Allocation of safety integrity levels to safety-related systems based on JIS C0508

摘要

One of the fundamental concepts of the standard, JIS C0508, is the target failure measures to be allocated to Electric/Electronic/Programmable Electronic Safety-Related Systems (SRSs), i.e., Safety Integrity Levels (SILs). In order to choose between the SILs, the standard classifies SRSs into two modes of operation. It was unclear which modes of operation should be applied to SRSs in the standard. The authors addressed this issue by proposing a new fault-tree model, and deriving algorithm to quantify the model and to estimate the frequencies of harmful events. The present paper demonstrates how to allocate SILs to SRSs based on the algorithm.