This paper explains how exida applies the requirements of IEC61508:2010 Route 2H to its process of certifying devices for use in safety applications.
Rather than having specific designs and a long list of specific rules that become obsolete, the IEC 61508 standard allows any safety instrumented function (SIF) design to be implemented. The standard allows the design to use old products or new technology. The standard allows innovation and good engineering. However, any SIF design must be verified with documented performance metrics which must match risk reduction requirements in the form of safety integrity levels (SIL). In order to verify that a design meets the needed risk reduction, the designer must check three performance criteria.
This paper is devoted to one of those performance criteria, viz., minimal architectural constraints which, per IEC 61508, may be met in one of two ways, i.e., via Route 1H or Route 2H. Furthermore, this paper deals exclusively with Route 2H because, for practical purposes, Route 2H produces a realistic SIL level for a given design and does not impose artificial redundancy.