Efficient assessment of safety instrumented systems

Faster compliance and identification of issues at a lower cost


With IEC 61511 representing good practice for the design and management of safety instrumented systems (SIS), an operator faced the challenge of how to efficiently apply the code to 12 brownfield platforms.

DNV GL solution

The solution was to generate a set of standard configurations that defined the minimum architecture needed for each type of SIS (e.g. high pressure protection in a pressure vessel). The risk from these configurations was assessed using fault trees and consequence analysis and shown to meet the operator’s risk criterion for industry standard failure rate data. A check list was created for each configuration to allow easy assessment of each SIS against its minimum requirements and a check was made as to whether actual failure data reflected the industry standard data. Non-standard systems were assessed by variation from the standard configurations.

Outcome and benefits

The assessment for all assets using a check-list approach against the standard configurations saved 50-70% over traditional approaches to IEC61511 compliance. Up to 90% of the safety critical instrumentation could be assessed quickly, with only the SISs that did not meet a standard configuration required a more detailed assessment.