SIL Verification Overview

Definitions of terms used in the SIL Verfication module of SIL Comp® and in the SIL Verification guides.


The physical item, for example a pump, temperature indicator or Logic Solver.

Requires the following data:

  • Subsystem – Determines if the device is a Sensor, Logic Solver or Final Element
  • Category – Is the device a temperature indicator, pump, valve etc.
  • Manufacturer
  • Description
  • Dangerous Failure Mode – Outlines what will cause a dangerous failure e.g. valve failing closed or temperature sensor failing high
  • λDDThe dangerous detected failure rate
  • λDUThe dangerous undetected failure rate
  • λSThe safe failure rate
  • Safe Failure Fraction (SFF) – The sum of safe and dangerous detected failures divided by the total failure rate
  • Source – The source from which the data comes from e.g. Exida certificate
  • Source Short – A short form of the Source
  • Type – Used for architectural SIL calculations, devices can be either Type A or B
  • Max Architectural SIL – The maximum architectural SIL that can be claimed for the device in a simplex (i.e. 1oo1) configuration


The device with additional data that is required in the PFD/PFH calculations.

Requires the following data:

  • Tag – Unique identifier (e.g. TIC-1001).
  • Mean Repair Time– How long it takes to repair the device when a fault is found
  • Proof Test Coverage – The percentage of dangerous failures that are revealed during a proof test
  • Proof Test Interval – How often the proof test is conducted
  • Periodic Automatic Testing Coverage – The percentage of dangerous failures that are revealed during periodic automatic testing (also referred to as Partial Stroke Testing)
  • Periodic Automatic Testing Interval – How often the periodic automatic testing is conducted


Consists of one or more elements that combine to make up sections of the SIF being analysed.

Requires the following data:

  • Dangerous Failure Mode – Selected from the Dangerous Failure Modes of the devices that make up the element being selected
  • Voting Type – The voting configuration in use i.e. 1oo1, 1oo2, 2oo3 etc.
  • β Factor – Only required for voting configurations with redundancies i.e. 1oo2, 2oo3 etc.


The complete Sensor, Logic Solver or Final Element subsystem that consists of defined channels.