In practice no system is infallible no matter how stringent the safety standards and procedures are concerning the release and use of gas in the process industries. Structural damage arising from an internal explosion often has serious repercussions. It is, therefore, imperative for engineers to be able to predict the extent of the damage that may occur, and to develop means to mitigate such effects. An accurate prediction of the structural behaviour requires an accurate formulation of the material＇s failure criteria. Experimental studies have shown that the response of masonry structures to gas explosions is non-linear. The cracking of masonry in tension and crushing of the material in compression are the major contributory sources of non-linearity. This paper presents a method of predicting the non-linear response based on the formulation of a numerical model to describe the material＇s failure criteria. The model has been validated using full-scale explosion test data provided by the Building Research Establishment in the UK. Although some minor discrepancies have been observed, overall the simulated values correlated very favourably with the actual test data. The probable causes of discrepancies are also discussed at the end of this paper.