In-Rack Fire Plumes

Abstract

A theoretical and experimental study of in-rack fire plumes in a combustible rack storage is presented. The commodity used in the experiments consisted of multiple-wall corrugated paper cartons equally separated in a steel rack, two cartons wide, two cartons deep and four cartons high. Free-bum tests were carried out mostly in reduced scale with verification in full scale. The centreline in-rack gas temperatures and velocities were measured at four elevations inside the rack storage and the heat release rate was measured above the rack storage with a hood system. In-rack temperatures and velocities are plotted using theoretically obtained quasi-steady correlations assuming a point source of buoyancy at floor level and entrainment only in the vertical flues. The theoretical correlations include convective heat release rate, vertical flue width and height above the floor. Temperatures for both reduced scale and full scale correlate reasonably well with the theoretically obtained relationships which have the same functional form as convective plume flow above a linear fire source (line plume). In order to obtain similar correspondance for the velocity in the two scales it was necessary to use Froude number scaling with storage height as length scale. The storage arrangement is found to be important for the initial flame spread and fire growth rate. The reduced scale study shows that the initial fire growth rate decreases with increasing vertical gaps (flues) and that the vertical and lateral flame spread rate increase when the lateral flue height increases. For the initial in-rack fire growth rate, the convective heat release rate was found to be better described by an exponential function rather than a power-law dependence on time to the third power.