IEC 61511: Safety instrumented systems for the process industry

Last edit: 26/06/2023

IEC 61511 (all parts) is intended as the process industry sector implementation of IEC 61508; it addresses the application of SISs (Safety Instrumented System) in the process industry.

Safety Instrumented Functions (SIF) are protective functions implemented in a Safety Instrumented System (SIS). A typical SIS is comprised of multiple SIFs; typically, each SIF has process sensors that measure a process deviation, a logic solver that executes the functional logic, and final control elements (e.g. valves) that bring the process to a safe state. The IEC 61511 series of standards addresses SIS based on the use of electrical, electronic, or programmable electronic technology in the process industry sector. IEC 61511 series also address a process Hazard and Risk Assessment (H&RA) from which the specification for SISs are derived.

The standard recognises that systematic failures come from human errors and they can be reduced with the implementation of solid organisational processes.

The first edition of the standard was issued in 2003. The second edition was published in 2016. The standard has four parts:

  • Part 1 – It is the only normative part of the series. It includes terminology, and requirements for specification, hardware design and application programming, commissioning, validation, operation, maintenance and testing of SIS components.
  • Part 2 – It is an Informative guidance on Part 1. It contains Annex A, that provides guidance and implementation examples of requirements outlined in Part 1.
  • Part 3 –  It is an informative part of the series that provides information on available methods to conduct Hazard and Risk Assessment (H&RA) to determine integrity requirements, i.e. Safety Integrity Level (SIL).
  • Part 4 – It is actually a Technical Report. It contains explanation and rationale for changes from Edition 1 to Edition 2.

Compliance with the IEC 61511 standard series will help assure reliable and effective implementation of SIS to achieve risk reduction objectives and thereby improving process safety.

IEC 61511 is recognized as a good engineering practice in most countries and a regulatory requirement in an increasing number of countries. End users in the process industry should use this standard series to develop their internal procedures, work processes, and management systems. Implementing a SIS lifecycle management system provides a framework for managing people, processes, and systems to improve overall safety and operational performance.

The standard applies when devices that meet the requirements of IEC 61508 series are integrated into an overall safety-related control system, to be used in a process sector application. It does not apply to manufacturers wishing to claim that their devices are suitable for use in SISs for the process sector; for this purpose, IEC 61508-2 and IEC 61508-3 have to be used.

The normative part does not contain any formula. The reason is that the spirit of IEC 61511-1 is to define what has to be achieved and not how to achieve it.