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:
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).
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.
"Focus on occupational safety in the prevention of process safety incidents is misleading at best and catastrophic at worst".