New insights are being gathered around the smouldering of certain treated wooden elements following bushfire events. The findings could inform new approaches to the protective treatments of timber used externally in bushfire-prone areas, to limit the risk of further damage.
Dr Felix Wiesner, Lecturer in Timber Engineering at the University of Queensland’s School of Civil Engineering, and the Centre for Timber Durability and Design Life’s fire expert, is conducting the research to evaluate the fire performance of Copper chrome arsenate (CCA) treated timber.
CCA is a wood preservative containing compounds of chromium, copper and arsenic. It has traditionally been used to protect timber and other wood products – especially those intended for outdoor use and landscape timbers – from attack by microbes and insects. Following bushfire events, although exposed CCA-treated timber can appear unaffected, the metals in the treatment can continue to combust over time, leading to smouldering.
Smouldering refers to the slow, sustained, flameless form of combustion which, despite its weak combustion characteristics, presents significant ongoing risk.
“The main risk is the loss of load bearing capacity of the structure, causing collapse,” said Wiesner.
“This means a comparably small wildfire could destroy the structure, which would have been less likely to happen without the CCA.”
PhD student, Mr Wenxuan Wu, is working with Dr Wiesner to examine the conditions that lead to smouldering in CCA-treated timber, including sleepers and other landscaping timber elements, following bush fire exposure. Understanding the nature of this process has the potential to inform the development of more practical timber treatment solutions.
The project also involves observing the performance of CCA-treated spotted gum utility pole sections with and without fire barriers, during and following exposure using small-scale fire testing apparatus.
“The fire barriers being tested as part of this project are protective metallic mesh wraps, coated with an intumescent product, which can be fitted to wood in-situ,” said Wiesner.
“This product expands under heat exposure, providing extra insultation to the timber underneath. Intumescent paints are already frequently used in construction to protect steel during potential fire events. They are not considered as a replacement for CCA, but as an added fire protection.”
The work will also identify critical fire and ventilation conditions.
“Systematically varying heat exposure will help determine what kind of fire might pose the biggest threat to the CCA-treated timber poles after the fire has passed. Similarly, we can vary the imposed ventilation to find out if there are critical wind conditions that enable smouldering to occur and sustain itself,” said Wiesner.
Find out more about the National Centre for Timber Durability and Design Life via this link.
