ISA 61511-3-2018 provides information on: the underlying concepts of risk and the relationship of risk to safety integrity (see Clause A.4); the determination of tolerable risk (see Annex K); a number of different methods that enable the safety integrity level (SIL) for the safety instrumented functions (SIF) to be determined (see Annexes B through K); the impact of multiple safety systems on calculations determining the ability to achieve the desired risk reduction (see Annex J). In particular, this part of IEC 61511: 1.applies when functional safety is achieved using one or more SIF for the protection of either personnel, the general public, or the environment; 2.may be applied in non-safety applications such as asset protection; 3.illustrates typical hazard and risk assessment methods that may be carried out to define the safety functional requirements and SIL of each SIF; 4.illustrates techniques/measures available for determining the required SIL; 5.provides a framework for establishing SIL but does not specify the SIL required for specific applications; 6.does not give examples of determining the requirements for other methods of risk reduction.