What is the difference between IEC 61511 and ISA-84?

The IEC 61511 and ISA-84 are two globally recognized standards used in the process industry to ensure functional safety of systems. Both standards outline requirements for the design, implementation, operation, and maintenance of safety instrumented systems (SIS). However, there are some key differences between the two standards.

Scope and Application

IEC 61511: The IEC 61511 standard, also known as Functional Safety - Safety Instrumented Systems for the Process Industry Sector, provides guidelines for the entire lifecycle of a safety instrumented system. It applies to all industries involved in the manufacturing, processing, handling, or storage of hazardous substances.

ISA-84: The ISA-84 standard, also called Application of Safety Instrumented Systems for the Process Industries, focuses specifically on the process industries. It offers guidance on implementing safety instrumented systems for processes that involve potentially hazardous materials.

Structure and Terminology

IEC 61511: This standard is structured into four main parts. Part 1 provides an and general requirements. Part 2 outlines the requirements for the entire SIS lifecycle. Part 3 covers the requirements for the SIS design and engineering phase. And part 4 addresses the validation, operation, and maintenance of the SIS. The terminology used in IEC 61511 is aligned with other IEC functional safety standards.

ISA-84: ISA-84 is divided into three parts. Part 1 introduces the concepts and terminology of safety instrumented systems. Part 2 provides detailed guidance on the application of safety instrumented systems. Part 3 focuses on examples of how to implement safety instrumented systems, including project planning and engineering. The terminology used in ISA-84 is specific to this standard and may differ from other functional safety standards.

Risk Assessment and Safety Lifecycle

IEC 61511: The IEC 61511 standard emphasizes the importance of conducting a comprehensive risk assessment to identify and evaluate potential hazards. It requires organizations to establish a safety lifecycle for their SIS, which includes various stages such as concept development, design, operation, and decommissioning.

ISA-84: ISA-84 also recognizes the need for risk assessment but provides less detailed guidance compared to IEC 61511. It suggests using other standards, such as ANSI/ISA 84.00.01, as references for performing risk assessments. Additionally, ISA-84 does not explicitly mandate a safety lifecycle, although it encourages following good engineering practices and industry standards.

In conclusion, while both IEC 61511 and ISA-84 serve as valuable resources for implementing safety instrumented systems in the process industry, they have distinct scopes, structures, and approaches. Organizations should carefully consider their specific industry and regulatory requirements when determining which standard to follow.