*Correspondence to: B. Moghtaderi, Industrial Safety and Environment Protection Group, Department of Chemical Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia. Contract/grant sponsor: Austraian Research Council; Wornalds; NAF Australia. FIRE AND MATERIALS Fire Mater. 22, 155 —165 (1998) Effects of the Structural Properties of Solid Fuels on Their Re-ignition Characteristics B. Moghtaderi,* B. Z. Dlugogorski, E. M. Kennedy and D. F. Fletcher Industrial Safety and Environment Protection Group, Department of Chemical Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia Department of Chemical Engineering, The University of Sydney, NSW 2006, Australia A set of small-scale experiments was carried out to study the effects of material structural properties on the re-ignition characteristics of solid fuels. The influence of other key parameters, such as the incident heat flux and pre-burn, was also carefully investigated. The experiments were conducted on specimens of wood and PMMA using a cone calorimeter. As expected, the effect of water on the re-ignition time was found to be significant. It was also found that the re-ignition characteristics of charring materials, such as wood, are quite different from non-charring materials, mainly due to the structural differences. Based on the experimental observations two different mathematical models were developed to analyse the data for both wood and PMMA samples. Calculations of the re-ignition time made using these models agree generally well with the measurements and confirm that the material structure plays a vital role in its re-ignition behaviour.  1998 John Wiley & Sons, Ltd. NOMENCLATURE A activation energy [see Eqn (23)] a pre-exponential factor (s) B constant [see Eqn (23)] C pre-exponential factor [see Eqn (23)] c specific heat (kJ kg K) D diffusion coefficient for Fick’s law (m s) d pore diameter (m) E activation energy (kJ mol K) h convective heat transfer coefficient (W m K) h  mass transfer coefficient (kg m s) H  latent heat of evaporation (kJ kg) h  heat of pyrolysis of component i (kJ kg) k thermal conductivity (W m K) k  Darcy’s coefficient (m s kg) ¸ thickness (m) M sample weight at the beginning of water-spray application (kg) M  initial sample weight (kg) M  mass fraction of volatile materials in the gas phase M  fraction of the remaining material m  amount of applied water (kg) m   critical amount of applied water (kg) m R  mass flux of volatile materials (kg m s) P pressure (Pa) %PB percentage (degree) of pre-burn q R   incident heat flux (kW m) R gas content (8.314 J mol) r  reaction rate of component i (kg m s) r  rate of water evaporation (kg m s) r l   rate of applied liquid water (kg m s) ¹ temperature (K) t time (s) t  drying time (s) t  ignition time of partially burnt material (s) t  re-ignition time (s) u velocity (m s) x space co-ordinate Z moisture content Greek symbols  porosity  progress variable [see Eqn (5)]  geometric factor  density (mass per unit total volume) (kg m) * l mass of liquid water per unit volume (kg m)  Stefan—Boltzman constant (5.6710 Wm K)  emissivity Subscripts R ambient 0 initial condition c char g volatile materials i ith component l liquid mix gas-phase mixture s solid material sat saturation condition v water vapour w wood CCC 0308—0501/98/040155—11$17.50 Received 19 September 1997  1998 John Wiley & Sons, Ltd. Accepted 6 August 1998