Self-heating poses a significant hazard for both open-cut and underground coal mine operations. One of the major problems facing the coal industry is producing reliable hazard management plans that require identification of the self-heating propensity in advance of mining, during transportation, and stockpiling.
The self-heating rate index R70 is obtained by monitoring the rise in temperature of coal samples under oxidation in an adiabatic oven. This value equates to the time taken for the coal sample to increase in temperature from 40ºC to 70ºC. The R70 value is then presented in the form of ºC/h.
Coals with an R70 value less than 0.5ºC/h are considered to be low propensity, those with an R70 value between 0.5-0.8ºC/h are considered to be medium propensity, and coals with higher R70 values are considered high propensity, and thus more prone to spontaneous combustions.