Abstract: Uncontrolled subterranean coal fires, mainly developed through the process of self-ignition, represent a challenging hazard of local dimension, but with global-scale distribution. One important effect of this spontaneous ignition process is the surface subsidence. Porosity and particle size fraction of the coal particles in the deposit, water and oxygen play the main role. Anina sterile heaps present a non-typical situation of waste-coal self-ignition. The fine coal is found in the sterile heaps distributed all over the actual urban area, being covered by human activities and residential buildings, so that, the human risk is present in several forms.