Coal can ignite spontaneously when exposed to oxygen, which causes it to react and heat up when there is insufficient ventilation for cooling. Pyrite oxidation is often the cause of coal's spontaneous ignition in old mine tailings. ... Once ignition temperature is reached, combustion occurs with oxidizers present (oxygen).

Why does wet coal self ignite?

"Drying coal is an endothermic process and lowers the temperature of the coal. Wetting (or gaining moisture) is an exothermic process and the liberated heat can accelerate the spontaneous heating of the coal."

What temperature does coal spontaneously combust?

The ignition temperature for coal, which depends on several factors such as coal rank, volatile matter content and particle size, varies between 160 and 685 °C for most coals. Under adiabatic conditions, the minimum temperature at which a coal will self-heat is 35–140°C (Smith and Lazarra, 1987).