Functional Safety: Safety Instrumented Systems for the Process Industry Sector - Part 3: Guidance for the Determination of the Required Safety Integrity Levels - Informative
This part 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 ANSI/ISA-84.00.01-2004 Part 1 (IEC 61511-1 Mod)@ ANSI/ISA-84.00.01-2004 Part 2 (IEC 61511-2 Mod)@ and ANSI/ISA-84.00.01-2004 Part 3 (IEC 61511-3 Mod)@ 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. For existing SIS designed and constructed in accordance with codes@ standards@ or practices prior to the issue of this standard (e.g.@ ANSI/ISA-84.01-1996)@ the owner/operator shall determine that the equipment is designed@ maintained@ inspected@ tested@ and operating in a safe manner.