Iceberg heuristic

The iceberg model

The "Iceberg model" is a heuristic often times used when discussing safety. The general idea is that the most visible (and "worrying") safety outcomes (eg, deaths) are but the tip of the iceberg. Below them other less visible events occur more frequently. The model has been used in different settings for referring to different safety concerns, including road events preventable by wearing seat-belts (1 death, 19 hospitalizations, 300 minor health care; see image 2), workplace safety (for each major injury there are 29 minor injuries and 300 near-misses; see image 3), insured and uninsured costs, etc.

The model spanned-off from Heinrich's (19311) pyramid (also known as Heinrich's Law) (see image 2). Although the actual numeric values are not dependable across industrial and service sectors, the model is used as an heuristic to represent that each accident or major event happens less often than less serious incidents, and these less often than near-misses, etc. It is also used as a preventative heuristic: if we pay attention to lower level events (eg, near-misses) and take corrective action at that level, we may help prevent the onset of higher level events (ie, incidents and accidents). Events decrease in frequency as they increase in severity because systemic, individual as well as random 'barriers' may 'capture' those events and prevent them from becoming any more serious (eg, as represented by the 'Swiss-cheese model').

Of course, the heuristic could also be expanded into a more constructive and inclusive model for human factors, were the base of the pyramid or iceberg is formed by normal behaviors, which occur far more often and conforms the bulk of a system's normal operations.

(Image 1 embedded from TapRoot on 7 November 2011)
(Image 2 embedded from NHTSA on 7 November 2011)
(Image 3 embedded from on 7 November 2011)
1. HEINRICH Herbert William (1931). Industrial accident prevention, a scientific approach. McGraw-Hill (New York, USA), 1931. (Quoted in HOLLNAGEL Erik [ed] (2009). Safer complex industrial environments: a human factors approach. CRC Press (UK), 2009. ISBN 9781420092486.)

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Swiss-cheese model Functional management system


Jose D PEREZGONZALEZ (2011). Massey University, New Zealand (JDPerezgonzalezJDPerezgonzalez).

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