Experimental study on downward flame spread of thermal insulation material inside the glass curtain wall configuration under the ambient wind

Due to the chimney effect caused by curtain wall configuration, facade flame spread poses a serious thermal hazard to upper floors. This work studied downward flame spread behavior of polyurethane insulation material in narrow interlayer space of curtain wall. Flame morphology, mass loss rate and flame temperature under different lateral winds were investigated in detail. Results indicated that downward flame spread was determined by the coupling effect of curtain wall configuration, stack effect, and ambient wind. Firstly, the pyrolysis front had an inverted V-shaped distribution under lateral wind effect. With increasing wind speed, flame inclination on windward side increased first and then decreased, and flame front on leeward side disappeared after a critical wind speed. Secondly, the confined space and ambient wind constructed a complex turbulent flow, which led to the nonlinear relationship between flame height and mass loss with wind speed. The peak temperature of gas flame near sample surface decreased due to cooling effect of wind. Thirdly, dripping mass, flame spread rate, and Froude number in downward flame spread were positively correlated with wind speed. Ambient wind and gravity increase the possibility of randomly melting-flame droplets from the original flame, thereby seriously increasing the risk of secondary ignition.