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Generation of firebrands from a wildland fire and their distribution downwind are studied using an analytical approach. The processes considered include emission of firebrands, wind-driven transport and the associated spot ignition. Emission of the firebrands from a fire front is treated as a stochastic process reflecting the interaction between gas flow plume and the burning fuel debris formed, with the emission rate being dominated by the rate of fuel consumption, emission factor and a function of firebrand sizes. Analogous to the random distribution of non-burning windborne particles, the transient distribution of firebrands downwind is described by a statistical pattern of Rayleigh form. Number and mass of firebrands landed downwind within the maximum travel distance are then determined by integration over the entire impact period during fire spread and burning-out processes. Application of the model to the bushfire occurred in Canberra, Australia in 2003 indicates that this model provides reasonable prediction in the distribution of firebrands downwind, and quantitatively exhibits the role of ember attack in massive destruction of houses at urban interface. Nomenclature A sMaximum cross-section area of a firebrand (m 2 ) C d Drag coefficient of a firebrand in flowing air (0.45) F e Firebrand emission factor for specific wildland fuels (kg -1 ) gAcceleration of gravity (m s -2 ) G(r i ) Rate of firebrands emitted from a fire source (m -2 s -1 ) H c Heat of combustion of wildland fuels (18,620 kJ kg -1 ) [1] h max (r i ) Height travelled by a firebrand with radius r i (m)Mass of firebrands distributed downwind at a location of x i -x 0 (kg m -2 ) m cr Critical mass of firebrands leading to successful ignition of the objects contacted (6.0 g) _ m f Fuel consumption rate in combustion zone determined byDistribution function of firebrands with radius between r i and r i + dr i (m -1 ) P f Ignition probability of houses downwind 12 r Radius (m) r 0Brand radius with the highest frequency of appearance (0.012 m) r i Brand radius (m) r max Maximum loftable brand radius (m) r min Minimum radius of lofted brands that play a role in igniting the objects contacted (m) t Time (s) t bEntire impact period of fire spread and the subsequent fire burning out (s) t cBurning duration of a firebrand (s) t r Flame residence time (s) t s Duration of fire spread (s) U g Up-draught gas velocity (m s -1 ) U tTerminal velocity of a firebrand at fall in still air (m s -1 )Distance between the initial firefront and the edge of the vegetations or the targeted area (m) x i Distance between a fire front and a target considered (m)Greek symbols b A correction factor (0.7) d(r i ) A parameter in association with the function p(r i , x) (m) g A coefficient determined based upon experimental results of Tarifa et al. [2] (0.435 mm 2 s -1 ) h f Angle of flame surface to the vertical k A constant determined based upon an experimental curve reported by Tarifa et al. [2] (2.86910 -4 s -2 ) q a Density of ambient air (1.2 kg m -3 ) q s Density of wil...

This paper reports results from an experimental study on low-temperature oxidation of a bituminous coal in an isothermal flow reactor. The rates of consumption of oxygen and the formation of carbon oxides were quantified by an on-line oxygen analyzer and a dual-column micro GC. Water produced during oxidation was measured using a drierite absorber. This allowed detailed calculations of mass balance during the oxidation experiments. It is observed that the rates of oxygen consumption and the formation of carbon oxides decreased with time, as opposed to the mass of coal sample, which tended to increase during the experiments. The integral amounts of gaseous products evolved in each experiment indicate that CO2 production is far larger than that of CO and the molar ratio among H2O, CO2, and CO production is about 21:3:1 at the present experimental conditions. It is proposed that the molar ratio of produced CO to consumed O2 be applied as an index for ranking coal propensity to self-heating and for determining the onset of spontaneous combustion.

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