Characteristics Of Gas Explosion Load And Leakage Explosion Quantitative Risk Assessment In The Utility Tunnel

Natural gas is an efficient and clean energy source for the 21^stcentury.The proportion of natural gas supply in China has increased year by year.With the increasing number of urban natural gas pipelines,gas safety accidents have occurred frequently.At present,China is promoting the construction of the utility tunnel and encouraging gas compartment included.Although this can reduce the number of gas safety accidents,once a natural gas pipeline leaks and blasts in the closed gas compartment,the consequences may be quite devastating.In this paper,the load characteristics of natural gas explosions in the utility tunnel was studied and a quantitative risk assessment（QRA）of the consequences of natural gas leakage and explosion in the utility tunnel was conducted.The main research contents and results are as follows:（1）The influence factors of the premixed natural gas explosion in the gas compartment was analyzed.Combined with existing theoretical model of the detonation flame acceleration length,a detonation possibility partition map for the utility tunnel was drawn and proper recommendations are given for the length of the fireproof compartment.Based on the response surface methodology and the FLACS software,a comprehensive method for predicting the explosion overpressure peak in the utility tunnel was proposed,which concerned about the influence of gas cloud size,position and ignition position on the explosion pressure peak.This proposed prediction method has a confidence level above 70%.（2）With a proper method for selecting samples in the risk assessment of leakage and dispersion in the utility tunnel,175 dispersion simulations were conducted to obtain the cumulative frequency curve of flammable cloud index,which can quantitatively reflect the direct consequences of leakage and dispersion in a typical utility tunnel.Under the premise of the safety system,the flammable gas cloud in the utility tunnel that can be formed is generally small.There is only 5%possibility that the equivalent flammable cloud will exceed 300m³.（3）Through 294 samples of combined dispersion and explosion simulation,a quantitative risk assessment of the consequences of natural gas leakage and explosion in a typical utility tunnel was conducted.The existing risk assessment system was refined at first.Correlations between the equivalent flammable cloud and the explosion overpressure peak and impulse were verified and established respectively.Based on the simplified ignition event tree,a single parameter cumulative ignition probability model suitable for the confined space is proposed,which can reflect the development process of the flammable gas cloud and time influence.Finally,the obtained exceedance probability curve of the explosion overpressure peak and impulse,combined with the risk acceptance,can be as an important reference for the selection of explosion load when considering the anti-explosion design of the utility tunnel.