November 20, 2022 | Mark Paradies

Apparent Cause Evaluation (ACE) – What is an ACE?

What is an ACE?

First, for those not in the nuclear industry … an ACE is an Apparent Cause Evaluation.

In the nuclear industry, management promotes official reporting of ALL problems. The result? Many problem reports don’t deserve a full root cause analysis (like those performed in major investigations). Some don’t deserve any evaluation or corrective actions.

How to Perform an Apparent Cause Evaluation

So how do nuclear industry professionals perform an ACE?

There is no standard method. But many facilities use the following “system” for the evaluation:

  1. Don’t waste a lot of time performing the evaluation.
  2. Make your best guess as to the cause.
  3. Develop a simple corrective action.
  4. Submit the evaluation for approval and add the corrective actions to the tracking and prioritization system.

That’s it.

How does that work? Not so good. Read about our opinion of the results here:

The Curse of Apparent Cause Analysis

The article was updated in 2022, but the opinions didn’t change much.

By the way, an ACE and an Apparent Cause Analysis are pretty much the same.

Better Process for Performing an Apparent Cause Evaluation

So what do we recommend for simple incidents that don’t get a full investigation (a full investigation is described in Using TapRooT® Root Cause Analysis for Major Investigations)? We describe the process fully in:

Using the Essential TapRooT® Techniques to Investigate Low-to-Medium Risk Incidents

Book 3

You could purchase the whole 10-book set at:

Here’s a flow chart of the process for simple investigations…

Simple TapRooT® 5-Step Process


We believe this is the minimum process for any investigation that will recommend corrective actions. Why? Because for all investigations, you need to find out what REALLY happened. Then you make an important decision …

Is there anything worth learning here?

Many investigations will stop here. There is nothing worth spending more time investigating OR FIXING.

The example in Book 3 is someone falling while walking on a sidewalk.

If you decide there IS more to learn, then a simplified TapRooT® Process is used.

This process includes identifying Causal Factors, finding their root causes using the Root Cause Tree® Diagram, and developing fixes using the Corrective Action Helper® Guide.

That’s it. No Generic Cause Analysis and no fixing Generic Causes.

Learn More About the New Way to Perform an Apparent Cause Analysis

Want to learn more? Read the book.

Or attend one of our 2-Day TapRooT® Root Cause Analysis Courses or our Virtual 3-Day TapRooT® Root Cause Analysis Courses. See the upcoming public course dates HERE.

Root Cause Analysis, Root Cause Analysis Tips
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