Formation of flammable clouds due to rupture of a natural gas pipeline

Despite all precaution procedures, accidental release of natural gas from its massive pipeline networks may occur. This paper considers the environmental impact of such releases from flammability view point for two specific scenarios. The high initial pressure of the pipeline resulted in a choked flow. Equilibrium between the pressure of the released gas and the ambient one occurs through a series of interacting expansion and shock waves. Transient mass flow rate, temperature, speed, and cross sectional area of the released jet have been calculated using principles of compressible fluid flow. Time-average values of such parameters have been utilized in the EPA-based Screen software to predict the resulting steady state concentration profiles. Flammable clouds with dimensions up to 3,000 x 26 m in the downwind and upward directions, respectively have been predicted for the first scenario. On the other hand, the results of the second scenario have indicated the formation of flammable clouds extending to 14 m and 160 m in the downwind and upward directions, respectively. Moreover, a parametric study of wind speed and atmospheric stability has shown strong effects on the size of the formed dangerous clouds. Such results have been discussed in relation to the involved mixing processes.