SRS (Safety Requirement Specification) is a description of the requirements and operation of a SIF(Safety Instrumented Function). This document contains all the essential information for designing the SIF in detail:

• Purpose of the SIF
• General requirements for the SIF
• The required SIL level, determined from a HAZOP/LOPA
• De vereiste mode van de SIF (Low Demand < 1/jaar, High Demand of Continuous Demand)
• The requirements for a manual shutdown.
• The required response time of the total SIF (Sensor - Logic Solver - Final Element), determined from a HAZOP/LOPA study, often in combination with a process engineering calculation (Process Safety Time (PST)). For example, how quickly does the pressure in a distillation column increase when the cooling water pump fails. The reaction time of the SIF must therefore be within the PST.
• The location and function of the sensors and actuators
• Definition of the safe state of the SIF (e.g. feed valve closed or pump stopped)
• Redundancy requirements to meet the SIL level or to increase availability
• Requirements for defining Common Cause Failures.
• Maintenance override functions (MOS, Maintenance Override Switches) or Operational override functions (OOS, Operational Override Switches) to allow, for example, start-up. These are preferably automatic and fall off automatically after a (preferably) short time.
• Leakage class of valves
• Communication with other systems
• Any preferred brands and models of components, for example to stock common spares of critical instrumentation.
• Requirements for the Test Intervals and the required Test Coverage Factors (TCF)
• Requirements related to Energize or De-Energize to trip
• Requirements for resetting after a shutdown (e.g. requirements for manual, semi-automatic, or automatic resetting of the final element after a trip).

SRS

The SIL verification program aeShield can generate an SRS in various formats (depending on the detailing). Format D of the aeShield SRS is fully compliant with IEC 61511 ed.2.