Glossary
Swiss Cheese Model
What is the Swiss Cheese Model?
The Swiss Cheese Model pictures a system's defenses as slices of cheese. Each slice is a barrier. Its holes are weaknesses. When weaknesses line up, a hazard can pass through several defenses and cause harm.
James Reason developed the model to explain how immediate errors and underlying organizational conditions can combine.
Examples
Healthcare
A medication error might pass through an unclear prescription, an ineffective checking process, and a missed final check. The question is which defenses should have caught it and why they did not.
Aviation
An investigation could examine how an equipment problem, fatigue, and a communication breakdown interacted. The model directs attention to the system around the final action.
Industrial safety
An equipment failure, ineffective alarm, and failed shutdown system could leave a plant without its intended protections.
Why it matters
Stopping at “someone made a mistake” can leave the conditions for another failure in place. Reason's account includes staffing, design, and management decisions, as well as front-line actions.
Limits of the picture
The holes can change over time and need not be equally dangerous. The image does not establish a fixed number of mistakes needed for a disaster. A diagram is a way to organize questions, not a completed accident investigation or a calculation of risk.