Summary
¦ Prospective new EU reaction to fire rules are affecting specification of fire protected wood.
¦ The new prEN 15912 standard takes into account fire retardant durability.
¦ Transition from the British to the EU timber product fire classification system is under way.
¦ The new edition of the WPA’s Fire Retardant Specification Manual is out in January.
Recently the National House-Building Council appealed to the Wood Protection Association (WPA) for assistance. It wanted continuing professional development training to help its London building control surveyors get their heads around timber fire retardant use and specification.
The episode told a story. Timber is being used increasingly overtly in an ever-wider range of applications in UK construction. Besides growth in timber frame, there’s been increasing use of other timber-based structural systems, plus a surge in the popularity of wood cladding and shingles. These ‘new’ applications have raised new questions about the technical performance of timber products and among the most frequently asked have been those about fire performance.
Adding interest and complexity to the subject is the continuing evolution of fire safety legislation and standards.
“Dynamic transition best describes what is happening in the fire protection industry,” said Arch’s UK fire retardant sales manager Jacqui Clay. “The introduction of new European reaction to fire standards is changing the way we think about specifying fire protected timber.”
The big news is the European reaction to fire standard prEN 15912. This is at draft consultation stage and could still be some way from enactment, but it promises important developments in timber fire protection emphasis and the treatment sector is being urged to adapt to it now.
“The likes of the WPA are already amending their criteria for product assessments based on the draft,” said Andrew Hughes, technical director of Arch Timber Protection and chair of the WPA technical committee.
Among prEN 15912’s stipulations is that durability of timber fire retardant protection is taken into account.
“It clearly makes sense for the service life of the retardant to match the product’s,” said WPA director Steve Young.
The new standard also evaluates impact of treatments on moisture absorption.
“This is also important as some products can cause staining, decay, poor paint adhesion, metal corrosion, and migration of chemicals in high humidity,” said Mr Young. “This is why WPA already classifies flame retardant treatments as DI, for dry interiors, HR, for humidity resistant requirements, and LR, for high humidity applications.”
Another change under way is the transition from the old British Standards system of timber product fire classification to the European. This forms part of the harmonisation of EU building sector standards under the Construction Products Directive (CPD). Under the new approach, fire performance for timber used in “permanent constructions”` is classified Euroclass B or C; the former being for products in key structural features, staircases and other designated escape routes, the latter for areas where lower ratings are acceptable, like buildings with no common access areas and shorter designated escapes.
Whether treated products meet these classifications depends on performance in the EN ISO 11925 ignitability and EN 13823 single burning item tests, and these must be conducted by notified bodies approved to issue European Classification reports.
The classification process also takes into account timber species, thickness and density of the tested material and its “field of application”, which means whether it’s mounted with or without an air gap behind and has a backing material.
CE marking of fire retardant-treated timber is also now coming into the equation where there is an EN product standard for a particular type of retardant-treated product (which currently means solid wood panelling and cladding and wood-based panels in construction). In the UK, CE marking isn’t yet compulsory, but that could change in the next few years.
Against this backdrop, it’s not surprising timber users, specifiers and merchants are approaching timber treaters for fire retardant guidance.
“The growth in the use of timber frame and such products as cladding mean that there are people coming to this issue for the first time and there is demand for education, so we spend quite a bit of time giving advice,” said Neil Ryan, managing director of PTG Treatments, one of the UK’s biggest industrial timber pre-treaters. “Just recently we’ve been called increasingly by timber framers, but it’s also local authorities, merchants, building inspectors.”
When fellow-WPA member Arch is quizzed on the topic, its advice is to ask three key questions about fire retardant-treated products. First, whether the treatment complies with prEN 15912. Second is if the treated product is independently certified with an EU Classification Report issued by a notified body for the specific timber and application.
Last, but not least, it urges specifiers and end users to ensure fire retardant treatments have been made and applied “correctly, under controlled-conditions with full traceability”.
“Fire performance can best be assured if the manufacturing and application of the retardant is carried out under an independent certification and accreditation scheme,” said Ms Clay. “ISO 9001, British Board of Agrément accreditation and WPA listing and approved status all provide this assurance.”
The WPA’s Flame Retardant Quality Scheme, which lists companies authorised to apply flame retardant treatment of timber and wood-based materials by pressure impregnation, has also has been developed for use as a “BS EN ISO 9001 quality schedule”, said Mr Young. These treaters are also included, along with listed retardant products, in the organisation’s Fire Retardant Specification Manual.
“The ultimate aim of fire retardants is to protect lives and the onus is on specifiers to ensure compliance [with latest standards],” said Ms Clay. “So you should choose both product and service provider carefully.”
Another view from representatives of the treatment sector TTJ spoke to is that it is preferable to opt for impregnation pre-treated products of proven performance rather than site-applied surface fire retardant treatments.
“When they’re applied by brush or spray on site, fire performance can only be assured if application is covered by an independent installer accreditation scheme,” said Ms Clay.
“There are question marks in particular over the durability of site-applied treatment and its ability to meet prEN 15912,” said Mr Young. “Whereas a long-term WPA test programme has shown that, even after 21 years, industrial impregnated pre-treated products suffer no loss of performance.”
The WPA provides further guidance on selecting fire retardants in its specifiers’ checklist. This will also form part of the third edition of its Fire Retardant Specification Manual, due out in January.
“In addition, we’re developing online and face-to-face CPD training,” he said. “The NHBC surveyors take their CPD course in January.”
