800°C. The evacuees sit on the rim of the escape chute and lower themselves slowly down. Around the evacuee a kind of cocoon is formed, much like a football in a nylon stocking. By pressing the legs tightly against the lining of the chute it becomes possible to stand up straight. As soon as the evacuee is standing up and slowly relaxes both legs, he or she will slide down through the chute. It is not necessary to go down at an awkward pace, because speed can easily be reduced by pressing the arms and legs against the side of the chute. This way, mass evacuations can be realized fast and safely.

Worldwide, over 3,000 Ingström Escape Chutes have been installed so far, mostly customised for a specific application, for instance, in tall buildings, ferries, grain silos, air traffic control towers, or giant shovels used in the mining industry. In addition, there is a mobile version, which can be attached to a sky lift or ladder truck.

"The Escape Chute consists of three separate layers," explains Dolf Woldringh, technical account manager at Teijin Twaron Composites. "The inner layer is made of two materials, also called the hybrid fabric. Twaron is applied along the length of the chute. This is done because of the fibre's flexibility and especially its strength. After all, the inner layer bears the load of the total chute and therefore must be able to withstand approximately 10,000 kilos. This means a maximum load of 5,600 kilos per metre width of fabric."

Flexible Rohvyl yarn based on PVC chlorofibre is used across the chute because these sections are not exposed to high forces.

Although Twaron was chosen mainly because of its high strength, its flexibility was also a determining factor.

"There are various types of escape chute. Some are stored away in containers. When the chutes are regularly used for drills, this means they have to be folded out and up a lot. Twaron is excellently suited for that purpose," adds Mr Woldringh.

An additional benefit is that Twaron is also heat resistant, even though that is not strictly necessary for application in the inner layer. The outer layer of the chute, made of flexible glass fibre, takes care of that. This layer provides protection against fire, heat, and smoke, and can resist temperatures of up to 800°C. When firemen spray the chute with water, it can even be used at higher temperatures than that. Finally, the cantered layer is made up of a very elastic 'spun cell' - made of Lycra and modlacrylic fibres - and can easily increase three times in size. It is this layer, comparable to an elastic knee supporter, which 'grabs' the evacuee as soon as the arms and legs are pressed against the chute.

That the chute really works, was demonstrated in Australia, in October 2000. A 540 ton mining shovel (more than five metres high) caught fire and the heat blocked the door of the cabin. The operator broke a window pane and got out onto the side platform, where the escape chute was mounted. He activated the chute and within 20 seconds was on the ground.

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Teijin Twaron and Mobiltex did not team up right from the start. Mobiltex first bought Twaron through a weaver in Finland. "But as this is a very specialist application, we now work directly with Mobiltex," said Mr Woldringh. "For us this application was a very exciting opportunity. The escape chute is a typical aramid application - extremely strong and very flexible."

Demand has increased in the aftermath of the terrorist attacks in the USA on September 11 2001.

"In particular, there is a growing demand for the chute in buildings," said Mr Woldringh. "After all, safety thinking has radically changed since 9/11. On the other hand, the chute does not come cheap. For safety's sake no price should be too high, but not all authorities think that way. And sometimes there is simply no money. Mobiltex also does business with companies and private individuals, but authorities represent a very important group of customers. There will definitely be growth. For Twaron it remains a true niche market, but still, is a unique product.

Future Materials - 22/05/2003