RISK ASSESSMENT OF A FIRE INVOLVING COMBUSTIBLE MATERIALS IN A WAREHOUSE

This paper presents the results of a numerical modeling into a rack fire in warehouse, and an identifi-cation of the visible flame shape when a fire is generalized over a whole warehouse after collapse of the roof. The model described here is a numerical implementation of a thermal and fluid-dynamic the-ory to predict the rate of flame spread. Evolution of the thermodynamic system is governed by the conservation equations for total mass, momentum (Navier-Stokes), energy and species mass fractions. Large-Eddy-Simulation method is used in which the large-scale eddies that govern the mixing of the gases are directly simulated. The sub-grid scale motion is calculated using the Smagorinsky model. The combustion process is assumed to be controlled by diffusion, permitting a mixture-fraction-based modeling approach The radiant flux vector in the energy equation is calculated by integrating the ra-diation intensity over all directions. The radiation intensity is found by solving a radiative transfer equation without scattering. A one-dimensional heat conduction equation for the condensed phase temperature is applied. The mass loss rate of volatiles from the solid fuel surface is assumed to obey the simple Arrhenius equation. At first, the work was focused to a fully coupled solution for a single rack fire configuration to both the fluid dynamics and radiative transport equations. The prediction for a single rack fire configuration is in good agreement with the experimental data. Then, the numerical model is extended to the determination of the flame height of a warehouse fire for comparison with the available correlations. It is found that the warehouse fire looks like a cone of flame with a rectangular base. NOMENCLATURE A frequency factor (kg/m2 s) cp specific heat (J/kg K) Cs Smagorinsky constant Deq equivalent diameter (m) E activation energy (J/mol) g acceleration of gravity (m/s2) h enthalpy (J/kg) H total rack height (m) Hf flame height (m) I radiation intensity (W/m2 sr) L warehouse length (m) ms mass loss rate (kg/m 2 s) p pressure (Pa