What happens between one by one explosions

During the fire atmospheric oxygen reacts with the coal that burns incompletely. During reaction, forms an explosive mixture of gases (CO, H2, CH4). Airflow and high temperatures support the reaction. Sufficient gas concentration leads to an explosion, which provides an additional airflow and an increase of temperature.
In 1940-60, such reactions are used in underground coal gasification technology. Air is pumped into the burning coal seam, and pumped up the gas mixture (CO, H2, CH4) was burned at thermal electrical power stations.