Determining and verifying the safety integrity level of the safety instrumented systems with the uncertainty and security aspects

Safety and security aspects consist of two different group of functional requirements for the control and protection systems. In the paper it is proposed that the security analysis results can be used as a factor increasing or decreasing the risk level. It concerns a process of determining required safety integrity level of given safety functions. The authors propose a new approach for functional safety risk analysis. In this case the security factor influences the value of required safety integrity level SIL by changing the frequency of accident scenario. It can be done by using the methodology of modified risk graph. On the other hand there is a verification of required SIL fulfillment for designed safety-related system which implements safety function. In this case the result of security analysis is affecting uncertainty of probabilistic model parameters. The proposed method takes into consideration the sensitivity analysis of probabilistic models of E/E/PE or safety instrumented systems SIS as well as the uncertainty of probabilistic results. It uses differential factors, which are helpful for effective verification of required SIL of the E/E/PE or SIS systems taking into account results of sensitivity analysis and/or assessment of uncertainty ranges obtained from probabilistic models developed.