Dilution ventilation is a widely used means of protection against the risk of explosion within gas turbine acoustic enclosures arising from the leakage and accumulation of flammable gas and its ignition from the turbine. In ASME 98GT-215 a safety criterion was proposed for the design of ventilation by defining the allowable size of flammable gas cloud as a proportion of the enclosure volume. This criterion was theoretically based, with a significant safety factor. Whilst generally viable, it was found to be difficult to achieve in some cases. A research project, described in ASME GT-2002-30469, was launched to define a criterion more accurately and with known conservatism based on a detailed programme of experimental explosions and Computational Fluid Dynamics (CFD) modelling. The $600k project was largely financed by the gas turbine industry, including suppliers and users, and by CFD contractors. The paper describes the project aims, its scope of work, and includes the main results, the new criterion and conclusions.