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Nikola Misic, Milan Protic, Artemi Cerda, Miomir Raos, Milan Blagojević
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Fire Effects

NRFSN number: 26261
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With climate change and the ever-drier climate, the issue of wildfires is becoming increasingly prominent, generating growing interest in the study of wildfires. The majority of the ongoing research is focused on surface wildland fuels with particular emphasis on dead and usually dry fuel. These insights are difficult to transpose to live fuels, particularly to crown fires. The flammability properties of dead and dry forest fuels are of little significance for understanding the onset and spread of crown fires. Hence, research regarding the flammability properties of fresh forest vegetation is very sparse. The same observation applies to crown fires, despite the fact that this type of wildfires is devastating, difficult to suppress, and usually having dramatic consequences. The aim of this paper is to determine how moisture dynamics of live crown samples (terminal parts of basal branches) of two coniferous species, Abies alba and Picea abies, influence their flammability properties. Experiments were performed in an adapted mass loss calorimeter with a custom-made sample holder in order to mimic the scenario of initiation of crown fires (surface to crown fire interface). Tests were performed with heat flux values of 50, 60, and 70 kW/m2 and with different moisture levels. At all heat flux values, the results show an increasing trend for the peak heat release rate when moisture content is reduced. A. alba samples reach higher peak release rates in comparison with P. abies samples. At heat fluxes of 50 kW/m2 and 60 kW/m2, fresh A. alba samples take longer to ignite than the P. abies samples. At the heat flux of 70 kW/m2, for the set of analyzed moisture contents, the ignition time interval for the A. alba samples is shorter than for the P. abies samples. The results of the principal component analysis (PCA) show that variables such as time to ignition (TTI), peak heat release rate (PHRR), and mean heat release rate (mean HRR) best describe the ignitability of the analyzed conifer samples.


Mišić N, Protić M, Cerdà A, Raos M and Blagojević M. 2024. Transition from Surface to Crown Fires: Effects of Moisture Content. Fire Technology Volume 60, pages 669–700.

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