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. 

We have spoken to the Health and Safety Executive about these definitions, and they agree that there are no universal definitions of immediate, underlying and root causes. For clarity, we will use the definitions from HSG245 on page 6 Investigating accidents and incidents: A workbook for employers, unions, safety representatives and safety professionals HSG245. 

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.

• They are already included in Introduction to Incident Investigation (NEBOSH HSE Introduction to Incident Investigation course book). 
• The DN1 book (Principles of Workplace Health and Safety in the UK) currently uses the definitions on page 3 of HSG245, which are very similar. These will be updated at the next reprint. 
• Other publications, such as Managing Health and Safety in the UK (National General Certificate), International Health and Safety (International General Certificate) and Process Safety Management (NEBOSH HSE Certificate in Process Safety Management) will also be updated when reprinted.