IEC 61508 vs. IEC 61511

Attribute	IEC 61508	IEC 61511
Safety Lifecycle	Defined in Part 1	Defined in Part 3
Safety Integrity Levels (SILs)	Defines SILs	Applies SILs to SIS
Functional Safety Management	Part 1	Part 1
Hazard and Risk Assessment	Part 3	Part 3
Safety Requirements Specification	Part 3	Part 3

Introduction

IEC 61508 and IEC 61511 are two important standards in the field of functional safety. While both standards are related to the safety of electrical, electronic, and programmable electronic systems, they have some key differences in terms of scope, application, and requirements.

Scope

IEC 61508 is a generic standard that sets out the requirements for ensuring the functional safety of electrical/electronic/programmable electronic safety-related systems. It applies to a wide range of industries and sectors where safety is a critical concern, such as automotive, aerospace, and process industries. On the other hand, IEC 61511 is a specific standard that focuses on the process industry sector, particularly on the safety of instrumentation and control systems in the chemical, petrochemical, and oil and gas industries.

Application

IEC 61508 is a foundational standard that provides a framework for the development and implementation of safety-related systems. It is applicable to all industries and sectors where safety is a concern, and it sets out general principles and requirements that can be tailored to specific applications. In contrast, IEC 61511 is a sector-specific standard that builds upon the principles of IEC 61508 but provides additional guidance and requirements that are specific to the process industry sector.

Requirements

IEC 61508 sets out a risk-based approach to functional safety, where the level of risk associated with a system determines the safety integrity level (SIL) that needs to be achieved. The standard defines four SILs (SIL 1 to SIL 4), with SIL 4 being the highest level of safety integrity. IEC 61508 also provides guidance on the development of safety requirements specifications, safety integrity levels, and safety lifecycle management. In comparison, IEC 61511 focuses on the application of IEC 61508 principles to the process industry sector, with specific requirements related to hazard and risk assessment, safety instrumented systems (SIS), and safety lifecycle management.

Documentation

Both IEC 61508 and IEC 61511 require the development of comprehensive documentation to demonstrate compliance with the standards. This includes safety requirements specifications, safety integrity level calculations, verification and validation reports, and documentation related to safety lifecycle management. However, the specific documentation requirements may vary between the two standards, with IEC 61511 placing a greater emphasis on documentation related to hazard and risk assessment, SIS design, and operation and maintenance procedures.

Compliance

Compliance with IEC 61508 and IEC 61511 is typically demonstrated through independent assessment and certification by a third-party certification body. Organizations that develop safety-related systems are required to follow the principles and requirements set out in the standards and provide evidence of compliance through documentation, testing, and verification activities. While compliance with IEC 61508 is a prerequisite for compliance with IEC 61511, organizations in the process industry sector must also ensure that they meet the specific requirements of IEC 61511 to achieve certification.

Conclusion

In conclusion, IEC 61508 and IEC 61511 are two important standards that play a crucial role in ensuring the functional safety of electrical, electronic, and programmable electronic systems. While both standards share common principles and requirements, they also have distinct differences in terms of scope, application, and requirements. Organizations that develop safety-related systems must carefully consider the requirements of both standards to ensure compliance and achieve certification.