A significant concern in the disposal of retorted shales is the potential ignition and uncontrolled burning in disposal piles. At the Anvil Points Oil Shale Retort Facility, near Rifle, Colorado, high temperatures approaching 500/sup 0/C (900/sup 0/F) were discovered within a retorted oil shale pile and zones of a powdery, low density, ash-like material. These zones are primarily caused by the continuing degradation of the retorted shale particles, resulting from internal combustion of residual carbon within the pile. The purpose of this study is to make an initial investigation of the effects of high temperatures on retorted oil shale in order to guide further research in this area. The work addresses particle breakdown, combustion front migration, and collapse susceptibility of retorted shale piles. The effects of prolonged heating on individual particle size is estimated by subjecting retorted shale particles to high temperatures in an oxidized environment. The collapse susceptibility of loose retorted shale during and after combustion is predicted by loading a sample inside a tube furnace. The field combustion front velocities are estimated by monitoring changes in temperature in a retorted shale sample at various distances from a heat source. Conclusions drawn from this study are: a weight loss of up to 12% can occur from combustion of residual carbon and carbonate decomposition of retorted shale particles; retorted shale particles break down to a fine ashlike material after being subjected to high temperatures in an oxidizing environment; a significant increase in pH occurs due to the loss of residual carbon; a volume reduction occurs with the addition of heat to a loaded sample with only limited access to air; and a combustion front on the order of 10/sup -6/ ft/sec can move through retorted shale at temperatures of 150/sup 0/ to 250/sup 0/C. 9 refs., 11 figs., 1 tab.