The role of extinction on the re-ignition potential of wood-based embers in bushfires
Behdad Moghtaderi A B , Tri Poespowati A , Eric M. Kennedy A and Bogdan Z. Dlugogorski AA Industrial Safety and Environment Protection Group, Discipline of Chemical Engineering, School of Engineering, Faculty of Engineering and Built Environment, The University of Newcastle, Callaghan, NSW 2308, Australia.
B Corresponding author. Email: behdad.moghtaderi@newcastle.edu.au
International Journal of Wildland Fire 16(5) 547-555 https://doi.org/10.1071/WF06029
Submitted: 6 March 2006 Accepted: 24 March 2007 Published: 26 October 2007
Abstract
The re-ignition potential of partially burnt wood-based embers was investigated theoretically by studying their extinction characteristics. An adaptation of Semenov’s thermal explosion theory was used in conjunction with a linear stability analysis to determine the critical particle size at which extinction occurs. Particles of various shapes were studied and the analysis was carried out for both thermally thin and thermally thick particles. The results of our analysis indicate that thermally thick embers are less susceptible to extinction than thermally thin ones and, as such, are more prone to re-ignition. The results also show that the extinction of wood embers is strongly affected by the particle temperature, particle shape, and reaction kinetics. The effects of ambient conditions were found to be less pronounced than particle properties.
Additional keywords: flame spread, mathematical modelling.
Acknowledgements
The authors wish to acknowledge the financial support provided to them by the Australian Research Council under the ARC-Discovery scheme and the University of Newcastle, Australia.
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1 Typically tens of metres and occasionally hundreds of metres ahead of the main front.
2 Bi ≡ Biot number ≡ hL/k where h is the convective heat transfer coefficient and L and k are the characteristic length and thermal conductivity of the particle, respectively.
3 In the absence of flame, oxygen can penetrate into the particle causing a char oxidation reaction on the internal surfaces of the particle. This process, however, is diffusion-limited.
