Hydrogen is a convenient energy storage medium; it can be produced from fossil fuels and biomassvia chemical conversion processes, or from intermittent renewable sources, like wind and solar, viaelectrolysis. It is the fuel of choice for the clean fuel-cell vehicles of the future. If the general publicare to use hydrogen as a vehicle fuel, customers must be able to handle hydrogen with the same degreeof confidence, and with comparable risk, as conventional liquid and gaseous fuels. For the safe designof retail facilities, through the development of appropriate codes and standards, it is essential tounderstand all the hazards that could arise following an accidental release of hydrogen. If it is to bestored and used as a high-pressure gas, the hazards associated with jet releases from accidental leaksmust be considered. This paper describes work by Shell and the Health and Safety Laboratory tocharacterise the hazards from jet releases of hydrogen. Jet release experiments have been carried outusing small leaks (circular holes ranging from 1 mm to 12 mm diameter) at system pressures up to 150barg. Concentration measurements were made in the unignited free jets to determine the extent of theflammable cloud generated. Ignited jets were observed both in the visible and infrared to determinethe flame size and shape. The experimental results for the extent of the flammable cloud and jet flamelength were found to be in good agreement with model predictions.