5 why root cause analysis for incident investigations [example included]

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5 why analysis is a technique for finding the root cause of a problem. It is an effective tool for EHS incident investigations where a safety team cannot immediately find the cause of an injury or accident.

Sakichi Toyoda, founder of the Toyota Motor Corporation, developed this technique for solving problems in his manufacturing process.

Toyoda found that by asking “why” five times, he could always find the underlying cause of an issue. This allowed the company to fix process problems for good, making the entire operation more efficient. Over time, Toyota teams used the 5 why root cause analysis technique to become a world leader in vehicle manufacturing.

Today, the “5 Whys” are a staple of the Six Sigma (process improvement) and lean methodologies that supply chain teams all over the world use. But 5 why analysis is also a useful technique that EHS professionals can use for incident investigations. And when it comes to OSHA recordkeeping, you want to make sure you accurately define, describe, and evaluate each workplace incident that happens.

Doing a 5 why analysis

Always start a 5 why root cause analysis by stating the problem that you want to deep dive. Then, proceed to ask yourself “why” the problem exists five times in a row, each time answering with a different root cause. Your answers should start relatively broad and get more specific with each “why.”

Here is an example of what that might look like:

Problem: I threw away twenty dollars’ worth of groceries this week.


  1. Why did I throw away the groceries? Because the groceries were rotten.
  2. Why were the groceries rotten? Because I didn’t use the groceries in time.
  3. Why didn’t I use the groceries in time? Because I forgot that the groceries were in the fridge.
  4. Why did I forget the groceries were in the fridge? Because the groceries were at the back of the shelf.
  5. Why were the groceries at the back of the shelf? Because I don’t have a system for organizing my fridge.
Do a 5 why analysis for injuries, property damage, or process improvements

At the end of this process, you should have a final root cause. Notice in the example that the obvious root cause (that the groceries were rotten) was not actually the primary root cause. A 5 why analysis should challenge you to go past your first assumptions about an issue to find the underlying problem.

EHS professionals can use this technique to address a variety of issues, including:

  • Process hazards
  • Common workplace injuries
  • Accidents
  • Property damage
  • Organizational safety culture

Once you have found the root cause of a problem, you can work on figuring out how to solve it. Sometimes, this may involve changing the process workflow, training module, or 5S. Other times, it may require you to address individual behaviors.

5 why root cause analysis technique

You can use the 5 Whys for workplace incident investigations. This technique is helpful for writing incident reports, especially when the root cause isn’t immediately obvious.

For example, maybe you need to do an injury investigation, but you don’t have any eyewitnesses or video footage. Finding the root cause will then rely on the questions that you ask the injured employee.

Once you have all the background information for the incident, use the 5 why incident investigation technique to figure out the root cause. Remember, your goal is to start with the broadest explanation for an incident and narrow it down to a more specific problem with each “why.”

Here are the basic steps of performing a 5 why incident investigation:

STEP 1: Define the problem. What was the negative result of the workplace incident?

STEP 2: Ask “why” five times to narrow down the root cause.

STEP 3: Decide the root cause once you’re finished asking “why.”

STEP 4: Find a solution to protect employees against the root cause in the future.

Consider this 5 why analysis example that you can use as a reference for your own investigation:

5 why analysis example
When performing a 5 why analysis, it’s important to keep your answers short and simple. You want each answer to only address the issue before it. If you provide too complex an answer, you won’t be able to distill the problem down to a base-level root cause.

Common root causes 

Root causes vary from incident to incident, but there are some common themes to look out for. Ergonomics are one of the biggest causes of manual labor workplace injuries. When workers don’t lift, bend, turn, etc. properly, they are more likely to suffer an injury. These injuries can be sudden or drawn-out from repetition over time. 

Another common root cause is a workplace hazard. An example of a workplace hazard would be a trailer door that doesn’t have a proper seal. This can cause water to leak into the building on rainy days, creating a slippery surface for workers who are loading a truck. 

Your 5 why incident investigation may also uncover a process issue that you need to fix. If, for example, the steps for completing a task compromise workers’ safety, you may need to change the actual workflow. Remember, the goal of a 5 why analysis is to reach the heart of a problem. You must go past the surface to find a root cause that you can address. 

Once you have found the root cause, make sure to track the progress of any action items. Follow up with your proposed solutions if you want to truly decrease the likelihood of the incident happening again. If you need a method for tracking those action items, consider a sitewide EHS incident management software system. It is a great tool for verifying whether your solutions have been implemented and evaluated. 

Monica Kinsey

Monica is a former warehouse operations manager with a passion for workplace safety. Her favorite topics to cover include safety leadership and continuous improvement.
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