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The Swiss Cheese Model vs Human Factors Analysis and Classification System (HFACS)

What is most effective, and how can it be integrated to be so?

Investigation is an excellent method of identifying root causes to an accident. Although, investigation alone is merely used as a reactive measure (Hudson, 2000). In the aviation context, Shappell and Wiegmann (2000) use Reason’s Swiss Cheese Model and the updated Human Factors and Classification System (HFACS) as a means to validate their conclusion that HFACS “bridges the gap between theory and practice by providing investigators with a comprehensive, user-friendly tool for identifying and classifying the human causes of aviation accidents” (p. 13). Interestingly, both the Swiss Cheese model and HFACS share some slight similarities and differences.


James Reason’s well known conceptual Swiss Cheese model outlines the basic ‘barriers’ that an organisation should have in place to prevent an accident. These include, “organisational influences, unsafe supervision, preconditions for unsafe acts, and unsafe acts” (Shappell & Wiegmann, 2000, p. 2). Conceptually, the model shows holes in the barriers, where if lined up in a catastrophic event or near miss is said to have occurred. The delineator with the Swiss Cheese model is that latent failures occur within an organisation yet are not able to be quantified.


The Human Factors Analysis and Classification System (HFACS) expands from the Swiss Cheese model, into a taxonomy of reportable accident causation characteristics. Working back from the accident, HFACS breaks each of Reason’s levels into further accident causation types, forming a taxonomy between “errors and violations” for level 1, “sub-standard conditions of operators and substandard practices of operators” for level 2, “unsafe supervision” for level 3 and “organisational influences” for level 4 (pp. 3-11). The key similarity to the Swiss Cheese model being the lack of ability to quantify data.


Overall, the Swiss Cheese model and HFACS share similarities in terms of the modelling, with the HFACS sharing the barriers, which are broken down further into taxonomy (Wiggins & Stevens, 1999). The taxonomy enables an organisation to collate reportable data, and formulate trends over time. However, one aspect that is not necessarily clear with both models is what an organisation can do proactively, in terms of using these models (Hudson, 2000). Although, hazard identification and risk management techniques have evolved, by means of using data mining and taxonomies to proactively mitigate hazards at each barrier. ICAO (2013) proposes a number of strategies to enhance overall organisational safety culture, which may be coupled with HFACS to strengthen the interfaces between each barrier.


References:

Hudson, P. (2000). Safety Management and Safety Culture: The long and winding road. The Netherlands: Centre for Safety Research, Leiden University.


International Civil Aviation Organisation. (2013). Safety Management. Annex 19, International Standards and Recommended Practices. Montréal, Canada: Author.


Shappell, S. & Wiegmann, D. (2001). Beyond Reason: Defining the holes in the Swiss Cheese. Human Factors and Aerospace Safety, 1(1), 59-86.


Wiggins, M.W. & Stevens, C. (1999). Aviation social science: Research methods in practice. Aldershot, UK: Ashgate.

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