Root Cause Analysis

What is root cause analysis?

Root cause analysis (RCA) is a systematic process of identifying the origin of an incident.


When feeling under the weather, it’s perfectly natural to address any pain or discomfort by some sort of first aid treatment or a superficial remedy. However, if you consult a medical professional, then the approach might be a little more thorough. You might find yourself being asked a series of specific questions about your condition and might even go through some laboratory tests to get to the source of your illness.

The same is true for plant and maintenance incidents. While an immediate response is usually required, there is always value in performing a systematic analysis of possible root causes.

RCA is the process that aims to identify the cause of a particular event. In the plant setting, this event usually refers to any potential problems that will disrupt standard operations. At a very high level the usual suspects (i.e. usual causes of problems) can be categorized as:

  • technical issues affecting physical parts
  • human causes, or when an assigned individual does not perform a task correctly
  • system causes, or lapses in processes

The general process of RCA requires you to describe what happened, why and how it happened, and what steps are needed to prevent the same event from happening in the future. The process can get very complex depending on the situation. Thankfully, some common methods were developed to aid in identifying the root cause.

Common methods used in RCA

5 Whys

The name of the method pretty much explains the steps: Ask why and ask it again. Asking “Why?” five times usually gets to the bottom of the problem, but don’t let the name stop you from asking more times. The idea is to drill down to the details of an event until you are left with the actual root cause.

An example involving a faulty mixer subjected to 5 Whys is shown below.

Fault tree analysis

A more visual method to determine root causes is by using a fault tree diagram. A fault tree diagram starts by having the problem at the topmost block. The immediate causes preceding the problem event are listed, then they branch out to form the second layer of the diagram. Each immediate cause branches out to its own prior causes. This process is continued until the most basic events are identified, which then become your potential root causes.

The same mixer can resemble the following fault tree diagram:

Fishbone diagram (aka Ishikawa diagram)

Another visual method to identify root causes is by using a fishbone diagram (also known as an Ishikawa diagram, named after its creator Kaoru Ishikawa). It starts by specifying the problem on the rightmost part of the diagram. The factors contributing to the main problem are then listed as categories. Specific causes under each category are then listed down to identify the source of the problem.

As a general guide, the following categories are used as starting points:

  • Environmental
  • People
  • Equipment/material
  • Procedures

Applying these basing categories as a starting point, the mixer problem can be translated into a fishbone diagram.

Implementing RCA

While RCA methods are very common and well-known to the maintenance community, there can be challenges to making RCA thrive.

The first step to mastering this process is knowing the methods that are available to conduct RCAs. The next steps are setting the proper mindset and improving the quality of execution to drive the initiative toward success.

Keep in mind the importance of collecting data accurately and involving the correct groups to analyze that data. To implement RCA effectively, it should be a repeatable process that is collaboratively executed by the group.


RCA is a powerful process that enables the organization to identify the source of a problem. Performing RCA processes effectively can significantly improve a plant’s performance by implementing correct solutions that last.