Multi-scale Experimental Study on Self-sustained Smouldering of CCA-treated Timber Poles

IRG/WP 23-40988

W Wu, L Yerman, J J Morrell, F Wiesner

While it is accepted that appropriate treatment with chromated copper arsenate (CCA) will extend the design life of wood markedly, there are concerns regarding the effect of treatment on fire performance. Smouldering combustion in CCA-treated timber infrastructure can self-sustain, destroying the timber elements, as the chromium and copper present in the CCA can act as catalysts of the smouldering combustion. While smouldering occurrences have been well described, there are no standard methods for assessing the characteristics of this phenomenon either in the laboratory or field. Small-scale thermogravimetric analysis (TGA) and bench-scale smouldering experiments were used to establish a multi-scale test methodology for quantitatively assessing the smouldering combustion in treated timber. Smouldering propagation rates and kinetic parameters were established to determine the condition under which self-sustaining smouldering was most likely to occur. TGA confirmed the catalytic activity of CCA and showed that the heat released from the oxidation reaction occurred at significantly lower temperatures. Bench-scale tests confirmed that a CCA-treated pole was prone to self-sustained smouldering while a similar untreated pole failed to smoulder. Smouldering propagated to the untreated heartwood, indicating that sufficient energy was released from the oxidation to maintain a self-sustained process. The results will be useful for examining conditions conducive to smouldering and exploring methods for limiting this phenomenon.

Keywords: thermogravimetric analysis; H-TRIS; CCA-treated wood; fire safety; smouldering combustion; durability

Conference: 23-05-28/06-01 Cairns, Australia

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