[Iec 61511 Part 1 Pdf
Addison Mauldin
IEC standard 61511 is a technical standard which sets out practices in the engineering of systems that ensure the safety of an industrial process through the use of instrumentation. Such systems are referred to as Safety Instrumented Systems. The title of the standard is "Functional safety - Safety instrumented systems for the process industry sector".
The process industry sector includes many types of manufacturing processes, such as refineries, petrochemical, chemical, pharmaceutical, pulp and paper, and power. The process sector standard does not cover nuclear power facilities or nuclear reactors. IEC 61511 covers the application of electrical, electronic and programmable electronic equipment. While IEC 61511 does apply to equipment using pneumatic or hydraulic systems to manipulate final elements, the standard does not cover the design and implementation of pneumatic or hydraulic logic solvers.
This standard defines the functional safety requirements established by IEC 61508 in process industry sector terminology. IEC 61511 focuses attention on one type of instrumented safety system used within the process sector, the Safety Instrumented System (SIS).
For existing safety instrumented systems (SIS) designed and constructed in accordance with codes, standards, or practices prior to the issuance of this standard (e.g. ANSI/ISA 84.01-1996), the owner/operator shall determine and document that the equipment is designed, maintained, inspected, tested, and operated in a safe manner.
The European standards body, CENELEC, has adopted the standard as EN 61511. This means that in each of the member states of the European Union, the standard is published as a national standard. For example, in Great Britain, it is published by the national standards body, BSI, as BS EN 61511. The content of these national publications is identical to that of IEC 61511. Note, however, that 61511 is not harmonized under any directive of the European Commission.
IEC 61511 covers the design and management requirements for SISs throughout the entire safety life cycle. Its scope includes: initial concept, design, implementation, operation, and maintenance through to decommissioning. It starts in the earliest phase of a project and continues through startup. It contains sections that cover modifications that come along later, along with maintenance activities and the eventual decommissioning activities.
ISA 84.01/IEC 61511 requires a management system for identified SIS. An SIS is composed of a separate and independent combination of sensors, logic solvers, final elements, and support systems that are designed and managed to achieve a specified safety integrity level (SIL). An SIS may implement one or more safety instrumented functions (SIFs), which are designed and implemented to address a specific process hazard or hazardous event. The SIS management system should define how an owner/operator intends to assess, design, engineer, verify, install, commission, validate, operate, maintain, and continuously improve their SIS. The essential roles of the various personnel assigned responsibility for the SIS should be defined and procedures developed, as necessary, to support the consistent execution of their responsibilities.
ISA 84.01/IEC 61511 uses an order of magnitude metric, the SIL, to establish the necessary performance. A hazard and risk analysis is used to identify the required safety functions and risk reduction for specified hazardous events. Safety functions allocated to the SIS are safety instrumented functions; the allocated risk reduction is related to the SIL. The design and operating basis is developed to ensure that the SIS meets the required SIL. Field data are collected through operational and mechanical integrity program activities to assess actual SIS performance. When the required performance is not met, action should be taken to close the gap, ensuring safe and reliable operation.
IEC 61511 references IEC 61508 (the master standard) for many items such as manufacturers of hardware and instruments and so IEC 61511 cannot be fully implemented without reference to IEC 61508. IEC 61511 is the process industry implementation of IEC 61508.[1]
ISA84, Instrumented Systems to Achieve Functional Safety in the Process Industries, has approved the newest edition of IEC 61511 as ISA and American National Standards Institute (ANSI) standards. The new standards will be designated in the U.S. as ANSI/ISA-61511, Functional Safety - Safety Instrumented Systems for the Process Industry Sector, Parts 1-3. The standards set forth requirements for the specification, design, installation, operation, and maintenance of a safety instrumented system (SIS) so that it can be entrusted to achieve or maintain a safe state of a process.
ISA84 developed the original ISA-84.01 standard on which the first edition of IEC 61511 was based. This new edition of IEC 61511, developed under IEC SC65A/MT 61511, was approved by ISA84 without modification-but not without concerns from several ISA84 members about the guidance and interpretation of IEC 61511-2, Part 2: Guidelines for the Application of IEC 61511-1. For that reason, ISA84 prepared a special foreword to ANSI/ISA-61511-2 that refers users to several ISA84 technical reports for guidance on the same topics. Those technical reports include:
In this blog series, I will cover the emerging trends in the valve assembly market, how these trends relate to the IEC 61511 requirements, and what's in a final element. When you look at the different devices that go into some of these safety systems, the final element becomes quite complex.
These requests are coming from EPC and Process Owners for specific valve assemblies related to specific projects. This indicates that Process Owners are looking to satisfy the requirements of IEC 61511 that relate to the integration and validation of final elements.
It might seem like overkill. Is it really necessary to buy a certified valve and a certified actuator? When we look at what goes into these final elements, you'll see quite a bit of complexity, which leads to the requirement within 61511 to demonstrate that the equipment used in these safety systems will function correctly.
In fact, sometimes, it can be better. But, there is a need for visibility, transparency, and traceability for what gets installed at the plant and run. Does it meet all the functional requirements of the safety requirements spec? Can it be audited? Does it demonstrate what it needs to do?
There's no prescriptive path in the standard saying that you must buy an integrated valve assembly or you can't do certain things, but there are requirements to show that traceability, and to show a reasonable amount of evidence for verification and validation that the system will function correctly.
When we think about the final element, what immediately comes to mind is the valve, the actuator, and probably some type of control device like a solenoid. That's the minimum you need in your final element, but most times, there's additional things.
Sometimes, some OEMs have these couplings and these connector devices included in their valve or actuator. They would then be part of the valve actuator assessment. However, many don't. There's a stem that could be connected to an actuator stem, but then you need an independent way of coupling it. Or you need the mounting bracket or you need the hardware to do it.
Understanding if all those parts are included in the OEM scope is important. Beyond that, there can be things such as feedback devices for automated testing or proof testing. There can be functional devices like quick-exhaust valves or volume boosters to make sure that the assembly is moving quickly enough. There can be double-acting actuators, or hydraulic / pneumatic-assist return actuators. In that case, the hydraulic supply or the pneumatic supply needs to be considered as well.
In addition to making sure we have the right parts included, we need to be able to show requirements traceability down through the design of the safety instrumented function and then to the specific devices in the final elements. I will cover that in part 2.
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The Basic Process Control System (BPCS) is one of the most relied upon and credited safeguards in a Process Hazard Assessment (PHA) and Layer of Protection Analysis (LOPA) study. How much credit can reasonably be applied for this protection layer is a commonly debated and often "thorny" topic. With the updates made to international standard IEC 61511 in 2016, the requirements clearly limit how much reliance can be placed on the BPCS category of safeguards including the level of independence needed. Part 1 of this series will discuss the BPCS independence requirements and Part 2 will review practical solutions to maximize independence and achieve IEC 61511 compliance. There will also be some discussion on how to handle reviews of existing facilities built under less stringent requirements.
The level of independence required for dual BPCS credits has been a subject of debate for many years in the industry. The IEC 61511 international standard specifies the requirement for this topic, however the details on how to comply have been an area left with different interpretations.
The path for dual BPCS credit within a common logic solver described by these two CCPS publications has since been superseded with the release of the 2016 version of IEC 61511 which provided more clarity on BPCS requirements for independence. The IEC 61511 standard allows for up to two BPCS protection layers to be credited either as safeguards or as part of the initiating event only when fully independent (sensor, logic solver and final element). The details of these independence requirements will be described in more detail below.
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