Universal Principles of Design, Updated and Expanded Third Edition

182 Swiss Cheese Model

A model describing how risks combine to cause accidents and other bad outcomes.

The Swiss cheese model is a risk management framework based on the metaphor of Swiss cheese slices stacked next to one another. Each slice of cheese represents a layer of defense against an undesirable outcome, and the holes in the slices represent weaknesses or gaps in those defenses. Having multiple layers of defense reduces the risk of bad outcomes when the layers have different weaknesses — i.e., their holes don’t line up. For example, in preventing the spread of an airborne virus, one layer of defense is vaccination, and another layer of defense is wearing a mask. Neither defense is perfect, but because they work to prevent infection ...