Enhancing the safety of underground utility tunnels: numerical analysis and mitigation of explosion risks from hydrogen-blended natural gas

The explosion risk of hydrogen-blended natural gas (HBNG) poses a critical challenge to the safety of hydrogen energy infrastructure. This study employed CFD simulations to investigate the explosion characteristics of HBNG in a tunnel. Results revealed a critical hydrogen blending ratio (HB_r) of 20 %, which maximized the maximum peak overpressure P_m and average peak overpressure P_a while minimizing flame propagation distance. The vapor cloud length (VC_l) was the dominant factor, contributing over 90 % to the explosion severity, with the average combustion rate increasing 20-fold as VC_l reached 150 m. Increasing ambient temperature (AT) attenuated overpressure by up to 37.6 %. A multi-factor prediction model was established for risk assessment. Strategically designed ventilation effectively mitigated explosion hazards, reducing peak overpressure and temperature by 99.77 % and 67.74 %, respectively. This study provides critical insights for the safety design and risk management of HBNG transportation systems in confined underground environments.