Swiss Cheese Concept

      Traditionally, error analysis has focused on identifying the cause. However, one basic finding from research is that accidents in complex systems only occur through the concatenation of multiple small factors or failures, each necessary but only jointly sufficient to produce the accident. Often these small failures or vulnerabilities are present in the organization long before a specific incident is triggered. All complex systems contain such latent factors or failures, but only rarely do they combine to create the trajectory for an accident.

Swiss Cheese, a food metaphor, suggests:

• Multiple contributors (the holes) are required for any adverse events to occur. All healthcare systems have many, many defenses (the cheese) to protect patients.
• Defenses in a system (the slices) are designed to prevent errors that result in adverse events.
• The defenses are static; healthcare is dynamic. Therefore, the holes change and the defenses erode in safety barriers resulting in increased risk.
• Usually, if one defense if breached, another layer of defense bounces back the danger. However, when the holes in the slices line up, adverse events can occur.