Effect of equilibrium relative humidity on explosion characteristics parameters of humid magnesium dust

In a humid environment, active metal magnesium is susceptible to the hydrogen evolution reaction with water, which significantly increases the risk of explosions in areas where magnesium is produced and used. In this paper, the effects of equilibrium relative humidity (ERH) on the explosion characteristics parameters of magnesium dust under various initial conditions (concentration, particle size and temperature) were studied using a 20 L explosion device. Additionally, the explosion mechanism was thoroughly analyzed by incorporating the oxygen content results of the explosion products. The research revealed that explosion characteristics parameters (P_max, (dp/dt)_max) of magnesium dust cloud initially increased and then decreased with rising ERH when the explosion system was in an “oxygen-rich” state. The maximum increments in P_max and (dp/dt)_max are 130 kPa and 10.73 kPa/ms, respectively. Moreover, a decrease in particle size and an increase in temperature facilitated the generation of more hydrogen from the humid magnesium dust. This phenomenon effectively improved the explosion characteristics parameters of the humid magnesium dust, thereby increasing the sensitivity and risk of the explosion system. However, in the case of a high degree of “oxygen-poor” state, the derived hydrogen instead became burdensome, resulting in an excessive amount of magnesium dust that was unavailable for reaction. This led to a decrease in the explosion characteristics parameters of humid magnesium dust, with the maximum decreases in P_max and (dp/dt)_max being 45.8 kPa and 2.1 kPa/ms respectively.