Abstract
The number, dimensions, and initial velocity of the firebrands released from burning Quercus suber, Eucalyptus globulus, Quercus robur, and Pinus pinaster trees were analyzed in laboratory experiments using a particle image velocimetry system. Additionally, the flame height, tree mass decay, vertical flow velocity, and temperature at the top of the trees were measured during the experiments. The relationship between the various parameters was analyzed and a good connection was found. The specimens burnt were mostly young trees, so large particles (e.g., pine cones, thick trunk barks, branches) were not included in this study as they were not present. Actually, the firebrands produced in the laboratory tests, mainly burning leaves, had a cross-sectional area of <1,600 mm2, having the potential to cause short distance spotting (up to tens of meters). Quercus trees are often considered to have a lower fire risk than eucalyptus or pine trees. However, in this study, Quercus suber and Quercus robur were the species that produced more firebrands, both in terms of number and total volume. The tests with Quercus suber were the only ones using specimens from an adult tree, confirming the great importance of the age of trees in the propensity to release firebrands. The results obtained with Quercus robur confirmed the high tendency of this species to originate spot fires at a short distance. Thus, these results are of great relevance to afforestation plans and to evaluating the risk of the presence of these species in wildland–urban interface areas.
Highlights
Spotting is one of the most relevant and common mechanisms of fire spread in wildfires, especially in extreme burning conditions
Due to data storage limitations of the system, the capture of particle image velocimetry (PIV) images was started after fire ignition, when the operators considered the burning process to already be in sustained development
*values found for Q. marilandica, Q. falcata, Q. nigra, and Q. phallus. +values found for P. taeda, P. elliottii, and P. echinatta
Summary
Spotting is one of the most relevant and common mechanisms of fire spread in wildfires, especially in extreme burning conditions. The analysis of the spot fires mechanism is frequently divided into four stages (Almeida et al, 2013): (1) release of firebrands, (2) lofting of the firebrands in the thermal plume, (3) downwind transport of the firebrands, and (4) ignition of the fuel recipient where the firebrands land. Most of Firebrands’ Release by Burning Trees the work seeking the determination of the maximum spotting distance is carried out in the second and third phases (e.g., Tarifa et al, 1967; Albini, 1979; Ellis, 2000; Hall et al, 2015) considering that firebrands, after leaving the thermal plume, travel at a velocity defined by the terminal velocity and the wind speed. Statistical analysis based on tests with different combinations of firebrand types and fuel bed recipients (e.g., Ganteaume et al, 2009; Viegas et al, 2014; Ellis, 2015) or in a shower of firebrands artificially generated that hit building façades or other relevant structures (e.g., Manzello et al, 2011; Manzello and Suzuki, 2014; Oliveira et al, 2014) was produced
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
