ABSTRACT
As a remedy for the weaknesses of the traditional methods, sophisticated risk assessment techniques are used in addition to the traditional ones. For example, fuzzy sets can address risk problems using natural or linguistic terms to express the variances of variables. Fuzzy sets are a valuable tool for modelling the uncertainty of the real world and human thinking. Fuzzy Fault Tree Analysis (FFTA) has been successfully applied in previous studies. Senol et al. (2015) employed an FFTA approach to analyze the root causes of contamination of chemical materials carried by ships and obtain the occurrence probabilities. Sivaprakasam et al. (2014) proposed an FFTA model capable of quantifying the fault tree of an LNG refuelling facility in the absence of sufficient data. Xu et al. (2013) also proposed an FFTA model using both qualitative and quantitative characteristics (Han and Weng, 2011) to determine risks regarding oil and gas leakage of a subsea oil and/or gas transfer system. In the same context, Miri Lavasani et al. (2011) proposed an FFTA methodology to identify the risks of oil and gas offshore pipelines. Chen et al. (2014) used a combination of the Failure Mode and Effect Analysis (FMEA) with the FFTA to quantify the occurrence probability of basic failure events for an oxygen-enhanced combustor demonstrating, among other things, the common base of the two combined methodologies (FMEA and FTA). Moreover, Wang et al. (2013) developed an FFTA model to measure the probability of the occurrence of the top events for fire and explosion of crude oil tanks. In the
1 INTRODUCTION
Safety during maritime operations is always at the top of the agenda in shipping business. Marine activities take place in a complex and often hostile sea environment; thus, they are high-risk operations and planning, realization and management are factors of special importance and consideration. The identification of safety aspects at an early stage of an operation is a task of high importance when we want to cope with the issues that could compromise the success of an operation (Suddle and Waarts, 2003). In order to address and determine the elements of safety, it is vital to link safety with risk. In essence, safety and risk can be assumed to be complementary terms (Suddle and Waarts, 2003).To assess the risks of a maritime operation, a risk assessment needs to be carried out. The main goal of risk assessment is to identify potential accidents, analyze the precautions, and finally evaluate the effects of the risk reduction measures (Jonkman et al., 2003). Traditional risk assessment techniques are carried out mainly on a quasi or fully probabilistic basis; one well-known technique is Fault Tree Analysis (FTA). FTA is a systematic approach to determining both quantitatively and qualitatively the safety and/or reliability features of a system or activity (Wang et al., 2013). FTA employs experience gained from previous accidents; hence, FTA is highly dependent on the accuracy of the recorded data. In addition, the construction of the tree depends on the experts’ relative experience regarding the operation; hence, the success of FTA techniques depends on the knowledge of the system and the experience of the
same framework, Shi et al. (2014) also proposed an FFTA model to assess risks for fire and explosion accidents for steel oil storage tanks. Other FFTA applications of previous studies can be found in the paper of Chen (2000). The aim of this study is to propose a novel approach of Fuzzy Fault Tree Analysis (FFTA) capable of evaluating the safety level of a marine activity. The proposed model applies fuzzy logic as a remedy to the uncertainty that comes from experts’ subjective judgment. To verify the strength of the proposed model, an STS transfer of an oil cargo operation is thoroughly analyzed and evaluated. This paper also highlights the negative effect of uncertainty in traditional FTA and the ability of fuzzy logic to elicit knowledge from experts in an effective and accurate way. The results demonstrate that fuzzy sets in combination with a traditional FTA can effectively indicate the safety level of a maritime activity such as an STS transfer operation. An original approach to the evaluation of risk with respect to the STS transfer of cargo is presented in this paper. To achieve this goal, the rest of the paper is organized as follows. In Section 2, the theoretical background of the FFTA is described. In Section 3, the STS transfer operation is presented, while in Section 4, the FFTA model is properly applied. Section 5 presents a discussion of the results. Finally, Section 6 concludes the paper.
