Explosive spalling of concrete elements under fire is still an important issue within the research community. In particular the effect of structural boundary conditions on performance of concrete in fire is still an area of interest. This paper represents the results of a major research executed on 99 high and normal strength concrete elements. The parametric study investigated the effect of restraint degree, loading level and heating rates on the performance of concrete columns subjected to elevated temperatures with a special attention directed to explosive spalling. The paper includes a useful comparison between the performance of high and normal strength concrete columns in fire. The paper illustrates a method of preventing explosive spalling using polypropylene fibres in the concrete. The paper ends with valuable conclusions drawn from the research. (C) 2004 Elsevier Ltd. All rights reserved.