Systematic experiments were carried out on explosions of coal dust-inertant mixtures. Explosion severity was gained by using Siwek 20 L vessel and factors strongly influencing inerting effectiveness, such as deflagration mechanism and inertant composition were taken into account. Tests of thermal-gravimetric analysis were conducted to identify the reaction mechanism of coal dust explosions. As a result, bituminous coal dust deflagrates via the homogeneous mechanism, while anthracite dust mainly features the mechanism of heterogeneous reaction. Results reveal that the inerting functional mechanisms are quite different for bituminous coal and anthracite dusts, and the homogeneous-combustion-dust is much easier to be inhibited than the heterogeneous-reaction-dust. Trends of higher inerting effectiveness are associated with better decomposability, more excellent performance of oxygen blocking. Moreover, the particular efficacy of free ammonia decomposed from monoammonium phosphate in flame extinguishing is identified. Added water shows the best inerting effectives due to particle aggregation induced by moisture, which gives the idea that humidification for coal dust is therefore a cost-effective approach for explosion prevention and mitigation.