SIL Verification Overview

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

Device

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
  • ?DDThe dangerous detected failure rate
  • ?DUThe dangerous undetected failure rate
  • ?SThe safe failure rate
  • Safe Failure Fraction (SFF) – The sum of safe and dangerous detected failures divided by the total failure rate, used when calculating Max SIL Architecture using IEC 61508 Route 1H
  • 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, used when calculating Max SIL Architecture using IEC 61508 Route 1H
  • Max Architectural SIL – The maximum architectural SIL that can be claimed for the device in a simplex (i.e. 1oo1) configuration
  • Base Response Time ? Used in the estimation of the achieved response time versus the process safety time
  • Base HFT ? Inherent Hardware Fault Tolerance of the device, used when calculating Max SIL Architecture using IEC 61511 method

?Element

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

Requires the following data:

  • Tag – Unique identifier (e.g. TIC-1001)
  • Justification ? Optional field for a tag description or further information
  • 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
  • Location ? set the location of the Device within the Site Structure.? Elements are filtered to the same location within the Site Structure when adding Branches.

Channel

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.
  • ? Factor – Only required for voting configurations with redundancies i.e. 1oo2, 2oo3 etc.

Branch

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