Accident and incident investigations provide valuable insights into how workplace accidents occur, helping organisations strengthen control measures, improve working practices and reduce future risk.
In this guide, we discuss how to conduct effective accident and incident investigations, identify immediate and underlying causes, and document findings that support continual improvement in workplace accident prevention.
What is the purpose of accident investigations?
Investigating accidents helps to ensure similar events don’t happen again. These are the key accident investigation questions to ask:
- What happened? Establish the sequence of events, including who was involved, where the incident occurred, what activities were taking place and how the incident unfolded.
- Why did it happen? Identify the immediate cause as well as the underlying organisational, procedural, environmental and human factors that contributed to the incident.
- Which control measures failed? Determine whether risk assessments, safe systems of work, supervision, training, maintenance or engineering controls were suitable, adequately implemented and followed in practice.
- Could it happen again? Assess whether similar hazards or weaknesses exist elsewhere in the organisation and whether the same incident could occur under comparable circumstances.
- What needs to change to prevent recurrence? Identify specific corrective actions, assign clear responsibilities, set realistic timescales and monitor whether the actions have been effective. The findings should be shared with teams so lessons can be learned.
When should a workplace accident investigation begin?
A workplace accident investigation should begin as soon as possible once any injured people have received medical attention and the area has been made safe.
Although there is no legal time limit for investigating a workplace accident, Health and Safety Executive (HSE) guidance recommends beginning the investigation straight away, or as soon as practicable, so evidence can be preserved and witness recollections remain accurate.
Early priorities should be to:
- Secure the scene. Prevent unnecessary disturbance while ensuring the area is safe and further harm is prevented.
- Preserve evidence. Record the scene before work resumes or equipment is moved, repaired or cleaned.
- Identify witnesses. Note who saw the incident or arrived immediately afterwards so their accounts can be obtained promptly.
What evidence should be collected during an accident investigation?
Every source of evidence provides a different perspective on the incident, so it is important to gather a range.
Interview witnesses promptly
Speak to witnesses as soon as possible while events are still fresh in their minds. Interview each person separately to avoid their recollections being influenced by others.
Ask open questions that encourage them to describe what they saw rather than confirm assumptions. Record factual accounts in their own words wherever possible.
Photograph and record the scene
Take photographs from multiple angles before the scene changes.
Capture the wider area as well as close-ups of equipment, vehicles, warning signs, PPE, spillages, damage and anything else that may have contributed to the incident. If available, secure CCTV footage promptly before it is overwritten.
Review relevant documents
Gather the documents that governed the work being carried out, including risk assessments, safe systems of work, permits to work and method statements. Compare what should have happened with what happened to identify gaps between procedures and practice.
Check maintenance and inspection records
Review inspection schedules, maintenance logs, defect reports and repair records for any equipment involved. Look for overdue inspections, recurring faults or previous defects that may have contributed to the incident.
Confirm training and competence
Check whether those involved had received appropriate training, instruction and supervision for the task. Training records should be considered alongside evidence of competence, experience and familiarity with the work, rather than treated as proof that the task was being carried out safely.
Examine the equipment involved
Inspect the equipment, tools or machinery involved in the incident and compare their condition with the manufacturer’s instructions and maintenance requirements. Where appropriate, isolate the equipment until it has been examined to prevent further use affecting the investigation.
Look for previous incidents
Review previous accident, incident and near miss reports to identify recurring hazards or trends. If similar events have happened before, consider whether earlier corrective actions were fully implemented and whether they were effective.
Corroborate the evidence
Avoid relying on a single source of information. Compare witness statements with photographs, CCTV footage, maintenance records and other evidence to build an accurate picture of what happened. Where evidence conflicts, investigate the reasons rather than making assumptions.
How do you identify the immediate and underlying causes of an accident?
Effective accident investigation looks beyond the immediate cause to identify the underlying factors that allowed the incident to occur. While the immediate cause explains what happened, the root causes explain why it happened.
An immediate cause is the event or condition that directly resulted in the accident, such as a wet floor or a pedestrian stepping into the path of a moving vehicle.
The underlying causes are the failures that enabled unsafe conditions to exist, such as inadequate maintenance, poor housekeeping, ineffective supervision, insufficient training or an unsuitable risk assessment.
For example:
| Investigation stage | Slip, trip or fall | Workplace transport |
| Incident | Employee slips in a warehouse. | Forklift narrowly strikes a pedestrian in a loading area. |
| Immediate cause | Wet floor. | Forklift and pedestrian entered the same area at the same time. |
| Underlying causes | Leaking pipe, missed workplace inspections, ineffective housekeeping procedures and no system for reporting hazards. | Poor traffic management, inadequate segregation of pedestrians and vehicles, restricted visibility and insufficient driver supervision. |
| Corrective actions | Repair the leak, improve inspection and housekeeping procedures, introduce a hazard reporting process and monitor its effectiveness. | Review the traffic management plan, improve pedestrian segregation, install additional signage and barriers, and provide refresher training for drivers and pedestrians. |
Stopping at the immediate cause means the same accident is likely to happen again. Identifying and addressing the underlying causes reduces the risk of recurrence.
Example of an effective workplace accident investigation procedure
Consider an employee who slips on a wet warehouse floor and suffers a sprained wrist.
A basic investigation might conclude that the employee slipped on a wet floor and recommend improving housekeeping and reminding employees to report spillages promptly. While these actions may reduce the immediate risk, they do not explain why the hazard existed in the first place or whether existing control measures were adequate.
An effective investigation would explore why the existing control measures failed. It might identify that:
- A routine inspection had taken place shortly before the incident, but the leak developed afterwards and there was no process for reporting new hazards between inspections.
- The housekeeping procedure required spillages to be cleaned promptly, but it did not clearly define who was responsible for dealing with leaks discovered outside scheduled cleaning times.
- Employees recognised the hazard, but assumed someone else had already reported it, resulting in no action being taken.
- The risk assessment considered spillages from work activities but had not identified water leaks from building services as a foreseeable source of slip hazards.
The investigation would recommend practical improvements, such as introducing a simple hazard reporting process, clarifying responsibilities for dealing with unexpected leaks, reviewing the risk assessment to include building defects and reinforcing the reporting procedure during team briefings.
Who should be involved in an accident and incident investigation?
Depending on the incident, the investigation team may include:
- The employee’s line manager or supervisor. They understand the task being carried out, the normal working practices and any operational challenges that may have contributed to the incident.
- A health and safety adviser. They can provide guidance on investigation techniques, legal requirements, risk assessments and whether existing control measures were suitable and effective.
- Technical specialists or maintenance personnel. Where equipment, machinery or engineering systems are involved, technical expertise can help determine whether defects, maintenance issues or equipment failures contributed to the incident.
- Employee or trade union representatives. They can provide valuable insight into day-to-day working practices, help ensure employees’ views are considered and support an open, transparent investigation.
- Witnesses. Witness accounts can help establish the sequence of events, identify factors that may not be immediately obvious and corroborate other evidence collected during the investigation.
- Senior managers, where appropriate. For serious or complex incidents, senior managers should oversee the investigation, ensure adequate resources are available, assign ownership for corrective actions and monitor progress until improvements have been implemented.
Bringing together different knowledge, experience and perspectives helps investigators develop a more complete understanding of the incident so they can implement more effective corrective actions.
What should an accident investigation report include?
An accident investigation report should record:
- Incident details. The date, time, location, nature of the incident and a factual description of what happened.
- People involved. The injured person, witnesses, investigators and anyone else involved, together with their roles where relevant.
- Evidence collected. A summary of the evidence gathered, such as witness statements, photographs, CCTV footage, inspection records and relevant documentation.
- Immediate and underlying causes. The direct cause of the incident together with the organisational, procedural or environmental factors that contributed to it.
- Corrective actions. The improvements needed to prevent similar incidents, ensuring they address the underlying causes rather than just the immediate hazard.
- Action owners and deadlines. Named individuals responsible for implementing each corrective action, together with realistic timescales for completion.
- Review date. A planned date to confirm whether the corrective actions have been implemented successfully and reduced the risk of recurrence.
Common mistakes in accident and incident investigations
Many investigations fail because they focus on the accident rather than the causes behind it.
| Investigation element | Poor incident investigation process | Effective investigation |
| Primary focus | Assigns blame | Identifies opportunities to improve safety |
| Causation | Identifies only the immediate cause | Identifies immediate and underlying causes |
| Evidence | Relies on assumptions | Uses evidence to reach conclusions |
| Corrective actions | Makes vague recommendations | Implements specific, measurable actions |
| Follow-up | Files the report away | Reviews actions and shares lessons learned |
When does the Health and Safety Executive (HSE) carry out an accident investigation?
An HSE accident investigation is only carried out following fatalities, serious injuries, dangerous occurrences and incidents that indicate a significant breach of health and safety law. Each incident is assessed against the HSE’s published incident selection criteria to determine whether an investigation is appropriate.
If an investigation is carried out, HSE inspectors may examine the accident scene, interview those involved, review relevant documentation and assess whether suitable control measures were in place.
Where breaches of health and safety law are identified, the HSE may take enforcement action, including issuing Improvement Notices, Prohibition Notices or prosecuting those responsible.
For more information, see the HSE’s Investigating Accidents and Incidents (HSG245) guidance.
Learn to conduct effective accident and incident investigations
Our Incident and Accident Investigation Training provides managers, supervisors and health and safety professionals with a practical framework for investigating workplace accidents and incidents.
Participants learn how to gather and evaluate evidence, interview witnesses, identify immediate and underlying causes, and produce effective accident investigation reports that support continual improvement.
Available as online eLearning, virtual classroom or face-to-face training, the course helps organisations improve workplace safety, strengthen compliance and build the confidence to conduct effective accident and incident investigations.
Find out more about Incident and Accident Investigation Training on our website or speak to our friendly team on 0203 011 4242 or email [email protected].
Adam Clarke
Managing Director (Consulting)
