How to Conduct a Root Cause Analysis of Workplace Accidents

• Root cause analysis helps you identify the underlying reasons behind an accident.
• Keep asking “why” until you uncover the real cause, not just the surface issue.
• A good accident investigation should result in corrective actions that are specific, practical and directly address the root cause.

Root cause analysis (RCA) is a systematic method for identifying the underlying cause of a problem. In workplace safety, it can help you determine exactly why an accident happened.

With this knowledge, you can prevent it from repeating.

Workplace accidents rarely result from a single mistake – and they are not purely a matter of chance.

While there is often an element of luck in how events unfold, every accident occurs within a broader set of conditions. Poor communication, unclear procedures, missing safeguards or inadequate training may all play a role.

Root cause analysis helps uncover the underlying factors that created the conditions for the accident to happen in the first place. Without it, investigations tend to focus on surface-level causes, leading to quick fixes that don’t prevent the accident from recurring.

You should carry out an RCA after a significant work-related accident or near miss.

(Near misses involve the same underlying conditions as serious accidents, but with one key difference: someone was lucky enough to avoid harm.)

By investigating what went wrong and why, you can uncover hidden risks and fix the systems or behaviours that created them.

In the UK, there’s no explicit legal duty to investigate work-related accidents. However, the law is clear: employers must take steps to protect their workers from harm.

The Health and Safety at Work etc. Act 1974 requires employers to ensure, so far as is reasonably practicable, the health, safety and welfare of their employees. This includes identifying potential hazards and implementing measures to mitigate risks.

The Management of Health and Safety at Work Regulations 1999 add to this overarching duty. They require employers to assess workplace risks and take preventive action.

Although root cause analysis is used after an accident, it can be used to prevent further harm. This is why the Health and Safety Executive (HSE) strongly recommends investigating accidents and near misses as part of an effective safety management system.

Your first priority is safety. Secure the area and provide medical assistance if needed. Stop nearby work and restrict access to the scene to prevent further harm.

Once the situation is under control, begin recording what is happening in real time. Keep a log of every action and observation made after the incident. This running record is especially useful in complex cases that may unfold over several days.

Report the incident as soon as possible:

• Notify the relevant supervisor and health and safety officer
• Record the date, time and exact location of the event
• Begin collecting evidence (e.g. photographs, videos, equipment damage, site conditions)
• Start logging key decisions and observations in a safety diary

Early reporting ensures nothing is overlooked and that evidence is preserved for the investigation.

Collect all relevant evidence to build a clear understanding of what happened and why. This includes:

• Scene Examination: Document the scene with photographs or sketches, noting the positions of equipment, materials and any environmental factors, such as lighting or noise.
• Documentation Review: Examine relevant records such as:
  • Risk assessments
  • Method statements
  • Training and competency records
  • Maintenance logs
  • Standard operating procedures
• Equipment Inspection: Check for faults, misuse or lack of maintenance. Was the equipment in safe working order and used as intended?
• Data Collection: Reconstruct the sequence of events by gathering available data, such as CCTV footage or access logs.

While not all investigations require a full team, the HSE recommends involving multiple people when analysing complex or serious accidents. Diverse skills and perspectives will help you understand the different technical, procedural and human factors involved in the event.

Your team might include:

• A safety officer or manager
• Someone familiar with the job or equipment involved
• A worker or union representative
• Someone not directly involved in the event

That last point may seem counterintuitive, but an outside perspective is valuable. Someone detached from the accident is more likely to ask the “obvious” questions that others might overlook due to routine, bias or overfamiliarity.

Interviewing witnesses is essential for understanding how the accident unfolded.

• Preparation: Conduct interviews while memories are fresh. Choose a quiet, private space to encourage open communication. Don’t interview witnesses together, or they may take cues from each other.
• Establish Rapport: Explain that the aim is to learn from the accident and prevent it from happening again, not to assign blame.
• Questioning Technique: Use open-ended questions to encourage detailed responses. For example:
  • “Can you describe what you saw?”
  • “Was anything different that day?”
    
• Active Listening: Pay close attention to the witness’s account. Ask for clarification without leading the witness. For example, don’t ask “So the machine was faulty, wasn’t it?” Reframe it as “What did you mean when you said it was ‘acting strangely’?”
• Documentation: Record the interview accurately, either through detailed notes or audio recordings (with consent).

Create a clear timeline of events using the information you gathered. Show what happened before, during and after the accident. This helps you understand where things went wrong.

Ask:

• What was happening at the time?
• Who was involved?
• What tasks were being carried out?
• What were the conditions (weather, lighting, noise)?

Use visual tools like flowcharts or diagrams to map cause-and-effect relationships and make sense of complex scenarios.

This is the most critical step – identifying the underlying cause. You need to learn not just what went wrong but why it went wrong.

Use a structured approach like the “5 Whys” to get to the root cause. For example:

• What happened? A worker slipped and fell
• Why? The floor was wet, and no wet floor sign was placed.
• Why? A wet floor sign was not available
• Why? There is a limited number of wet floor signs
• Why? No one is accountable for ordering them.
• Why? There is no formal system for monitoring and replenishing basic safety supplies.

In this example, the final “why” points to a system-level Failure. You may need to continue asking “why” when investigating more complex incidents, but five is often enough to get to the root cause.

Common root causes in workplace safety often involve gaps in how work is planned or managed. These can include a lack of proper training, poor supervision, unclear communication, unsafe ways of working or missing safety measures like guards, signs or barriers.

If you’re reading this, you likely already understand how important a thorough accident investigation is – but recognising its value is only the first step.

Our online Accident Investigation course introduces the principles of effective investigation, including how to conduct a root cause analysis.

Whether you’re new to investigations or want to strengthen existing processes, this course helps you lead investigations that produce meaningful safety improvements.