Swiss cheese model

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.

The model was originally formally propounded by James T. Reason of the University of Manchester,[1] and has since gained widespread acceptance.

Latent failures include contributory factors that may lie dormant for days, weeks, or months until they contribute to the accident.

[9] In the early days of the Swiss cheese model, late 1980 to about 1992, attempts were made to combine two theories: James Reason's multi-layer defence model and Willem Albert Wagenaar's tripod theory of accident causation.

A more correct version of the combined theories is shown with the active failures (now called immediate causes), preconditions and latent failures (now called underlying causes) shown as the reason each barrier (slice of cheese) has a hole in it, and the slices of cheese as the barriers.

This use has become particularly common when applied to oil and gas drilling and production, both for illustrative purposes and to support other processes, such as asset integrity management and incident investigation.