IEC TR 61508-0:2005

Overview

IEC TR 61508-0:2005 is a foundational technical report developed by the International Electrotechnical Commission (IEC) introducing the concept of functional safety for electrical, electronic, and programmable electronic (E/E/PE) safety-related systems. This document provides a crucial overview of the principles, structure, and practical implications of the IEC 61508 series, targeting those involved with industrial safety, control systems, and the development of standards in sectors where functional safety is a concern.

This technical report should be read in conjunction with the first edition of the IEC 61508 standards. It is especially relevant for professionals determining the applicability of IEC 61508 to their operations, for system developers, or for standards developers considering functional safety requirements.

Key Topics

• Definition of Functional Safety: Functional safety refers to the part of overall safety that depends on a system or equipment operating correctly in response to its inputs. It helps control risks by ensuring that safety-related systems perform their intended safety functions under all expected conditions.
• Safety Functions and Integrity: Hazard analysis and risk assessment determine the need for functional safety. Safety function requirements define what the system must do to prevent hazards, while safety integrity requirements address the probability that the safety function will operate correctly as needed.
• Example Use Case: The report offers practical examples, such as a machine with a rotating blade and a safety interlock which prevents operation when safety covers are open, illustrating how hazard analysis and risk assessment derive safety requirements.
• Challenges in Functional Safety: Achieving functional safety is complex due to possible random hardware failures, software errors, common-cause failures, human error, and environmental factors. The standard addresses methods to minimize such failures.
• Objectives of IEC 61508: The standard supports both safety and economic performance, applies a risk-based approach, and provides a framework for use in both generic industry applications and specific sectors.
• Safety Integrity Levels (SIL): IEC 61508 introduces four safety integrity levels, each with increasing requirements and decreasing acceptable risk of dangerous failure.

Applications

IEC TR 61508-0 and the broader IEC 61508 series are relevant to a variety of industries and applications, including:

• Industrial Automation: Emergency shutdown systems, process plant safety controls, and dynamic positioning for marine vessels.
• Transport: Railway signaling, automotive safety systems, and fly-by-wire control systems in aviation.
• Medical Equipment: Systems that control exposure doses in medical radiotherapy devices.
• Machinery Safety: Guard interlocking, emergency stopping systems, and machine monitoring to prevent operator injury.
• Product and Sector Standards: Provides a basis for developing or assessing new sector-specific and product safety standards.

The framework is used by system designers, integrators, regulators, and end-users for:

• Developing safety-related E/E/PE systems
• Drafting or updating sector or product-specific safety standards
• Assessing conformity and supporting certification processes
• Specifying, validating, commissioning, and maintaining safety-critical systems

Related Standards

IEC TR 61508-0:2005 provides an introduction and overview to the following parts of the IEC 61508 series:

• IEC 61508-1: General requirements
• IEC 61508-2: Requirements for E/E/PE safety-related systems
• IEC 61508-3: Software requirements
• IEC 61508-4: Definitions and abbreviations
• IEC 61508-5: Methods for the determination of safety integrity levels
• IEC 61508-6: Guidelines on application of Parts 2 and 3
• IEC 61508-7: Overview of techniques and measures

Additional guidance and reference are provided by:

• IEC Guide 104: Preparation of safety publications
• ISO/IEC Guide 51: Safety aspects and inclusion in standards

For further information, users are encouraged to access IEC’s online resources or contact their national committees.

Keywords: IEC 61508, IEC TR 61508-0, functional safety, safety integrity levels, E/E/PE safety-related systems, industrial safety standards, risk assessment, hazard analysis, international standards, electrical safety.