NEBOSH Incident Investigation

Question 1

What does Heinrich's domino theory of accident causation propose?

Accepted Answer

Accidents result from a chain of sequential factors (social environment, fault of person, unsafe act/condition, accident, injury) and removing one 'domino' can prevent the injury

Answer

Heinrich's domino theory (1931) proposes that accidents result from a sequence of five factors like a row of dominoes: social environment/ancestry, fault of person, unsafe act or mechanical/physical hazard, the accident event, and injury. Removing any one domino — particularly the middle one (unsafe act/condition) — breaks the chain and prevents injury.

Question 2

What is the 'Swiss cheese' model of accident causation?

Accepted Answer

Reason's model showing that accidents occur when hazards pass through aligned holes (weaknesses) in multiple defensive layers — each layer has gaps, and an accident happens when the gaps line up

Answer

James Reason's Swiss cheese model shows that organisations have multiple layers of defence (procedures, training, engineering controls, supervision). Each layer has weaknesses ('holes') that may allow hazards through. An accident occurs when the holes in several layers momentarily align, allowing a hazard to pass through all defences.

Question 3

What is the '5 Whys' technique used for in incident investigation?

Accepted Answer

Repeatedly asking 'why' to drill down through symptom-level causes to identify the root cause of an incident

Answer

The 5 Whys technique involves asking 'why?' repeatedly (typically around five times, though it may be more or fewer) to move beyond the immediate or obvious cause of an incident to identify its root cause. Each answer becomes the basis for the next 'why', progressively uncovering deeper systemic issues.

Question 4

Under RIDDOR 2013, which of the following events must be reported to the relevant enforcing authority?

Accepted Answer

A fracture of any bone other than fingers, thumbs, or toes suffered by a worker as a result of a work-related accident

Answer

RIDDOR 2013 requires reporting of specified injuries including fractures other than to fingers, thumbs or toes. Other reportable injuries include amputations, permanent loss of sight, crush injuries, burns requiring hospital admission, scalping, and any injury leading to loss of consciousness or requiring resuscitation.

Question 5

What is a fishbone (Ishikawa) diagram used for in root cause analysis?

Accepted Answer

To visually organise potential causes of an incident into categories (such as People, Methods, Materials, Machinery, Environment, Management) to systematically identify root causes

Answer

The fishbone or Ishikawa diagram organises potential causes of an incident into main categories branching off a central spine. Common categories include People, Methods, Materials, Machinery/Equipment, Environment, and Management. This structured approach ensures all potential contributing factors are systematically considered rather than jumping to obvious conclusions.

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NEBOSH Incident Investigation