What is this standard about?
It’s the second part of the European standard on the functional safety of safety instrumented systems. It provides guidance on how to apply the recently amended first part of the standard: BS EN 61511-1:2017.
Who is this standard for?
The BS EN 61511 series applies to a wide variety of industries within the process sector, with the scope of application extended by the 2017 revisions. It will be used in the following sectors:
- Chemicals
- Oil and gas
- Pulp and paper
- Non-nuclear power generation
- Pharmaceuticals
- Food and beverage
Why should you use this standard?
Safety instrumented systems (SIS) are engineered controls that protect critical process systems. The specific control functions performed by a SIS are called Safety Instrumented Functions or SIFs. This standard provides guidance on the specification, design, installation, operation and maintenance of SIFs and related SIS as defined in BS EN 61511-1.
- It’s recognized as good engineering practice in most countries and is a regulatory requirement in an increasing number.
- Its use will help assure reliable and effective implementation of SIS to achieve risk reduction objectives, thereby improving process safety.
- End users in the process industry should use this standard 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 also provides implementation examples of requirements outlined in Part 1 and is organized so that clauses correspond with the same clause in BS EN 61511-1 (with the exception of the annexes).
What’s changed since the last update?
The main changes are as follows:
- Clarification of the interpretation of the standard in areas that in the past have been subject to misinterpretation, for example removal of the concept of safe failure fraction (SFF), clarifying that reliability data must be derived from the performance in the operating environment.
- Enhanced requirements in areas which have previously been poorly addressed, for example the addition of security risk assessment and consideration of errors in the human interface, strengthening of requirements on operations and maintenance particularly when in degraded modes, normative requirements for competence, Factory Acceptance Test and for provision of suppliers functional safety management systems, strengthening of the requirements for Functional Safety Assessment, particularly during Change Management and in conduct of Functional Safety Audits as well as the requirements for analysis and impact assessment during change.
- Closer adherence to the Basic Functional Safety Standard IEC 61508, for example the addition of the concept of high demand mode, the provision of an additional route to compliance with hardware fault tolerance, the methodology for handling the highest levels of risk reduction and for allocation of SIFs to a SIS, constraints on the claims that can be made with respect to a BPCS and the independence of protection layers.
- Reduced repetition of requirements, for example integration of the application programming requirements into the SIS lifecycle and consolidation of programming requirements into a ‘flatter’ lifecycle appropriate to data driven systems.
- In particular, removal of much of the guidance on application programming from Part 1 to Part 2, together with significant enhancement of that guidance and provision of worked examples, provides greater clarity.