A Comprehensive Guide to Accident Investigation

A Comprehensive Guide to Accident Investigation

While every employer must take steps to protect their staff from experiencing harm while at work, it is an unfortunate truth that accidents do occur in the workplace that result in injury or ill health.

When accidents and incidents do occur, it is important that they are fully investigated in order to understand what went wrong and how to stop it from happening again.

In this article, we will look at the stages of an accident investigation, and outline what a typical investigation looks like. Before we do, it is important to be aware that the information provided in this article is generic, and that this method may not be suitable for all accidents.

Near Miss

Before investigating

Before an accident investigation can take place, there are several things that need to be done.

Following an adverse event, the first thing to do is to take any emergency actions necessary, such as providing first aid and controlling any potential secondary events (such as explosions and fires).

After this, the evidence should be identified and the scene preserved as best as possible. Depending on the severity of the event, this may require work to be stopped and barriers put in place to prevent people from tampering with the scene.

Finally, the event should be reported to the person responsible for health and safety in the organisation, who can decide on any further action required. It must also be reported to an enforcing authority (the HSE or local authority in most cases) if required by the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013 (RIDDOR).

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The structure of an accident investigation

There are several different methods that an organisation can use to investigate an adverse event, the steps for one of which are shown below:

  • Step 1: Gather the information
  • Step 2: Assemble and analyse the information
  • Step 3: Identify suitable risk control measures
  • Step 4: Create and implement a risk control action plan

Step 1 - Gather the information

The first step of an accident investigation is to gather all of the relevant information about the adverse event. This should be done as soon as possible because information will be fresh in the minds of witnesses and physical conditions will have had less time to change.

Be aware that the amount of time and effort spent gathering information should be proportionate to the level of investigation. However, this should not prevent all available and relevant information from being gathered.

There are three main sources from which relevant information can be obtained: direct observation, documents and interviews.

Direct observation

Direct observation of items such as the scene, premises, workplace, environmental conditions, equipment, materials and injuries can provide a range of useful information about what happened during the adverse event.

The information recorded from direct observations may take several forms, including:

  • Photographs
  • Sketches
  • Measurements
  • Notes

Accidetn Investigation - Direct Observation


There are several documents that should be taken and analysed as part of an investigation. These include:

  • Written instructions
  • Training records
  • Safe systems of work
  • Risk assessments
  • Policies and procedures
  • Records of inspections, tests and examinations


Interviews, along with written statements, are highly beneficial to an investigation. They should be carried out with as many relevant parties as possible, such as:

  • The injured person(s)
  • Witnesses
  • People who carry out a similar role or task
  • Those responsible for testing the equipment
  • Those with specialist knowledge of the equipment and/or process.

When conducting interviews, it is important not to assign blame or determine why certain events occurred – the goal at this stage is to gather facts and ascertain exactly what happened.


Once the initial information gathering process has been completed, there are a set of 17 questions, set out by the HSE, that the investigation team must answer regarding the event. These questions will help to establish exactly what happened, as well as highlight any information or lines of enquiry that may have been missed:

  1. Where and when did the adverse event happen?
  2. Who was injured/suffered ill health or was otherwise involved in the adverse event?
  3. How did the adverse event happen?
  4. What activities were being carried out at the time?
  5. Was there anything unusual or different about the working conditions?
  6. Were there adequate safe working procedures and were they followed?
  7. What injuries or ill health effects, if any, were caused?
  8. If there was an injury, how did it occur and what caused it?
  9. Was the risk known? If so, why wasn’t it controlled? If not, why not?
  10. Did the organisation and arrangement of the work influence the adverse event?
  11. Was maintenance and cleaning sufficient? If not, explain why not.
  12. Were the people involved competent and suitable?
  13. Did the workplace layout influence the adverse event?
  14. Did the nature or shape of the materials influence the adverse event?
  15. Did difficulties using the plant and equipment influence the adverse event?
  16. Was the safety equipment sufficient?
  17. Did other conditions influence the adverse event?

Once all of the questions have been answered, the investigation team should be left with a clear picture of exactly what happened leading up to, and during, the adverse event.

Step 2 - Assemble and analyse the information

The second step of carrying out an investigation is to analyse the information gathered about the adverse event. The main reason for doing so is to establish its immediate, underlying and root causes, which can be used to learn from past failures and prevent future occurrences.

An analysis should be completed systematically to ensure that it is objective and unbiased, and completed alongside employees, trade union representatives, and experts (if required).

Analyse the Information

Once complete, an investigation team should be able to clearly identify the sequence of events and conditions that led up to and caused the adverse event.

The ‘why’ method

The ‘why’ method is a useful tool for organising your findings and establishing what happened during an adverse event. This method involves taking the incident and constantly asking ‘why’ it happened, until the answer is no longer meaningful.

Let’s look at this method in action. John broke his leg at work and, by asking why this happened, we are able to establish:

  • Who the vulnerable person was (John was on the ladder).
  • What the hazard was (he fell due to gravity).
  • The circumstances that brought them together (John fell off the ladder).

If we look at why he fell off the ladder, we can establish that it slipped, which occurred because it was not tied down, which occurred because he did not have the necessary equipment required to tie it down, and so on.

By continuing to ask why each of these events happened until the answer is no longer meaningful, we can understand exactly what happened to John and determine the underlying and root causes of those problems that led to the accident.

Human failings

When completing an investigation, it may be the case that some of the causes of an adverse event came about in part due to the actions of a specific worker or set of workers. Errors of this nature are called human failings and can be divided into three types: skill-based errors, mistakes and violations.

When analysing the findings and establishing the causes of an adverse event, it may seem like an easy solution to blame it all on the worker themselves and write the event off as a human failing. However, doing so is counter-productive and may alienate the workforce, which in turn would undermine the safety culture in the workplace.

Instead, you should ask those involved to explain why they acted as they did without prejudice or comment. This will help better understand the reasons behind the immediate causes and may potentially reveal some additional underlying causes. For example, it may have been the case that the production deadline was too short and removing the guards saved a significant amount of time.

Step 3 - Identify suitable risk control measures

Once you have established the causes of the adverse event, the next step is to identify suitable risk control measures.

While analysing the information gathered about the adverse event, there may have been several risk control measures that were identified as having failed, or that would have prevented the event from happening if they had been in place.

These measures should be collated along with any other possible measures or changes that could address the immediate, underlying and root causes of the event. Some measures will be more difficult to implement than others, but this should not prevent them from being listed at this stage.

Evaluate risk control measures

Once a list of possible risk control measures has been created, each measure must be evaluated to assess its effect on the level of risk a hazard poses, how effective it is at preventing the adverse event from recurring, and whether or not it can be implemented successfully.

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Some workplace risk control measures are more effective and reliable than others so, when assessing these measures, they should be considered in the following order:

  • Measures that eliminate the risk, such as replacing a hazardous substance with a safer one.
  • Measures that combat or reduce the risk at its source (including engineering controls), such as installing a guard around a saw blade.
  • Measures that rely on human behaviour (including administrative controls), such as providing personal protective equipment.

When evaluating risk control measures, always consider whether similar risks exist within the organisation, and if the same measures identified in this investigation could be implemented elsewhere to prevent a similar adverse event from occurring.

Also, it is important to identify whether or not similar adverse events have happened in the past, and consider why this is the case. An adverse event occurring multiple times should justify the use of more costly control measures and prompt immediate action to implement them.

Step 4 - Create and implement a risk control action plan

After identifying potential risk control measures, and determining which of them should be implemented, an action plan can be created that details which specific control measures will be implemented, and how this will be done.

The first thing to do when creating a risk control/risk management plan is determine which measures that are of the highest priority and need to be implemented immediately. To help determine which measures are high priority, think about the following questions:

  • What is essential to securing the health and safety of the workforce today?
  • What cannot be left until another day?
  • How high is the risk to employees if this risk control measure is not implemented immediately?

Those risk control measures that do not control high priority risks must be put in the action plan in order of priority, and have a timescale and person responsible for their implementation assigned to them.

The objectives of an action plan must deal effectively with the immediate, underlying and root causes of the adverse event, and be SMART:

  • Specific
  • Measurable
  • Agreed
  • Realistic
  • Time-bound

For example, ‘the site manager (John Smith) will install an edge protection system on all currently erected scaffolds by the 15th June 2021 (next week), and update the site safety checklist and risk assessment to ensure that edge protection is installed on all future scaffold operations’ is a much more suitable objective than ‘install barriers on scaffolding.’

Action Plan - Scaffolding Safety System


Deciding on where and how to implement control measures requires knowledge of the organisation and how work is carried out. For this reason, safety professionals, employees and their representatives should all contribute to the creation of this action plan alongside those with the authority to approve it.

Once the action plan is completed, a specific person must be put in charge of it. Their role will be to monitor the progress of the action plan, ensure that it is executed successfully and communicate information about its progress to employees and their representatives.

Reviewing risk assessments

All adverse events suggest that the risk assessments and safe working practices currently in place are insufficient and must be reviewed. Failure to do so is likely to be a breach of regulation 3(3) of the Management of Health and Safety at Work Regulations 1999.

When reviewing a risk assessment, it is important to consider what the findings of the investigation indicate about your risk assessments in general. It may be the case that they are insufficient and require creating from scratch.

Also, be aware that the Management of Health and Safety at Work Regulations 1999 do not require employers with fewer than five employees to record the significant findings of their risk assessment, but they are still legally required to have completed the risk assessment process, and to review this assessment after an adverse event.

Identifying trends

At this point, the accident investigation is almost complete. The final thing to do is ensure that the relevant regulatory authority has been notified about the adverse event, if it is reportable under RIDDOR, and that it has been recorded in the organisation’s accident book if required.

This should have been done before the investigation began, but it could have been the case that the severity of the event was not known at that time, or that the regulatory authority required additional information that was only available once the investigation had been completed.

This information can also be used to monitor health and safety performance and identify trends that can highlight other areas of concern within the organisation that require investigating.

Once this has been done, the investigation is complete. Once again, be aware that the approach taken in this article is one of a number of possible approaches, and it may be the case that another approach is more suitable for your organisation.

For more information on accident investigation, and how to manage safely in a workplace, consider taking one of our great value training courses: