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Combined Heat and Power and Combined Cycle Gas Turbine plants have become larger and more popular in recent years for local power and heat generation, and for main stream power generation. Many are based on gas turbines within acoustic enclosures. Complex fuel supply pipework to the turbines at high pressure gives rise to an explosion hazard within such enclosures in the event of foreseeable small leaks if appropriate ventilation is not provided. Health and Safety Executive investigations have exposed poor ventilation in some cases to the extent that explosion relief or significantly improved ventilation has been required. The paper describes the investigations, with reference to incident data, ignition probability, current relevant standards, and ventilation performance modelling by computational fluid dynamics. Suggested criteria for the evaluation of existing and new plant, and risk reduction measures, are described.

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.