A Method of Calculating Safety Integrity Level for IEC 61508 Conformity Software

In the functional safety standard (IEC 61508), development methods and quantitative analytical methods are defined for establishment of safety-related systems. However, only development methods are recommended to establish the software of safety-related systems. That is, the safety integrity level for software is determined only by the number of the development methods applied to practical safety-related system development. This is not reasonable to evaluate the safety integrity level, because various risk factors should be taken up. In this paper, we propose how to calculate the safety integrity level for software. Especially, we propose the calculation method based on software reliability growth models that have been utilized for many years in the large-scale system development.