Imagine that in the corner of a room is a garbage bin where someone has just tossed a lit cigarette. The embers of the cigarette catch on bits of paper, and a small fire starts. Smoke starts to rise from the container. Now imagine the difference it makes whether this room is an indoor swimming pool or a large storage shed: the danger presented by the fire is vastly different.
© Fotolia, 2012
Until recently, the European fire code would have considered these buildings to be interchangeable, leading to unnecessary precautions in some buildings and under-protection in others, and greater health and safety risk to residents in the event of a fire. However, a cluster of European Commission (EC)-funded projects spanning the last two decades has perfected a new model of fire progression, called the "natural fire safety concept" (NFSC). This new model has now been successfully implemented in building codes across the continent, allowing construction of safer buildings at less cost than before.
In the past the Eurocodes, the EU's building codes, modelled fires as a linear phenomenon which was uniformly distributed and which heated the entire room at the same rate. This was a very crude model, but was used for the sake of simplicity. Real fires actually have a period of increasing heat and then decreasing heat, and the vast majority start locally - for instance in an electrical circuit or a kitchen - and then spread.
This oversimplification was especially problematic for steel buildings. Steel is a very good structural material, often used for multi-storey office buildings as well as large open arenas and sports halls. However, the downside of steel is its fire performance: at high temperatures steel deforms. Under the old Eurocodes, steel beams had to be covered with fire-resistant materials such as drywall, making steel buildings prohibitively expensive in some countries.
Since the natural fire concept more accurately mimics a real fire, it allows for greater protective mechanisms where they're truly needed, and less where they aren't.
"It's safer to calculate the real fire that could occur in the building, and to reinforce the structure only where it's needed," says Olivier Vassart, Senior Research Engineer at ArcelorMittal and one of the collaborators on the EC research project. "So you optimise the calculation, and at the end you have a safer and a cheaper building."
The NFSC has been developed with the assistance of nearly €5 million of research funding by the European Commission over the last 15 years. The research has spanned 20 EU member countries and included computer modelling, laboratory testing, and full-size test fires in purpose-built multi-storey buildings. From these experiments the team has developed practical design principles for architects to use in fireproofing their structures. Crucially, a few years ago these principles were accepted into the Eurocodes, meaning that new buildings can be designed based on the NFSC a compelling example of scientific research translated into real-world progress.
The natural fire concept is still being improved upon. For instance, in July 2012 the group launched a research project examining buildings in which fires tend not to spread - for instance, parking garages. Results from these specialised investigations will allow the NFSC model to be further tailored to different types of structure.
And though construction hasn't fully recovered from the recession yet, Vassart says the sector's slowdown has given engineering firms time to study the new protocol and learn how to implement it. His office is seeing an increase in engineers interested in switching to natural fire modelling this year - which will likely translate into safer and cheaper steel buildings in the years ahead.