An experimental study into the hot surface ignition of coal dust layers has been conducted. Two coals were examined: Prince coal from the Cape Breton Development Corporation and Pittsburgh coal from the United States Bureau of Mines. The effect of admixed inerts (dolomite and limestone) on the dust layer ignition temperature has been analyzed using a steady-state thermal explosion model. The analytical procedure used for evaluating the ignition temperature of a dust layer, heated from below and losing heat from its upper surface by convection, is an extension of the thermal explosion model of Thomas (Ref. [8]); namely, that of Thomas and Bowes (Ref. [15]). To commission the hot plate apparatus and validate the model predictions, a series of experiments were undertaken using sodium dithionite. This material is known to exhibit self-heating and there have been previous layer ignition temperature studies with which to compare results. It was demonstrated that an adequate estimate of the critical ignition temperature may be readily obtained by this analytical method. Furthermore, computed values of the critical ignition parameters for layers of coal dust admixed with inerts, accounting for changes in thermal conductivity, were in reasonable agreement with experimentally determined values.