IEC 61508 is intended to be a basic functional safety standard applicable to all kinds of industry. PE safety-related systems, other iec 61508 1 pdf safety-related systems and external risk reduction facilities.
All phases are concerned with the safety function of the system. 7 are guidelines and examples for development and thus informative. Central to the standard are the concepts of risk and safety function. PES are covered by the detailed requirements of IEC 61508.
The standard advises that ‘Either qualitative or quantitative hazard and risk analysis techniques may be used’ and offers guidance on a number of approaches. One of these, for the qualitative analysis of hazards, is a framework based on 6 categories of likelihood of occurrence and 4 of consequence. Class IV: Acceptable as it stands, though it may need to be monitored. A risk assessment effort yields a target SIL, which thus becomes a requirement for the final system. Part 2 and 3 of IEC 61508 give guidance on activities to perform in order to attain a SIL. SIL specifies an allowable frequency of dangerous failure.