Assessment of operational risks of LNG and FLNG vessels during manoeuvring in bad weather conditions

In bad weather conditions, manoeuvring of a liquefied natural gas (LNG) carrier in open sea at floating LNG (FLNG) terminals can be associated with operational risks of potential consequences to human safety, environment and economy. Due to limited knowledge and experience with the FLNG technology, it is difficult to perform risk evaluations. Expert judgments are often employed to analyse and assess LNG risks using the risk matrix technique. However, human behaviour may influence the outcome of risk analyses resulting in an uncertain risk level. To deal with the uncertainty of expert opinions, two fuzzy set approaches are introduced in this paper. The first is a rule-based fuzzy model using Sugeno method for fuzzy inference. The second is a trapezoidal fuzzy set approach "simplified approach". Risk parameters were translated into a number of fuzzy sets, and a fuzzy risk value was calculated for several hazardous scenarios at different phases during ship berthing operations. The calculated fuzzy risk values were found to be consistent with the results of risk matrix technique.