Why We’re Technically the Best: Key Takeaways From Our Latest Webinar

In our most recent webinar, I had the pleasure of joining forces with two of my brilliant colleagues, David Wiseman and Rachel Evans, to explore a bold but accurate topic: why our tools stand at the top of the market from a technical perspective.

It’s a big claim, sure. But after years of guiding thousands of evaluations, helping customers compare options, and watching technology evolve, we've developed a deep understanding of what real-world engineering teams need, and how to build software that genuinely supports them.

Below is a recap of the session, including the concepts David demonstrated and answers to some excellent questions we received during the live event.

Experience That Shapes the Tools

Our team has collectively spent decades helping engineers evaluate Fault Tree Plus and our Reliability Workbench suite. Through that work, we've seen just about every scenario, requirement, constraint, and head-scratcher imaginable.

This history gives us something rare:
A wide-angle view of how people are actually doing fault tree analysis, not only how they theoretically should. That perspective directly shapes our features, our UI decisions, and our roadmap. It’s one reason we confidently say our tools are built on deep technical insight, not buzzwords or guesswork.

Highlights From David’s Technical Demonstration

David walked through several advanced capabilities in Fault Tree Plus that help engineers analyze complex systems with flexibility and precision.

1. Partial Analysis – Because Sometimes You Only Want the Essentials

Instead of recalculating an entire fault tree, you can choose specific gates and run analysis only on those. This is especially valuable for massive models where waiting for full-tree calculations feels like waiting for a tax refund.

Engineers can select:

• Two gates

• Ten gates

• Or any custom grouping

…run the partial analysis and get instant insights into just the portions that matter.

2. Sensitivity Analysis – Understanding the Impact of Change

One attendee asked if sensitivity analysis can adjust repair times using fixed numeric values rather than percentages.

• Sensitivity uses multipliers, not absolute increments.

• You can define values (e.g., 5 steps), and the tool applies multipliers such as 0.01, 0.11, 1.01, and so on.

• This applies to failure rates, repair rates, and repair times.

A practical example:
If you're evaluating a safety mechanism that checks for faults every few milliseconds, you can increase or decrease the test interval and instantly see the effect on system availability. This feature also works beautifully for manual inspections in process safety systems.

3. Understanding the Rare Approximation in Importance Analysis

Another great question touched on the difference between the Rare approximation option in custom calculation settings and the “Use Rare Approximation” checkbox under Importance calculations.

Here’s the short version David explained:

• Importance metrics (such as Fussell-Vesely) require calculating the top event probability multiple times.

• Without approximation, the tool might have to perform full fault tree calculations two or three times, which gets costly for large trees.

• The Rare approximation speeds this up by estimating these recalculated results without performing the entire computation again.

For most fault trees, this approximation still delivers highly reliable insight while dramatically cutting computation time.

Your Participation Keeps These Webinars Valuable

We had a big turnout again, thank you to everyone who joined live and asked such thoughtful questions. These sessions have grown in popularity, and we truly appreciate the engagement.

Until next time,
Jeremy

VP America's Business Development

http://www.isograph.com

jeremy.hynek@peakavenue.com

Q&A from the webinar:

How can the following problem be solved: I have a CCF below a modularized gate, but i cannot NOT modularize the gate, because i need the gate multiple times (x20), so I´m using the option "Quantity" (which is only available, if the gate is modularized)	There is no way to have a CCF shared across multiple, modularized gates. However, there could be a workaround if the CCF is sufficient to fail the gate on its own. Place the modularised gate beneath an OR gate along with an event to represent the CCF. This CCF may be copied to other, similar OR gates above the other modularised gets in the tree. Give the CCF event failure parameters consistent with the calculated probability of the CCF model.
Hi, can we say that Fault tree analysis is better than RBD analysis	To some extent it depends on the application, as RBD is often considered more intuitive for system availability analyses, especially where process is concerned. However, FTA does have more comprehensive logic. For example, it is better able to handle sequencing and NOT logic with gates like NOT, XOR and PAND.
How does the Cross Product Calculation differ from Esary-Proschan's Min Cut Upper Bound calculation?	The cross product is a method that is based on the addition law of probability, whereas the Esary Proschan (EP) is based on the product law. In the latter case, the program works out the probability of each cut NOT happening (1-cut set prob) and multiplies the value to get the probablity og no cut sets occuring. This is then subtracted from 1 to get the probability that at least one set happens. However, the key difference is that the cross product includes a step to remove repeated events from the product terms using Boolean algebra, thus accounting for dependency between sets. EP does not have this step, which is why it can drift above the correct answer for trees with events that appear in multiple sets.
Hi ! Is that possible (or do you plan to make it possible) to get a feature to identify in which top level fault tree contributes each basic event (and at which order)? (for example: SELV_JAMMED_CLOSED => TP1_FAULT_TREE (order 1), TP3_FAULT_TREE (order 4), …	This may be covered by the Appearance data. Open the results summary and select a TOP gate. Select the Appearance option in the middle of the dialog. This window will list all the events that contribute to the selected gate, how many sets it appears in, and of what order. This data can be exported to a CSV file for further analysis.
Under the approximation custom options one of the options is the rare approximation as discussed.  On the Calculation tab of the project properties dialog there is a check box labeled “Use rare approximation” under “Importance calculations”.  What is the difference between these?	Many importance measures, such as Fussel Vessely and Birnbaum, require the program to essentially recalculate the gate probability, either using adjusted imports or after concelling some terms. By selecting the Rare approx for importance it speeds up these calculations. Some accuracy is lost, but this is not the priority for importtance. Instead, what matters is the relative value for each event.
Does Isograph perform RBD modeling of software systems distributed in multi-region and multi-AZ deployment patterns? The determination of this will be essential in making the adoption decision of Isograph. Furthermore, could you please organize a workshop on RBD modeling?	We have users who model computer systems and data centres using RBD. We have 2 RBD modelling tools depending on requirements. The RBD tool in Reliability Workbench uses Boolean and probability analysis (similar to FTA) whereas the RBD tool in Availability Workbench uses (Monte Carlo simulation, which is useful for modelling complex maintenance strategies, etc. We can look into providing a similar webinar or workshop for these tools, too!
Can Sensitivity be used to increase the repair times by a number rather than a percentage? I am thinking about the impact that mobilization times may have in the overall availability of a system.	It is not possible to adjust MTTR or repair rate to an absolute value, though it is not adjusted to/by a % either. The adjustment factors are multiplicative, so it should be possible to choose the repair values you want to try by selecting the multiplying factors accordingly.
Can you show how we can have separated subtrees, that we evaluate separately and then add / link to a larger system tree?	Individual gates may be analysed separately of the rest of the tree by checking the partial analysis box in the gate properties and selecting Perform Partial Analysis in the Analysis menu. In Reliability Workbench, it is not possible to feed this result to a tree in a different project file, though it can be appended to another tree using the append facility. However, the PeakAvenue platform will allow users to link one tree to another so that results are passed on for further analysis.
But can we import partial analysis in different larger trees? For instance I might have a upper system, but implementing different version of an equipment, so I would have a FTA for each version of that equipment	See above. Trees can be appended, but for a 'true link' this will be implemented in the PeakAvenue Platform.
Can we import data from FIDES analysis ?	Yes. It is possible to licence the FIDES handbook in the Prediction part of Reliability Workbenh and pass calculated failure rates to a FTA.
FIDES is available in the RWB Prediction module.
Are these .rwb files available to download so we can poke around in them ourselves?	The files used in this webinar are supplied with the Reliability Workbench installation. If you download and install the demo version you will find the FaultTreeReactor.rwb file in the Projects directory.
Was the Fussell-Vesely bar graph created with the Isograph reports tool? Have there been webinars presented on use of the parts library and creation of reports?	The FV plot is from the plot view of Reliability Workbench. Select the Plot button above the diagram. Then, select Importance from the menu to the right of the buttons. Click the Plot Options button and select a gate for the plot then click OK. Future webinars may cover these topics, though I believe there is an instructional video on reports on the Isograph Software YouTube channel.