---
title: "Calculating SIF Achieved PFD and Verifying Integrity"
slug: "calculate-sif-pfd-and-verifying-integrity"
updated: 2026-10-27T23:12:24Z
published: 2026-10-27T23:12:24Z
canonical: "ims-handbook.cenosco.com/calculate-sif-pfd-and-verifying-integrity"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://ims-handbook.cenosco.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Calculating SIF Achieved PFD and Verifying Integrity

You need to verify that the Achieved PFD is less than the Target PFD.

(The Target PFD is normally [calculated during the LOPA Assessment](/v414/docs/calculating-the-sif-analysis-target-pfd-1), but if not connected to a LOPA it could also be a static value that you [enter on the SIF Analysis General Tab](/v414/docs/general-tab#assessment-summary).)

When you click **Calculate PFD![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/image-1660660586119.png?sv=2026-02-06&spr=https&st=2026-10-28T16%3A00%3A53Z&se=2026-10-28T17%3A00%3A53Z&sr=c&sp=r&sig=qlI4ogs2u2WUNJZMfaCRxX%2FfQEoM9w4zayu5EeCfYcM%3D)**in the Approval Area IMS calculates the (90% upper limit of the) Achieved PFD. And then compares this with the Target PFD. The design is deemed to be OK if the 90% upper limit of the Achieved PFD is less than the Target PFD. If this is true a green checkmark will show next to the Achieved PFD.![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(405).png?sv=2026-02-06&spr=https&st=2026-10-28T16%3A00%3A53Z&se=2026-10-28T17%3A00%3A53Z&sr=c&sp=r&sig=qlI4ogs2u2WUNJZMfaCRxX%2FfQEoM9w4zayu5EeCfYcM%3D)The 90% upper limit of the Achieved PFD is less than the Target PFD, thus a green checkmark shows.

Take note that if you have selected **Continuous** (rather than **Demand**) mode in the [Assessment Summary on the General Tab](/v414/docs/general-tab#assessment-summary) then you will be verifying the DFR (Dangerous Failure Rate), rather than the PFD.

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(406).png?sv=2026-02-06&spr=https&st=2026-10-28T16%3A00%3A53Z&se=2026-10-28T17%3A00%3A53Z&sr=c&sp=r&sig=qlI4ogs2u2WUNJZMfaCRxX%2FfQEoM9w4zayu5EeCfYcM%3D)DFR will show, when you selected Continuous in the Assessment Summary.

The **Calculate PFD** button also checks the hardware [Fault Tolerance](/v414/docs/verifying-sif-design-dangerous-fault-tolerance-requirements) on the SIF Design. The result will be shown by the Subsystem's Fault Tolerance indicator. If there is a problem with the SIF hardware Fault Tolerance, concerning the SIL, the Subsystem Fault Tolerance indicator will turn red. From a methodology and design perspective, this may imply that, in such a case, additional hardware must be added to the SIF design, or the SIL of the SIF must be reduced.

SIF Analysis PFDs can also be batch calculated - see [SIF Analysis Main Screen](/docs/listing-sif-analyses-the-overview-grid#batch-pfd-calculations).