Spot fires: fuel bed flammability and capability of firebrands to ignite fuel beds

A series of tests were conducted under laboratory conditions to assess, on the one hand, the capacity of several fuel beds to be ignited by firebrands and to sustain a fire and, on the other hand, the capability of different types of firebrands to ignite fuel beds,. Fuel beds and firebrands were selected amongst the most common in Southern Europe. Regarding fuel bed flammability, results show that grasses are more flammable than litters and, amongst litters, Pinus species are the most flammable. The increase of bulk density and FMC involves an increase of the time-to-ignition, and a decrease of the other flammability parameters. The capability of firebrands to ignite fuel beds is higher when the firebrands drop in flaming phase and with no air flow than in glowing phase with air flow. Logistic regression models to predict fuel bed ignition probability were developed. As a whole, results show a relationship between ignition probability of fuel bed and type or weight of firebrands. Pinus pinaster cone scale, Pinus halepensis cone scale, Eucalyptus globulus leaf and bark can have ignition probabilities at least twice higher than bark of Pines when fallen in flaming combustion