Reliability block diagrams IEC 61508
For determining the safety integrity level (SIL) reliability block diagrams (RBD) can be used. SIL is a measure for the effectiveness of the security features. The SIL is depending on the reliability in case of hazard and the shutdown in case of error. The required SIL can be detected by a hazard and risk analysis. In failure analyses according to IEC 61508 within an FMEA only the first failure is considered. But with the reliability block diagrams also a two fault safety can be guaranteed (SIL 4).