Abstract: Abstract: In this paper, we used a small-size experimental bench to investigate the downstream fire spread characteristics of polyurethane foam under symmetrical fire source conditions. The results of the study show that the spread characteristics of polyurethane foam under symmetric fire conditions are mainly affected by the heat transfer between fire sources and the restricted angle spatial configuration. The fire spread is accompanied by flame splitting and separation, and the temperature field on the surface of the sheet reaches a steady state when the symmetric flames fuse. The fire spread is dominated by thermal convection heat transfer after the flames intersect and fuse, resulting in the radiation and airflow velocity of the upper part is always higher than that of the lower part, and the radiant heat flux of the upper part reaches a steady state in the flame fusion zone. The values of flame height z and Z/Q2/5 in the stable flame zone were obtained by using McCaffrey plume model, and the flame height was obtained by using a self-programmed MATLAB program, and the calculated results were found to be consistent with the experimental phenomena; the mass loss rate in the fire spreading process was linearly distributed in a three-stage relationship, and the fire spreading rate and the heat release rate in the steady-state combustion zone showed a certain power relationship.

Key words: Key words: polyurethane foam, downstream fire spread, building fire, chimney effect