Swiss cheese model of accidents

The Swiss cheese model of accident causation was originally proposed by British psychologist James T. Reason and has since gained widespread acceptance in many risk-analysis and management fields including process safety. 

FIGURE 52.1 The use of Reason s Swiss cheese model of accident causation for the management of medical equipment risk. (Adapted from Reason, J. 2000. British Medical lournah 320 768-770,18 March.)... 

The study of patient safety is the study of complexity. The study of complexity invites us to understand key concepts that can be applied to patient safety. Basic concepts from the fleld of patient safety are sharp and blunt end active and latent failure the Swiss Cheese Model of Accident Causation slips, lapses, and mistakes and hindsight bias and the fundamental attribution error. Key concepts from organizational analysis, such as normalization of deviance, diffusion of responsibility, tightly coupled work processes, and sensemaking, introduce practical lessons from high-reliability organizations. Application of specific lessons to health care are explored in Chapter Five. 

The Swiss Cheese Model of Accident Causation is a prerequisite for understanding the dynamics of the emerging risk and organizational defenses that are necessary to improve safety. Figure 4.2 illustrates the model, using its metaphor, a wedge of Swiss cheese. The model was described in detail in Chapter Three here, a metaphorical exploration of the model amplifies its implications for accepting leadership responsibility. 

Swiss Cheese Model of Accident Causation (Introduction) A metaphorical, visual representation of the nature of emerging risks in complex systems characterized by vulnerabilities as well as defenses. 

Mgiire 13.1 The Swiss cheese model of error and accident causation Error management and Swiss cheese... 

The Swiss cheese model (see Figure 1.3 in Chapter I and Figure 3.2) offers another useful way to envision how failure to contain a hazard could result in a serious consequence if the process safety barriers and controls have weaknesses— the holes in the slices of Swiss cheese. For example, in order to prevent the risk of an accident, such as hydrocarbon release, a number of barriers (i.e., risk reduction... 

When there is less fear of blame and punishment, people become more open to discussing errors and near misses (Barach and Small 2000). Near misses are an important source of information as they are accidents that almost happened. Since they differ only slightly from accidents, they can teach us a lot about causes of error in a workplace. This is described by (Reason 1990) in his Swiss cheese model seen in Figure 3.2. There are a variety of factors that affect whether or not an accident occurs. The factors influencing a situation are likened to slices of Swiss cheese which contain a number of holes. These holes represent weaknesses which could lead to errors. Accidents occur when the holes in each slice (or variable) align, while near misses occur when most, but not all, of the factors necessary for an accident are present. In this way, near misses can provide cracial information about imidentified risk factors. 

The Swiss Cheese Model represents the nature of emerging risks in complex systems, with their defenses and vulnerabilities. Undetected vulnerabilities or denigration in defenses create conditions for errors to concatenate to produce medical accidents. 

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. 

On the TRIPOD website (http //www.energypublishing, org/tripod), the method is described as a theory (sic ) for understanding incidents and accidents, in particular to allow the root organisational causes and deficiencies to be uncovered and addressed. TRIPOD can be seen as an elaboration of the ideas in the Swiss cheese model. The AcciMap is a method to develop a map of an accident by means of the abstraction hierarchy. The original description can be found in Rasmussen,... 

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 Swiss cheese model theorized by Reason (1990, 1997) indicates that there are a number of defensive layers and their associated holes between hazards and potential losses. These holes are in continuous motion, moving from place to place, opening and shutting. Holes are caused by latent conditions and active failures. No one can foresee all possible accident scenarios. Therefore, some defensive layers with holes will be present from the establishment of the system or will develop unnoticed or uncorrected during system operations. When such holes line up in a number of defensive layers, hazards come into direct contact with potential losses and an accident occurs. 

Requirements for avoiding potential losses and accidents are to prevent the holes in Swiss cheese model from lining up. This means that when one of the holes, which had hned up due to latent conditions, is shut, losses and accidents do not occur. Therefore, it is important to find the relationships between holes and latent conditions for preventive measures. The objective of this research is to find the relationships between holes and latent conditions in colhsions. If the relationships can be determined, efforts can be directed to specified latent conditions in order to shut holes or prevent collisions. 

Fukuoka, K, 2015, WMU Journal of Maritime Affairs, Visualization of a hole and accident preventive measures based on the Swiss cheese model developed by risk management and process approach. New York Springer New York, LCC, Doi 10,1007/sl3437-015-0076-2. 

Figure 4.1 also illustrates the additive nature of a job s safety risks. That is, added safety risks associated with each factor cumulatively increase the job s overall safety risk. The additive nature of risk is well captured by Reason s (1990) Swiss cheese safety model. Each factor represents a risk layer, and the probability of an accident increases as the number of risk layers increases. Where possible a job which a new employee is entering should be striped of as many risk layers as possible. As will be discussed below, more senior employees, who are experienced, are likely to be better able to cope with job risks which are difficult or impossible to remove. 

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. 

Causality models based on event chains (or dominos or layers of Swiss cheese) are simple and therefore appealing. But they are too simple and do not include what is needed to understand why accidents occur and how to prevent them. Some important limitations include requiring direct causality relationships, subjectivity in selecting the events to include, subjectivity in identifying chaining conditions, and exclusion of systemic factors. 

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