What does the Swiss Cheese model illustrate in incident causation?

• A. A single defense is sufficient.
• B. Multiple layers of defense with holes.
• C. Random accidents with no defenses.
• D. People are always at fault.

Answer: (B)

The Swiss Cheese model shows that safety relies on multiple layers of defense, each with holes. Each barrier or safeguard has weaknesses, and when the gaps in several layers align, a hazard can slip through all defenses and lead to an incident. This captures why accidents usually come from a chain of events involving latent conditions and active failures across different parts of an organization, rather than a single mistake. It also guides improvement: add or strengthen layers, reduce the size and number of holes in each layer, and catch issues earlier so that the holes don’t align.