IEC 62061: Functional Safety of Machinery

Last edit: 26/06/2023

IEC 62061 is one of the two Functional Safety Standard for machineries, the other being ISO 13849-1. On 22 March 2021, after 16 years from the first edition, a new one was published! 

IEC 62061: Safety of machinery – Functional safety of safety-related control systems.

On 7 April 2022, it was published in the Official Journal of the European Union and officially became a harmonised standard to the Machinery Directive.  The old IEC 62061:2005 edition will remain in force until 11 October 2023.

The standard is derived from IEC 61508 and it is addressed to the machinery sector: it allows the verification of the level of Reliability reached by a Safety Control System (SCS).

The IEC Maintenance team (MT62061), working on the new version of IEC 62061, started the activity at the end of 2016. The text used as the starting point was not the one of the previous 2005 version but it was the latest text coming from the merger activity of IEC 62061 and ISO 13849-1: the so called ISO 17305 project. That is one of the reasons why the new edition of IEC 62061 is closer in the approach to ISO 13849-1: the team mediated the IEC 61508 formalism with the pragmatism of ISO 13849-1. 
There are several differences between the 2005 edition and the new one, the main one of which is the fact it can now be used also for non-electrical systems. Other significant changes are:

  • There are various improvements and clarification on Architectures and Reliability (Clauses 6 and 7).
  • There is a shift from "SILCL" to "maximum SIL" of a subsystem (Clause 7).
  • The use of cases for software (Clause 8)
  • Requirements on independence for software verification (Clause 8) and validation activities (Clause 9) were added.
  • New informative annex with examples (Annex G)
  • New informative annexes on typical MTTFD values, diagnostics and calculation methods for the architectures (Annex C, Annex D and Annex H).

The standard in not using anymore the acronym SRECS (Safety Related Electrical Control Systems), since it is now applicable to Pneumatic and Hydraulic systems as well. The new acronym is SCS: Safety-related Control System.

The reliability of the Safety Function

IEC 62061 indicates the reliability of the safety control system using the concept of SIL:

[IEC 62061:2021 – 3.2.24] Safety Integrity Level (SIL): discrete level (one out of a possible three) for specifying the safety integrity requirements of the safety-related control functions to be allocated to the SCS, where safety integrity level three has the highest level of safety integrity and safety integrity level one has the lowest.

SIL 1 is the lowest level and SIL 3 is the highest. SIL 4 is not applicable in Machineries.

The Safety Integrity Level is measured in PFHD. In the new edition there is a change of its definition. In the past it was called "Probability of dangerous Failure per Hour (PFHD)". It is now called "Average frequency of a dangerous failure per hour". It is a better definition since the value is not a probability [dimentionless] but a frequency [1/h].

The values are illustrated in the table 3 of the standard.