Effect of solid inertants and sample inclination angle on fire hazard of metallic powder layers

Compared to non-metallic powders, metallic powders usually have a greater layer fire hazard because of high flame temperatures. In this paper, the effects of solid inertants and sample inclination angle on the fire hazard of three metallic powder (iron, titanium, and magnesium) layers were investigated. Flame spread velocity (FSV) was mainly dependent on the particle size and enthalpy of combustion of metallic powders. For example, FSV of iron powders jumped from 0.4 to 4.7 mm/s when the particle size decreased from micro scale to nano scale. The FSV of micro Ti powder layers reached 12.8 mm/s, which was much higher than the value (1.7 mm/s) for micro Mg powder with similar particle size. Inclination angle significantly influenced the FSV of nano Ti powder because of a long flame length resulting from a predominantly homogeneous reaction. For other tested powders, sample inclination angle had little effect on FSV because of a short flame length resulting from a predominantly heterogeneous reaction. Addition of small amounts of solid inertant decreased the layer fire hazard of iron and titanium powder with high melting points, while increasing the fire hazard of magnesium powder because of its low melting point. The melting characteristics of metallic powders should be considered when preventing or mitigating fire hazard using solid inertant technology. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.