Impact of hydrogen blending on the formation of flammable atmospheres in enclosed spaces due to gas leaks

This study addresses the potential impact of hydrogen addition to natural gas (NG) on the formation of flammable atmospheres due to small gas leaks. First, the effect of hydrogen blending on leak rate in realistic situations is estimated with an alternative flow model validated with experimental data for a wide range of gases and pressures on real and manufactured leaking coupons. Second, the temporal evolution of gas concentration in ventilated rooms and the time to reach flammable conditions is predicted for NG/hydrogen blends, showing that hydrogen addition leads to faster gas build-up. This may have practical consequences, for example, on required response times to attend emergency calls due to gas leakages . In general, hydrogen addition results in a faster formation of flammable atmospheres, but differences with respect to natural gas are less severe than expected from the usual ideal flow model, which tends to overestimate leak rates and may lead to a too conservative assessment of actual behaviors in most practical situations.