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IEC 61511 and ISA 84.00.01-2004, Clause 10, requires that a Safety Requirements Specification (SRS) be prepared for all Safety Instrumented Systems (SISs). The Clause presents a number of items to cover in the SRS, but provides little or no guidance on how a SRS should be developed, organized, or maintained. This lack of guidance results in Operating Companies, SIS Consultants, and Engineering Companies producing a variety of SRSs that vary widely in format, content, and quality. In practice, these SRSs have become extremely expensive to produce and maintain, and really do not meet the intended functionality and value.

This white paper reviews the purpose and usage of a SRS, identifies some issues observed in SRSs produced by various organizations, provides some practical suggestions for SRS preparation, and discusses the advantages of a Data-Driven SRS.