The R70 test was performed on a series of coal samples taken from different locations in a US longwall mine. The values obtained produced a definite relationship between R70 and ash content, with the exception of one anomalously low result. An ash analysis of the sample showed that it had a high sodium (Na2O) content in response to the presence of the sodium zeolite mineral, analcime. A multiple regression of the R70, ash content and sodium (Na2O) content of the samples produced a self-heating rate prediction equation with an R2 of 0.98. This equation can now be used to predict the R70 self-heating rate of the coal at any location throughout the mine, thus assisting with hazard management planning.