Experimental study on thermal conditions affecting smouldering behaviour of CCA-treated wood using fire propagation apparatus

: This study examined how external thermal exposure affected the self-sustained smouldering behaviour of chromated copper arsenate (CCA)-treated wood. A Fire Propagation Apparatus was used, varying incident heat flux and exposure duration to emulate passing wildfire scenarios. Wood density and CCA retention were kept within narrow ranges. Responses from ignition through smouldering propagation were evaluated using mass loss, thermocouple temperature, and exhaust-gas carbon monoxide (CO) and carbon dioxide (CO 2 ) concentrations over time. The time to peak CO or CO 2 aligned with the time to peak mass-loss rate, providing a practical and robust indicator of smouldering severity. Smouldering severity was governed mainly by total incident energy rather than heat-flux intensity or duration alone; tests with comparable incident energy produced similar severities. Increasing total incident energy deepened char, increased thermal penetration, and increased mass loss at the onset of self-sustained smouldering after flameout. However, smouldering severity does not increase linearly with incident energy. At bench scale, smouldering propagation was not perfectly one-dimensional despite the initial heating being almost one-dimensional. These findings identify total incident energy as a practical control parameter for reproducing wildfire-analogue exposures and provide an operational severity metric to support development of monitoring protocols, severity-based fire classifications, product screening and targeted intervention strategies.