Confirmation of incident definitions (immediate, underlying and root causes)
18th December 2025
We have recently received feedback that some definitions differ slightly across NEBOSH publications. These are the definitions of immediate, underlying and root causes.
The Health and Safety Executive agree that there are no universal definitions of immediate, underlying and root causes. For clarity, we will use the definitions on page 6 of Investigating accidents and incidents. A workbook for employers, unions, safety representatives and safety professionals (HSG245).
These definitions are:
- Immediate cause: the agent or injury or ill health (the blade, the substance, the dust, etc).
- Underlying cause: unsafe acts and unsafe conditions (the guard removed, the ventilation switched off, etc).
- Root cause: the failure from which all other failings grow, often remote in time and space from the adverse event (eg failure to identify training needs and assess competence, low priority given to risk assessment, etc).
These definitions will be used in our course materials going forward. At present, please note the following:
- These definitions are already included in Introduction to Incident Investigation (NEBOSH HSE Introduction to Incident Investigation course book).
- Principles of Workplace Health and Safety in the UK (DN1 course book) currently uses a definition from page 3 of HSG245, which is very similar. This will be updated at the next reprint.
- Other publications, such as Managing Health and Safety in the UK (National General Certificate course book), International Health and Safety (International General Certificate course book) and Process Safety Management (NEBOSH HSE Certificate in Process Safety Management course book) will also be reviewed and updated as required when reprinted.
