The objective is to specify the requirements for the safety instrumented functions.
- To define the safe state of the process for each identified safety instrumented function;
- The assumed sources of demand and demand rate on the safety instrumented function;
- Requirement for proof-test intervals;
- Response time requirement for the sis to bring the process to a safe state;
- The safety integrity level and mode of operation(demand/continuous) for each safety instrumented function;
- A description of SIS process measurements and their trip points;
- Requirements relating to energize or de-energize to trip;
- Requirement for resetting the SIS after a shutdown.
- Maximum allowable spurious trip rate ; as per IEC 61511.