Root Cause Analysis Techniques

1. Meaning of Root Cause Analysis

Root Cause Analysis (RCA) is a systematic method used by an organisation to identify the underlying reasons behind an accident, injury, workplace complaint, health problem, quality failure, or other adverse event.

The purpose of RCA is not merely to identify the person who made the immediate mistake. Instead, it asks:

Why did the failure occur, and what organisational or system-level conditions allowed it to occur?

For example, if a worker is injured because a machine guard was missing, a superficial investigation may conclude:

Worker touched moving machine → injury occurred.

A proper RCA goes further:

Why was the guard missing? → Why was the machine operated without it? → Why did inspection not detect the problem? → Why was maintenance delayed? → Was there inadequate supervision, training, risk assessment or safety policy?

Thus, RCA focuses on prevention of recurrence.

In Japan, this approach is particularly relevant to occupational safety and health because employers have statutory and judicial duties concerning worker safety and health. The Industrial Safety and Health Act requires employers to take necessary measures to prevent occupational hazards and health impairment.

2. Objectives of Root Cause Analysis

The major objectives are:

1. Identify the actual cause of an incident.
2. Distinguish immediate causes from underlying causes.
3. Identify failures in management systems.
4. Determine whether the incident was foreseeable or preventable.
5. Identify weaknesses in training and supervision.
6. Examine workplace conditions and equipment.
7. Determine whether policies and procedures were properly implemented.
8. Develop corrective and preventive measures.
9. Prevent recurrence of similar incidents.
10. Create documentary evidence for safety-management improvements.

3. Main Root Cause Analysis Techniques

A. The “5 Whys” Technique

The 5 Whys technique repeatedly asks “Why?” until the underlying cause is identified.

Example

Suppose a worker falls from a platform.

Why did the worker fall?
Because there was no effective guardrail.

Why was there no guardrail?
Because it had been removed during maintenance.

Why was it not replaced?
Because the maintenance work was incomplete.

Why was incomplete maintenance accepted?
Because there was no proper inspection before restarting the machine.

Why was there no inspection?
Because the organisation had inadequate restart procedures and supervision.

The RCA therefore moves from:

Fall → missing guardrail → maintenance failure → inspection failure → management-system failure.

Advantages

• Simple.
• Inexpensive.
• Easy for supervisors and HR/safety teams.
• Useful for workplace accidents.
• Helps avoid blaming the individual worker.

Limitation

Five questions are not necessarily sufficient. Some incidents have multiple independent causes, so investigators should not stop automatically after exactly five questions.

4. Fishbone / Ishikawa Diagram

The Fishbone Diagram, also known as the Ishikawa Diagram, identifies possible causes under different categories.

Common categories include:

• Man/People
• Machine
• Method
• Material
• Measurement
• Environment

For workplace safety, additional categories can include:

• Management
• Training
• Supervision
• Workload
• Communication
• Working hours
• Organisational culture

Example: Workplace Injury

Problem: Worker suffers injury while operating machinery.

Possible causes:

People

• Inadequate training
• Fatigue
• Poor communication

Machine

• Defective guard
• Poor maintenance
• Outdated equipment

Method

• Unsafe operating procedure
• No lockout/tagout procedure
• Inadequate emergency procedure

Environment

• Poor lighting
• Excessive noise
• Crowded workspace

Management

• Inadequate supervision
• Insufficient safety inspections
• Production pressure

This technique is useful because it prevents the investigator from focusing exclusively on employee behaviour.

5. Fault Tree Analysis (FTA)

Fault Tree Analysis starts with an undesirable event and works backward to identify the combination of conditions that could have produced it.

For example:

Top Event:

Serious workplace accident

Possible causes:

Machine failure OR human error OR unsafe environment

Machine failure could involve:

• defective component
• inadequate maintenance
• manufacturing defect

Human error could involve:

• inadequate training
• fatigue
• unclear instructions

Environmental factors could involve:

• inadequate lighting
• excessive temperature
• inadequate workspace

FTA is especially useful for complex technical systems where several causes interact.

6. Event and Causal Factor Analysis

This technique reconstructs the incident chronologically.

Investigators identify:

1. What happened first?
2. What happened next?
3. What conditions existed?
4. What decisions were made?
5. Which controls failed?
6. What finally produced the incident?

Example

Employee assigned excessive workload
↓
Long working hours
↓
Fatigue develops
↓
Warning signs appear
↓
Supervisor fails to intervene
↓
Employee's condition deteriorates
↓
Serious health consequence

This method is particularly useful where the incident developed over a long period rather than occurring because of one sudden event.

The Japanese Supreme Court has recognised the importance of examining the accumulation of excessive fatigue and psychological burden when assessing an employer's duty of care.

7. Barrier Analysis

Barrier Analysis examines the protective measures that should have prevented an incident.

Barriers may be:

• Physical guards
• Warning systems
• Safety procedures
• Training
• Supervision
• PPE
• Medical examinations
• Working-hour controls
• Emergency systems

The investigator asks:

What barriers should have prevented the event?

Then:

Which barriers were absent, inadequate, or bypassed?

Example

Chemical exposure occurs.

Expected barriers:

Proper storage → ventilation → PPE → training → monitoring → emergency response

If several barriers failed, the RCA identifies each failure rather than blaming the employee alone.

8. Change Analysis

Change Analysis compares:

Normal working conditions

with

Conditions existing immediately before the incident.

Investigators ask:

• Was a new machine introduced?
• Was there a change in personnel?
• Was a new supervisor appointed?
• Did workload increase?
• Did working hours change?
• Was a procedure changed?
• Was maintenance postponed?
• Was production increased?

Example

A workplace historically had few accidents. After a new production system was introduced, accidents increased.

RCA may identify:

New production target → increased speed → inadequate training → increased workload → safety controls bypassed → accidents.

9. Pareto Analysis

Pareto Analysis uses incident data to identify the causes responsible for a significant proportion of problems.

For example, an organisation records:

Management can then investigate the causes generating the largest number of incidents.

It is particularly useful for large organisations with substantial incident data.

10. Bow-Tie Analysis

Bow-Tie Analysis combines:

• Threats
• Preventive barriers
• Top event
• Mitigation barriers
• Consequences

Example:

Inadequate machine maintenance
→ Machine failure
→ Worker injury

Preventive barriers:

• Maintenance schedule
• Inspection
• Safety checks

Mitigation barriers:

• Emergency stop
• Protective equipment
• First aid
• Emergency response

This method is useful for analysing both prevention and consequence management.

11. Root Cause Categories

During RCA, investigators should generally examine at least the following categories:

A. Human Factors

• Lack of training
• Fatigue
• Inexperience
• Communication problems
• Excessive workload

B. Equipment

• Defective machinery
• Poor maintenance
• Inadequate safety devices

C. Procedures

• Missing procedures
• Outdated procedures
• Poor implementation
• Failure to follow procedures

D. Management

• Inadequate supervision
• Poor risk assessment
• Production pressure
• Insufficient safety resources

E. Workplace Environment

• Noise
• Heat
• Dust
• Poor ventilation
• Inadequate lighting

F. Organisational Factors

• Safety culture
• Staffing levels
• Working-hour practices
• Reporting systems
• Internal communication

12. RCA in Occupational Health and Mental Health

Root Cause Analysis is not restricted to physical accidents.

It can also be used for:

• Occupational stress
• Mental-health problems
• Burnout
• Long working hours
• Workplace harassment
• Karoshi-related risks
• Return-to-work problems
• Repeated sickness absence

For example:

Mental-health deterioration

Possible contributing factors:

Excessive workload

• long working hours
• insufficient rest
• workplace conflict
• lack of managerial intervention
• failure to respond to warning signs

The Japanese Ministry of Health, Labour and Welfare explains that employers have a safety-consideration obligation under Article 5 of the Labour Contract Act, including responsibilities relating to workers' mental health.

13. Importance of Documentation

A proper RCA report should record:

1. Date and location.
2. Persons involved.
3. Description of incident.
4. Immediate cause.
5. Contributing factors.
6. Root causes.
7. Evidence collected.
8. Interviews conducted.
9. Relevant policies.
10. Training records.
11. Inspection records.
12. Corrective measures.
13. Responsible persons.
14. Implementation deadlines.
15. Follow-up review.

Documentation is important because RCA should result in actual corrective action, not merely a written explanation.

14. Corrective and Preventive Actions

After identifying the root cause, organisations should implement corrective measures.

For example:

The effectiveness of corrective action should subsequently be reviewed.

15. Relevant Japanese Case Laws

The following cases are particularly useful when discussing RCA in the context of occupational safety, health, employer responsibility, foreseeability and organisational failures.

1. Dentsu Case — Supreme Court, March 24, 2000

1998 (O) Nos. 217 & 218

An employee worked prolonged overtime, developed depression and died by suicide. The Supreme Court recognised an employer's duty to take care that an employee's physical and mental health was not harmed by excessive accumulation of fatigue and psychological burden. The Court also considered the employer's knowledge of excessive working hours and deterioration of health.

RCA relevance:
An investigation should examine not merely the employee's final act but the chain involving workload, working hours, managerial knowledge, health deterioration and failure to intervene.

2. Toshiba Case — Supreme Court, March 24, 2014

The case concerned an employee whose health deteriorated after increased work demands and whose requests for workload reduction were not adequately addressed.

RCA relevance:
The case illustrates the importance of examining:

• Workload;
• Employee health information;
• Requests for assistance;
• Management response;
• Working conditions; and
• Preventive intervention.

The Japanese Ministry of Health, Labour and Welfare specifically identifies the Toshiba case in its collection of mental-health employment cases.

3. Asbestos Construction Workers Case — Supreme Court, May 17, 2021

2018 (Ju) No. 1447

The Supreme Court examined governmental regulatory responsibility concerning asbestos exposure at construction sites. The judgment discusses statutory safety and health measures, including ventilation, prevention of hazardous exposure, protective equipment and worker safety education.

RCA relevance:
The case demonstrates why an investigation should examine long-term exposure pathways, preventive controls, workplace conditions, regulatory standards and protective measures, rather than concentrating only on the final injury or disease.

4. Truck Hub / Recall Case — Supreme Court, February 8, 2012

2009 (A) No. 359

A truck accident involved a wheel/tire separating because of damage to a hub. The Court examined whether personnel responsible for quality assurance should have taken improvement measures, including recalls, after earlier information indicated the possibility of a similar defect.

RCA relevance:
This case demonstrates the importance of:

• Previous incident information;
• Defect patterns;
• Risk assessment;
• Internal information;
• Corrective action; and
• Prevention of recurrence.

It is a strong example of why RCA should examine previous warning signals, rather than treating each accident as an isolated event.

5. Local Government Employee / Police Officer Health-Duty Case

The Supreme Court has recognised that an employer's duty of care can require consideration of the circumstances of work comprehensively, including excessive fatigue and psychological burden.

RCA relevance:
The case supports a comprehensive approach rather than examining one isolated action. Investigators may need to consider workload, work environment, management decisions and other surrounding circumstances together.

6. Pneumoconiosis/Asbestos-Exposure Cases

Japanese Supreme Court decisions concerning occupational exposure have examined employers' statutory responsibilities for preventing health impairment, including measures relating to dust, ventilation, protective equipment and safety education.

RCA relevance:
These cases demonstrate the importance of analysing the entire exposure-control system, including engineering controls, PPE, education, monitoring and regulatory compliance.

16. Relationship Between RCA and Employer's Duty of Care

RCA is especially important where an employer has a legal obligation to provide a safe working environment.

The central questions should therefore include:

Was the risk foreseeable?

Was the risk identified?

Were appropriate preventive measures available?

Were those measures actually implemented?

Did management know about warning signs?

Were complaints properly investigated?

Were previous incidents analysed?

Was corrective action taken?

These questions are consistent with the broader Japanese legal approach to employer safety and health responsibilities. The Supreme Court has recognised a duty of care concerning excessive fatigue and psychological burden, while the Industrial Safety and Health Act establishes statutory obligations concerning occupational hazards and health protection.

17. Practical RCA Procedure

A practical investigation can follow these steps:

Step 1 — Define the incident
Clearly identify what happened.

Step 2 — Preserve evidence
Collect photographs, documents, equipment information and relevant records.

Step 3 — Interview witnesses
Obtain accounts from workers, supervisors and managers.

Step 4 — Establish the timeline
Determine what happened before, during and after the event.

Step 5 — Identify immediate causes
Determine the direct physical or behavioural cause.

Step 6 — Identify contributing causes
Examine training, equipment, workload, procedures and environment.

Step 7 — Apply RCA techniques
Use 5 Whys, Fishbone, FTA, Barrier Analysis or other appropriate methods.

Step 8 — Identify root causes
Determine which management or system weaknesses allowed the incident.

Step 9 — Implement corrective measures
Remove or control the identified causes.

Step 10 — Verify effectiveness
Check whether the corrective action actually reduced the risk.

Conclusion

Root Cause Analysis is a preventive management tool, not merely an accident-reporting exercise. Its central purpose is to move from “Who made the mistake?” to “Why did the system allow the mistake or unsafe condition to produce harm?”

The principal techniques include 5 Whys, Fishbone/Ishikawa Analysis, Fault Tree Analysis, Event and Causal Factor Analysis, Barrier Analysis, Change Analysis, Pareto Analysis and Bow-Tie Analysis.

In employment and occupational-safety matters, RCA is particularly valuable because Japanese case law demonstrates the importance of examining workload, fatigue, psychological burden, workplace conditions, management knowledge, preventive measures and organisational systems when determining responsibility and preventing recurrence.