The Safety Requirements Specification (SRS) is one of the key documents for delivering functional safety.
Below is a list of the other lifecycle phases that depend materially on the availability and quality of the SRS:
The SRS would also be a typical input into any Modification (what are we changing in the specification?) and any review of a SIFSafety Instrumented Function demand (did it work as it was supposed to?).
The SRS also provides a signpost to other key documents related to the SIS. The SRS should reference “down” to the tags of the SIF components and “up” to the Hazard and Risk Assessment documentation. It should be possible to use the instrument tag to locate the particular SRS that describes the need for that particular instrument. And from the SRS you should be able to find the LOPA scenario that concluded a SIF with a given RRFRisk Reduction Factor was needed. And from the detail in the SRS you should be able to find the lines in the HazOp worksheet that identified the initiating events that could bring about the harmful event that the SIF is protecting against.
It is very likely (despite what the idealised safety lifecycle might suggest) that the SRS will be updated through the SIS design process (as the design and the specification of the design evolve together. And the SRS will be updated again, once the instrument tags are known (towards the end of the design process) and following Modifications, re-validation of Hazard and Risk Analysis documentation and re-visiting other lifecycle activities.
The Safety Requirements Specification could be considered to have 4 main sections:
Support to systems integrator working on anaerobic digester projectIndustry: Power
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Review of SRS client templateIndustry: Mining / Metal / Cement
Development and verification of SRS for pharma clientIndustry: Pharma / Bio-Tech
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