Risk Ranking of the Hydraulic Winch System

The probability of occurrence is determined for each basic event (Table 6.4) and the severity of the same basic events is as shown in Table 6.5. The risk estimation and ranking of these basic events can be carried out. For the pipe flange leak event, the probability of occurrence was 

From Table 6.6, the risk evaluation for the pipe flange failure can be summarised as being (0.5 Low, 0.5 Imp, 0.8 Low, 0.6 Mod, 0.1 Low and 0.1 Low). Using the minimum-maximum inferencing, this can be reduced to 0.8 Low, 0.6 Mod and 0.5 Imp. The numbers 0.8,0.6 and 0.5 represent the degree of belief and not the membership function of the particular linguistic term. Similarly, the risk evaluation for all other basic events is carried out. The results of the evaluation are shown in Table 6.7. 

Weighted mean for event pipe flange leak is calculated as follows  

Lack of reliable safety data and lack of confidence in safety assessment have been two major problems in safety analysis of various engineering activities. This is particularly true in FSA due to the fact that the level of uncertainty is high. In ship safety assessment it may often be difficult to quantify the probability of undesired events occurring and the associated consequences due to this very reason. 

The described approach addresses these concerns and offers an alternative solution. Its application can be extended to sub-systems within an operating system to nerate a list of components, which are ranked according to their priority for attention. This can help the owners and operators of ships to improve operating and maintenance strategies. This approach can be adopted within the FSA framework for generic ships and the results obtained ftom the analysis can be further utilised in Step 4 of the FSA (MSA (1993)). Due to the fact that precision is not forced, it would be appealing to use this approach in situations where reliable safety data is scarce and hard to come by. 

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