Investigation of Leakage Dispersion and Explosion Hazard Characteristics of Alkane Flammable Gases in Cross-Sea Bridge Environments

This is the authors' abstract. We don't add key points for this paper.

To elucidate the mechanisms governing flammable gas dispersion and explosion hazard evolution in cross-sea bridge environments, the FLACS numerical model was employed to systematically investigate the dispersion behaviors and explosion responses of methane, ethane, and propane under varying wind velocities and leakage rates. The results show that gas physicochemical properties dominate dispersion patterns under quiescent conditions. Low-density methane disperses primarily upward due to buoyancy, whereas high-density propane tends to accumulate near the bridge deck under gravitational effects, forming high-concentration gas clouds. Ethane exhibits a relatively uniform dispersion pattern. Under windy conditions, wind velocity becomes the dominant factor controlling gas migration, driving all gases rapidly in the downwind direction while substantially reducing dispersion differences caused by density variations. Increasing the leakage rate significantly enlarges both the dispersion distance and the extent of high-concentration regions; however, the growth rate gradually diminishes, indicating that atmospheric turbulent mixing constrains the expansion of hazardous zones. Explosion simulations further demonstrate that higher wind velocities and leakage rates promote flame propagation and enlarge high-temperature regions. However, the maximum explosion overpressure does not increase monotonically with leakage magnitude but is primarily governed by the degree of correspondence between the local gas concentration and the optimum flammable concentration. The consequences of flammable gas accidents on cross-sea bridges are jointly determined by gas density, ambient wind field, leakage intensity, and concentration distribution, indicating that large-scale leakage does not necessarily result in the most severe explosion damage. These findings provide new insights into risk assessment, hazardous zone determination, and emergency response planning for hazardous chemical transportation across cross-sea bridges.