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Performance of Wood Based Products in Fire

23 April 2019

Gordon Ewbank, Chief Executive, Wood Protection Association Gordon Ewbank, CEO, Wood Protection Association
The timber sector is in a renaissance and, therefore, the case for an old and traditional building material that is finely engineered is coalescing with the agenda of the day. From wood’s environmental sustainability and footprint, its aesthetic appeal and its extremely positive contribution to the healthy buildings agenda, this long-established construction material offers a wealth of architectural possibilities. But it’s important to understand how timber handles and performs in fire and how flame retardant treatments are used to enhance the fire performance of wood as well as wood-based products.
 
How does a particular material react when it is exposed to a flame? Does it readily ignite? Does it give off heat? It is the reaction to fire which is a property of a material and this can be very specific and vital to mitigating fire growth. These properties are the materials:
  • ignitability
  • heat and smoke generation
  • burning particle release; and
  • rate which flame spreads over its surface.
 
Once a fire is more developed, then containment becomes the top priority of a building’s design with the use of compartmentalisation a common strategy. At this stage, it is the fire resistance ratings of building elements such as walls, floors and fire doors that then becomes critical. It is the property of the building components, not just a single material, but a composite material element. Fire resistance ratings are often quantified in time. A good example of this is a fire door which has a number of layers of material. The purpose of this building component is to provide containment so the fire cannot pass through the door.
 
More difficult to ignite
A fire-retardant treatment will enhance the reaction to fire properties of wood-based materials, reducing ignitability and the consequent spread of flame. This will slow down the development of a fire, allowing significantly more time for the occupants of a building to escape and for the fire to be extinguished.
 
It’s important for a contractor to know what they have specified; a flame retardant treated material is not enough. It needs to be the reaction to fire performance, Euroclass B for example, and a supplier must have a certificate to prove that is the case. It cannot be a generic certificate, rather an official classification certificate for that species of timber. If it isn’t, then the contractor should say that is not good enough. Therefore, always select a flame retardant with a verifiable performance.
 
The Wood Protection Association (WPA) operates two independent quality schemes with the first part being the approval scheme for the flame retardant additives. This means an independent expert panel will have assessed the test certification to ensure it is valid and appropriate to the end use. WPA will then grant an approval to that particular formulation product.
 
The second part is the WPA Benchmark Flame Retardant (FR) quality scheme which is based on an independent audit and quality assurance check for companies applying these formulations, or building them in, at the time of panel manufacture.
 
The WPA is trying to tick all the boxes for the supply chains. If you can get the approval for the formulation, the manufacturer and the stockist/distributor then we know what the contractor is specifying and buying is the right thing.
Post-Grenfell, the construction industry, and those associated with it, have become risk averse, and the Government’s changes to the building regulations to restrict the use of non-combustible materials in high rise buildings is a classic example of that. A more sophisticated solution to that challenge would have been far more appropriate. This had a major impact on a number of sectors including some elements of timber. There is going to be more companies who will incorporate flame retardants in products at the point of manufacture to get a CE mark and this will definitely be the future. Post-treatment of timber products will ultimately fade away.
 
Gordon Ewbank, recently delivered a presentation on Performance of Wood-Based Products in Fires to a packed audience at CABE’s BuildEng Southern Regional Conference. These popular one-day conferences and exhibitions are open to all constructions professional and run throughout the country.
 

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