This paper describes work performed by a consortium led by the UKHealth and Safety Laboratory(HSL)to identify the safe operating conditions for combined cycle power generating systems running on high hydrogen fuels. The work focuseson hydrogenand high hydrogensyngas and biogas waste-stream fuel mixtures, which may prove hazardous in the event of a turbine, or engine flame out, resulting in a flammable fuel mixture entering the hot exhaust system and igniting.The paperdescribesthe project,presentingsome initialresults from this work,including the development of large scale experimental facilities on the550 acre HSL site near Buxton, Derbyshire, UK. Itdescribes the large scale experimental facilitywhichutilisesthe exhaust gas from a Rolls-Royce Viper jet-engine (converted to run on butane) feeding into a 12 m long, 0.60 m diameter instrumented tube at a pre-combustion velocity of 22 m/s. A variable geometry simulated heat exchanger with a 40 %2blockage ratioispresent in the tube. Flammable mixtures injected into the tube close to the Viper outlet, together with make-up oxygen, are thenignited. Extensive optical, ionisation, temperature and pressure sensors areemployed along the length of the tube to measure the pressures and flame speeds resulting from the combustion event. Some preliminary results from the test programmeare discussed includingdeflagration to detonation transitions at high equivalence ratios.