Spontaneous combustion of coal stockpiles can occur when the environment temperature exceeds the critical self ignition temperature (CSIT), which strongly depends on the pile volume. Measurements of the self-heating rates of a low-rank coal were carried out at various ambient air temperatures using pile heights of 2.5 to 10 cm (laboratory-scale) and 2.5 to 100 cm (large-scale), simulated using cubic wire-mesh baskets of different sizes. The experimental results demonstrated the feasibility of using the established Frank-Kamenetskii model in prediction of coal pile self-ignition. The larger-scale experiments showed quite different temperature variations during the heating process compared with the laboratory-scale experiments. Gas emissions and height changes of the piles revealed characteristics of the different stages of heating. Analysis of data obtained from the larger scale tests demonstrated that prediction of CSIT based on laboratory experiments is reliable and useful. Relationships for CSIT and safe storage time of the coal are proposed as a function of stockpile volume for volumes up to 100 m(3).