A modified flame surface density (FSD) combustion model has been developed and applied to simulate the deflagration of a highly turbulent premixed flame inside a semi-confined explosion chamber. The chamber was of 500-mm length and 150 turn x 150 mm cross-section. A stoichiometric methane-air mixture was ignited to initiate the explosion. High turbulence levels were generated through interaction of the propagating flame with three consecutive solid obstacles of rectangular configuration. High speed laser sheet flow visualisation techniques ere used to obtain experimental data. Turbulent flow field has been calculated using a compressible eddy viscosity model. The model formulation and results obtained are presented and discussed in terms of model performance at all stages of flame propagation from ignition until venting. The transient developments of flamelet mean. turbulence. and curvature stretch were formulated and implemented in the model. The model predictions for flame shape, speed and pressure history has been compared with the highly resolved experimental data. Experimental and numerical results of spatio-temporal dynamics are found to be in good agreement. Moreover, the predicted flame stretch is presented and discussed. (C) 2003 Elsevier Science Inc. All rights reserved.