Building external wall insulation materials are widely used in the construction industry, which is one of the main materials for building energy saving. In order to study the combustion characteristics and fire spread behaviour of typical exterior wall materials at different pressures. Four environmental pressures of 40KPa, 60KPa, 80KPa, and 101KPa were set in an experimental cabin, measuring the quality, temperature, heat radiation, and heat flow of rigid polyurethane foam (RPU) through experiments. The experimental results are as follows: the masses loss curve of RPU combustion approximately obeyed the quadratic curve, which was similar to the general solid fuel combustion law; the mass change was the most dramatic at 101KPa, the lower the pressure, the slower the mass change; as the pressure decreased, the flame temperature increased slightly, and the spread of the fire slowed down; as the pressure decreased, the peak value of the thermal radiation curve decreased, and the curve tends became flat, but the horizontal axis time increased, indicating that the total heat release remained the same.

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