ISO 13849-1:2023 changes course, all directions towards design methodology

by Jan 5, 2024Machine Safety

Introduction:

The International Standardisation Organisation (ISO) sets standards in all areas of industry. ISO 13849-1 Safety of machinery – Safety-related parts of control systems – Part 1: General principles for design, is the benchmark for control system design. In 2023, ISO published a new version of the standard. Our team is always at the forefront of the latest advances in machine and workplace safety. The Intervention Prévention team has analyzed and studied the new version. Our verdict is clear: the standard has improved and become an even more effective tool. This article describes the changes in the standard’s methodology and design tools, particularly in its appendices.

Development:

When comparing the 2015 and 2023 versions, the safety and performance evaluation elements are the same. A few assessment tools have been improved, notably the frequency and avoidance probability assessment tools. These changes will be discussed later in the article. The major difference between the 2015 and 2023 versions is in the design process. ISO’s new design methodology emphasizes planning and, above all, the implementation of safety from the very start of equipment design. For several years now, the most successful companies have been using a design methodology in which the planning phase is more important, and design (drawing, calculation, component selection) takes place further down the design line. When the product is ready for testing, these companies make rapid iterations to improve and correct any remaining shortcomings. The new version attempts to push designers to enter safety functions directly into the specifications. This methodology will save companies time, energy and money. There’s no need to select components after the design stage, and changes are avoided. What’s more, the security level of the components and the architecture can be chosen at the very start of development, thus increasing overall security performance.

In today’s automation industry, companies are increasingly turning to the principles of KDM (Kaizen Design Method). When designing equipment, design teams take the time to define the customer’s needs. Based on these needs, the functions to be performed by the equipment are defined. Once the functions have been determined, the technology or concept to accomplish the function is found. ISO 13849-1:2023 interferes with this vision of design. In the 2015 version, the emphasis was on validating the safety-related control system. The designer was designing a piece of equipment. Once the operating functions were defined, the risk was assessed and the safety-related control systems designed accordingly. Of course, version 2023 still explains how to validate safety-related control systems. Designers are now asked to define safety-related functions at the same time as other functions, and to include safety in each operational function. The aim is to achieve intrinsically safe functions (limiting speed, force, torque, etc.) more often, and to reduce design time and costs. This leads the designer to produce a safe concept from the outset, rather than securing his equipment later.

In terms of the standard’s tools, version 2023 adds quantitative notions to the assessment of exposure frequency (section A.3.2) and the evaluation of avoidability (Table A.1). This corrects a shortcoming of earlier versions, where designers could justify certain choices in a more qualitative way. The new appendices and their design tools are listed below:

  • Annex L on immunity to electromagnetic interference (EMI);
  • Annex M on specifying safety requirements. In this new annex, you’ll find the standards and sections of ISO 13849-1 that explain how to design the most popular and common safety functions;
  • Appendix N on failure avoidance in software design;
  • Annex O on safety-related values for components or parts of control systems. In this appendix, different technologies are given a “typical” value according to their level of integration. This enables the integrator or designer to know whether a component will be simple and easy to integrate, or whether they will have to search for the data or test the components.
    • Device type 1: highest level of integration, with known failure modes (e.g. light curtain, safety component).
    • Device type 2. Intermediate integration level. Failure modes are unknown because the component is not designed for safety, but can be used for safety. The integrator must then find additional data (DC, circuit structure, CCF, etc.). (e.g. pressure sensor, proximity switch, etc.).
    • Device type 3. Low level of integration. Failure mode depends on operating cycles. Access to application data (number of hours, activations, operations, etc.) is required to assess safety. (e.g.: components subject to wear, pneumatic valves, switches, control devices, etc.).
    • Device type 4. This type is a special case of type 1. It is a component with a non-random failure mode. A failure will always result in a safety condition, or there is a fault exclusion in accordance with section 6.1.10.3 of ISO 13849-1:2023.

Conclusion:

In conclusion, version 2023 of ISO 13849-1 has changed both from a methodological and a technical point of view. The current methodology requires designers to include safety functions right from the drawing up of specifications. Companies are bound to gain by applying these principles, as they will be able to save time and energy at the end of the project. What’s more, certain intrinsic safety features can be designed and identified, saving companies a great deal of time and money. At Intervention Prévention, several customers who use our PSSR (pre-startup safety review) services have begun to include us right from the design stage of their equipment and robot cells. This enables us to correct the design before manufacturing and assembly.

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Intervention Prévention Inc.

Intervention Prévention œuvre dans le domaine de la sécurité au travail en offrant des services spécialisés répondant aux normes CSA Z462 – Sécurité électrique en milieu de travail, CSA Z460 – Maîtrise des énergies dangereuses : Cadenassage et autres méthodes, et CSA Z432 – Protection des machines. Nos domaines d’expertise sont donc reliés au cadenassage, à la sécurité électrique et à la sécurité machine. La satisfaction de nos clients est le gage de notre compétence

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