Effect of inclination angle on fire hazard of melting dust layers

Combustible dusts deposited on ground or surfaces present a fire hazard to process industries. It was found that flame spread on an upwardly inclined surface was significantly faster than on a horizontal surface. However, hazard during downward inclined fire spread has been underestimated for dust layers having melting capability. In this paper, the effects of melting fluidity, sample inclination angle, and layer thickness on the fire hazard of four melting dusts were investigated. For sulfur with its excellent melting fluidity, dust layer inclination at a small angle can significantly increase downward flame spread velocity (FSV). For anthraquinone having a moderate melting fluidity, upward or downward dust layer inclination significantly increased FSV. For polystyrene and magnesium having weak melting fluidity, dust layer inclination angle had relatively little effect on flame propagation. Increasing thickness of dust layers significantly enhanced the promotion effect of the inclination angle on the flow of molten material, which in turn affected FSV. As a result, melting fluidity coupled with a large inclination angle and high layer thickness would significantly enhance dust layer fire hazard. These findings should be taken into consideration wherever powders having melting capability are encountered in process industries or in certain public activities.