Wood protection Association

This article is from the Wood Protection Association website

(continued from previous page)

For more about wood protection visit the Wood Protection Association

Changes in standards
In a spirit of cooperation with the European Commission, the UK timber preservation industry, starting in the late 1980s, threw itself into the work of the European Standards Commission (CEN) to develop performance standards for wood preservatives. These, it was thought, would be needed for compliance with the Construction Products Directive, itself published in December 1988. In the event, wood preservatives were not classified as construction products in their own right but as components of products such as poles and structural timber that are construction products within the meaning of the directive.

At the time the UK had a perfectly good set of standards governing preservative composition and the treatment of timber in all end uses following so-called process specifications. In these, the process was defined in terms of the concentration of preservative and the combination of vacuum and pressure periods during the treatment. These, followed correctly, conferred the appropriate level of durability on otherwise non-durable timber and effective quality assurance schemes could be operated at minimal cost giving confidence in the performance of the treated timber. This approach had evolved independently and different from the industry elsewhere in Europe and the UK had to accept in the preparation of the new performance standards that a different approach would have to be adopted. Preservatives would, in the future, be defined not in terms of their composition, but how they perform in a series of biological tests. Timber treatment would be defined not in terms of the treatment process but in terms of the penetration of the preservative into the timber and how much was deposited (the retention) in the penetrated zone – so-called results specifications.

After vast expenditure by the industry in time and travel, a series of new European standards emerged reflecting the approach outlined above. These became published as British Standards in accordance with the UK’s obligations as members of CEN and the industry set to to prepare national guidance for the UK. This was published in 2003 as BS 8417: 2003 Preservation of timber- Recommendations. The old conflicting British Standards BS 5589 and BS 5268: Part 5 were declared for obsolescence in late 2003 and so the UK timber and timber preservation industry is poised on the brink of the brave new world of results specifications.

BS 8417 continues the tradition established in the old standards of explaining the factors affecting choice of preservative treatment. These include an assessment of the biological hazard faced by timber in service; the desired service life; the options for choosing naturally durable timber; and an assessment as to whether treatment (or timber with higher levels of natural durability) is unnecessary, optional, desirable or essential.

Having made a decision to choose treatment, a preservative must be selected along with the combination of penetration and loading to give the required performance. The performance specifications on which BS 8417 is based give the specifier the opportunity to choose any combination of preservative, penetration and retention but in practice it is expected that the guidance in 8417 will be followed. The European performance standard for preservatives gives national bodies the freedom to declare retention requirements for existing products without further testing and this has been done for CCA, creosote, certain solvent-based preservatives and boron compounds. The requirements for other older preservatives have yet to be declared. For newer preservatives introduced over the past ten years or so while the new standards were being worked on, performance is expressed in terms of the amount of preservative shown to be effective in biological tests – it is expressed as the ‘critical value’. For such preservatives, BS 8417 then guides the specifier to the appropriate retention (expressed as a multiple of the critical value) of any preservative for which the manufacturer declares a critical value.

Quality assurance procedures with these results specifications will include analysis of treated timber for penetration and retention – an added cost for the treater and eventually for the customer. However, a concession to established UK practice won by the UK team at CEN, means it will be possible to rely on a particular process to achieve the penetration and retention required without carrying out the analyses each time. Such a procedure has to be confirmed by repeat testing at intervals but it makes QA much more manageable and cost effective for the treater.

Changes in regulations
Wood preservatives have been subjected to rigorous controls in the UK since the early 1970s, first under the voluntary schemes with which Wood Protection Association members complied, and since 1986 under the Control of Pesticides Regulations (CoPR). Independent experts assess products for safety before approval is granted and tough conditions are placed on their sale and use. Now a new EU –wide system of approvals will be introduced as the Biocidal Products Directive (BPD) procedures take effect over the next ten years, replacing the CoPR.

The BPD procedures will involve a re-assessment of all wood preservatives but the European Commission has felt it necessary to introduce restrictions, via directives, on creosote and chromated copper arsenate (CCA) preservatives ahead of those reviews. This has been prompted at least partly by political considerations reflecting restrictions in place in some member states at the time of their joining the EU. The Wood Protection Association and its members afford the safety of the public and that of people working in the industry the utmost importance and fully support the principles and objectives set out in the directives. To this end, association members have closely monitored developments preceding the adoption of the directives, and already supply and use preservatives that comply with their requirements well before they come into force.

Creosote
From 1 July 2003, approval for DIY uses of creosote was withdrawn and restrictions were introduced on certain uses of creosote-treated timber. Most of the restricted uses are in any case not suitable for creosoted timber due to risk of staining clothing from contact with any creosote there may be on the surface. Consequently, the major uses of creosoted timber for poles, fencing and sleepers have not changed. The WPA has advised suppliers and users of creosoted timber to review their handling, use and disposal procedures and this has largely been completed. Sale and use of old creosoted timber, typically railway sleepers and poles, continues and this is an environmentally appropriate method of disposal.

For DIY use, alternatives to creosote have long existed and the gap in the DIY market created by the loss of brush-applied creosote grades has been filled by existing and some new formulations. The WPA is concerned that the public is not well informed about the correct choice of product for various DIY uses and a number of products are now on sale that appear to be creosote replacements but in fact do not offer the same level of preservative performance. The WPA is seeking to improve point of selection material available to the public to help them make the best choice.

CCA
The directive includes restrictions on CCA preservatives and CCA-treated timber reflecting the outcome of a recent review which identified concerns about potential risk to the health of children in frequent contact with treated wood, risks arising from household burning of waste wood treated with CCA and risk of effects on aquatic organisms in certain marine waters. Nevertheless the restrictions do not apply to CCA-treated wood already in place. This mirrors the position in the USA where the Environmental Protection Agency has advised there is no reason to remove or replace existing CCA-treated structures, including decks or playground equipment. This is now supported by the US Consumer Product Safety Commission, which has recommended that no further action be taken to regulate wood treated with CCA.

The directive does require EU member states to introduce regulations by 1 July 2004 that will severely restrict the use of CCA-treated timber especially in construction and, for example, most fencing uses. DIY use will stop. However, preservative manufacturers have placed great emphasis on research and development for many years and wood preservatives formulated without arsenic are already available and in fact already in widespread use. The performance of timber treated with alternatives to CCA in many uses, including construction, is excellent. The UK timber preservation market has responded to the publication of the directive by switching a considerable proportion of production capacity to alternative preservatives. Sufficient CCA treatment capacity will remain to satisfy those uses where confidence is required in very long service life in the higher hazard and critical end uses such as motorway fencing. This is expected to continue while service experience with alternative products for such uses accumulates. In many such situations creosote continues to be one of the options for treatment alongside the water-based alternatives. The Wood Protection Association looks for an orderly transition to alternative wood preservative types starting with those end uses where decades of reliable durability to ensure safety in use is not an essential requirement.

Confidence maintained
Although the industry faces a challenging time, the Wood Protection Association and its members are managing the changes so that specifiers and users will find they have sufficient information to choose treatments that maintain confidence in timber in all situations. The WPA website is being developed as a major source of information for specifiers and users that will include the forthcoming update to the WPA (formerly BWPDA) Manual. WPA information is expected to be available via the AskTRADA website.

Dr C R Coggins
© BWPDA 2003