The rapid growth in the installation of large gas turbines for power generation has led to the need for guidance on mitigating measures should a gas leak occur. Normal mitigation measures include ventilation to prevent the build-up of a large flammable cloud and detection to bring early attention to a gas leak. Dilution ventilation was, and remains, the preferred basis of safety for gas fuelled gas turbine acoustic enclosures. Current proposals for dilution ventilation design are based on a criterion which suggests that the accumulation resulting from a gas leak which would trigger the gas detection alarm should, as an iso-surface bounding the 50% of the Lower Explosive Limit, be no more than 0.1% of the net enclosure volume. The results of a large-scale experimental study are presented which illustrate that this criterion is likely to err on the side of caution, but that there is no clear case for its relaxation. The application of dilution ventilation as a basis of safety when gas turbines are instead housed in a large turbine hall is shown, through a combined measurement and Computational Fluid Dynamics research study, to be less applicable. In this case the focus shifts towards gas detection.