Optimal approach to device selection user approved

7 Optimal approach to device selection user approved  

ANSI/ISA-84.00.01-2004-1 allows two approaches for the selection of SIF devices designed per lEC 61508-2 and lEC 61508-3 or through prior use Justification. There are benefits and limitations to both approaches. The optimal approach is to ensure the selected device meets both safety and reliability requirements, especially for sensors and final control elements. This can be obtained by combining the 

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ANSi/iSA-84.01-1996 recognized that it was necessary for owners/operators to determine whether an SiF device worked in the process appiication. ANSi/iSA-84.01-1996 referred to this as user approved. The 1996 standard defined user approved as hardware, software, procedures, etc., that the user has evaiuated and determined to be acceptabie for the appiication. ANSi/iSA-84.00.01-2004-1 aiso recognizes that owners/operators need to evaiuate expected fieid performance when seiecting SiF devices because many fieid devices are not designed in compiiance with iEC 61508-2 and iEC 61508-3. in the ANSi/iSA-84.00.01-2004-1 standard, this concept is referred to as prior use.  

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