What’s ‘Swiss Cheese model’ ?

[Ref MULTIMODAL SAFETY MANAGEMENT AND HUMAN FACTORS, Wiki]

Swiss cheese model (a.k.a Cumulative act effect model) is broadly used to study the accident/incident causation – considers the interaction between latent conditions and errors and their contribution to organizational accidents.

Systems comprise various organizational levels that contribute to the production of system outputs (e.g decision makers, line management, productive activities and defenses.) Each of the levels has various defenses in place (e.g protective equipment, rules and regulations, engineered safety features, etc). Holes or weaknesses in defenses created by latent conditions and errors create “windows of opportunity” for accident trajectories to breach the defenses and cause an accident. Accidents occur when the holes line up in a way that allows the accident trajectory to breach each of the defenses that are in place.


James Reason (the founder of the model) hypothesized that most accidents can be traced to one or more of four (4) failure domains:

  1. organizational influences
  2. supervision
  3. preconditions
  4. specific acts – e.g unsafe act

The Swiss Cheese model includes two (2) types of failures:

  1. active failures
  2. latent failures

Active failures:
Encompass the unsafe acts that can be directly linked to an accident

Latent failures:
Include contributory factors that may lie dormant for days, weeks, or months until they contribute to the accident. Latent failures span the first three domains of failure in Reason’s model.

In theory, lapses and weaknesses in one defense do not allow a risk to materialize, since other defenses also exist, to prevent a single point of failure. The Swiss cheese model was originally formally propounded by Dante Orlandella and James T. Reason of the University of Manchester,[1] and has since gained widespread acceptance.

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