Continued research from the FWPA-supported National Centre for Timber Durability and Design Life (NCTDDL) is seeking to address the fire risks associated with copper-based timber treatments and protect the ongoing use of timber for outdoor use in Australia. Source: Timberbiz
This research supports FWPA’s focus on driving industry advancement through strategic research and initiatives to drive growth and productivity for members and the forest and wood products industry.
Copper-based treatments are widely used across the country to increase the durability of timber products, particularly in external settings. Treatments such as copper chrome arsenate (CCA) are a cost-effective way to protect wood from rot, insects and fungi, prolonging its life outdoors.
CCA-treated timber is the most common and is recognisable to many by its green tint. While its use is restricted in some settings including playgrounds and picnic tables (due to concerns around its arsenic content), it is commonplace in applications such as fencing, landscaping and utility poles.
However, research has shown copper-based treatments can increase the risk of smouldering – a form of slow, sustained and flameless burning which can continue undetected after a fire has ended.
This means a timber structure can appear intact following a fire but continue to smoulder and eventually fail over time.
In the case of an electrical post for example, this can cause critical impacts including power outages, particularly in remote areas where arranging repairs for a single pole can be costly and time-consuming.
NCTDDL Director, Professor Tripti Singh explained these factors pose a significant risk to the ongoing use of timber in these environments, as people look for alternatives.
“Combatting smouldering risk is critical to protecting timber as a material of choice for outdoor use,” said Dr Singh.
“Timber boasts exceptional sustainability credentials. To support and grow its ongoing use in outdoor applications across Australia, it’s important to strengthen fire safety measures while maintaining the durability that makes it such a reliable material.”
Since 2021, PhD student Wenxuan Wu has conducted research to understand the relationship between copper and wood with regards to their burning behaviour.
Mr Wu studied CCA as well as its most common alternatives, alkaline copper quaternary (ACQ) and copper azole (CA). He examined how the treatments affect burning and analysed differences in burning behaviour from a chemical perspective.
The study initially used a ‘movable radiant panel system’ to simulate a passing bushfire, measuring the effects on treated and untreated wood samples.
“After observing the smouldering behaviour of various copper-based preservatives, we looked at how fast smouldering would destroy the infrastructure and how this was affected by other factors such as wood density, preservative concentration and fire intensity,” Mr Wu explained.
“Often flames are seen as the main markers of fire, but the metals in these preservatives act as catalysts to promote smouldering combustion. Once smouldering starts, it typically self-sustains and continues until no infrastructure is left.”
The study found that lower timber density and higher concentrations of preservatives also increase the severity of smouldering. Because all three elements in CCA are catalysts for smouldering, it was found to be the highest risk in terms of time to burn, as the smouldering reaction can occur even at lower temperatures and in lower concentration.
Mr Wu’s project is set to be completed in 2024.
In 2023, Zeinab Darabi commenced a new research project building on Mr Wu’s findings and seeking a practical solution.
In particular, she is investigating potential additive products that could be incorporated into copper-based treatments to counteract their burning behaviour.
Beginning with a review of existing literature to understand which chemical products may offer this functionality, Ms Darabi tested different chemicals to determine the best candidate for smouldering inhibition. She has now completed preliminary trials of possible additives.
There are two key aspects of fire retardancy: flame and smouldering. While there are chemicals that can impact one or both, Ms Darabi explained that eliminating smouldering behaviour is the main goal of her study. Copper-based preservatives do not change flame behaviour, but they do increase smouldering. This means that adding a smouldering inhibitor to treated timber will allow it to burn and quench as if it were untreated.
Ms Darabi explained that ensuring the additive does not leach is also an important focus, as most commercial smouldering inhibitors are leachable.
“Exposure to high humidity or running water can cause the chemicals to leach from wood products, eliminating their effects from the timber,” she said.
“Introducing an oil-based additive can prevent leaching, but this creates its own challenge as the most common copper preservatives are water-based. This means that the preservatives and the non-leachable chemicals that can prevent smouldering do not naturally want to mix – they are literally oil and water. We will need to develop a stable emulsion of the two components to create a single product that can provide durability and reduce smouldering.”
If successful, this emulsion would be the first formulation of its kind in the industry.
NCTDDL Research Fellow, Dr Luis Yerman is the main supervisor of both research projects. He explained further work will be required to make a new preservative commercially viable.
“Treatments like CCA are widely used and integrated into production lines across the country,” said Dr Yerman.
“We can’t introduce an entirely new step in the process and expect processors to integrate the additional infrastructure, cost and time this would require. To make this an economically feasible option, we need to find an additive that can be incorporated into copper-based treatments and applied as one product using existing processes. Ideally, treatment plants will not have to change anything other than the treatment formulation.”
Dr Chris Lafferty, Head of Research, Development and Extension at FWPA, echoed this sentiment, saying the potential benefits of this research stretch beyond current applications of copper-treated timber.
“The more we understand how these treatments work, the greater confidence and trust we can build in those looking to use timber in these settings,” Chris said.
“In Australia’s unique climate of bushfire risk, fire safety is a key concern. The potential to develop products that reduce the risks and impacts of fire damage could open new opportunities to expand timber’s use into new markets.”
