Applying the Swiss Cheese Model to a MedSun Report
MedSun: Newsletter #9, November 2006

Historically, in medicine and in other industries, accidents have been thought to be the result of individual human error, which is commonly referred to as the “person approach.” This approach views unsafe acts as those arising from atypical mental processes—such as forgetfulness, inattention, carelessness, negligence, and recklessness. Many limitations have been posed by this theory, and this approach is likely to have prevented developments toward safer health care practices.

In the early 1990s, cognitive psychologist James Reason began to analyze failures occurring within complex organizations or as part of systems. Through close examination of errors in such organizations, Reason questioned the customary person-centered model of error. He began to view accidents as imperfections in the multifunctional layers of systems, and he referred to this as the “system approach” to failure. This perspective concentrates on the conditions under which persons work and on the development of defenses to guard against errors or to mitigate their effects.

Reason portrays the system approach to failure through his “Swiss Cheese Model,” which explicates a perfect system as one with layers of defenses, barriers, and safeguards. In reality, systems are more like slices of Swiss cheese: they are characterized by many “holes” in various locations across the institution. The alignment of holes in the many layers of systems can line up and permit a trajectory for hazardous circumstances.

This Swiss Cheese Model was applied to an August 2006 MedSun report in order to analyze and better understand the system failures that led to patient harm. The MedSun report Event Description and analysis are presented below.

Additional Information:

For additional information on James Reason’s Swiss Cheese Model, go to

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