Abstract：
In the absence of relevant accident probability statistics, in order to improve the overall safety of the Liquefied
Natural Gas (LNG) system, we need to solve the problems that traditional safety analysis methods cannot consider. These are the
internal correlation of complex systems, component interaction and macro control. The analysis ideas are scattered and we need
to ensure the accuracy of the forward results of stratification, rollover and fire accident of LNG repositories, A STAMP-STPA
(Systems-Theoretic Accident Model and Processes)- (Systems-Theoretic Process Analysis) based a forward model of typical
LNG repository accidents was established, making the follow-up system of unexpected trouble analysis and accident cause
analysis better and more comprehensive. First, according to the equipment and facilities, process and their correlation with each
other involved in stratification and rollover accidents and fire accidents of LNG storage tanks, a preliminary risk analysis of
the accidents was carried out, and then the factors leading to the accidents were identified, and the key nodes of the risk were
ascertained. On this basis, the safety requirements and safety constraints of the accident system were analyzed, including control
and feedback operations that may lead to accidents. A STAMP model was established which included the control and feedback
relationships among the relevant facilities, components, and control feedback loops. Second, the STPA method was adopted
to identify four unsafe control behaviors in the LNG safeguard process (including failure to provide control behavior, error or
unsafe supply control behavior, failure to provide control behavior in a timely manner, and premature end of control behavior),
and analyze the initial value (such as tank LTD parameter), current state (such as infusion operation) and state transition (such
as tank and cooling completion preparation) involved in the overall process of the accident from two aspects of insufficient
execution of control behavior, feedback error or insufficiency, and then understand the key causes of unsafe control behaviors,
and established the complete forward model of typical accidents in LNG storage tanks. Finally, combined with specific accident
cases to verify and analyze the effectiveness and practicality of the typical accident forward model of the LNG storage tank,
and visualize the analysis results in the form of knowledge graphs. The study shows that the model can systematically analyze
typical LNG accident processes of LNG tanks in complex systems from the perspective of control and constraints, which makes
the accident evolution process more intuitive and the reasons for unsafe control behaviors clearer; and fully considers the causal
relationship of various risk factors in the stratification, rollover and fire accidents forward from the system perspective, thus
providing feasible and effective value information for the subsequent safety management of LNG storage tanks.
