Coal fires often emerge spontaneously when the coal comes into contact with aerial oxygen.

Some fires along coal seams are natural occurrences when the coal seam reaches the surface because of mountain building or erosion.

Mine fires arise when oxygen contacts deep coal seams because of ventilation. They also occur in abandoned mines where leavings of coal ignite.

Coal fires also develop when coal is relocated. Fires on stockpiles of coal, coke and mine spoils containing sufficient amounts of coal are well known. Fires also emerge during transportation in ships or railway waggons.

If the reaction temperatures are between 150º and 500° Celsius, imperfect combustion or smouldering takes place. This kind of combustion is characterized by a lack of oxygen.

Above 500º Celsius and in presence of a sufficient quantity of oxygen, the burnings are called glowing combustions (up to 1000º Celsius) or open fires (more than 1200º Celsius). These burnings are complete combustions.