What does the Swiss Cheese Model illustrate in safety management?

What does the Swiss Cheese Model illustrate in safety management?

• A. Multiple layers of defense can fail if holes align, allowing an accident.
• B. All layers of defense are perfect and never fail.
• C. Accidents occur only due to one unfixable flaw.
• D. Defenses are irrelevant to accident causation.

Answer: (A)

Think of safety defenses as several layers of protection stacked like slices of Swiss cheese. Each layer has holes—weak spots born from latent conditions (things built into the system, such as design flaws, organizational pressures, or inadequate training) or active errors (people making mistakes in the moment). A hazard has to pass through every layer to cause harm, so normally the holes in one layer are offset by solid parts of other layers, and the system blocks the accident. Problems occur when holes line up across multiple layers. If the weaknesses align at the same time, a path through the defenses opens, and the hazard can slip through all the barriers, leading to an accident. This view helps explain why accidents are often the result of multiple contributing factors across different parts of the system, not a single mistake or a single broken rule. In aviation, for example, an equipment issue (hole in the maintenance layer) combined with a procedural deviation (hole in the procedures layer) and a momentary lapse in monitoring (hole in the supervision layer) can align, allowing an unsafe event to occur. Strengthening safety means reducing the size and number of holes, or adding more defenses, so the chances of an alignment are kept very small.

Think of safety defenses as several layers of protection stacked like slices of Swiss cheese. Each layer has holes—weak spots born from latent conditions (things built into the system, such as design flaws, organizational pressures, or inadequate training) or active errors (people making mistakes in the moment). A hazard has to pass through every layer to cause harm, so normally the holes in one layer are offset by solid parts of other layers, and the system blocks the accident.

Problems occur when holes line up across multiple layers. If the weaknesses align at the same time, a path through the defenses opens, and the hazard can slip through all the barriers, leading to an accident. This view helps explain why accidents are often the result of multiple contributing factors across different parts of the system, not a single mistake or a single broken rule.

In aviation, for example, an equipment issue (hole in the maintenance layer) combined with a procedural deviation (hole in the procedures layer) and a momentary lapse in monitoring (hole in the supervision layer) can align, allowing an unsafe event to occur. Strengthening safety means reducing the size and number of holes, or adding more defenses, so the chances of an alignment are kept very small.