Andy Montoya
The Swiss cheese model is a model used in risk analysis and management. It likens human systems to slices of Swiss cheese, with holes representing weaknesses in the system. The model was developed by James T. Reason of the University of Manchester and has gained widespread acceptance. It has been applied in various fields, including aviation, engineering, healthcare, and computer security. The Swiss cheese model helps identify and mitigate risks by understanding that no system is perfect and that multiple layers of defence are necessary to prevent failures.
| Characteristics | Values |
|---|---|
| Application | Aviation safety, engineering, healthcare, emergency service organizations, computer security, defense in depth, oil and gas drilling and production, asset integrity management, incident investigation |
| Concept | Human systems are like slices of Swiss cheese with randomly placed and sized holes; each slice is a different type of defense |
| Purpose | Used in risk analysis and risk management to prevent a single point of failure |
| Creator | James T. Reason of the University of Manchester |
| Other Names | Cumulative act effect |
| Criticism | Too broad and not supported by other models |
| Example | A fence is one slice of Swiss cheese, with holes; CCTV cameras are another slice; security patrols are another slice |
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What You'll Learn
The Swiss cheese model of accident causation
The Swiss cheese model likens human systems to multiple slices of Swiss cheese, stacked side by side. Each slice of cheese represents a different type of defence or safety-critical system, and the holes in the cheese represent weaknesses or lapses in that defence. The model illustrates that, while one defence may have a lapse or weakness (a hole in one slice of cheese), there are other defences in place (other slices of cheese) to prevent a single point of failure. This is the principle behind layered security, as used in computer security and defence in depth.
In the early days of the Swiss cheese model, attempts were made to combine James Reason's multi-layer defence model with Willem Albert Wagenaar's tripod theory of accident causation. This resulted in a period of confusion, as the slices of cheese were labelled 'active failures', 'preconditions', and 'latent failures'. A more correct version of the combined theories shows the active failures (now called immediate causes), preconditions, and latent failures (now called underlying causes) as the reasons each barrier (slice of cheese) has a hole in it, with the slices of cheese representing the barriers.
The Swiss cheese model has been applied in various fields, including aviation safety, engineering, healthcare, and emergency service organizations. For example, in healthcare, a latent failure could be the similar packaging of two different drugs stored close to each other in a pharmacy, contributing to the administration of the wrong drug to a patient. This research led to the realization that medical errors can result from "system flaws, not character flaws", and that factors such as greed, ignorance, or laziness are not the only causes of error. The Swiss cheese model is also widely used in process safety, particularly in oil and gas drilling and production, for illustrative purposes and to support other processes such as asset integrity management and incident investigation.
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Defence in depth
The Swiss cheese model is a model used in risk analysis and management. It was developed by James T. Reason of the University of Manchester. The model likens human systems to multiple slices of Swiss cheese, with holes of varying sizes and positions. Each slice of cheese represents a different defence or safety-critical system, and the holes represent weaknesses or failures in these systems.
The defence in depth strategy is based on the Swiss cheese model. It recognises that no security system is perfect and that there will always be holes that can be exploited. By layering multiple slices of cheese (or defences) behind each other, the risk of a threat becoming a reality is mitigated. This is because, even if a threat manages to get through one layer of defence (a hole in one slice of cheese), there are other defences in place to prevent a single point of failure.
For example, in the context of security for a small estate, the fence could be one slice of Swiss cheese, with holes that a potential intruder could exploit. The addition of CCTV cameras and security patrols adds further slices of cheese, each with their own pattern of holes. By layering these defences, the chances of a successful intrusion are reduced.
Overall, the defence in depth strategy, inspired by the Swiss cheese model, provides a robust framework for managing risks and ensuring that small, individual failures do not align to create a trajectory of accident opportunity.
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James Reason's multi-layer defence model
The Swiss cheese model of accident causation, originally proposed by James Reason, likens human system defences to multiple slices of Swiss cheese, stacked side by side, with randomly placed and sized holes in each slice. The holes in the slices represent weaknesses in individual parts of the system, which are continually varying in size and position across the slices. The model asserts that the risk of a threat becoming a reality is mitigated by different types of defences, which are "layered" behind each other. Thus, in theory, lapses and weaknesses in one defence (a hole in one slice of cheese) do not allow a risk to materialize, as there are other defences (other slices of cheese) in place to prevent a single point of failure. This is the fundamental idea behind James Reason's multi-layer defence model.
In the early days of the Swiss cheese model, attempts were made to combine James Reason's multi-layer defence model with Willem Albert Wagenaar's tripod theory of accident causation. This resulted in a period of confusion, where the Swiss cheese diagram was represented with slices of cheese labelled 'active failures', 'preconditions', and 'latent failures'. However, a more correct version of the combined theories acknowledges these labels as the reasons for the holes in the cheese slices, with the slices themselves representing the barriers or defences.
The Swiss cheese model is also used as the principle behind layered security in computer security and defence in depth strategies. In cybersecurity, defence in depth refers to using multiple security products and practices to protect an organization against a wide range of threats. This strategy is based on the idea that a single security product cannot fully safeguard a network from every possible attack. By implementing multiple security measures, organizations can effectively mitigate a broad spectrum of threats and limit the damage caused by attackers.
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Willem Albert Wagenaar's tripod theory of accident causation
The Swiss cheese model of accident causation is a model used in risk analysis and risk management. It likens human systems to multiple slices of Swiss cheese, which have randomly placed and sized holes, stacked side by side. The risk of a threat is mitigated by different types of defences "layered" behind each other. This model was originally propounded by James T. Reason of the University of Manchester and is sometimes called the "cumulative act effect".
In the early days of the Swiss cheese model, attempts were made to combine James Reason's multi-layer defence model with Willem Albert Wagenaar's tripod theory of accident causation. This resulted in a period of confusion, as the Swiss cheese diagram was represented with slices of cheese labelled 'active failures', 'preconditions', and 'latent failures'.
Willem Albert Wagenaars' tripod theory of accident causation is not detailed in the sources available. However, accident causation theories are both an art and a science that seeks to understand the deeper roots of why accidents happen. They explore the various factors that contribute to accidents, such as human behaviour, unsafe conditions, and the environment. Accident analysis methods like TRIPOD, Fault Tree Analysis, and STEP are used to predict future accident scenarios and prevent accidents from happening in the future.
Accident causation theories provide insight into the complex factors that play a role in workplace incidents. They help identify patterns and underlying causes, promoting a safer environment. Other examples of accident causation theories include Petersen's Accident Causation Theory, which adapts Ferrell's human factors of overload and states that accidents are caused by human error and/or system failure. The 5M Model for Accident Causation identifies five core areas where failing factors may appear: Man, Machine, Medium, Mission, and Management.
The Swiss cheese model has been applied to aviation safety, engineering, healthcare, and emergency service organizations. It is also used as the principle behind layered security in computer security and defence in depth.
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Lapses and weaknesses in one defence
The Swiss cheese model, also known as the cumulative act effect, is a model used in risk analysis and management. It was developed by James T. Reason of the University of Manchester. The model likens human systems to multiple slices of Swiss cheese, with holes of varying sizes and positions in each slice. Each slice represents a different type of defence, and the holes represent lapses and weaknesses in those defences.
According to the model, no defence is perfect, and each will have its own weaknesses. For example, a fence may have blind spots, and CCTV cameras may have limited coverage. These weaknesses are like the holes in Swiss cheese, which allow something to pass through. However, just as multiple slices of cheese are stacked to prevent cheese from falling through, multiple layers of defence are necessary to prevent a single point of failure.
The Swiss cheese model recognises that no amount of defence is 100% effective, and criminals or hazards can still get through. This is where defence in depth comes in, which involves having multiple layers of protection. By having multiple slices of cheese, or defences, the chances of a threat impacting an organisation are reduced. This is because the holes in one slice of cheese, or defence, may be covered by the slice next to it.
Despite its widespread acceptance, the Swiss cheese model has been criticised for being too broad and lacking sufficient support from other models. Nonetheless, it has been applied in various fields, including aviation safety, engineering, healthcare, emergency services, and computer security. By understanding the model, organisations can identify and address weaknesses in their defences, adding new layers of control to improve their security systems.
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Frequently asked questions
The Swiss cheese model is a model used in risk analysis and management. It likens human systems to multiple slices of Swiss cheese, which have randomly placed and sized holes. The holes represent weaknesses in individual parts of the system.
Each slice of Swiss cheese represents a layer of defence or control. For example, a fence is one slice of Swiss cheese, with holes. The CCTV cameras are another slice, the security patrols another slice, and so on.
When the holes in the Swiss cheese momentarily align, a risk becomes an incident. This is called a "trajectory of accident opportunity" by James Reason.
The Swiss cheese model has been criticised for being too broad and not being supported by other models. It is also based on the assumption that no security system is perfect, which may not be true in all cases.
