During the utilization of coal in large power plants, one of the major logistical issues is related to spontaneous ignition of the coal. This characteristic of coal depends on the rank and type of the coal, the content of the moisture and volatile matter as well as particle size distribution. This paper presents the novel approach for determination of spontaneous ignition potential of the coal developed as the internal laboratory experimental method. The experimental tests were performed by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) of tested samples at five different heating rates: 3, 5, 7, 10 and 20 K min(-1) under an air atmosphere. The TGA results were used for determination of tangent slope of the mass loss rate curves in the zone of the release of volatiles at considered heating rates for all coal samples. The linear interpolation of the data obtained by performed tangent slope analysis and heating rates provides the straight line unique for each tested sample. According to the standard method, the slope of the obtained straight line is defined as thermogravimetric index of spontaneous ignition (TG(spi)). In addition, a new formula for determination of TG(spi) index was provided. Three different coal samples were analyzed and classified according to the spontaneous ignition potential, based on the obtained values for TG(spi) by standard procedure and also using a newly proposed method. By varying the gradient of linear dependence of self-heating coefficient against reference temperatures (T-ref,T-i), the mass and heat transfer limitations for different coals were discussed. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.