Bow-tie was born very early in the presentation of a new course, the Graduate Diploma of Occupational Hazard Management, I believe in 1979. This was the first university post graduate course on the general subject of safety that was offered in Australia and I was the senior lecturer in charge of defining and developing content along with an industry advisory group. More of the background is towards the end of this article.
During an Accident Phenomenology class I was explaining the meaning of what I called the Generalised Time Sequence Model (GTSM) to a group of students. The GTSM presented the simple point that when something goes wrong (an Event) there is a Reason/Mechanism for it and afterwards there is Result/Outcome. It is the Result/Outcome that results in observable Consequences (damage, injury, loss). With a little reflection it is clear that the same Event could have various different Reasons/Mechanisms for occurring and various different Results/Outcomes. In both my 1991 book Accident Analysis and Risk Control and my more recent 2015 book Occupational Risk Control: predicting and preventing the unwanted I show this model as a linear sequence of lozenge shapes. I had presented this graphically on a time line using elongated lozenge (1991) or rounded shapes, see below, in the 2015 book:
The students stared at me when I made this point. Their blank stares were unnerving, so as I wiped the blackboard (yes, it was in the good old days of chalk-and-talk) I thought about how to present the diagram noticeably differently. I drew a circle in the middle of the board, to represent the Event and the idea came to me of showing possible Reasons/Mechanisms also as circles on the left of the Event – meaning earlier in the time-line. I drew a separate line from each of these circles to the Event circle. I commonly explain this using a fall as the example Event – one circle for slips, another for trips, another for …several more… and so on.
I turned around and lights in the eyes of each and every student were all on!
Encouraged by this I continued, using the same graphics to represent the Results/Outcome of an Event – there are four basic ones for a fall: regained stability (the null outcome); arrested fall (eg. hanging on to the handrail); complete fall to ground; complete fall to another level. Like this:
As I finished someone exclaimed “that looks like a bow-tie!” I stood back from the board and said, “so it does!”. All lights in the eyes stayed on.
I further pointed out that not only was this a useful unifying concept (energy and process together, see below) but it also makes clear the fact that control measures could be applied to each possible Reason/Mechanism as well as to each possible Result/Outcome. The control measures for a slip will not be the same as those for a stumble, for example.
I recall two students from ICI in Melbourne, Australia were in that group. Given the subsequent various attributions of the origin of the model (see the Wikipedia entry and other papers for these) I think it highly likely that these students took the graphic and used it, without acknowledging its source and it spread from there.
Because of that communication success I have subsequently used exactly that graphic to make the point in numerous industry courses and in a 1992 manual on accident investigation. As an example, one of these courses, but I can’t recall exactly when, was to a group of safety people from the petrochemical industry – I recall the refinery in Altona, Victoria, Australia. I have also used it in industry courses for engineers and others on risk analysis methods in various industries in Australia (power generation, petrochemical industry), Saudi Arabia (petrochemical industry), India (steel industry), Thailand (mines) and South Africa (mines).
The historical context of this needs to be understood to fully appreciate how revolutionary (in other words: weird, odd, academic, or in those days “far-out!”, in these days “blue-sky” and so on) it actually was.
“Accidents” and Heinrich’s “unsafe acts” (Heinrich, H.W. (1959) Industrial Accident Prevention, A Scientific Approach. New York: McGraw Hill) were all there was in the general mind space in the 1970s. Heinrich said a lot more than unsafe acts, but mostly he was selectively read at that time, as I suspect he still is. The idea we should talk about accident causation perhaps rather than accident cause was breathtakingly new. It is fair to say that practitioners had no knowledge of Haddon and Co’s refutation of accident theory and statements about energy damage (see below).
To illustrate the atmosphere just a little, at a National Safety Council of Australia conference in Melbourne at that time I suggested a reasonable definition of the term safe or safety was “an acceptable level of risk”. An angry and affronted member of the audience sprang to his feet immediately to announce that he and everyone in the audience knew that safety was actually a state of mind. Hmmm! No-one had taught me how to handle interjections of that nature.
The late Eric Wigglesworth (Wigglesworth, E.C. (1972) A Teaching Model of Injury Causation and a Guide for Selecting Countermeasures. Occupational Psychology, 46, 69–78.) was a member of the course industry advisory group and he introduced me to literature worth reading. Those were pre-internet days of course. I was searching for something of a standard that could be taught at a post graduate level and it was not easy to find. I had decided two subjects were needed and named them Accident Phenomenology (to the shock of my colleagues at the university – “please explain!”) and Risk Philosophy. I had no idea what I would use for content.
I first became aware of the need for scientific effort to focus on the process leading to the phenomenon of interest from geology and biology academics at the BCAE and secondly as a result of reading Haddon (Haddon, W. (1973) Energy Damage and the Ten Countermeasure Strategies. Journal of Trauma, 13(4), 321–31). Prior to that, as a mechanical engineer I was grounded in the mathematical sciences of Newton and Kelvin, with a little chemistry and had never considered how the non-mathematical sciences got on. The phenomenon of interest in this field is damage (which term can include injury and ill-health).
The GTSM, being founded on a time line, is a process model – this happens then that then the next…
Haddon also pointed out the (rather obvious in hindsight) significance of energy sources in this process. One of his co-researchers JJ Gibson (Gibson, J.J. (1961) The Contribution of Experimental Psychology to the Formulation of the Problem of Safety – A Brief for Basic Research. In: Jacobs, H.H. et al., Behavioral Approaches to Accident Research. New York: Association for the Aid of Crippled Children) had made this point earlier. In Paul Swust et al (Occupational safety theories, models and metaphors in the three decades since WWII in the United States, Britain and the Netherlands: a literature review,Safety Science 62 (2014) 16–27) mention is made of earlier papers on this, the earliest being that of Deblois in 1927. I now knew on what my Accident Phenomenology course was to be based-a development of this idea beyond a mere statement of it.
A little later I discovered Rowe’s exceptional (and largely ignored!) work (Rowe, W.D. (1977) An Anatomy of Risk. New York: John Wiley and Sons) and also that of Jean Surry, a Canadian industrial engineer and academic. Rowe’s was the only academically credible text I could find covering the whole field of Risk scientifically and it remains unsurpassed in my view. Rowe modelled Outcome pathways following an event, although defining the event in an unsatisfactory and uncharacteristically circular manner as “what resulted in Outcomes” and Outcomes as “what followed an event”. Jean Surry showed elegantly how Outcomes involving human decision-making could be modelled using decision trees, although she didn’t call it Outcome.
I realised that Rowe’s event could be properly defined as “the point in time when control was lost of the potentially damaging properties of the energy source of interest”. This resulting model was not only comprehensive (there is a finite number of energy forms) but also objective and so suitable for scientific and hence engineering application. I now knew on what the content of my course in Risk Philosophy would be based: properly understand the notion of risk (it is not just a synonym for chance), connect it with energy damage (or non-energy Threats) and then consider how to identify, estimate the significance of, understand the control options for and then evaluate these options. You might note that this sequence does not concur with the numerous risk Standards. I well recall the moment of this revelation – I was standing alone and almost freezing, were it not for the meagre glimmer of heat from a reluctant fire in the Ballarat food co-operative one winter Saturday morning, where I was the only one on duty to sell potatoes to early environmentalists. Very few people ventured out that day, so I had lots of uninterrupted thinking time. The penny dropped and I knew I had the content for the Risk Philosophy course.
So, on the chalk board that day some months later, I defined the Event as the point in time when control is lost over the potentially damaging properties of the gravitational potential energy of the person who is about to fall – in short “a fall begins”.
What is now universally known and used as the bow-tie model or diagram creates a unifying theory that joins energy damage and risk theory with the work of risk engineers: Fault Tree Analysis; Event Analysis (what Rowe called the Outcome) up to that date.
At least, it should do.
However, those who continue to believe in “cause-effect/consequence” ideas have hi-jacked it into their comfort zones regardless of the cautions of the scientific literature. The literature (old and modern) decrying the use of ’cause’ ideas in science is generally ignored. Even the ISO (see ISO/IEC/IEEE 16085) does this! They replace Mechanisms with Causes, Outcomes with Consequences and energy with Risk Source. We have no need of metaphysics to understand this simple field, which has nothing obscure or mysterious about it. Damage is simply a probabilistic by-product of otherwise deterministic processes. To an engineer, it is no more complex than reliability and maintenance theory, with which it has a lot in common. Chemistry stepped away from Alchemy, Astronomers from Astrology and we, too, should turn away from metaphysics and towards the physical science of physics.
As I have written elsewhere (Viner 2015 above) – ideas in the industrial accident field, the nuclear risk field and those driven by engineers’ needs to solve problems associated with the cold war and the space race all occurred separately but at similar times. I was initially and briefly disappointed to realise that my insight into a coherent theory was actually in direct accord with what risk engineers had been doing all along! However, the engineering methods had not had a focus on energy and hence had no theory for deriving an Event (Top Event etc.) of interest nor for the structure of Mechanism (Fault Tree) analysis.
Such was the state of thought in the occupational safety field in those days and into which abyss the bow-tie model in all its initial purity was dropped on that day to subsequently be subject to all forms of graffiti.