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5. Common causes
5.1 Preamble
KooN-type redundancy reduces the probability of RIS failure. However, it is necessary to take into account the possibility that certain causes may lead to the simultaneous failure of redundant equipment.
ISO 12489 introduces the notion of common cause of failure by pointing out that, while mathematically it is possible to consider that the probability of failure of "N" similar pieces of equipment with 1ooN redundancy is "p N " (p being the probability of failure of a piece of equipment), in practice it is not possible to "indefinitely" reduce the probability of failure of a system simply by increasing the number of redundant pieces of equipment. To illustrate this, the standard takes the example of...
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Common causes
Method for assessing the probability of failure of a RIS
Bibliography
Standards and norms
- Analysis techniques for dependability – Reliability diagram block and Boolean methods - IEC 61078 -
- Functional safety of safety-related electrical/electronic/programmable electronic systems – chapters 1 to 7 - IEC 61508 -
- Sécurité fonctionnelle des systèmes instrumentés de sécurité pour le secteur de l'industrie des procédés continus - IEC 61511 -
- Analysis techniques for dependability – Reliability...
Organizations
French National Institute for Industrial Environment and Risks (INERIS) http://www.ineris.fr
Instrumentation Society of America (ISA) https://www.isa.org/http://www.isa-france.org
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