The paper describes the results from experimental studies and theoretical predictions of the final overpressures developed on combustion of a partial volume inside a larger closed vessel. The partial volume is assumed flammable whilst the remainder of the volume is initially filled with air alone. Particular attention is given to partial volumes of hydrogen-air mixtures. The accuracy of two theoretical models for predicting the final equilibrium pressure throughout the entire closed volume are also assessed. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.