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(re safety differently ADQ5.d)

(published 12/3/17).


5. The article incorporates a piece on Dekker’s book, ‘Safety Differently’. It says “a wave of world class thinkers at the cutting edge of human factors research...are leading in new directions our thinking about why people behave as they do” (psychologists Hollnagel, Reason and Dekker are named). It then says, “At the same time, they are challenging many of the safety profession’s most fundamental articles of faith, such as the “Domino” theory of accident causation and the “Heinrich triangle” model of accident numbers and severity”.    



a). What is currently accepted as regards “why people behave as they do” at work?

b). What is wrong with the contemporary view identified at a). above?

c). What “new thinking” on human behaviour is being advocated and why?

d). What is the basis for the cited Professor’s beliefs that Heinrich’s Dominos and  triangles are amongst the safety profession’s most fundamental articles of faith? 


The aspect of the question relating to the triangle was dealt with here and the other aspect is dealt with in Part 1. below. Part 2. commences an associated discussion regarding ‘emergence’, ‘complexity’ and ‘a systems perspective’.

Part 1:

The cited professors have long held a multi-causal, systemic view driven by a belief that management and/or organisations cause most, if not all, accidents. As Reason (1990 p.476) put it when introducing the Swiss cheese model, “A point has been reached in the development of technology where the greatest dangers stem not so much from the breakdown of a major component or from isolated operator errors, as from the insidious accumulation of delayed-action human failures occurring primarily within the organizational and managerial sectors”.  

Whilst critical of Heinrich (1931), his dominos can hardly be their real issue when, a). Petersen’s (1971) multiple causation theory and Bird’s (1974) ‘updated’ dominos were well in place, b). Reason’s (1990) Swiss cheese model had replaced dominos with cheese slices, c). Hollnagel (2004) used barriers and layers of defences and both he and Reason rely on linearity (Dekker 2014). Furthermore, Reason Hollnagel and Paries (2006) say “It is now broadly recognized that accidents in complex systems occur through the concatenation [i.e. series or linear connection] of multiple factors [and all] complex systems contain such potentially multi-causal conditions”.

Since Hollnagel, Dekker and Reason are of the same 'school', it may suffice for now (along with ADQ4a. Part 1.) to refer solely to Professor Reason.

The metaphor at the heart of the Swiss cheese model is the psychological precursor or latent failure (now latent condition) and was introduced in Reason (1990). In 1989, the UK Health & Safety Executive publication HS(G)48 – Human Factors in Industrial Safety contained aspects that were clearly from Reason. The 1999 2nd edition was entitled HS(G)48 – Reducing Error and Influencing Behaviour and Reason’s influence is now both obvious and acknowledged. The terms active failures and latent failures are used (also in the 2000/03/05/07 and latest edition) and Reason (1990/1997) is cited as further reading.     

The following is from a Phd thesis (Arnold 2009) supervised by Professor Dekker. At p.12, the thesis introduction says “By the 1990s the concept of barriers and defences in depth...primarily using Reason’s (1990) Swiss Cheese Model (SCM) of failure...was well established in many socio-technical industries including ATM”. 


Interim Comment (1):

Given the above and ADQ4a Part 1., the claim that Heinrich’s (1931) domino theory is a fundamental article of faith of the safety profession is strained and specious. The questions that naturally emerge are, then, what is the real issue and how, or why, does (or should) it involve Heinrich?


Part 2:

The paragraph cited above from Reason (1990) p. 476. continues with...

“These residual problems do not belong exclusively to either the machine or the human domains. They emerge from a complex and as yet little understood interaction between the technical and social aspects of the system”.  

Coming forward in time, we see the Swiss cheese model (SCM) described as “a heuristic explanatory device for communicating the interactions and concatenations that occur when a complex well-defended system suffers a catastrophic breakdown” (Reason et al 2006). That is, it shows retrospectively how the “multitude of functions and entities in a complex socio-technical system interact and depend on each other” but, has no predictive capability.


Interim Comment (2):

A systems perspective holds that certain outcomes in complex socio-technical systems are emergents of multiple interactions. However, in Part 1. above, Reason et al  offered that all accidents in complex systems are caused by a linear series of multiple factors and all complex systems contain such potentially multi-causal conditions. Consequently, that statement and the extracts from Reason (1990) & Reason et al (2006) in Part 2. could lead some to ask if ‘a systems perspective’ is not just an alternative title for a general SCM philosophy. Such a question would not be unwarranted because Reason (1990) said, when introducing the SCM, that the problems in complex systems “emerge”. Furthermore, in The Human Contribution, Reason (2008) says a system perspective is “any accident explanation that goes beyond the local events to find contributory factors in the workplace, the organization and the system as a whole”. Either way, Reason’s use of the phrase “accident explanation” makes it clear that ‘a systems perspective’, like the SCM, will have no predictive capability and, very likely then, neither will notions of emergence and complexity.














A Definition of Emergence

The Institute of Industrial Accident Investigators. All rights reserved.