Swiss cheese model human error

Reason (21) has described a model for looking at human error that portrays a battle between the sources of error and the system-based defenses against them. This model is often referred to as the "Swiss cheese model" because the defenses against error are displayed as thin layers with holes that are described as latent error in the system. Figure 26.5 demonstrates the model as applied to medication error. Each opportunity for error is defended by the prescriber, pharmacist, nurse, and patient. When a potential error is identified and corrected (e.g., dose error, route of administration error) the event becomes a "near miss" rather than an ADE. In those cases in which the holes in the Swiss cheese line up, a preventable medication error occurs. The Swiss cheese model provides an interesting framework for research in this field. 

The associations of distinct detection mechartisrrts to differerrt types of errors led Thomas to propose an organic approach according to which variability in performance and human error requires parallel defense strategies and an adaptive approach and not the traditional serial protective layers as illustrated by Reason s Swiss Cheese Model. 

A description of the three types of accident models can be found in Hollnagel, E. (2004), Barriers and Accident Prevention, Aldershot Ashgate. As already mentioned in the Comments on Chapter 3, the book also provides a detailed analysis and characterisation of various barrier systems. The best known among the many accident models are the Domino model put forward by Heinrich in 1931, and the Swiss cheese model described by Reason, J. (1990), Human Error, Cambridge Cambridge University Press. 

The systems approach seeks to identify situations or factors likely to contribute to human error. James Reason s analysis of industrial accidents revealed that catastrophic safety failures almost never result from isolated errors conunitted by individuals. Most incidents result from smaller and multiple errors in components and environments with underlying system flaws. Reason s Swiss Cheese Model describes this phenomenon. Errors made by individuals can result in disastrous consequences due to flawed systans that are represented by the holes in the cheese. Reason believed human error would happen in complex systems. Striving for perfection or punishing individuals who make errors does not appreciably improve safety. A systems approach stresses efforts to catch or anticipate human errors before they occur. Reason used the terms active errors and latent errors to distinguish individual errors from system errors. Active errors almost always involve frontline personnel. They occur at the point of contact between a human and some element of a larger system. Latent errors occur due to failures of the organization or designs that allow inevitable active errors to cause harm. The terms sharp end and blunt end correspond to active error and latent error. The systems approach provides a framework for analysis of errors and efforts to improve safety. 

In aviation, the taxonomy called Human Factors Analysis and Classification System (HFACS) has been established see Shappell Wiegmann (2000), to understand accidents based on several factors than mere human error. The HFACS taxonomy are based on the Swiss Cheese Model from Reason (1997), looking at accidents as unsafe acts based on preconditions, unsafe conditions and organisational influences, in order to avoid blaming the human element. However, the HFACS method has no exploration of resilience, and should be extended to cover resilient acts, based on preconditions of resilience, resilient conditions and High Reliable Organisational influences. 

The basic Domino Model is inadequate for complex systems and other models were developed (see Safeware [115], chapter 10), but the assumption that there is a single or root cause of an accident unfortunately persists as does the idea of dominos (or layers of Swiss cheese) and chains of failures, each directly causing or leading to the next one in the chain. It also lives on in the emphasis on human error in identifying accident causes. 

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