Swiss cheese model

The Swiss cheese model of accident causation is a model used in risk analysis and risk management. It likens human systems to multiple slices of Swiss cheese, which has randomly placed and sized holes in each slice, stacked side by side, in which the risk of a threat becoming a reality is mitigated by the differing layers and types of defenses which are "layered" behind each other. Therefore, in theory, lapses and weaknesses in one defense do not allow a risk to materialize (e.g. a hole in each slice in the stack aligning with holes in all other slices), since other defenses also exist (e.g. other slices of cheese), to prevent a single point of failure.

The model was originally formally propounded by James T. Reason of the University of Manchester,^[1] and has since gained widespread acceptance. It is sometimes called the "cumulative act effect". Applications include aviation safety, engineering, healthcare, emergency service organizations, and as the principle behind layered security, as used in computer security and defense in depth.

Although the Swiss cheese model is respected and considered a useful method of relating concepts, it has been subject to criticism that it is used too broadly, and without enough other models or support.^[2]