Laboratory characterization of firebrands involved in spot fires

Abstract

& Introduction Wildfires are considered the most important disturbance in the Mediterranean Basin, and some are propagated over long distances due to lift-off and ignition of firebrands. & Objectives To improve our knowledge of firebrands involved in spotting fires, flammability characteristics of eight types of firebrands commonly generated by wildfires in Southern Europe were determined under laboratory conditions. & Results All the firebrands tested showed 100% ignition frequency but with a wide range of time to ignition and flaming duration. Weight loss during combustion was exponentially related to time, and there was a decrease in the ratio of the weight at temperature T to the initial weight with increasing temperatures. In our experimental conditions, there was a significant effect of fuel moisture content on time to ignition, flaming duration, combustion and thermal decomposition. On the basis of the characteristics analysed, three firebrand groups have been identified in relation to spotting: heavy firebrands with ability to sustain flames, efficient for long-distance spotting (pine cones); light firebrands with high surface-to-volume ratio, efficient for short-distance spotting (leaves and thin barks); and light firebrands with low surface-to-volume ratio, efficient for short and, occasionally, long-distance spotting (all the other types of firebands).

Assessing the flammability of surface fuels beneath ornamental vegetation in wildland–urban interfaces in Provence (south-eastern France)

“…Before each ignition test, litter depth, biomass and bulk density were measured. The ignition setup was operated according to a protocol used in previous studies (Ganteaume et al 2009(Ganteaume et al , 2011a(Ganteaume et al , 2011b, using a consistent Pinus sylvestris (Scots pine) deadwood piece (2 × 2 × 1 cm) that was left at room temperature to equilibrate to ~7% moisture content. The wood piece was placed on a 500-W epiradiator at a constant temperature of 415ºC and emitting a constant 7.5 W cm -2 radiation (Epiradiator Standard NF P 92-509-1985) until ignition, as described in Ganteaume et al (2009).…”

“…The importance of non-woody surface-fuel in wildfire has been addressed in numerous studies in terms of the effects of its arrangement (Bradstock and Cohn 2002) and morphology (Scarff and Westoby 2006), for instance. The flammability of the leaves or needles of the main Mediterranean species regarded as fuel or firebrand involved in spot fires has already been assessed in several studies (Valette 1990;Dimitrakopoulos and Papaioannou 2001;Ganteaume et al 2009Ganteaume et al , 2011aGanteaume et al , 2011b but the flammability of litters sampled under vegetation planted in hedges remains to be assessed.…”

“…Regarding ornamental vegetation, Long et al (2006a) provided flammability data for horticultural beds by evaluating the effect of the type of mulch, planting composition and drought conditions on fire spread and heat release in both field and controlledenvironment conditions. Several experiments were carried out on firebrands but very few used surface fuels (Manzello et al 2006a(Manzello et al , 2006b(Manzello et al , 2007(Manzello et al , 2008(Manzello et al , 2009Ganteaume et al 2011b). …”

The Spotting Distribution of Wildfires

“…We measure heights z in metres, and masses m in kilograms (though it will be noted that typical firebrand masses are on the order of grams). Notice that one may be interested in many more characteristics of the firebrands launched: the firebrand type, for example, could be important [46,47].…”

“…The results of [47] suggested that there are three firebrand groups which are important for spotting. These include: heavy firebrands with the ability to sustain flames, which are efficient for long-distance spotting (e.g., pine cones, cylindrical brands); light firebrands with high surface area-volume ratios are effective for short-range spotting (e.g., Eucalyptus or pine bark plates).…”