Abstract: The control function of safety-prevention measures and the effect of mitigating safety measures on reduction of accident consequences are seldom considered in the analysis assessment of a general long-distance natural gas pipeline risk． A method that can quantify the effect of the explosion proof wall in quantitative risk analysis of a long-distance natural gas pipeline is proposed． Firstly，the attenuation rate calculation formula of the explosion proof wall resisting explosion shock wave overpressure of a long-distance natural gas pipeline is defined，and then the method to solve the attenuation of shock wave overpressure in a sensitive target area after the explosion proof wall is used． Finally，through correcting the accident parameter value based on the energy equivalent principle， an analysis is performed of the risk reduction level of a sensitive target area surrounding pipeline after the explosion proof wall was constructed． The case study suggests that the average rate of reduction of shock wave overpressure in sensitive target area after the explosion proof wall about 50. 05% was constructed; the individual and the social risk is reduced to an acceptable level． The quantitative characterization method of safety measures in quantitative risk assessment can provide technical reference for the construction of safety facilities in the surrounding area of a longdistance natural gas pipeline． 

Key words: natural gas, explosion proof wall, risk assessment, rate of reduction, long distance transportation pipeline