The fire performance of aluminium
Following a spate of fires in modern metal-clad, warehouse-type buildings, concern is growing among firefighters about the methods of fire protection being used in the construction of such premises. I would argue that aluminium cladding and aluminium standing-seam roof systems, incorporating glass wool insulation, make a valuable contribution to saving lives and buildings in the event of fire.
In short, when the heat's on, aluminium saves the day.
The safety of the public and firefighters should be the key consideration when it comes to the design and construction of metal-clad buildings such as superstores, warehouses and a wide variety of other commercial and industrial premises. Fundamental design problems affecting the performance in fire of such buildings were recently highlighted when the Loss Prevention Council (lpc) renewed its call for better fire protection. This followed the fire at Wakeley Brothers near Rainham in Kent.
No manufacturer of roofing and cladding systems should be immune to the concerns and the growing debate about fire safety. KAL-SYSTEMS can make a positive contribution to overall fire performance depending, of course, on design, insulation properties, detailing, components and the construction methods employed.
For more than 20 years the fire performance of aluminium-based systems has been proven and documented. My own experience, over 23 years, also convinces me that their properties can preserve the integrity of a structure in such conditions.
Two skins of aluminium with glass or rock insulation provide outstanding durability, insulation properties and a rapid venting facility, while an outer skin of aluminium with steel inner provides fire resistance where necessary. As a bi-metal company, Hoogovens feels that KAL-SYSTEMS allow us to use the best properties of both metals without their individual characteristics creating problems and risks when used as a total construction.
Classified as non-combustible, aluminium will neither burn nor give off poisonous fumes. Instead, at 600degrees C it will melt locally to the seat of the fire, providing a rapid venting facility where the smoke and heat can be dissipated. This minimises the spread of flame and damage to the building and its structural integrity. In many situations, aluminium systems may confer lower insurance premiums on this fact alone.
As soon as venting begins, the temperature within the building drops rapidly and the smoke is also quickly evacuated, thereby potentially allowing firefighters to enter and extinguish the fire from within before it spreads to other parts of the premises.
The comparative performance of steel versus aluminium-based roof decking systems was demonstrated by the results of tests carried out by the Swedish Fire Protection Association as far back as 1977. The results are available in a report issued by the Swedish Council for Building Research, No 17 - 1978: Fire Engineering Properties of Aluminium Roofs. The tests were later re-conducted in Britain at bre Cardington, where they were filmed and photographed. Results were exactly comparative.
Fourteen tests were performed in specially constructed test buildings. The roof construction was constructed from aluminium sheeting but, for comparison, identical tests were also carried out with steel metal decking built-up construction.
A fire pocket was placed in the experimental buildings and the results were studied. Measurement points were located at a distance of 2m and 8m respectively from the seat of the fire and about 200mm under the surface of the roof.
In both cases, a temperature peak occurred after about two to three minutes. This peak was momentarily higher under the aluminium roof due to the fact that the bright metal sheet reflects the heat towards the measurement point. But after a few seconds, when the aluminium sheet began to melt, the temperature dropped rapidly. After about five minutes it dropped to around 300degrees C, while the temperature under the steel roof remained at more than 700degrees C. The temperature at the measurement point in the steel roof was twice as high as the corresponding measurement point under the aluminium roof. It took over 30 minutes for the temperature under the steel roof to drop to the level it reached after five minutes under the aluminium roof.
The results of these tests demonstrated, of course, not only the valuable sacrificial function provided by the aluminium but also the capability of steel to provide fire resistance where required.
Roofing system insulation is also another vital consideration in fire protection, and yet many designers remain unaware of the risks and continue to specify in ignorance, relying on current and, in parts, outmoded statutory guidance. This is currently under review and I hope independent bodies will set new standards taking due consideration of all aspects of material performance.
A spate of fires involving certain forms of metal building envelope construction has realised grave doubts about sheeting and cladding performance, and current media interest by certain organisations - with dubiously founded claims and counter-claims - has only served to confuse the specifier.
Currently ignored by the Building Regulations, certain panels are put through fire tests which some experts believe are inadequate. According to the Building Research Establishment (bre), in the worst cases some burn at a ferocious 1000degrees C, belch highly toxic gases and may collapse in less than five minutes!
After a spate of fires in food processing buildings and cold stores, some brigades are refusing to enter buildings known to be clad in high- risk cladding products. At a recent industry body meeting, one senior officer said that when called to modern metal-clad constructions the whole of the building is often on fire. Having established that no people are inside, fire crews will step back from the conflagration and fight it from outside rather than go inside and risk the building collapsing on them.
I heard a story recently about a building burning down which stored rock fibre insulation. It implied that the insulation had contributed to the fire. This surprised me, as rock fibre is non-combustible. I was then told by the 'other side' that this was a load of tosh and that only the wrappings of the insulation were damaged in the fire and that this insulation was simply re-wrapped for later use.
One fire officer stated his own system preference, one which we have always applied to kal-zipregistered here at Hoogovens. Along with just about everyone else in his line of work, he called for a change in regulations to make the installation of sprinklers mandatory and also urged early consultation with fire authorities at the design stage of these types of new buildings.
As primary metal roll-formers of roofing and cladding systems, we are to a large extent the innocent bystander in the current claim and counter- claim within the industry. There are factors, admittedly unrelated to fire performance, which in our view contribute towards making glass wool the most efficient and effective form of insulation - for example, the ability to follow the complex contours of modern building shapes and the maintenance of the thermal properties of the insulation over its entire envelope.
Just as important in our thinking, however, is that kal-therm, our insulation products, are to be the choice of specifiers when stringent fire performance is required. Choosing a less expensive system at the cost of fire performance is not an option in our book.
Aluminium twin-skin, more usually referred to as double-skin systems, incorporating glass or rock as the thermal insulant, have a long and successful track record going back 40 years. And, with their proven insulation and fire performance, I can see no good reason why their popularity should diminish.
Indeed, with a continuing trend towards flowing and dynamic roofscapes - where the roof is one of the principal creative expressions of the building - I anticipate that multi-component systems (steel for strength, aluminium for durability, steel for fire resistance, aluminium for rapid venting, and non-combustible insulation materials of rock and glass), with their immense design flexibility, really will give the designer, building owner and occupants total peace of mind, security and safety.
The facts are out there. Let's use them.