Margin cost based optimization of performance and cost in safety related system

In the design of Safety Instrumented System (SIS), the cost of construction and maintenance of the system should be taken into account comprehensively under the circumstance that the safety level is guaranteed. The average possibility of failure on demand (PFD_avg) of SIS is the main criteria to assess its safety performance. The paper focuses on the safety performance and cost optimization of SIS. Based on discrete Markov model and the concept of “margin cost” in microeconomics, the concept of “margin cost based on PFDavg (MCPFD_avg)” is put forward. Moreover, the paper puts forward a method to deal with the safety performance and cost optimization of SIS simultaneously. Finally, an example is given to prove the feasibility of the method which can reduce total cost when the safety performance of SIS can also be ensured. It gives a new method to design SIS and helps people further realize the relationship of safety performance and cost.