Creosote is the pre-treatment preservative of choice for UK Over-Head Line (OHL) wood poles and provides poles with a service life of 45-55 years. There are millions of these poles in GB. Creosote for amateur use was banned in the UK in 2003 and industrial creosote now has to conform to certain formulation restrictions. Further revision is planned for 2018 (EU Directive 2011/71/EU) and if this results in a full ban it will cause severe disruption to the supply of timber OHL supports and render UK energy provision more expensive unless a replacement preservative type which can provide similar efficacy is in place.
The project identifies a suitable preservative by firstly reviewing the literature in the area to identify candidate preservative types. It
then tests these preservatives by carrying out an accelerated-ageing test of wood poles treated with different preservatives; and
assessing the results by analysing samples at different times during the test.
Benefits
This project has the potential to deliver financial benefits to customers if Creosote is prohibited. In this circumstance it would look to deliver benefits by enabling DNOs to continue to utilise wood poles that are cheaper than man-made alternatives.
Based on the SPM license area, there will be an estimated 4,000 wood poles replaced each year in ED1. Assuming this is typical of the 14 license areas this equates to ~56,000 poles being replaced/year.
So whilst at this time it is difficult to calculate the solution cost, it is potential to estimate that every incremental increase cost of £100 per pole has the potential to add £5.6m to cost of maintaining the GB network/year. So finding a solution that is as close as possible to the cost of Creosote will alleviate the risk of this added cost.
Learnings
Outcomes
The APPEAL project has delivered the following key outcomes:
Technical outcomes: This demonstrated that alternative preservatives (RVP, Tanasote, Koppers copper) provide equivalent decay resistance to creosote. It confirmed no measurable decay in treated round timbers after 36 months of accelerated testing, and established that untreated timbers fail rapidly under identical conditions
Quantitative performance results: I) Untreated timber decay progression:
- 18 months: 67.5% severe decay
- 24 months: 73.75%
- 30 months: 90%
- 36 months: 100%
II) Treated timbers:
- No discernible decay across all time points
- Residual strength maintained at ~100%
Innovation and TRL progression: The project increased confidence in the deployment of alternative preservatives, advancing them towards Technology Readiness Level (TRL) suitable for adoption.The fungal cellar testing approach is now validated as a robust evaluation method for future asset innovations.
Additional findings: Surface characteristics vary by treatment (e.g., copper-based systems showing softer surfaces, potentially improving climb ability). Leaching simulations confirmed long-term preservative retention with minimal loss of efficacy
In summary, the project confirmed that alternative preservative treatments (RVP, Tanasote and copper-based systems) provide equivalent resistance to biological decay when compared to creosote under accelerated conditions. Untreated control samples degraded rapidly, while treated samples showed no measurable deterioration over a 36‑month period and retained full structural integrity.
The fungal cellar methodology has been validated as an effective test platform for future evaluation of timber treatments. The project has increased confidence in the adoption of non-creosote solutions and supports progression towards regulatory-compliant, environmentally acceptable alternatives.
Lessons Learnt
- Effectiveness of accelerated decay testing: The project demonstrated that accelerated fungal cellar testing provides a reliable and repeatable approach for simulating long-term timber degradation. The rapid deterioration of untreated samples confirmed that multiple decades of in-service exposure can be effectively replicated within a 36‑month period.
- Importance of measurement validation: The importance of equipment validation and redundancy in measurement techniques was highlighted by the Pilodyn issue. Instrument calibration and verification are critical. The use of multiple assessment techniques (Pilodyn penetration, visual inspection, and physical probing) was critical in delivering reliable and corroborated results. Reliance on a single measurement method would not have provided sufficient validation.
- Value of multiple sample types: Testing of full-scale round timber was identified as essential, as it better represents the behaviour of in-service poles compared to small-section samples. Inclusion of round timber (pole-scale specimens) provided more representative results than smaller stake samples. Larger timbers demonstrate different decay resistance characteristics and are more reflective of real assets
- Robustness of preservative treatments: This project showed that the modern alternatives to creosote offer equivalent performance. The long-term durability can be achieved without reliance on traditional high toxicity preservatives.
- Experimental design improvements: Incorporating internal baseline measurements (e.g., above – ground measurements) improves resilience against data inconsistencies. Environmental variables must remain tightly controlled to ensure repeatability.
