Reason's Swiss Cheese Model

Reason’s Swiss Cheese Model explains how accidents or errors happen in complex systems. Imagine multiple slices of Swiss cheese stacked together, each representing a layer of defenses like protocols, training, or safety checks. Each slice has holes—weaknesses or lapses. When the holes align across all layers, a hazard can pass through all defenses and cause an accident. The model emphasizes that errors often occur because flaws in different layers line up, rather than from a single mistake. Strengthening each layer’s defenses reduces the chance that holes will align, preventing harmful incidents.