IEC 61508

By Graphic Products Editorial Staff

What exactly is IEC 61508? Let’s start at the beginning. The International Electrotechnical Commission (IEC) governs everything related to electrical and electronic technologies. The IEC 61508 title is: Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems. What does IEC 61508 require? We'll need to start with some definitions.

The International Electrotechnical Commission (IEC) defines safety as:

Freedom from unacceptable risk of physical injury or of damage to the health of people, either directly or indirectly as a result of damage to property or to the environment.

A second definition that is important is that of “functional safety.” The IEC defines functional safety as:

Functional safety is part of the overall safety that depends on a system or equipment operating correctly in response to its inputs. Functional safety is achieved when every specified safety function is carried out and the level of performance required of each safety function is met.

The third definition we'll need to know is the definition of “E/E/PE.” What does “E/E/PE” mean? Here is the official IEC definition:

E/E/PE is an abbreviation of electrical/electronic/programmable electronic. 3.2.6 of IEC 61508-4 defines this as based on electrical and/or electronic and/or programmable electronic technology.

IEC 61508 covers electrical, electronic, and programmable electronic systems that, if they should fail, a safety hazard will result.  It does not matter what the E/E/PE system is controlling, IEC 61508 covers the design and operation of the E/E/PE system, not the machines, equipment, process, or system being controlled.

IEC 61508 is applicable to any safety-related system that contains an E/E/PE device.

Is Complying With IEC 61508 Required?

No. This standard is not referenced by OSHA nor does it have the status of a harmonized European standard. The standard provides guidance for developing safe E/E/PE systems. Manufacturers who have designed system in compliance with IEC 61508 may identify their products as conforming to IEC 61508. On the purchasing side buyers can look for E/E/PE systems that are IEC 61508 compliant, and know what they are getting.

What Is In The IEC 61508 Standard?

The IEC 61508 standard has seven parts. The first four provide the normative safety requirements. The “normative” requirements are those with which it is necessary to conform in order to be able to claim compliance with the standard.  The last three parts (5-7) contain recommendations and guidelines that are defined as informative. They provide additional information that helps in understanding or meeting the requirements of IEC 61508. However, it is not necessary to conform with the recommendations in parts 5, 6 and 7. The seven parts of IEC 61508 are:

  • IEC 61508-1 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 1: General requirements
  • IEC 61508-2 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems
  • IEC 61508-3 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 3: Software requirements
  • IEC 61508-4 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 4: Definitions and abbreviations
  • IEC 61508-5 - Functional safety of electrical/electronic/programmable electronic safety related systems - Part 5: Examples of methods for the determination of safety integrity levels
  • IEC 61508-6 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3
  • IEC 61508-7 - Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 7: Overview of techniques and measures

IEC 61508 Hazard And Risk Assessment

The standard requires that the elimination of hazards be a priority and in particular eliminating hazards at the source. This is equivalent to the primary method of addressing any safety hazard that uses engineering controls to eliminate the hazard. Of course, this requires that the hazards be identified through a hazard and risk assessment. IEC 61508 states, “The EUC (Equipment Under Control) risk shall be evaluated, or estimated, for each determined hazardous event.”

What is the definition of “EUC?” Here is what the IEC says:

The EUC is the set of all equipment, machinery, apparatus or plant that gives rise to hazardous events for which the safety-related system is required. In the case of a safety-related protection system on an offshore platform, for example, the EUC is all parts of the platform that could affect the safety requirements.

The standard allows the method used for the risk analysis to be selected by those needing to do the analysis. It states that “either qualitative or quantitative hazard and risk analysis techniques may be used.” Annex B of part 5 provides guidance on the selection methods for determining safety integrity level requirements.

IEC 61508 Functional Safety Assessment

The IEC defines a functional safety assessment as:

...the critical activity that ensures functional safety has actually been achieved based on compliance with the relevant clauses of this standard. Those carrying out the functional safety assessment shall be competent, shall have adequate independence and shall consider the activities carried out and the outputs obtained during each phase of every lifecycle and judge the extent to which the objectives and requirements of IEC 61508 have been met.

The reason for a functional safety assessment is to determine if the E/E/PE system achieves safe operation based on it being compliant with the relevant clauses of the IEC 61508 standard.

IEC 61508 Summary

What this means is that IEC 61508 is a set of standards that describe how a control system that uses electricity to operate should be designed to ensure safe operation of the equipment it controls. These standards include the design of software as well as the hardware. In addition, a risk assessment needs to be conducted to identify all potential hazards, such that the system can be verified as properly performing all safety related functions.

Don't Forget Labeling

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