The mechanisms involved in premixed magnesium and hydrogen hybrid and synthetic MgH2 dust cloud explosions were investigated. The results revealed that trace amounts of H2 in Mg explosions can markedly increase explosion severity. Furthermore, H2 addition can weaken the influence of oxygen deficiency on Mg explosion. Moreover, the explosion intensity of synthetic MgH2 was far stronger than that of premixed Mg/H2 mixture or Mg alone because the vacancy defects in Mg and H atoms can form after dehydrogenation of MgH2, which caused that Mg and H2 are prone to oxidation and nitrification in air atmosphere at a low temperature, thereby promoting the explosion. This demonstrates that the explosion risk of MgH2 (even other H2 storage materials) is related to its H2 storage capacity and dehydrogenation temperature. Therefore, for H2 storage materials, the better H2 storage performances can exhibit higher explosion risks.