Architectural constraints in IEC 61508: Do they have the intended effect?

作者：Lundteigen Mary Ann^*; Rausand Marvin

来源：Reliability Engineering & System Safety, 2009, 94(2): 520-525.

DOI：10.1016/j.ress.2008.06.003

• Safety instrumented system
• Hardware fault tolerance
• Safe failure fraction
• Systematic failure
• Probability of failure on demand

The standards IEC 61508 and IEC 61511 employ architectural constraints to avoid that quantitative assessments alone are used to determine the hardware layout of safety instrumented systems (SIS). This article discusses the role of the architectural constraints, and particularly the safe failure fraction (SFF) as a design parameter to determine the hardware fault tolerance (HFT) and the redundancy level for SIS. The discussion is based on examples from the offshore oil and gas industry, but should be relevant for all applications of SIS. The article concludes that architectural constraints may be required to compensate for systematic failures, but the architectural constraints should not be determined based on the SFF. The SFF is considered to be an unnecessary concept.

• 出版日期2009-2