Research On Risk Assessment Of LNG Carrier Spill Accident Under Uncertainties

The Liquefied Natural Gas(LNG),which is mainly composed of methane,is a clean,efficient and economic energy.As one of the greenest energy in the world,it has great advantages in terms of pollution reduction and environment protection.The consumption rate of LNG has increased rapidly in recent years,which also promotes the demand for LNG carriers.LNG carriers have a lot of potential risks.When spilled,safety of crew would be threatened by cryogenic LNG.Meanwhile,with the diffusion of spilled LNG,fire and explosion would easily occur.Risk assessment of LNG carrier spill accident carries several uncertain problems:(1)uncertainty of the causes of LNG spill accidents;(2)uncertainty of human factors;(3)uncertainty in the process of risk assessment.Considering such uncertainties,a fault tree model for LNG spill accident during the entire process of LNG carriers’ operations is constructed in the thesis.Human reliability analysis(HRA)is performed to predict human errors in LNG carriers’ handling operations.Finally,the results of fault tree analysis and HRA are synthesized.Monte Carlo simulations are used to conduct risk assessment on LNG carriers’ handling operations.The main research contents of the thesis are as follows:(1)Safety profile of LNG carrier.Physico-chemical properties of LNG and corresponding LNG carrier spill risks are introduced.Historical accident of LNG carriers is analyzed.The results can be further applied to the following steps of risk identification and assessment.(2)Risk identification of spill accident of LNG carriers’ operation process based on Fault Tree Analysis(FTA).Based on LNG hazard characteristic analysis and the results of historical data analysis,risks of LNG carriers’ navigation,handling and berthing operation are identified.A FTA model is constructed and qualitative analysisis conducted according to the structural importance of the risk indicators.(3)Human reliability analysis of LNG carriers’ handling operations based on Cognitive Reliability and Error Analysis Method(CREAM).CREAM is introduced to human error prediction of LNG carriers’ handling operations.Based on assessment of common performance conditions,triangular fuzzy numbersare applied to calculate the weight of the risk influence factors.The cognitive functions,common failure modes and sectionsare obtained.Finally,human error probabilities of LNG carriers’ handling operations are calculated for further study.(4)Risk assessment of spill accident of LNG carriers’ handling operations based on Monte Carlo simulation.Based on results of FTA and HRA,spill accident probability and typical consequence scenariosare calculated using Monte Carlo simulation.Comprehensive analyses on the results are conducted by comparing with the personal risk standards.This work incorporates fault tree analysis,CREAM method and Monte Carlo simulation to deal with uncertainties associated with risk identification,human reliability and risk probability quantification,respectively.The results of the risk are illustrated as probability intervals instead of certain values,so as to embody uncertainties better.