April 20, 2022 | Mark Paradies

Extent of Cause … Extent of Condition

Just How Similar is Similar?

In the nuclear industry, the terms “extent of cause” and “extent of condition” are often used and misused because of misunderstanding “similar.”

Therefore, I will define each of the “extents” and then provide an example from the wind turbine industry.

But this article isn’t just for nuclear professionals. Everyone should understand the concepts of extent of condition and extent of cause. So, read on for more information and an example from the renewable power industry.

Extent of Condition

What is the definition of EXTENT OF CONDITION. My definition of extent of condition is:


Extent of condition evaluations are usually done soon after an accident/incident to decide if additional immediate actions are needed to address the risk of additional failures while a root cause analysis is being conducted.

Usually, extent of condition looks for similar equipment-related conditions. For example, if a bearing fails, are similar bearings used in similar circumstances or equipment that could also fail?

Extent of condition can also be applied to human error-related Causal Factors. For example, if a valve is opened accidentally, are there similar valves that might be opened accidentally?

The trick to performing an extent of condition evaluation is to decide how “similar” the condition/Causal Factor has to be. For example, on the equipment side, does the bearing have to be the identical type in exactly the same service? Evaluating this “sameness” will be a matter of engineering judgment and the risk presented by additional failures before a complete root cause analysis and corrective actions are completed.

Extent of Cause

My definition of extent of cause is:


Once again, the part of this evaluation that requires judgment is …

“How similar is similar?”

Extent of cause is usually performed after the specific root causes are identified for a set of Causal Factors that led to an incident/accident. The extent of cause is used to decide if a specific root cause needs to be analyzed to find the Generic Causes behind the specific root causes. This can lead to more extensive corrective actions.

Real-World Example of Extent of Cause/Condition

Let’s look at a real example from the wind turbine industry to help illustrate these definitions and their use. This example is outlined in a story in Wind Power Monthly at THIS LINK.

In this example, a turbine blade failed in service. Before the root cause analysis was finished, another turbine blade of the exact type (B53) failed under very similar circumstances.

The obvious question at this point is … how extensive is the application of the B53 blade? It was found that 700 wind turbines (mostly in the US) used that blade. The manufacturer then asked users to curtail the use of the affected turbines. That’s an extent of condition temporary corrective action.

The “extent of condition” in this case was limited to just the B53 blade because two of those blades had failed. However, one might ask if the manufacturer should have looked at other blades as well. Could the problem (adhesive bond failure at the attachment point for the blade) have affected other types of blades?

This example demonstrates the judgment that must be used when deciding how far is far enough when performing an extent of condition evaluation. At first, no extent of cause was considered. But when the second blade broke, an extent of condition temporary corrective action (not using turbines with this type of blade) was implemented. Perhaps if a blade of a different type had failed due to a similar condition, the temporary corrective action might have been expanded to all blades using similar technologies (perhaps beyond the B53 type).

The risk of failure (a blade falling off) was real (injury of someone being struck or property damage) but was decided to be fairly limited. Perhaps in some other industries (for example, the nuclear industry), the sensitivity to regulatory and press reaction would lead to an immediate extent of condition evaluation and an even more extensive temporary corrective action. It is all in the judgment of the evaluator and management team and their risk tolerance.

The root cause analysis of the two failures showed manufacturing problems with that particular blade type. This made the extent of cause analysis fairly easy to perform in that the manufacturing process for this type of blade was fairly unique. Thus, the corrective actions included inspections of B53 blades and repairs to any found to be delaminating because of the specific causes that had been identified.

Also, the generic corrective actions included additional safeguards in the manufacturing process to prevent future failures and an additional safeguard for current and future blades of this type to ensure the elimination of future failures. This demonstrates how extent of cause can be used to help develop corrective actions for Generic Causes.

Learn More About Root Cause Analysis

Would you like to learn more about root cause analysis and preventing failures? Then attend our 5-Day TapRooT® Advanced Root Cause Analysis Team Leader Training to learn the TapRooT® method for identifying and correcting root and generic causes. See this link for upcoming course dates around the world:


Or contact us by CLICKING HERE to schedule training at your site.

Equipment Reliability / Equifactor®, Root Cause Analysis Tips
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