New Requirements of the IEC 61511

To prevent dangerous phenomena such as fires, explosions or the release of hazardous materials from causing damage to people, the environment or property, manufacturers are required to set up safety barriers. These barriers can be either preventive, by reducing the probability of occurrence of these phenomena (prevention barriers), or mitigating, by limiting their consequences (mitigation barriers).

Experience has shown that major industrial accidents are generally the consequence of a chain of undesirable events combined with safety barrier failures. Safety instrumented functions (SIF), provided by safety instrumented systems (SIS), are a type of safety barrier that complements the other types of barrier that can be implemented to ensure safety.

Standards IEC 61508 (generic) and IEC 61511 (for the processing industries) are standards that can be used not only during the design phase, but also throughout the life cycle of RIS. They provide requirements for each activity in the safety life cycle of these systems. Accidents such as the one at Buncefield in 2005 confirm that, for the vast majority of users, some of the basic requirements of these standards have been misinterpreted, misapplied or, in some cases, completely ignored.

With this in mind, a new version of the IEC 61511 was published in 2016 with the aim of :

• clarify and/or reinforce certain requirements ;

• Part 2 of the standard provides a more practical guide to implementing the requirements of Part 1.

This new version retains the fundamental principles of the previous 2003 version, while introducing substantial modifications to certain activities in the security lifecycle.

After a first section of the article dedicated to some basic reminders about functional safety, the changes introduced in the new version of the IEC 61511 are presented. The third and final section of the article is devoted to the new requirements for calculating RIS failure probabilities.