Determining Safety Integrity Level by Considering Uncertainty Aspects in Fuzzy Environment (Case Study on Train Braking System)

The industry has been faced with the difficulty of Safety level determination of safety systems. Some standards including ISAS 84.01 and IEC61508 have provided some guidelines but there is no a complete and comprehensive understanding about these standards and their accomplishment. It should be noted that the security analysis is one of the most important factors to measure the risk level, as its measurement in certain environment is difficult, so in this study a new approach is proposed to analyze the risk level of safety instruments in fuzzy environment. The new methodology is applied on a train barking system as a case study and the results indicated that the level of safety integrity level is influenced by the security factors. The determination of safety integrity level needs to implement the safety functions and the uncertainty of probabilistic model parameters, which are affected by the results of security analysis. The level of safety integrity in fuzzy environment is calculated by proposing fuzzy fault tree analysis and the results have been compared with the concluded results obtained from certain methods.