Challenges and Application of Fuzzy Analytic Hierarchy Process to Engineering Safety Risk Decision Making Process

Risk management is becoming increasingly important for railway industry in order to safeguard their passengers and employees while improving safety and reducing operation and maintenance costs. However, in many circumstances, the application of probabilistic risk analysis tools may not give satisfactory results because the risk data are incomplete or there is a high level of uncertainty involved in the risk data. When the uncertainty in the risk data is very high, subjective risk analysis incorporating fuzzy reasoning approach (FRA) and fuzzy analytic hierarchy process (FAHP) modelling have proved to be more suitable in risk estimation. This Chapter will address these issues to give a background of problems and challenges in current practice of safety risk analysis in the railway industry. The use of FRA and FAHP techniques is especially appropriate in the railway environment because of the volume of experience, which is still available from long-term employees. Safety risk analysis is a hierarchical process where risk information obtained at lower levels may be used for risk assessment at higher levels. The FAHP is widely used in risk decision making process to solve imprecise hierarchical problems where the risk data are incomplete or there is a high level of uncertainty involved in the risk data, particularly, in the process of risk decision making. However, the application of FAHP in risk decision making the risk analysts often face the circumstances where a large number of pairwise comparison matrices have to be established by expert knowledge and engineering judgements. There may be a lack of confidence that all comparisons associated with a system are completely justified in a rigorous way. This is particularly true when a complex system needs to be analysed or when subjective judgements should be involved. This Chapter also presents recent development of a modified FAHP approach that employs fuzzy multiplicative consistency method for the establishment of pairwise comparison matrices in risk decision making analysis. The use of the described method yields a higher level of confidence that all of comparisons associated with the system are justified. In the meanwhile, the workload in determining the consistency of the judgements can be reduced significantly.

A case example on risk assessment of shunting at Hammersmith depot in London Underground is used to illustrate the application of the FRA and FAHP in safety risk analysis and decision making. The FRA is employed to estimate the risk level of each hazardous event in terms of failure frequency, consequence severity and consequence probability. This allows imprecision or approximate information in the risk analysis process. The FAHP technique is then incorporated into the risk model to use its advantage in determining the relative importance of the risk contributions so that the risk assessment can be progressed from hazardous event level to hazard group level and finally to railway system level. The methods described in this Chapter can evaluate both qualitative and quantitative risk data and information associated with a railway system effectively and efficiently, which will provide risk analysts, managers and engineers with a method and tool to improve their safety management of railway systems and set safety standards.