Benchmark study on international functional safety standards
Résumé
International functional safety standards are becoming a major reference for the development and validation of safety related systems. Thus, the quality of these standards and the way they are applied are particularly critical. That is why different partners (Total, PSA, RATP, INERIS) decided to realize a study on this subject in the framework of the IMdR. This study was realized by Ligeron. The motivations and the main results are given in this paper. Various industrial sectors have developed their own standards by taking into account sector-based practices and constraints and without reference to a common state of the art. Consequently, there are strong disparities between the standards and often important inconsistencies with the state of the art in safety and reliability engineering. Each standard defines its own multiple degree qualification scale like SIL for the IEC 61508, ASIL for the ISO 26262, DAL for DO 178, Category for machines. Each one introduces its specificities and leans on different hypotheses. Different semantics and definitions are in use and similar terms are used with different meanings. Furthermore the principles, the underlying hypotheses or the simplifications introduced are sometimes ambiguous or scientifically questionable. In front of those difficulties of interpretation and use, it appears necessary to list the standards, make a critical analysis and compare them in order to identify the convergences, the main differences and the possible weaknesses. The study was split in 4 steps : identification of existing functional safety standards ; feedback on standards application ; standards comparison and critical review ; vocabulary status. The results of the identification and analyze of standards provide : vocabulary comparison and analysis ; main qualification criteria ; conditions for standards applicability ; benefits and limitations of each standard ; relevance of each standard with regards on technologies and operation philosophy.