An accident-book entry records an event. A post-incident investigation report explains what the evidence supports, why existing controls failed and what must change. That difference matters. A report written to satisfy a form can blame the person nearest the event and leave the same conditions in place; a disciplined report gives leaders a defensible route from immediate response to verified corrective action.
Know what the report is—and what it is not
The report is the reasoned output of an investigation. It is not the initial accident-book record, a near-miss form, a RIDDOR submission, an insurer notification or an HR disciplinary report. Those records may inform or follow the investigation, but each has a different purpose and test.
HSE's HSG245 workbook presents investigation as a way to find what went wrong, learn lessons and prevent recurrence. The depth should be proportionate to actual and potential consequences, the likelihood of recurrence and the complexity of the event. A low-potential first-aid event may need a short documented review; a serious injury, dangerous occurrence or high-potential near miss needs a more structured investigation with competent people and protected evidence.
Define the scope at the start: the event, location, activities, time period, people involved and questions to answer. Record who commissioned the work and who is investigating. If senior leaders, conflicting accounts or likely enforcement or civil claims are involved, consider independence and legal advice early without assuming that copying a solicitor automatically makes the report privileged.
HSE: investigating accidents and incidents (HSG245) ↗ · Related guide: workplace accident-book records →
Preserve evidence and build a factual chronology
Make the area safe first, including emergency care and controls for continuing danger. Then preserve perishable evidence where it is safe and lawful to do so: photographs, equipment condition, guarding, settings, permits, CCTV, access records, training evidence, maintenance history, risk assessments, procedures and environmental conditions. Record who obtained each item, when, its source and any limitations.
Construct a chronology that distinguishes established facts, witness accounts and unresolved points. Use times where available, but do not manufacture precision. A CCTV timestamp, machine log and recollection may differ. Show the discrepancy and explain how it affects the conclusion rather than forcing a neat story.
Interview people promptly and separately where practical. Ask them to describe what they saw, heard and did in their own words. Use open questions, test the sequence and invite correction. Avoid language such as 'why did you ignore the rule?' that assumes the conclusion. Give witnesses a fair opportunity to check the factual accuracy of their account.
Separate immediate, underlying and root causes
An immediate cause is close to the event: a hand entered a danger zone, a vehicle reversed into a pedestrian route, or a substance escaped. Stopping there usually produces weak recommendations such as 'take more care'. Ask what made that action or condition possible.
Underlying causes can include an unsuitable guard, poor layout, workload, defective maintenance, confusing instructions, inadequate supervision, a permit failure or a risk assessment that did not reflect the real job. Root causes sit in the management system: procurement, design, planning, leadership, assurance, change control or resource decisions that allowed the underlying weakness to persist.
Test each proposed cause against the evidence. If the report says a worker lacked competence, identify the task standard, training, instruction, supervision and observed gap. If fatigue, medication or a health condition may be relevant, seek competent advice and avoid diagnosis. Describe what is known, what remains unknown and whether the conclusion would change if the uncertainty were resolved.
Write a report that a decision-maker can audit
Start with a short executive summary: what happened, actual and credible potential outcome, principal findings, urgent controls and key actions. Follow with scope and method, site and process description, factual chronology, evidence considered, findings, causal analysis, recommendations and appendices. A reader should be able to trace each important conclusion to evidence.
Use an evidence table for complex events, showing the item, source, relevance and limitation. Label photographs and plans. Quote only where the exact words matter; otherwise summarise accurately. Keep speculation out of findings and put unresolved questions in a clear limitations section.
Record notification decisions separately. Whether an event is reportable under RIDDOR depends on the Regulations' categories and facts; completing an investigation does not replace prompt consideration of the reporting deadline. Equally, a non-reportable event can still deserve a thorough investigation because its potential consequences were serious.
Related guide: RIDDOR reporting → · HSE: accident and near-miss investigation tool ↗
Use a structured investigation for serious or contested events.
HR + SAFETY can provide proportionate post-incident investigation support, evidence review and a clear report where the consequences, complexity or internal conflicts require a more independent approach.
Discuss an incident investigationTurn findings into controlled action
A recommendation should address a cause and use the hierarchy of control. Prefer elimination, substitution, engineering and design changes before relying on reminders, retraining or discipline. Training may be part of the answer, but it is rarely sufficient where the report identifies defective equipment, unworkable instructions or unmanaged production pressure.
For every action, name the risk or finding addressed, the owner, target date, interim control and evidence required for closure. 'Review procedure' is not a complete action. State what must change and how effectiveness will be checked—for example, an engineering test, observation of the revised task, worker consultation or an audit after a defined operating period.
Update connected risk assessments, safe systems, permits, maintenance, emergency plans and contractor information. Share the learning at the level people need. A toolbox talk may explain the control change without disclosing personal information or turning a colleague's injury into workplace gossip.
Protect fairness and confidential information
An investigation may collect names, witness evidence, health information, images and opinions. Health information is special-category personal data. Identify and document the lawful basis and special-category condition, explain how information will be used, restrict access and avoid attaching clinical detail unless it is necessary for the safety conclusion.
Keep the safety investigation distinct from any disciplinary process. The same evidence may be relevant, but a conclusion that a control failed is not automatically proof of misconduct. If disciplinary action is considered, follow a fair HR process, disclose relevant evidence and give the employee an opportunity to respond.
Plan retention and disclosure with the possibility of regulator, insurer, representative or legal interest in mind. Write factually and professionally. Do not alter original records, overwrite witness accounts or remove inconvenient evidence when a draft changes.
ICO: workers' health information ↗ · Related guide: workplace HR investigations →
Post-incident report quality checklist
- Define the investigation scope, competence, independence and evidence-preservation plan.
- Separate confirmed facts, accounts, inference and unresolved questions.
- Build a chronology that acknowledges timing conflicts and missing evidence.
- Identify immediate, underlying and root causes supported by evidence.
- Address health factors only with necessary information and competent advice.
- Write recommendations against causes and the hierarchy of control.
- Give every action an owner, deadline, interim control and closure test.
- Update risk assessments and systems, communicate learning and verify effectiveness.
The value of a post-incident investigation report is not its length. It is the strength of the chain from evidence to cause, from cause to control and from control to verified closure. Write for the manager who must act and the reviewer who may later need to understand why the decision was reasonable.
This guide provides general information for UK employers. It is not legal advice and should not replace advice based on the facts of a specific matter.