Functional safety – Safety instrumented systems for the process industry sector – Part 3: Guidance for the determination of the required safety integrity levels
|Publication Date:||1 March 2003|
|ICS Code (Industrial automation systems in general):||25.040.01|
This part of IEC 61511 provides information on
- the underlying concepts of risk, the relationship of risk to safety integrity, see Clause 3;
- the determination of tolerable risk, see Annex A;
- a number of different methods that enable the safety integrity levels for the safety instrumented functions to be determined, see Annexes B, C, D, E, and F.
In particular, this part
a) applies when functional safety is achieved using one or more safety instrumented functions for the protection of either personnel, the general public, or the environment;
b) may be applied in non-safety applications such as asset protection;
c) illustrates typical hazard and risk assessment methods that may be carried out to define the safety functional requirements and safety integrity levels of each safety instrumented function;
d) illustrates techniques/measures available for determining the required safety integrity levels;
e) provides a framework for establishing safety integrity levels but does not specify the safety integrity levels required for specific applications;
f) does not give examples of determining the requirements for other methods of risk reduction.
Annexes B, C, D, E, and F illustrate quantitative and qualitative approaches and have been simplified in order to illustrate the underlying principles. These annexes have been included to illustrate the general principles of a number of methods but do not provide a definitive account.
NOTE Those intending to apply the methods indicated in these annexes should consult the source material referenced in each annex.
Figure 1 shows the overall framework for IEC 61511-1, IEC 61511-2 and IEC 61511-3 and indicates the role that this standard plays in the achievement of functional safety for safety instrumented systems.
Figure 2 gives an overview of risk reduction methods.