Fire and Materials最新文献

Wildfires arriving at a brush-cleared vegetation near vulnerable assets in the Wildland-Urban Interface (WUI), experience significantly reduced fire propagation, intensity, and associated risks. However, assessing the effectiveness of fuel reduction on fire behavior remains challenging due to limited understanding of ignition and propagation mechanisms in live vegetation. To fill this gap, a simplified approach was designed, focusing more on the combination of physical modeling with new empirical data rather than providing new insight in the physical process modeling. Burning experiments were conducted on cypress trees at two scales of live vegetation, the “laboratory scale” and the “real scale,” to gather data on fire behavior in cypress canopies with varying fuel moisture content (FMC) and bulk density (BD), using two ignition methods. A semi-empirical model, based on the physical model Fire Dynamic Simulator was developed, using the “laboratory scale” data as inputs, while the data recorded at “real scale” were used to validate the model. Laboratory-scale experiments showed consistent results when ignition was initiated by flame contact. In contrast, indirect radiant heat ignition was highly variable due to the influence of gaps between leaves. At the real scale, BD had a significant impact on fire behavior. The model evaluation showed it could simulate fire auto-propagation in live vegetation much more precisely compared to current physical models, leveraging the precise fire behavior data obtained at the laboratory scale.

The hot-particle ignition is a common cause of wildland and building fires. This study investigates the ignition of three typical fuels (straw, pine needles, and cotton) in the wildland-urban interface (WUI) by a hot metal particle of different temperatures and void ratios. In the absence of wind, the ignition of cotton is the easiest, where a flame occurs directly without clear smoldering. As the particle becomes hollow, the required minimum particle temperature for igniting cotton becomes smaller, because of a longer contact time between particle and fuel surface. Once ignited, the flaming of cotton is the weakest, with a mass loss of less than 25% because of an intensive charring. The burning of straw and pine needles is intense, with a large flame height and very little residue. Materials with finer and thinner structure like cotton are easy to initiate a flame by a hot particle while hard to sustain smoldering ignition. The hollow-structure or large-porosity materials like straw are prone to smoldering ignition under a weaker spot heating source. The fast-cooling void particles cannot induce a smoldering ignition of all three WUI fuels, because smoldering ignition requires a longer effective heating duration. This study helps understand the ignition propensity of WUI fuels by a hot particle and the subsequent flame-spread and burning process, which supports the fire protection design for WUI communities.

To seek a fire-resistant fuel, the reaction to fire of Algerian Phoenix dactylifera leaves known for their thermal resistance was compared to that of three highly flammable Algerian fuel particles: Eucalyptus globulus leaves and Pinus halepensis and Pinus canariensis needles. By using a small-scale cone calorimeter, their thermal properties were investigated under a low irradiance of $�\; ��\; �3.5�\; ��\; �\mathrm{kW}�\; �/�\; �m^2��$, while their ignition and combustion properties were examined with irradiances of $�\; ��\; �17.5��$ and $�\; ��\; �50�\; ��\; �\mathrm{kW}�\; �/�\; �m^2��$. Eucalyptus globulus leaves were found the most ignitable fuels with the largest released heat, while Phoenix dactylifera leaves were found by far the least ignitable fuels with the smallest released heat, particularly under large heat flux intensities. Based on a theoretical analysis of thermal and ignition properties, a new flammability/spreading index combining the ignitability and combustibility metrics was proposed to rank these fuels. This index was compared with the fire retardancy index used for polymer composites and adapted to these plants because it uses a cone calorimeter. A similar ranking order was obtained between the two indices for the considered fuels, where Eucalyptus globulus leaves were found by far the most fire-spreading fuels particularly at large fire intensity. On the other hand, Phoenix dactylifera leaves appeared by far the least fire-spreading fuels particularly at large fire intensity. The possible use of <