KANBrief 1/09
Between 1997 and 2000, nine European testing and research institutes and two industrial enterprises took part in the CEN/ STAR (action group at CEN whose main objective is to increase cooperation between research and standardization) “STSARCES“ (Standards for Safety-Related Complex Electronic Systems) project, led by the French and sponsored by the EU, in order to support the standardization of safety-related parts of controls. The contribution made to the project by the BGIA, the occupational safety and health institute of the DGUV, served as a basis for the EN ISO 13849-1 standard (Safety of machinery – Safety-related parts of control systems – Part 1: General principles for design).
What prompted the CEN/STAR STSARCES project?
The growing refinement and enhanced flexibility of production technology necessitates increasingly complex safety functions. These can be achieved only by means of microprocessor technology. Examples are the monitoring of movement and speed, and the optical safeguarding of areas. This presented the task of guaranteeing the reliability of this technology, which is not intrinsically safe, and of assessing it by testing.
The established standard for safety-related controls, EN 954-1, was no longer sufficient, since it assumed proven mechanical, electromechanical, hydraulic and pneumatic technologies. IEC has published the IEC 61508 (functional safety of electrical/electronic/ programmable electronic safety-related systems) series of standards for the functional safety of electronic and programmable electronic systems. Since, however, this standard is geared heavily to the circumstances in the process industry, with its typically complex safety networking of the plant components, application of the standard has been beyond the capability of many machine manufacturers. The STSARCES project had the function of supporting standardization work in the interests of promoting the use of innovative and fl exible technology. The result is a standard by which the safety level required in machine construction can be demonstrably attained, yet which remains within the abilities of designers.
In what way do the project results benefit ISO 13849–1?
Since many product standards contain references to the Categories of EN 954-1, the proven qualitative system of Categories was retained. It was however extended by a probability-based quantitative evaluation in the form of the “performance level“, which was developed from the IEC series of standards. As a result, even cutting- edge technologies can be addressed in a suitable manner.
STSARCES was able to describe certain fundamental subjects which concern the quantitative aspects of functional safety specific to the area of machinery. For its users, EN ISO 13849-1 simplifies the quantitative evaluation of their products, and in many cases relieves them of one of the most difficult sub-tasks, that of mathematical modelling. In the form of the “designated architectures“, the system structures studied and modelled within the project constitute a basis for classification and straightforward quantification of common control systems performing safety functions. At the same time, advanced users of the standard are free to demonstrate observance of the quantitative requirements themselves with reference to the technical variables and principles which it defines.
Why did the BGIA join the STSARCES project?
Work on the development of standards for products of relevance to OSH is a core function of the BGIA. In this specific case, it was particularly urgent for the discrepancy to be eliminated between technological development and the standards of relevance to certification. Financial support from the European Union enabled an internal research project to be conducted. Together with partner organizations and industry representatives at European level, we were able to exploit the results in order to develop concepts capable of attracting a consensus for the standardization of innovative safe technologies.
At the BGIA, STSARCES permitted targeted development of expertise in the area of probability theory, this being one of the key elements for demonstration of the safety of complex technologies.
What relevance do research projects have for standardization?
It is highly advantageous for the theoretical principles underpinning provisions of standards to be developed not only with the necessary care, but also independently of commercial interests. Safety standards must formulate, in technical terms, the safety level dictated by ethical and economic constraints, and make this safety level testable. The STSARCES project is a good example of how research results can be transferred to the field by a close intermeshing of research and standardization.