A self-heating intensity index (SHII) based on the highest (pixel max.) and lowest (pixel min.) values taken from satellite thermal maps of burning coal waste dumps are proposed. The index enables the classification of such fires in Ukrainian- and Polish coal waste dumps. Both in Ukraine and in Poland, varying thermal intensities during 1985–2019 are revealed, using the SHII and following thermal intensity threshold values, namely, extreme thermal activity (> 7), advanced (3–7), moderate (3–1.5), initial (1.5–1), no activity (< 1). The SHII shows decreasing thermal activity in the selected Ukrainian coal waste dumps during 2017–2019. It aids in reconstructing the thermal history of the dumps. Analysis of satellite images revealed a large number of burning coal waste dumps in the Donetsk Coal Basin (Ukraine) with high thermal activity. Such burning likely reflects large amounts of organic matter and sulphides in the dumped material subjected to self-heating and self-burning processes, lack of compaction of the coal waste and/or high methane contents. Comparison of SHII values calculated from satellite- and drone thermal-camera images were compared to show that SHII from drone thermal images have much higher values than those from satellite images; the former have better resolution. Thus, SHII from Landsat- and drone images should be used separately in dump heating studies.

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Gaseous emissions from seven self-heating coal waste dumps in two large coal mining basins, Upper and Lower Silesia (Poland), were investigated by gas chromatography (GC-FID/TCD), and the results were correlated with on-site thermal activity, stage of self-heating as assessed by thermal mapping, efflorescences, and surface and subsurface temperatures. Though typical gases at sites without thermal activity are dominated by atmospheric nitrogen and oxygen, methane and carbon dioxide are present in concentrations that many times exceed atmospheric values. On average, their concentrations are 42.7-7160 ppm, respectively. These are levels considered harmful to health and show that coal waste fire can be dangerous for some years after extinction. At thermally active sites, concentrations of CH and CO are much higher and reach 5640-51,976 ppm (aver.), respectively. A good substrate-product correlation between CO and CH concentrations indicates rapid in-dump CH oxidation with only insignificant amounts of CO formed. Other gas components include hydrogen, and C-C saturated and unsaturated hydrocarbons. Decreasing oxygen content in the gases is temperature-dependent, and O removal rapidly increased at > 70 °C. Emission differences between both basins are minor and most probably reflect the higher maturity of coal waste organic matter in the Lower Silesia dumps causing its higher resistance to temperature, or/and a higher degree of overburning there.