Functional safety

What does functional safety mean?

Labyrinth of standards

The causes of hazards and therefore the technical measures applied to avoid them can vary widely. As a result, different types of safety are differentiated by the cause of potential hazards, for example.

"Functional safety" is the term used when safety depends on the correct function of a control system.

Risk assessment plays a central role with regard to functional safety requirements. The steps you need to consider when assessing and reducing risk on machinery come from the standard EN ISO 12100. The evaluation and verification of safety functions are the prevail of the standards EN ISO 13849 and EN IEC 62061, provided the required safeguarding is dependent on a control system. The safety integrity requirements (PL, SIL) are derived from the risk estimation.

Functional safety standards - ISO 13849 and IEC 62061

Functional safety describes the part of a system’s safety that depends on the correct function of the safety-related control system. Safety generally depends also on other risk-reducing measures, which are considered in accordance with EN ISO 12100. E-STOPs, safety gates, light curtains or speed monitoring are just some of the typical safety devices used to safeguard plant and machinery. The rising level of complexity of plant and machinery means that programmable control systems are increasingly being used alongside conventional relays. Both ISO 13849 and IEC 62061 ensure compliance with international legislation, e.g. the Machinery Directive. Both standards are paramount for plant and machine builders, because many B and C standards refer to them directly.

Revision of the standards EN ISO 13849 and IEC 62061

Both standards need to be updated to continue to represent the "state of the art". The latest edition of IEC 62061 was published on 19 February 2021. The impetus to revise both standards stemmed not just from the routine revision and upgrade to the state of the art, but also from the many discussions that took place during the failed attempt to unify the two standards within IEC ISO 17305.

The content of IEC 62061 is known, but the changes to EN ISO 13849 are not yet finalised; however, it is clear that both new editions:

  • Require a clear description of the safety requirements specifications, including information such as
    • Operating modes in which the function is active (always, only during maintenance, etc.)
    • How safety functions are monitored
    • When and how to test the safety function
    • The associated fault reaction
    • Reaction times
  • Changed methodology on how to define the required safety level (PL or SIL)
  • Changed requirements with respect to the application software, in line with the complexity and selected programming language
  • Allow subsystems that were developed in accordance with one standard to be used within the other


Existing safety concepts must be closely scrutinised

Plant and machine builders should re-assess existing safety concepts with regard to the changed risk classification in the standards. In some cases, there will be greater flexibility with regard to the proposed risk parameters. Whether there are any effects on existing safety assessments must be tested on a case-by-case basis.

Transition periods after ratification?

IEC 62061 was published in February 2021; however, due to ongoing discussions in the standards committees, it might be 2022 for EN ISO 13849. It is far from clear whether there will be a transition period for publication of the standards in the Official Journal and if so, how long this might be. For this reason, it is advisable to deal with the expected development at an early stage, in other words now.
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Standard IEC 62061

Quo vadis "functional safety"?

Arrows leading to standards

Automation is also seeing a trend towards digitalisation. The rising level of complexity means that configurable or programmable control systems are increasingly used to safeguard plant and machinery. When designing machine controllers, this question often arises in the course of the risk assessment: How do you select the required safety level for safety-related control functions? Manufacturers must select and then combine the components in accordance with certain criteria. The risk estimation looks at the probability of a component failing to danger. The probabilities of failure of the various components must then be examined together. The required safety level is determined via graphs, which illustrate the severity of injury and the frequency or duration of exposure. The greater the risk, the higher the controller's safety-related requirements. Every safety function is examined in the process. For example, protection against unintended restart or shutting down via the E-STOP function in the case of danger, or even ensuring that the machine is still safe should the controller fail. 

Productivity must also be considered alongside demands for a safe machine. If not, the incentive to tamper with safety devices will increase.

The requirements of safety-related parts of machine control systems are defined in both ISO 13849 and IEC 62061.

Transition periods and harmonisation

Publication of ISO 13849-1 was originally planned for 2021 and was postponed to 2022. It is far from clear when it will be harmonised into the EU standard EN ISO 13849-1, whether there will be a transition period for publication of the standard in the Official Journal and, if so, how long this might be.

The process of harmonising IEC 62061 into EN IEC 62061 took one year. As soon as an international IEC or ISO standard is published as an EU standard in the Official Journal of the European Union, presumption of conformity applies. That means that a manufacturer who abides by the specifications of the standard can assume that he complies with the health and safety requirements of the Machinery Directive and so, as part of the conformity assessment with the declaration of conformity, can affix the CE mark to his machine. The ratified, international standards can be applied as soon as they have been published on the IEC and ISO websites. However, it is advisable to deal with the expected development at an early stage.

Timetable Status  Timetable  Status 
ISO 13849-1 (FDIS) 
  • Published
IEC 62061 (FDIS) 
  • Published
ISO 13849-1 Planned for 2022 IEC 62061
  • Published
EN ISO 13849-1  Open EN 62061 
  • Published
EN ISO 13849-1 (harmonised)  Open EN 62061 (harmonised) 
  • Published

Functional safety at a glance

Consultation on functional safety

The aim of functional safety is always to protect humans and machines from hazards. In Europe, the relevant functional safety standards in the engineering sector are listed in the Machinery Directive. Download our "Functional safety" poster now and discover at a glance the procedure for risk assessment and risk reduction in accordance with EN ISO 12100. You can draw on two important standards, derived from this A-standard:

  • EN ISO 13849-1: Applicable for electrical, electronic, programmable electronic, hydraulic, pneumatic, mechanical systems
  • EN IEC 62061: Applicable for electrical, electronic, programmable electronic systems

Important parameters for the reliability of safety-related functions are the safety integrity level (SIL) and performance level (PL).

Download functional safety poster

Safety of machinery - ZVEI flyer on functional safety

The subject of machinery safety is of great importance, not only in Europe but also in many other world regions. In Europe, it's primarily the Machinery Directive that's relevant for the safety of machinery and production plants. This is where the essential health and safety requirements are stated and specified through standards. ZVEI (German Electrical and Electronic Manufacturers' Association) has published a flyer on the two most important standards – EN ISO 13849 and EN 62061 – providing clear information on the application of the two standards and the differences between them.

Download flyer

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Further information

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