Swiss cheese model

James Reason offered another useful model, often referred to as the Swiss cheese model, that explains how the many factors can converge, resulting in an incident (Figure 6-5). A company tries to promote safety and prevent catastrophic incidents hy putting into place layers of system defenses, depicted in Figure 6-5 as slices of Swiss cheese. Essentially, the term system defenses refers to the safety-related decisions and actions of the entire company top management, the line supervisors, and the workers. This model recognizes that each defense layer has weaknesses or holes. 

The Swiss-cheese model approach is consistent with the X-ray data, which show that the distance apart of ions remains constant or decreases on melting while the volume increases -20%. In this respect, it is more consistent with experiment than... 

Fig. 1.5. (a) A typical link-element structure in the Swiss-cheese model of continuum percolation in two dimensions. The channel width is denoted by 6. (b) The dashed lines indicate the outline of the rectangular bond which approximates the narrow neck of a channel. 

In continuum percolation (see Section 1.2.1(g)), we suppose that the defects are introduced in a solid sample as randomly placed insulating holes with the shape of a circle (in two dimensions) or a sphere (in three dimensions) and we include the possibility of overlap of the defects (Swiss cheese model). This last possibility gives near Pc an infinite cluster with the the links having different cross-sectional width 6. This property is essentially responsible for the differences between lattice and continuum percolations. 

In the discrete lattice model, discussed above, each bond is identical, having identical threshold values for its failure. In the laboratory simulation experiments (discussed in the previous section) on metal foils to model such systems, holes of fixed size are punched on lattice sites and the bonds between these hole sites are cut randomly. If, however, the holes are punched at arbitrary points (unlike at the lattice sites as discussed before), one gets a Swiss-cheese model of continuum percolation. For linear responses like the elastic modulus Y or the conductivity E of such continuum disordered systems, there are considerable differences (Halperin et al 1985) and the corresponding exponent values for continuum percolation are higher compared to those of discrete lattice systems (see Section 1.2.1 (g)). We discuss here the corresponding difference (Chakrabarti et al 1988) for the fracture exponent Tf. It is seen that the fracture exponent Tf for continuum percolation is considerably higher than that Tf for lattice percolation Tf = Tf 4- (1 -h x)/2, where x = 3/2 and 5/2 in d = 2 and 3 respectively. 

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. 

Process safety incidents are rarely caused by a single catastrophic failure, but rather by multiple events or failures that coincide and collectively result in an incident. This relationship between simultaneous or sequential failures of multiple systems is illustrated by the Swiss cheese model, as shown in Figure 1.1, where hazards are contained by multiple protective barriers that may have weaknesses or holes. ... 

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. 

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... 

Figure 3.2 Swiss Cheese Model (CCPS, 2007b)...

Regardless of whether one uses the process safety pyramid, the Swiss cheese model, or something else (for example, the anatomy of an incident model discussed in HEP 3), the concepts of... 

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 effective management of medical equipment-related risk requires a meaningful and practical framework or paradigm from which to start. As described here. Reason s modified Swiss cheese model provides one such paradigm. Metaphorically and conceptually, the model also tends to be readily understood, which further aids in its acceptance as a risk management tool. 

Perneger, T.V. 2005. The Swiss cheese model of safety incidents Are there holes in the metaphor BMC Health Services Research. 5 71. 

Reason reinvented the Domino Model twenty years later in what he called the Swiss Cheese model, with layers of Swiss cheese substituted for dominos and the layers or dominos labeled as layers of defense that have failed [172,173]. 

Figure 3.2 Swiss cheese model on how the hazard penetrates through holes of barriers.

Young, M., Shorrock, S., Faulkner, J. 2005. Seeking and finding organisational accident causes comments on the Swiss cheese model. Retrieved Febmary, 28, 2007,... 

The role of voids in the structure of a-Ge and a-Si was discussed in some detail by Ehrenreich and TumbuU (1970) which propose a tentative swiss cheese model in which voids of different sizes are included into a random network. The presence and coalescence of such voids by the annealing of a-Ge films has been detected by electron microscopy by Barna, Bama, and Pocza(1972). 

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 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. 

An important component of the Swiss Cheese Model depicted in Figure 3.3 is the individual plane. This plane represents the protective defenses put up by workers at the sharp end to deflect failure and vulnerability from becoming transformed into harm. Individual workers create safety at the sharp end aU the time as they encounter hazards and opportunities for failure and continually stop them before they reach patients. It is when worlqjlace stresses erode the coping resources... 

Concept to Action Using the Swiss Cheese Model to Deconstruct Risk-Prone Conditions and Improve Safety... 

As a participant in his hospital s patient safety initiative, pediatric emergency physician Tom Hellmich attended several educational sessions where he learned about basic concepts in safety, such as hindsight bias and the Swiss Cheese Model. The lessons proved useful during a particularly busy week at work. In one day, two children, one in the hospital s emergency department and the other in an inpatient unit, suffered a cardiac arrest, requiring a code to be called. 

On a table in the break room, staff members gathered around while Hellmich sketched a version of the Swiss Cheese Model on a piece of paper. He began to explain how a team is affected by the systems that surround it. The discussion grew into a series of meetings where staff members conducted a multicausal analysis of the code. 

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