sil verification

SILcet – Tool for SIL Verification

SILcet tool helps you in calculations and SIL verification tasks of Safety Instrumented Functions (SIF).

  • Both the SILcet tool and the training course have been developed following the recommendations of the IEC-61508 and IEC-61511 Standards for safety functions in the process industry.
  • SILcet is an Excel workbook that uses formulas and macros in Visual Basic.
  • The technical requirements for the use of SILcet are the following: Windows 7, 8, 10, 11 and Excel (version 2013 or later).

What is it for?

  • For calculating the average probability of failure on demand (PFDavg) and the probability of failure per hour (PFH) of the Safety Instrumented Function (SIF), as well as the MTTFS (Mean Time To Fail Spuriously).
  • Calculates the SIL (Safety Integrity Level) of the SIF taking into account the three requirements contemplated in IEC-61508 / IEC-61511 Standards (systematic capability, probability of failure and architectural constraints).
  • The architectural constraints table can be selected according to Route 1H (IEC 61508) or Route 2H (IEC 61508) or IEC 61511 Route (derived from 2H). A different Route can be selected for each element in the SIF.
  • In addition to the SENSOR, LOGIC SOLVER and ACTUATOR subsystems, a fourth subsystem can be added to include in the calculation any other concept (human errors, power system, etc.).

What types of architectures can we use?

  • It allows selecting different architectures for each of the subsystems of the SIF.
  • Low Demand Mode (PFDavg): 1oo1, 1oo2, 2oo2, 1oo2div, 2oo2div, 2oo3, 2oo4, 1oo2D, 2oo4D, 1oo3, 1oo4, 1oo5, 3oo3, 4oo4, 5oo5, 3oo4, 3oo5, 4oo5, 2oo (1oo2), 1oo (2oo2), Nx1oo2, and MooN (for less usual architectures).
  • High Demand Mode (PFH): 1oo1, 1oo2, 2oo2, 1oo2div, 2oo2div, 2oo3, 2oo4, 1oo2D, 2oo4D, 1oo3, 1oo4, 1oo5, 3oo3, 4oo4, 5oo5, 3oo4, 3oo5, 4oo5, Nx1oo2, and MooN (for less usual architectures).
  • It allows to calculate complex configurations combining several groups of architectures (download COMPLEX ARCHITECTURES MANUAL).

What parameters do we need?

  • Failure rates of each SIF element (SD, SU, DD, DU), type of element (A or B) and systematic capability.
  • Cpt (“Coverage of proof tests”), Test Interval (TI), Life Time (LT), Beta Factor for common cause failures, MTTRdd (Mean Time To Restore dangerous detected failures), Start-up Time (Start- up), and selection of how to act in case of a detected dangerous failure (process trip).
  • It allows entering previously calculated values of PFDavg, PFH and MTTFS.
  • Optionally, the calculation of the β factor can be performed for common cause failures according to one of the methodologies recommended in IEC-61508.
  • It allows you to enter the cost of each component to compare the cost of different design alternatives of the SIF.
  • It allows adding other terms that affect the value of PFD and MTTFS, such as when using bypasses.
  • Option: Multiplying factors on the calculation parameters to quantify the effectiveness of SIS maintenance.

User Database

  • The user can create a database with the elements used in the project that include the failure rates, the type of element, the cost, the systematic capability, etc. Since version 6.0 it is possible to read data from an external Excel file for several users to share the same data source.
  • There are 4 databases for the elements of the SENSOR, LOGIC SOLVER, ACTUATOR and OTHERS subsystems.
  • Option to calculate failure rates automatically if transmitter “out of range” diagnostics are implemented in the PLC.

Comparison of Safety Instrumented Functions

  • Comparison of SIL calculations of different SIF designs.
  • Function to perform a rapid test of the sensitivity of the SIF by modifying the main parameters (the macro calculates 12 variants of the same SIF by modifying the TI, Cpt and DU / DD parameters).
  • Macro to generate up to 10 lists of the selected SIFs in order to compare different configurations, for example by introducing different correction factors of the main parameters (failure rates, Cpt, TI, LT, Beta, MTTRdd, Start-up Time).

Report generation

  • It allows to generate three types of reports of up to 70 SIFs (project safety functions). With the same license it is possible to use and save an unlimited number of Excel files, one per project or unit (70 SIFs per file).
  • Option to show in the reports the logical diagram of the architecture of each SIF (download sample report).
  • The tool is in English and the reports can be configured in any language.
  • New sheets «SMRY» and «DEV» to create a quick summary of results and a list of the elements used (download SMRY example and DEV example).
  • New SRS_Tool to create any type of Report.

Other options

  • Calculation of PFDavg when functional tests are performed “online” without stopping the process (example: Partial Valve Stroke Test every 30 days without process shutdown, and Full Valve Stroke Test every 4 years during plant overhaul). The formulas are based on the technical document ISA TR84.00.03.
  • SIL Calculator: easy-to-use option to calculate SIL and MTTFS with 19 architectures and 4 subsystems (sensor, logic solver, 2 x actuator).
  • Calculations for Batch processes.
sil verification


  • Excel Tool “SILcet”
  • User Manual
  • Formulas used in the calculations
  • Installation & Troubleshooting
  • Template in Word with an example of SIL Verification Report (plus Annexes)
  • Excel tool: Beta Factor Calculator
  • Simple Excel tool: “Cpt Calculator”

Training Course (optional):

“Design of SIFs and SIL calculation”, which includes real examples both for the modernization of existing SIS and for the design of new projects. This course is also available online (also a version in spanish).

What`s the best option SILcet or exSILentia?

Read more

Some references used to develop SILcet:

-Standards: IEC 61508:2010, IEC 61511:2016, ISA TR84

-ISA Book: Safety Instrumented System Design

-Exida Book: Final Elements in SIS

Complex Architecture Safety Function
Complex Architecture SIF