To gain an understanding of the risks associated with a hydrogen pipeline failure, Air Products commissioned GL Industrial Services UK to perform two experiments where a buried 6 diameter pipeline at an initial pressure of 60 bar was intentionally failed using an explosive charge to generate a full bore release of hydrogen gas from two open ends, simulating a pipeline rupture event in which a ground crater is formed naturally in the surrounding soil by the released gas. The first experiment was performed with the pipe buried 1m deep in a typical soil and the second experiment was performed with a 1m deep backfill of a mixture of sand and soil. The hydrogen released was ignited immediately following the pipeline failure. Following initiation of each experiment, the properties of the hydrogen gas release and resulting fire were measured. The two experiments were conducted under similar conditions, with the main differences being the nature of the soil used for the pipeline backfill and the wind speed (which was significantly higher in the first experiment). The initial pipeline pressure was very similar in the two experiments, with complete depressurisation of the gas pipeline and reservoir taking place over a period of approximately 80 seconds. Maximum flame lengths of up to approximately 100m were measured in each experiment. A number of previous experimental programmes have been carried out by GL in order to investigate the fire characteristics of natural gas releases from ruptured pipelines, conducted under nominally similar conditions. Recently, experiments of this type were also conducted to investigate releases of mixtures of hydrogen and natural gas. The paper will present a high level overview of the results including a discussion of the observed differences between the release and fire behaviour of the different gases.

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