SIL requirements to instrumented safety functions shall be documented in a Safety Requirements Specification document (SRS) in accordance with the IEC61511 standard.
The SRS shall contain necessary information and requirements, such as:
- Description of the instrumented functions
- The safety integrity level of each function
- Definition of the safe state of each function
- Demand rate
- Requirement for proof-test intervals
- Response time requirements
- Survivability requirements in case of accidents or extreme environmental conditions
Detailed requirements to the contents of the SRS are given in IEC 61511-1.
The SRS shall serve as input to the design process, and also include requirements related to subsequent operation of the system.
