Risk Assessment Of LNG Carriers Leakage During Loading And Unloading Operation Based On FTA

With the increasing import and export amount of liquefied natural gas(LNG),the frequency of LNG carrier loading and unloading operation will be more frequent,and the research on the security of LNG carrier has become a hot spot gradually.The Process of loading and unloading is a crucial part of LNG carriers,but a very high risk in that it has short operating time,tight operating plan and complex operating procedures,even a slightest mistake will happen to liquid cargo leakage accident or fire and explosion accident,which will bring huge loss to the ship,port,loading and unloading berth,marine environment and personnel.Therefore,the risk assessment of LNG carrier during loading and unloading has great significance to strengthen the safety management of LNG carrier on the process of loading and unloading operations,as well as protect human life,health,property and the marine environment.Firstly,the physical and chemical properties and potential danger of LNG are summarized,and the basic ship classification,loading and unloading process and the historical accident occurred since 1964 are introduced in this research.Secondly,the risk factors on LNG ship loading and unloading are found,which embodied in the unsafe behavior of the people,the equipment failure and quality defects,management factors and environmental factors.Based on the fault tree analysis,a fault tree model which takes LNG carrier leakage on loading and unloading as a top event was established,and the minimum cut sets and structure importance coefficient were analyzed,and the probability of the top event by acquiring the probability of each basic event was calculated.Than a simulation of the leakage of LNG ship loading and unloading operation is carried out on the LNG project,which aims at calculating the concentration,velocity of leakage and diffusion of dangerous medium,and simulating the diffusion of vapor cloud state of different types of fire or explosion.The types of fire explosion(pool fire,cloud spread,vapor cloud explosion,flash fire and BLEVE fireball)are simulated and the risk of hazardous media leakage is calculated as well as the risk range.Eventually,some suggestions and measures about preventing the accidents are put forward,so as to to reduce the probability of accidents and improve the safety level of the LNG carrier,to a certain extent,which also can provide an important reference basis for the shipping administration and policy makers.