When Safety Instrumented Systems (SIS) are required within an installation, the first step would be to document the requirements. This document is often called a Safety Requirement Specification (SRS). The IEC 61511 standard specifies the general requirements for a SRS. It is important that a SRS is clear, concise, complete and consistent.
The SRS should contain the functional and integrity requirements for each Safety Instrumented Function (SIF). The SRS can be seen as the main reference document after which the design, installation, validation and operation of the system must follow.
A SRS is a multidisciplinary document that can ultimately be used by the Instrument / Control Engineer to design a Safety Instrumented System.
Sometimes we experience that companies are struggling when they need to implement a SIS. Our first suggestion would be to start creating a SRS together with a multidisciplinary team in order to specify and document all the requirements.
A pitfall can be that too less or too much is documented. A SRS of half a page is often way too little, while a SRS consisting of multiple pages is often way to complicated.
Consiltant believes that a maximum of 1 to 2 pages is enough in order to document all the relevant information. Therefore we created a SRS template and example which indicates all the relevant requirements. Not too little, not too much.
Below you can download a free SRS template, which is made in Excel, to be freely used in order to create SRS documents.