The basic laws of pneumatics could hold the solution to rescuing people from the tops of burning skyscrapers, a team of German engineers has claimed.
A company called Engineering Voigt has developed a concept that envisages people descending gently to safety through steel escape tubes, like pistons through a cylinder.
The proposal is the latest example of a huge global effort to develop innovative skyscraper rescue systems since September 11, which saw victims at the top of the World Trade Centre trapped and beyond help.
According to Voigt, a network of vertical tubes running down the building to a hermetically sealed room below street level would allow pneumatic principles to come into play.
Escapees would don safety harnesses that would hang below discs with the same diameter as the escape tube itself. When the disc enters the tube, Voigt said this week, it would compress the air below, slowing its descent. A valve on top of the disc would be used to regulate the rate of descent to 2-3m per second.
Voigt said the tubes would be heavily insulated, allowing them to be used for the maximum possible time before becoming too hot to enter. Each could serve several floors of a building and would be entered via designated access points.
Once they reached the sealed basement room, evacuees would pass through an airlock system to a tunnel connecting them to the outside world.
Klaus Huebner of Innopat, the company attempting to commercialise the system, admitted that it seemed highly futuristic, but claimed it was based on well-established technical principles. ‘It applies pneumatics in a way that we believe could save many people from a tall building,’ said Huebner.
He claimed the Voigt system offers several potential benefits over other methods of escape being considered following September 11.
One of the most ambitious uses friction of the body against the escape tube to slow people’s descent, but Huebner claimed this was ineffective much above 10 storeys because of the potential for injury.
‘The other good thing about the pneumatic system is that it does not rely on electrical power being maintained,’ he added.
Engineering Voigt, which is based in Bad Saarow-Pieskow near the East German-Polish border, claimed to have successfully tested a model of the system in its laboratory.
It is attempting to patent the concept in Germany and to interest local construction and engineering firms in mounting larger-scale trials.
Gordon Masterton, chairman of the Institution of Civil Engineers’ structural and building group, said the Voigt proposal was one of the more ambitious examples of how engineers and architects are reinventing their approach to building safety.’The World Trade Centre forced us to think the unthinkable in relation to the safety of buildings themselves and the effectiveness of evacuation systems,’ said Masterton.He said that even assuming the basic concept worked in practice, it would need to be able to get a large number of people out to be considered worthwhile.
But he said the proposal was generally in line with current thinking. ‘Having a system that is not compromised by a failure of power inside the building is an attractive proposition,’ he said.
Sidebar: Arup says improved safety need not be costly
High-rise buildings can be made safer and the effects of disasters such as the September 11 attacks can be mitigated at little cost to owners and developers, according to consultant Ove Arup.
Improved fire protection, design of floors to resist collapse (as in buildings in seismic zones), modelling and improved management systems for evacuation all have a part to play in alleviating anxiety among high-rise workers, said a report from Arup’s Extreme Event Mitigation taskforce.
Last week’s report from the US Federal Emergency Management Agency, which concluded little could be done to safeguard buildings against aircraft strikes, missed the point, said Arup director Peter Bressington. ‘I’m amazed at the US attitude. You can’t say to people in high-rise buildings, ‘There’s nothing we can do about it.”
More robust fire protection for structures is a prime concern, he said. In the World Trade Centre sprayed fire protection on the floor trusses and dry-lining protecting the staircase core were blown away by the blast. Bressington suggests intumescent paint as part of the solution. ‘Only a localised part would be blown off. Spray-on mineral wool used in the US has no robustness at all.’
Concrete fire protection is effective provided fixings are robust, but at extreme temperatures explosive spalling occurs as moisture trapped in the material turns to steam. Polypropylene fibres incorporated into the concrete mix melt and allow the steam to escape. ‘Concrete buildings will generally perform better in an impact and in fire. But that doesn’t mean all buildings should be concrete,’ said Bressington.
Structurally Arup advocates modelling possible disasters in buildings to gain a better understanding of what might happen. The firm modelled the effect of a jet engine crashing into a key structural member. It discovered that a direct hit from the shaft of a jet engine would punch straight through a steel column. It would also punch a hole in a reinforced concrete wall, but not cause collapse. Even a lighter wing structure can destroy a standard steel column, depending on the speed of impact.
A small design change, adopting a ductile connection between floor supports and the supporting frame, used in seismic zones, would allow floors to sag but not break away, avoiding progressive collapse triggered by debris from upper floors falling on to lower ones. ‘The cost would be negligible and it would cover a lot of eventualities,’ said Bressington. He said the detail used on the WTC was ‘not unrobust’ but there were doubts about whether it had been built as designed.