Characterization of the Hazards from Jet Releases of Hydrogen

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