Enhancing the fire performance of wood as a construction material
The positive environmental profile of wood is driving a surge in its use as a construction material. Building Regulations require that in the event of a fire the buildings design and choice of materials will provide sufficient time for its occupants to exit safely. Wood is long established and understood construction material. In this article, the Wood Protection Association (WPA) explains how flame retardant treatments are used to enhance the fire performance of wood and wood based materials used in building projects.
Reaction to fire performance is vital
In the critical early stages of a fire, it is the reaction to fire properties of the various materials and substrates exposed that are vital to mitigating fire growth. These properties are the materials ignitability, heat and smoke generation, burning particle release and rate ate which flame spreads over its surface .
Once a fire is more developed, then containment becomes the top priority of a buildings 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. Fire resistance ratings are often quantified in time (minutes).
Wood is a long-established construction material
The performance of wood in a fire is well understood. Rigorous testing regimes such as those required to meet the ‘Euroclass’ reaction to fire standard (BS EN13501) have added to this understanding.
Flame retardants work by making wood more difficult to ignite and by slowing the rate at which a fire is able to develop, improving the performance of wood and improving its reaction to fire rating from Euroclass ‘D’ to either Euroclass C (limited lateral spread of flame) or ‘B’ (very limited lateral spread of flame) the latter being compliant with Building Regulations.
Flame Retardant Treatments
There are two tried and tested ways that flame retardant properties can be effectively conferred on solid wood and based materials:
1. The treatment of finished products under factory controlled conditions that are independently quality assured and
2. The incorporation of an appropriate flame retardant as an integral part of product manufacture (e.g. FR MDF, OSB or plywood) under an
independent quality scheme.
The brush or spray application of superficial FR coatings on a construction site is not recommended as the required product loading/thickness cannot be assured.
Flame Retardant Product and Process Quality Assurance
The WPA operates two complementary, independent quality schemes to verify flame retardant treated wood has been treated/manufactured appropriately for its end use. These are:
1 A flame retardant product approval scheme and
2 A treatment process quality assurance scheme called ‘WPA Benchmark FR.’
The flame retardant product approval scheme involves an in-depth review of fire test data on particular flame retardant formulations by an independent panel of experts.
‘WPA Benchmark FR', is a quality scheme based on an independent audit and quality assurance check for companies applying these formulations or building them in at the time of panel manufacture.
Flame retardants treatments approved by the WPA and WPA Benchmark FR product processors/product manaufacturers are listed in the ‘Quality’ section of its website and in the FR Specification Manual. This Manual which includes a Specifiers Checklist to help designers make informed decisions about the right choice of flame retardant materials is available as a free download from the WPA website www.wood-protection.org publications section.