Fire Safety Science Digital Archive

A computer simulation for upward fire spread has been developed. The simulation of the fire growth and spread consists of four major components (modules): 1) preheating of the unburned fuel, 2) upward fire spread, i.e. determination of the location of the pyrolysis front, 3) pyrolysis of the material, and 4) combustion of the pyrolyzing gases. For the heat-up and pyrolysis modules of the code, integral models have been used which accurately predict (within 1% t o 2%) transient heat-up and transient pyrolysis when compared with exact analytical solutions. The pyrolysis front location, Zp is calculated to order (?z)3 by taking an intercept of a straight line, connecting the temperatures (real and/or virtual) of the nodes containing Zp, with the pyrolysis temperature tp. The Combustion module of the code calculates the heat flux distribution on the wall from the combustion of the pyrolyzing gases by providing expressions for the flame height, Zf, the convective, q”c, and radiative heat fluxes, q”r, based on experimental data from the literature. The components as well as the whole algorithm of the Upward Fire Spread and Growth (UFSG) code have been compared against exact analytical solutions including transient heat-up, transient pyrolysis and flame spread. As an example, it is demonstrated that transient pyrolysis even for non-charring materials significantly affects upward fire spread rates. This result explains recent experimental data on laminar upward flame spread. In addition, a comparison of numerical predictions with turbulent upward flame spread data is made, and the results are very satisfactory.