In October, 60 delegates representing buyers and specifiers of treated timber, treatment companies and preservative suppliers attended a workshop at the Building Research Establishment to hear a range of speakers outline measures that the industry has to implement following changes imposed from Europe.
Headlined ‘Specifying timber durability with confidence: the new way forward with preservatives’, the workshop had two main aims : to deliver on a BRE commitment to publicise a key output from a DETR-funded contract on standards development in the field of wood preservatives and coatings; and to seek input from users and treaters to the final stages of the review of the BSI Draft for Development DD239 which aims to put a UK perspective on the range of new European standards.
Dr Frank Brooks, of Protim Solignum Osmose and chairman of the main BSI wood preservation committee B/515, set the scene by reviewing the long-established basis for the specification of wood preservatives and their application in the UK. A narrow range of preservatives complying with product specifications such as BS 144 for creosote and BS 4072 for CCA preservatives have been used mostly in accordance with the specifications set out in BS 5589 and BS 5268 Part 5. Timber for treatment must be in a suitable condition – preferably at the anticipated in-service moisture content or at least below 28% – and then the preservative is applied using a set of vacuum and/or pressure cycles designed to give the desired life of timber in service conditions.
Dr Brooks suggested that this approach helped the industry to meet its obligations under the Trades Descriptions Act since it was practical to demonstrate that a particular process had been used to treat a particular batch of timber rather than prove that every piece was penetrated with the required amount of preservative. Advantages included ‘specifier-friendly’ specifications, simple procedures at the treatment plant, treatment certificates summarised the contract and low cost quality assurance procedures. Disadvantages included no possibility of assessing the correctness of treatment by analysis and the rigidity of the system inhibiting process and preservative development. A few commodities, such as poles, are treated already using a combination of gross retention and penetration, but even these must fall in line with the new system.
Responding to the need to harmonise the approach to wood preservation across Europe, the industry played a key part in the preparation of a new range European standards. These have been published in the UK by BSI and the key ones deal with the conditions in which timber is used: BS EN335 – hazard classes; BS EN599 – performance of wood preservatives; and BS EN351 – the penetration and retention classes which may be selected by a specifier and guidance on sampling of treated timber to demonstrate compliance.
These new standards co-exist for a period with the old British Standards. DD239 sets out a framework for specifiers to interpret the new standards and to base specifications on penetration and retention requirements thought to reflect the old process specifications. Provision is made for the range of traditional preservatives with recommended penetration/retention combinations for different timber types, end uses and service life requirements. These are based on best estimates of what has been achieved in practice. Guidance is also given for new preservatives whose performance is demonstrated by testing according to BS EN599 but which have little or no evidence from longer term tests or in service. Such recommendations do come with a ‘health warning’ but are based on reasonable assumptions about long-term performance derived from the behaviour of older preservative types.
Dr Brooks drew attention to differences in interpretation among European countries but emphasised that since a common system underpinned them all, it should be possible for UK treaters to supply to other European markets and vice versa. He concluded that where countries have adopted a highly regulated system for control of treated wood, the timber industry has prospered because of the confidence generated in its durability. In spite of the costs and extra work that change brings, he felt the new system could provide that confidence and would create an opportunity for treated wood to maintain and expand its market.
Ed Suttie, from the BRE Centre for Timber Technology and Construction, described in detail how the new standards deal with the requirement for a combination of penetration and treated-zone retention of preservative in the treated wood. He explained how tests to the performance standard BS EN599 provide a ‘critical value’ for each preservative to which a factor is applied, according to the judgment of the specifier or in accordance with published guidance, to derive the retention required to give the desired service for treated timber commodities. A batch of treated wood has to be sampled and analysed using a statistically valid number of samples in order to demonstrate compliance. The new standards also give guidance on the so-called Acceptable Quality Level (AQL) appropriate for the type of timber being treated. The AQL gives the extent to which a set of samples may vary, yet still meet the specified requirements.
Mr Suttie then described a BRE case study on the application of the new system to the treatment of poles. It highlighted the difficulties with a rigid regime requiring a defined combination of penetration and retention. The natural variability of wood leads to the need to set the requirements at a level which can be achieved commercially, yet delivers confidence in the durability of treated wood. The new standards allow for agreement between specifier and treater on the establishment of a process/preservative combination that reliably delivers the required combination of penetration and retention. Mr Suttie showed how this could operate, suggesting that quality assurance systems would play a key role in underpinning the confidence needed between the two parties.
Two speakers from the British Wood Preserving and Damp-proofing Association spelled out the role the industry is to play in delivering confidence in the new system. Dr Chris Coggins, BWPDA director, said that the industry was coming to the end of a period of settled confidence in a narrow range of preservative types. There was now a need to provide a means of assessing claims of product performance by manufacturers. This would be met by the new BWPDA Preservative Approval Scheme. It will assess the performance of preservatives, particularly new formulations, that do not comply with the established range of British Standard or BWPDA Manual product specifications. He explained that, although the performance specification BS EN599 had been introduced, it dealt only with basic efficacy requirements and placed the onus on specifiers to be satisfied that a particular preservative could be used to give the necessary service life of a treated commodity, and that other characteristics such as performance of fixings, glues and surface coatings would not be adversely affected by the preservative, and that health, safety and environmental protection aspects of the use of wood treated with the preservative are in accordance with acceptable standards and/or legislation. An independent panel, to include the BRE, will carry out data assessments on preservative performance and will ensure confidence in the scheme.
The BWPDA Manual, now updated and published annually, will list approved preservatives and provide the most up-to-date guidance on treatment specifications and processes. It will be the vehicle to treaters and specifiers for new information on the application of the new standards as more experience is gained.
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“The BWPDA Manual, now updated and published annually, will list approved preservatives and provide the most up to date guidance on treatment specifications and processes. ” |
BWPDA president Alan Parks showed how the association intends to ‘square the circle’ by introducing an approved treater scheme. This will build on quality assurance systems such as BS EN ISO 9000, but add a requirement that plant operators hold the new National Vocational Qualification developed by BWPDA and are listed on the BWPDA register of qualified plant operators. The register will require plant operators to undergo regular refresher training to ensure familiarity with treatment and health, safety and environmental protection requirements as the legislation evolves. Treatment plants on the scheme will have to be designed and operated in accordance with the code of practice developed jointly by BWPDA and the main UK regulatory agencies, including the Health and Safety Executive and the Environment Agency. Approved treaters will have documented operating procedures, will mark batches of treated timber to ensure traceability and be required to demonstrate long-term financial stability.
Peter Walters, of Charles Ransford and Son, wound up the presentations with a hard-hitting assessment of the new regime asking ‘will it do the job?’ He drew attention to the problems of a ‘results’ specification based on penetration and retention. Inherent timber variability and the requirements for analysis added to the treater’s costs and commercial risks of supplying to such a specification. He showed examples of fence posts treated to the existing standards which had variable penetration but which had given decades of good service life. The new system must be able to accept such variability when the evidence is there. He suggested there would be a difficult period of adjustment to the new system on the part of specifiers, treaters and users. In a competitive market the question ‘who pays?’ must be asked.
During the session these key points emerged:
Summing up, Dr Coggins said the practical implications of the new regulations were far from clear and ongoing review of the working of the standards and their interpretation for the UK would be needed. The workshop had spent a long time on problems arising with the treatment of poles, so that implied much work is still needed to make the new system workable for all commodities. There are implications for liability of treaters working to a results specification, which would need careful attention to the detail of contracts for supply of treated timber to avoid disputes and litigation. The BSI committee responsible for DD239 will need input from all in the industry to make the review process as effective as possible.
