NEBOSH Incident Investigation 1 — Questions and Answers
Question 1: What does Heinrich's domino theory of accident causation propose?
- Accidents are purely random events that cannot be predicted
- 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 (Correct answer)
- All accidents are caused by equipment failure alone
- Accidents only occur when multiple workers are present
Correct 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
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?
- A model showing that Swiss workplaces are safer than others
- 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 (Correct answer)
- A model based on the shape of workplace floor plans
- A theory that accidents are caused by food contamination
Correct 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
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?
- Asking five different witnesses about what happened
- Repeatedly asking 'why' to drill down through symptom-level causes to identify the root cause of an incident (Correct answer)
- Identifying five possible preventive measures
- Checking five different regulatory requirements
Correct answer: Repeatedly asking 'why' to drill down through symptom-level causes to identify the root cause of an incident
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?
- Any minor cut or bruise requiring a plaster
- A fracture of any bone other than fingers, thumbs, or toes suffered by a worker as a result of a work-related accident (Correct answer)
- A worker taking a single day off due to a headache
- A near-miss that no one witnessed
Correct answer: A fracture of any bone other than fingers, thumbs, or toes suffered by a worker as a result of a work-related accident
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?
- To map the layout of a workplace
- To visually organise potential causes of an incident into categories (such as People, Methods, Materials, Machinery, Environment, Management) to systematically identify root causes (Correct answer)
- To track the timeline of events leading to an accident
- To calculate the financial cost of an incident
Correct answer: To visually organise potential causes of an incident into categories (such as People, Methods, Materials, Machinery, Environment, Management) to systematically identify root causes
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.
Question 6: Why is near-miss reporting considered important in incident investigation and prevention?
- Near-misses are legally required to be investigated under RIDDOR
- Near-misses share the same root causes as actual incidents — investigating them provides an opportunity to identify and fix hazards before someone is actually harmed (Correct answer)
- Near-miss reports are only important for insurance purposes
- Near-misses only need to be recorded, not investigated
Correct answer: Near-misses share the same root causes as actual incidents — investigating them provides an opportunity to identify and fix hazards before someone is actually harmed
Near-misses are essentially accidents where the outcome was fortunately not harmful. They share the same causal factors as actual injuries and occur much more frequently. Investigating near-misses is a proactive opportunity — identifying and addressing the underlying hazards and system failures before they result in actual harm to people.
NEBOSH Incident Investigation 1
What does Heinrich's domino theory of accident causation propose?