Explosion venting of indoor hydrogen-blended natural gas: Distribution law of compound hazards driven by "leakage-accumulation" effect

The leakage and accumulation patterns of hydrogen-blended natural gas (HBNG) in residential kitchens under varying hydrogen blending ratios (HBR) were investigated using computational fluid dynamics. The spatial and temporal distribution patterns of compound hazards such as overpressure, flames, and high-velocity airflow generated by explosion venting were also explored. Research indicates that after the leakage of HBNG, gas clouds accumulate on the ceiling of rooms. The overall pattern of leakage and accumulation remains consistent at different HBRs, while the time taken for the concentration of accumulated gas clouds to reach the lower explosive limit decreases linearly as the HBR increases. The leakage and accumulation of gas exacerbate the complexity of explosion-venting hazards. Compared to ideal homogeneous conditions, explosions of inhomogeneous accumulated gas clouds result in longer overall flame lengths and higher wind speeds. The overall flame length, explosion overpressure, and wind speed of inhomogeneous accumulated gas clouds were positively correlated with the HBR. As the HBR increased, the vent-opening time for the inhomogeneous gas cloud decreased, while the time to reach the maximum overpressure increased. In addition, the intensity of the secondary explosion outside the vent increased in a parabolic manner with increasing HBR. The range and magnitude of fluctuations in the flame speed behind the secondary explosion zone also increased. The research results provide a scientific basis for the safety design and retrofitting of venting and explosion resistance in residential buildings using HBNG.