May 9, 2018 | Mark Paradies

Root Cause Analysis Tip: Why Did The Robot Stop? (Comparing 5-Why Results with TapRooT® Root Cause Analysis Results)

Find the Root Cause

I hear people say that 5-Whys is a good root cause analysis system for “simple” incidents. So, I thought I would show a simple incident that was provided as an example by a very experienced 5-Why user and compare it to the analysis that would be performed using TapRooT®.

Taiichi Ohno, the father of the Toyota Production System and the creator of the 5-Why method of root cause analysis, is the source of the example – a robot failure. He used the example to teach employees the 5-Why technique while he was at Toyota. Here is the example as he described it…

1.    Why did the robot stop?

–    The circuit has overloaded, causing a blown fuse.

2.    Why did the circuit overload?

–    There was insufficient lubrication on the bearings, so they locked up.

3.    Why was there insufficient lubrication on the bearings?

–    The oil pump on the robot is not circulating sufficient oil.

4.    Why is the pump not circulating sufficient oil?

–    The pump intake is clogged with metal shavings.

5.    Why is the intake clogged with metal shavings?

–    Because there is no filter on the pump.

For Mr. Ohno, that was the end of the root cause process: Install a filter and get back to work. But this isn’t even the start of the root cause analysis process in TapRooT®.

Let’s look at this incident using TapRooT® and see how 5-Whys compares to the advanced TapRooT® Root Cause Analysis System.

TapRooT® Root Cause Analysis

TapRooT® is more than a tool. It is a systematic process with embedded tools to help an investigator find and fix the root causes of a problem. It starts with either the TapRooT® 5-Step Process for low-to-medium risk incidents or the the TapRooT® 7-Step Process for major investigations. The 5-Step Process is shown below…

To start investigating the problem, one gathers evidence and draws a SnapCharT® (shown below being drawn by a team in a TapRooT® 2-Day Root Cause Analysis Course).

Notice that the 5-Whys that Mr. Ohno asked in the example above turned out to be mainly the sequence of events leading up to the failure in the  SnapCharT® (shown below).

The SnapCharT® makes the example event easier to understand than the 5-Why example above. Plus, the SnapCharT® goes beyond the 5-Whys by indicating that there was no low oil pressure alarm.

In TapRooT®, if the investigator decides that there is more to learn, the investigator continues to collect evidence (grows the SnapCharT®) to expand his/her understanding of what happened. A good TapRooT® Investigator would have several areas to look at.

First, what happened to the filter? Was it forgotten during maintenance or was it never designed into the system?

Next, where did the metal shavings come from? Metal shavings in a lube oil system are unusual. What was the source?

The new information provides a fairly complete understanding of what happened and is shown on the SnapCharT® below.

Notice that in TapRooT®, we complete the collection of evidence about what caused the metal filings and what caused the filter to be missing. These were significant issues that were left out of the 5-Why analysis. This type of omission is common in 5-Why analyses – even when experts apply 5-Whys. Thus the problem isn’t with the investigator or their training – it is embedded in the 5-Why system.

Causal Factors

Once one understands what happened, the third step is to identify the Causal Factors that, if eliminated, would have stopped the accident from occurring or reduced the seriousness of the incident. A simple technique called Safeguard Analysis is used to do this. The four Causal Factors for the Robot Stops incident were identified as:

  1. Mechanic A uses cloth to cover openings in system.
  2. Mechanic A does not report metal shaving contamination.
  3. Mechanic B does not install oil filter.
  4. Operator does not know oil pressure is low.

Where Mr. Ohno only had one root cause, TapRooT® has already identified four Causal Factors. Each of these Causal Factors could have multiple root causes so TapRooT® is already highlighting one of the weaknesses of 5-Whys: that it usually focuses on a single cause and misses additional causes (and the needed corrective actions for those root causes that aren’t identified).

TapRooT® Root Causes

In fourth step of the TapRooT® 5-Step Process, each Causal Factor is analyzed using the Root Cause Tree® to guide the investigator to the Causal Factor’s root causes. The tree is described in detail in the TapRooT® Book (CLICK HERE for info).

For this example, we won’t show the entire analysis of all four Causal Factors using the Root Cause Tree® and Dictionary. For people who would like to know more about the 15-question Human Performance Troubleshooting Guide and the way the tree is used to help investigators find causes beyond their current knowledge, we recommend  attending a 2-Day or 5-Day TapRooT® Course.

However, we will describe the analysis of the Causal Factor “Operator doesn’t know oil pressure is low.”

This starts out on the tree as a Human Performance Difficulty that leads us to the Human Performance Troubleshooting Guide. When asking the 15 Questions, two questions get a “yes” for this Causal Factor and guide us to the Human Engineering, Procedures, and Training Basic Cause Categories on the back side of the Root Cause Tree®.

Copyright © 2015 by System Improvements, Inc.
Used by permission. Duplication prohibited.

In analyzing these categories, no causes are found in the Procedures or Training Basic Cause Categories. However, two root causes are found to be applicable in the Human Engineering Basic Cause Category (above).

Thus, it was determined that if the operator needed an oil pressure display/alarm (displays NI root cause) to make the detection of a problem possible (errors not detectable root cause). If the display/alarm had been present, then the robot could have been stopped and fixed before damage to the bearings had occurred. Thus, the incident would have been made significantly less severe.

The corrective action for these two root causes would be to install a bearing lube oil pressure indicator and a low bearing lube oil pressure alarm to notify the operator of impending equipment problems before the bearing would lock up.

After analyzing just one Causal Factor using the TapRooT® Root Cause Tree® we have found that even an expert like Taiichi Ohno could miss important root causes when using 5-Whys. But there is more. There are still three more Causal Factors to analyze (and then Generic Causes – an optional technique in the 5-Step Process).

Why would you use a root cause tool with known, proven weaknesses? Why would you risk lives, your corporate reputation, and large sums of money on an inferior approach to problem solving? If something is worth fixing, it is worth fixing it right! Learn and apply TapRooT® Advanced Root Cause Analysis to find the real root causes of problems and effectively fix them. Attend an upcoming course to learn more.

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