Massive release of sour gas and dispersion of fatal hydrogen sulfide brought about by gas sweetening unit leakage are a major threat to the safety of sour gas processing plant.By analyzing the leakage and atmospheric conditions

the scene of accident

caused by the leakiness of gas sweetening unit

were determined.Based on large eddy simulation of turbulent flows

H2S dispersion in complex terrain was simulated.The peak time for accident was estimated

hazard regions were ranked and the influences of terrain on dispersion could be summarized as spatial obstacle

channeling and aggregation.Dose-response relationship for acute H2S poisoning was used to assess the cumulative effects of H2S on the public and calculate the lethal percentages.The maximum distances

downwind deflection angles

maximum widths and areas of the lethal regions were obtained.The application in one sour gas processing plant in mountainous area shows that the accident will cause high death risk around the plant and adjacent road

and not lead to mortality in the nearby residential area and planned highway.Based on the features of the accident

recommendations to establishing emergency planning zone

taking immediate shelter and implementing priority relief are suggested for emergency response.