Drill Down to the Root Cause to Ensure Worksite Safety After an Incident

Tools such as the fishbone diagram and the 5 Whys technique can help worksite incident investigations identify the root causes of workplace accidents and improve safety protocols.

• By Bobby Albright
• Apr 11, 2024

According to the U.S. Bureau of Labor Statistics, a worker died every 96 minutes from a work-related injury in 2022, a 5.7 percent increase over the previous year.

Worksite fatalities and incidents are preventable. If an incident occurs—including fatalities, injuries or near-misses––a vital step in preventing future incidents is identifying the direct cause, the indirect cause and the root cause during a worksite incident investigation.

The direct cause is the moment of the incident that caused the injury, illness or fatality. That could be exposure to a fume or gas, a caught-in (or between), struck by, or other incident types. The indirect cause is what may have contributed to the incident occurring but is not the primary reason for the incident.

The root cause is the underlying reason why unsafe conditions exist or why a safety procedure was not followed. Effective incident investigators use tools and interview techniques to identify the root causes.

OSHA’s comprehensive incident investigation guide provides information on the full investigative process. The following are useful techniques specific to finding the direct cause, indirect cause and root cause in an accident investigation, which is step three in OSHA’s guide.

Go Fishing

A simple and effective tool used in worksite incident investigation is the fishbone diagram. Fishbone diagrams provide a way to organize evidence collected from the scene and during interviews.

The incident problem is placed at the head of the fish. Possible contributing causes are added on the smaller “bones” listed under categories including management, equipment, process, environment, materials and people. An example of a fishbone diagram is available on the Nevada Safety Consultation and Training Section website.

Using the diagram, investigators can organize facts and information about the incident scene as well as details from witnesses and interviews, while adding subcategories as needed. Within each category, investigators can drill down to identify root causes using the 5 Whys technique explained below.

Ask Why, Then Dig Deeper

The 5 Whys interview technique was developed at Toyota and became popular in the 1970s. Toyota still uses it to solve problems today.

The 5 Whys method is simple. When an incident occurs, investigators drill down to its root cause by asking "why" five times. On occasion, asking “why” three or four times, or maybe 7 or 8 times may be sufficient, but generally, it takes five “whys” to reveal the underlying issue. In addition, during the 5 Whys process, other questions may arise and branch off the main line of questioning that needs to be answered. Make note of this and return to it after completing the current line of questioning. The following is an example scenario regarding the use of the 5 Whys technique in a worksite accident investigation:

Background: You are notified there has been a fatality on site involving an employee crushed by a forklift. After gathering information at the scene, interviewing witnesses and collecting training and maintenance records, you create a timeline of events and begin to drill down through the information with questioning. How should you proceed?

• 1) Ask the first why: “Why did the forklift tip over on the employee?”

Several witnesses stated that while the employee was operating the forklift, he turned sharply and at a high speed on a slightly uneven surface. The forklift tipped over. Witnesses said he was thrown from the seat. You verify the uneven surface at the scene.

• 2) Ask the second why: “Why was the employee thrown from the forklift?”

Witnesses state the employee jumped into the seat to move a forklift parked in the wrong area and he wasn’t wearing a seatbelt. Through inspection and maintenance records review, there was nothing wrong with the seat belt at the time of operation. Training records state he was proficient at operating the forklift. Another line of questioning is revealed: “Why wasn’t the operator wearing his seatbelt?”

• 3) Ask the third why: “Why was the forklift parked in the wrong area?”

In speaking to the forklift operators, this was a newer construction project, and the parking area wasn’t clearly established yet. Some employees parked forklifts where they thought the parking area would be located. Only a few workers knew where the parking area would be established.

• 4) Ask the fourth why: “Why did only some staff know where to park the forklifts?”

The forklift operators said that they hadn’t completed site-specific training yet because their lead forklift operator was gone for the previous two weeks. He planned to give the site-specific training when he returned.

• 5) Ask the fifth why: “Why didn’t another forklift operator or a site manager complete the site-specific training in the absence of the lead forklift operator?”

Upon reading through the forklift safety and training plan, there is no secondary person named in the absence of the competent person/lead forklift operator. The chain of command is stopped with no emergency contingency.

The root cause identified here is that the safety plan must include a secondary person appointed and trained to perform the site-specific job training in the absence of the lead forklift operator. Next, the investigators will repeat the 5 Whys process to find out why the employee did not use the seat belt while operating the forklift.

Citing “human error” as the root cause of an accident is not effective. Oftentimes, failures in training, safety programs and other underlying issues are contributing factors in incidents.

Explore Additional Techniques

The fishbone diagram and 5 Whys tools are not meant to be used exclusively. Ideally, a combination of tools will be used, which may include logic/event trees and timelines. No matter the techniques and tools used, the answers to four essential questions must be answered following an incident:

• What happened?
• How did it happen?
• Why did it happen?
• What needs to be corrected?

Finally, Implement Corrections

Once underlying issues and root causes have been identified, it is essential to create a plan to address and correct safety issues. In the 5 Whys scenario above, the worksite’s management will need to update the safety plan to include a secondary person appointed to perform the site-specific job training in the absence of the lead forklift operator. Additionally, the employees must be notified of the plan’s update.

Employees rely on their employers to provide a safe work environment. The workplace morale and safety culture will deteriorate after an incident if nothing is done to correct safety issues.

With these tools in mind, teams can effectively identify root causes and ensure corrections are addressed to maintain a safe and healthy worksite for everyone.