The Research For Domino Effect Probability Model Of Chemical Tank Explosion Caused By Fragments

Shock wave, thermal radiation and fragments are the three main reasons for domino effect. As the projection distance and direction of fragments are both random, the consequences of accident caused by fragments are very serious. Such as 1984 in Mexico City, the chain explosion caused by fragments of exploded LPG tank burned the construction area for 27 hectares, caused 544 deaths, more than 1800 injured and 1,200,000 evacuated. Therefore, the research for domino effect caused by fragments is not only very difficult but also very necessary.As the basis of domino effect, domestic and foreign researchers have built many impact probability models. In this paper an improved impact probability model based on the Monte Carlo method is derived to analyze the randomicity of the projection distance and direction of the fragments. The difference from the previous models is that the size of bursting vessel is not ignored, that means the initial projection height and the projection horizontal displacement of the fragments are not considered as zero. The Comparison of results show that the impact probabilities would be larger if the size of bursting vessel is considered. The influence on the impact probability is higher than 10% when the distance of target is lower than 7 time of the diameter of bursting spherical tank. So the influence of size of bursting spherical tank on impact probability cannot be ignored.Damage probability model is both the key and difficult for domino effect. In the Nguyen's damage probability model, a critical residual thickness is defined and considered as a constant, and the impacted vessels would be damaged if the perforation is greater than the thickness of the shell or the residual thickness is less than the critical value. In this paper, based on the API 579 method for safety assessment of the vessels shell with damaged area, a new damage probability model is achieved. At first, the complex pits formed by the impaction of explosion fragments are simplified as conical pits. Then, the calculation equations of the residual strength coefficients of the conical pits on the cylindrical vessel and the spherical tank have been derived, respectively. And a solving method of the critical residual strength coefficient has been set up according to the plastic failure theory. Finally, a model for judging the impacted vessel would be damaged or not is established, according to the comparison between the residual strength coefficient and the critical value. Based on the new model, it was found that the damage probabilities will increase with the perforation and are also influenced by the cone angle of the conical pit. So it can be proved that the hypothesis of the Nguyen's model, that the critical residual thickness is a constant, is unreasonable. Comparison results of the two models show that the prediction of the damage probabilities of the new model is larger than that of the Nguyen's model. The assessment results of this model are more reliable.As the basis of improved impact and new damage probability model built in this paper, single and multiple probability model of domino effect are built. Initial projection vertical angle, filling factor and the volume of target tank have greater impacts on the single domino effect probability.Striking the domino effect probability accurately and quickly is very important for evaluating the risk of explosion fragments in engineering. In this paper, the engineering impact probability formula that fits for fragments of spherical tank has been fitted out.