Question 1 of 7: Accident Causation Theories

Question 1: Accident Causation Theories (20 marks: 6/7/7)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Elements of Domino Theory (Heinrich)

Heinrich modelled an accident as a chain of five "dominoes" that fall in sequence; the injury occurs only if the whole chain falls, and removing any one domino stops it:

1. Ancestry / social environment — inherited or environmental traits that shape attitudes.
2. Fault of the person — carelessness, poor training, undesirable traits.
3. Unsafe act and/or unsafe condition — the central, controllable domino.
4. Accident — the event itself.
5. Injury / loss — the outcome.

Key point: removing the third domino (the unsafe act/condition), typically through guarding, training or supervision, breaks the chain and prevents both accident and injury.

(ii) The Four M's — System-Safety Factors (diagram)

System-safety theory holds that accidents result from interactions among four elements; a failure or mismatch in any one, especially in combination, produces the accident:

      MAN (human)              MACHINE (equipment)
      - error, fatigue,        - design, guarding,
        skill, attitude          reliability, defects
             \                        /
              \                      /
               +------> ACCIDENT <--+
              /                      \
             /                        \
   MEDIA (environment)          MANAGEMENT (system)
   - workplace, weather,        - policy, training,
     noise, housekeeping          supervision, procedures

• Man — the human and their capabilities/limitations. Machine — the equipment/technology. Media — the working environment/conditions. Management — the organizational system that governs the other three. Control any/all to prevent the accident.

(iii) Single-Factor Theory and Its Limitation

• Single-factor theory holds that an accident has one primary cause; find and remove that single cause and the accident is prevented.
• Limitation: real accidents almost always result from multiple interacting factors (the four M's). Attributing an accident to a single cause—often "operator error"—is over-simplified: it misses the underlying contributing causes (design, environment, management), stops the investigation prematurely, encourages blame rather than system improvement, and leaves other contributing hazards uncontrolled, so recurrence is likely.