Lump coal may undergo fragmentation when exposed to high temperatures thus changing the particle size distribution of the coal [1]. Primary fragmentation occurs during devolatilization. In fixed-bed gasification, fragmentation may lead to a change in permeability of the coal bed resulting in non-ideal reaction conditions, where unstable gasifier conditions arise. The aims of this study were to quantify the degree of size degradation (primary fragmentation) and to use the data to optimize coal blends with respect to thermal fragmentation. It was found to be possible to quantify the degree of size degradation for a given coal source. The current experimental procedure was changed to achieve a substantial reduction in the time it takes for analysis; this alternative method taking only 2-3 h. Different coals gave significant differences in the amount of fragmentation they undergo. The amount of thermal fragmentation of non-caking coal under 2.6 MPa pressure can be predicted from the thermal fragmentation values obtained under atmospheric conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.