Ever since it emerged that the collapse of the World Trade Centre was actually caused by raging fires, safety experts have been putting their heads together to see how fire protection and escape routes can be improved in new landmark buildings.
After the collapse of the World Trade centre, tall landmark buildings have metamorphosed from symbols of capitalism's power into large and vulnerable targets. So, the question occupying industry minds is how to prevent the same terrible tragedy being visited on the additions planned for London's skyline.

The consensus is that the twin towers withstood the initial impact of the aircraft and subsequent explosion very well.

It was the aircraft's fuel burning that caused the steel supporting the building to heat up to the point that it could no longer support the weight above it. The collapse happened so quickly because the steel insulation was blown off, leaving the steel itself unprotected. The structure above the flames sagged into the storeys below it, causing the structure to collapse like a house of cards.

How do we protect new tall buildings from similarly devastating fires? Only a week after the event, RIBA president Paul Hyett called for a joint working group to be set up, to investigate the issues of fire protection and the means of escape from tall buildings.

Most experts believe it is inevitable that the regulations will be revisited – BS 9999, the standard that covers fire safety, was under review anyway. Part A of the Building Regulations, which covers structure, is also being reviewed. "Document A is currently out for consultation and I would expect to see quite a few extra comments on it because of New York," says Jeremy Hodge, managing director of the Fire and Risk Sciences division of BRE.

Reviewing the regulations
There are two approaches to deciding on the levels of fire safety in buildings: regulation and fire engineering. Part B of the Building Regulations, which deals with fire safety, contains prescriptive guidance in the form of tables. This straightforward element is part of its appeal – as well as its avoidance of the extra cost of hiring specialist engineers.

Fire engineering, on the other hand, is a considered assessment of the type, use and requirements of a building. It also considers risk, and can come up with higher levels of protection than demanded by the regulations. Mick Green, partner at Buro Happold, says: "The whole structure and the fire protection could resist an extreme event if you carry out the correct design process."

Fire engineers believe their method is ideal for designing high-risk buildings, as those extra risks and additional requirements are factored in.

BRE's Hodge, however, is more cautious. He is in favour of fire engineering – but only if it is used properly. He believes any changes to the regulations may incorporate additional guidance for fire engineers and thinks further rules for tall buildings may be introduced; currently there is only one set of rules for buildings more than 30 m high.

Making buildings more resistant to the sort of events witnessed in New York would require a radical change in the way the fire performance of buildings is considered and a complete overhaul of fire protection standards. Peter Bressington, director of Arup's fire engineering division, says: "If there is a change, this will be very significant because we will have to take account of deliberate attacks from outside."

It is unlikely that all new buildings will be upgraded to take account of this risk, as this type of event is much more likely to happen to tall, high-profile buildings in cities. Martin Kealy, technical manager at WSP Fire, believes that "there should be something in the regulations that requires a risk assessment to see if a building is a target, and whether it needs higher levels of fire protection and resistance to hydrocarbon fires".

Structural strategies
The design of the structure is key to how a building performs in a fire – and the longer the building stays up, the more time people have to escape. A concrete core would offer better fire resistance than the steel used at the World Trade Centre, and would be more likely to suffer partial rather than total collapse, according to Kamran Moazami, vice-president of consulting engineer Cantor Seinuk, now part of WSP.

Buro Happold's Green believes that tying the structural steelwork together using really good connections is an important first step in reducing the risk of a building progressively collapsing. Tensile forces could be transferred into adjacent members, potentially reducing the overall load on any one piece of structural steel. If a column fails, a beam attached to that column – and to an adjacent column – would go into tension, rather than crashing downwards.

Extra structural steel and less weight on the roof of the building could also improve performance. Hodge says larger steel members perform better in a fire as they take longer to heat up and are therefore slower to fail. He emphasises the need for a risk management approach, as not all parts of a building will need thicker steel members or additional fire protection. Another suggestion comes from Arup, who published a report on the disaster last week. The report suggested that buildings include a "collapse" floor every 10 storeys. These would be capable of carrying the weight of the debris of the floors above. Hodge questions the wisdom of placing excessive weight at the tops of tall buildings. Currently the roof is a handy place to put water tanks and plant and heavy mass dampers to balance out the building's wind-induced sway.

Events in New York showed that the fire protection of steelwork is vital to prevent collapse. Fire protection is simply insulation placed around the steel that slows down the rate of heat transfer from the fire to the steel. Kealy says the current requirement of two hours of fire protection for steelwork in tall buildings needs review, and the issue of resistance to hydrocarbon fires needs to be addressed.

The technology to protect steel against the conditions seen in New York exists in the oil rigs of the North Sea. Hodge says the New York incident should be defined as a rapid fire rather than an explosion. The fire protection used in the oil industry has to be able to resist this type of aggressive fire. David Sugden, chief executive of the Association of Specialist Fire Protection says four-hour protection against a hydrocarbon fire is quite possible.

Escaping to safety
A stronger structure with better fire protection will give people more time to escape, but it can take many hours to evacuate a very tall building. More, and wider, stairs seem like an obvious answer to cope with total evacuation, but they take up valuable space. One possibility is the inclusion of fireproof "safe havens", common on oil rigs, to give people somewhere to escape to. Hodge believes another answer is escape chutes – like a fairground helter-skelter. These would not take up much room but would enable people to speed to the bottom very quickly.

Perhaps the ultimate answer may be to turn the adage "do not use the lifts in a fire" on its head. Hodge believes the lift should be the first resort when it comes to escape routes. Lifts are the fastest way of escape from a building, and a fireproof lift shaft would allow people caught above a fire to speed through it safely, and would have the additional advantage of retarding the progress of fires. Arup's fire division is investigating this possibility, but there are a number of issues to be resolved such as ensuring that the power supply to the lift is protected, and that there is a protected escape route on the ground floor.

The costs of making buildings that stand up better to the sort of fire we saw in New York may not be that great. Sugden and Kealy say doubling the money spent on the fire protection – a small amount in the overall cost of a building – would make them resistant to a hydrocarbon fire. Hodge says spending an extra 2-4% of the total cost of the project on the building's structure and its fire protection would go a long way towards much better performance.

Given the scale of the loss of life in New York and the potentially massive financial consequences, particularly if there is a world recession, this may be a small price to pay – even if it is only for the peace of mind of those working in the next generation of tall buildings.