Definition:
The Safety Requirements Specification (SRS) is a detailed document that captures all functional and integrity requirements for the entire Safety Instrumented System (SIS) and each Safety Instrumented Function (SIF). It is often the most important deliverable the engineering team will produce. A LOT of information goes into this document.
At times, the SRS can be so complex and long, it is split into multiple documents. One common way is for a single large document, confusingly called SRS by title, is released. Then multiple SIF specific documents are then released where many of the SIF specific decisions are made. Together these documents would meet all the requirements of an SRS.
Another way to think of this is that the SRS is a document that documents numerous decisions on HOW the SIS will be designed.
Key Points:
- Forms the basis for system design and validation.
- Should be updated throughout the lifecycle.
- There are many requirements for an SRS in 61511-1 that it can get very long and complex. An SRS may be split into multiple documents. For example, a single larger document for SIS and then sub-documents for each SIF.
Example:
SRS includes trip points, response times, proof test intervals, and SIL targets.
See Also: SIS, SIF, safety lifecycle
Cited Source:
- IEC 61511-1:2016, Clause 10.3.