Hydrogen Integration into Natural Gas Pipelines: Risk Analysis and Regulatory Recommendations

As hydrogen (H2) blending into natural gas (NG) systems gains momentum, understanding the safety implications of hydrogen-natural gas (H2NG) blends in urban distribution pipeline networks becomes critical. While regulations exist for natural gas pipeline systems, limited guidance is available for intermediate H2NG blends. Therefore, this study presents a quantitative risk assessment (QRA) approach for urban gas distribution systems downstream of city gates, covering residential, commercial, and recreational areas. It combines leak frequency analysis from HyRAM+ v5.1.1 with computational fluid dynamics (CFD) and consequence modeling in PHAST and SAFETI v9.0 to evaluate the risks associated with H2NG blends – B1 (20% H2 in NG) and B2 (40% H2 in NG), pure H2, and natural gas in the gas distribution network. The results show that higher hydrogen content leads to expanded flammable zones and elevated cloud heights, with 20% and 40% H2 blends extending lower flammability limit (LFL) distances by 10% and 25% respectively, compared to NG. Individual risk rises progressively by 21.2% for B1, 54.3% for B2, and nearly doubles for H2 in commercial zones. Societal risk contours shift upward, especially in recreational areas. Importantly, current clearance distances under CSA Z662 are found to be insufficient for hydrogen-rich blends, with recommended increases between 22%–46%. These findings support a blend-specific, consequence-informed approach to safety planning for hydrogen integration in Canadian distribution networks.