Storing coal in large piles has the inherent risk of spontaneous combustion. There are many industry guidelines to the best method for storing coal in piles. These guidelines include avoidance of spontaneous combustion with regard to pile angles, compression and surface smoothing. Even strict adherence to these guidelines (particularly with the more volatile coals) may in some circumstances not be enough. An early warning system to prevent the onset of fire remains the best and most reliable solution.