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This paper presents a systematical experimental study on eruptive fire over a pine needle fuel bed in trench configuration in still air to elucidate the essential mechanism of eruptive fire. The fire spread characteristics under different slope angles (0–40°) and trench aspect ratios (0.1–0.4) are investigated by a comprehensive analysis of experim...
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... was found that when the slope angle increases from 25° to 26°, the ROS has a sudden increase (Figure 3). Besides, a significant rise in flame depth was observed in experiments (see the embedded photos in Figure 4). For quantitative analysis, the front and rear positions of the flaming combustion zone are identified by the temperatures, respectively, rising to and dropping to 300°C, the distance between which is estimated to be the flame depth. ...
Context 2
... 10 indicates that under certain conditions of fire eruption, the radiation and convective heating may play comparative roles, or even convective heating may play a more significant role in fire acceleration. Figure 6 reveals that the flame attachment modifies the airflow in its close vicinity, while experimental observations ( Figures 5 and 6) and the data of flame depth (Figure 4) verify that the induced hot gas flow (convective heating) enhances the combustion intensity and the rate of spread. In return, the increased intensity further enhances the airflow. ...
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Citations
... From a fire behavior modeling point of view, canyon-like terrain morphology and steep slopes are associated with eruptive or blow-up fire behavior (Viegas 2005;Chatelon et al. 2014;Xie et al. 2017;Liu et al. 2022), which consists of a sudden and explosive acceleration of the rate of spread of the fire front with a corresponding higher energy and heat convection development (Viegas 2005, Viegas and Pita 2004, Viegas and Simeoni 2011, Rodrigues et al. 2018. According to Viegas and Simeoni (2011), such fire eruptions are not necessarily restricted to crown fires and moreover may take place in single fuel layer as is the case in beech stands during the vegetation dormancy. ...
... Viegas and Simeoni 2011, Chatelon et al. 2014, Rodrigues et al. 2019, eruptive fire behavior is often associated with steep slopes combined with canyon-like terrain configuration. Considering the small vertical extent of direct fire signs (charred bark), it is likely that the f lames were strongly tilted uphill almost to the point of being parallel to the combustible litter layer (f lames attached to slope; Liu et al. 2022). Our study confirms this hypothesis even for winter surface fires burning in a single litter fuel layer within a beech stand. ...
In the complex Alpine topography, canyon-like terrain morphology combined with steep slopes may cause sudden changes in fire behavior, for instance, turning fast-spreading surface fires into eruptive fires. This phenomenon was observed during the vegetation dormancy in mountain beech (Fagus sylvatica L.) stands, a forest type usually spared from wildfires. The aim of this study is to understand the impact of eruptive fire behavior on the post-fire trajectories of beech trees. To this end, over the course of 3 years, we monitored the post-fire dynamics of 100 beech trees subjected to different fire intensities in February 2020, including a small-scale eruptive fire behavior associated with a steep slope (~41.4° on average) and canyon-like terrain features. Dendrometric and sylvicultural parameters and fire-related damages such as the presence of bark blackening, scars, foliage loss, crashes of branches or whole trees, and parasitic attacks were assessed. The observed medium to high fire severity was highly dependent on the position of the tree within the eruptive fire sector, whereas the relationship with dendrometric and sylvicultural tree characteristics, such as the crown position or the stem diameter, was less clear. Due to the lethal temperatures generated by the heat convection within the eruptive fire sector, the exposed bud and cambium tissues of the beech trees partially or totally failed to develop in the first post-fire season. Beech crown and stem tissue killed by exposure to convective heat fluxes rapidly dries out, loses its elasticity, and becomes brittle. Starting from the second post-fire season, this greatly increases the risk of the crashing of these crown parts and/or entire trees. A detailed understanding of the factors leading to an eruptive fire behavior would highly benefit the fire risk assessment and the detailed planning of the firefighting tactics in mountain areas, eventually increasing the safety of firefighters and preventing post-fire natural hazards, such as rockfall, erosion, surface runoff, and debris flow.
... The model gives a new expression of the ROS that takes into account the pronounced acceleration of the fire spread with the increasing slope. It is tested against three different series of laboratory fire experiments (Butler et al. 2007, Liu et al. 2014, Liu et al. 2022) conducted without wind and in which the terrain slope angle varies ranges from 0 to 35° and against a field scale experimental fire conducted in Corsica across shrub species under weak wind and steep slope conditions (28°). ...
... The numerical results obtained by the proposed model against the experiments performed by Butler et al. (2007), and by Liu et al. (2014Liu et al. ( , 2022 are plotted in figs. 2 and 3, respectively. Note that Butler and his co-authors (2007) calculated the normalized ROS (ratio between ROS and ROS0, obtained for zero-wind and zero-slope) in all their set of experiments. ...
O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos países do Sul da Europa, bem como em algumas regiões dos EUA, Canadá e Austrália, onde estamos habituados a enfrentar a presença de incêndios muito grandes e devastadores, continuamos a ter eventos que quebram recordes. Alguns países, como os da Europa Central e do Norte, que não estavam habituados a ter grandes incêndios, experimentaram-nos durante estes anos. Os anos anteriores foram muito exigentes para todo o Mundo, também noutros aspectos que nos afectaram a todos. Referimo-nos às restrições impostas pela pandemia que limitaram as nossas reuniões e viagens, afectando em muitos casos a saúde dos membros da Comunidade Científica Wildfire. Felizmente, conseguimos encontrar novas formas de comunicação, ultrapassar essas limitações e manter-nos em contacto uns com os outros. Durante semanas e meses, para muitos de nós, as reuniões pessoais e o trabalho de grupo foram substituídos por ligações em linha. Apesar da economia de dinheiro e tempo, e da facilidade de reunir uma grande variedade de pessoas que estas reuniões desde que nos apercebêssemos de que não substituem as reuniões presenciais, que trazem consigo outras dimensões inestimáveis, que fazem parte da comunicação pessoal e ajudam a construir uma comunidade científica.
... The model gives a new expression of the ROS that takes into account the pronounced acceleration of the fire spread with the increasing slope. It is tested against three different series of laboratory fire experiments (Butler et al. 2007, Liu et al. 2014, Liu et al. 2022) conducted without wind and in which the terrain slope angle varies ranges from 0 to 35° and against a field scale experimental fire conducted in Corsica across shrub species under weak wind and steep slope conditions (28°). ...
... The numerical results obtained by the proposed model against the experiments performed by Butler et al. (2007), and by Liu et al. (2014Liu et al. ( , 2022 are plotted in figs. 2 and 3, respectively. Note that Butler and his co-authors (2007) calculated the normalized ROS (ratio between ROS and ROS0, obtained for zero-wind and zero-slope) in all their set of experiments. ...
