Pedestrian incidents and forensic tribology: An analysis
03 April 2018
Like many fields, tribology or friction analysis is very broad. It is a postgraduate field since its foundations rely upon prior knowledge of several dynamic undergraduate subjects. Although its history is very old, tribology centres around an analysis of understanding dynamic surface interfaces and interactions.
As with any aspect of forensic analysis, forensic tribology applies to past events, seeking to clarify and so understand them, either to ensure they don’t happen again or, if they are desired, or even serendipitous, that the subject event is fully understood, and so improved upon by those discovered design factors that are disclosed by a close audit of that prior event.
Its commonest use is still for metal-on-metal analysis, such as occurs in all forms of dynamic machinery and equipment
So, for example, one could be talking about a vehicle on a road surface and the analysis of the tyre interaction with the particular road surface – vehicular tribology. Its commonest use, however, is still for metal-on-metal analysis, such as occurs in all forms of dynamic machinery and equipment.
From this dynamic perspective, and the primary focus of this article, it is used for pedestrian slip and fall analysis, both of the flooring surface, be it interior or exterior, and the footwear. Tribology is the parent field for such accidents and so it is important for an engineer to be fully cognisant of what the scientific, pedagogic and ethical implications are.
There is a general equation of crucial importance for the combined adhesion and the hysteresis components of the coefficient of friction occurring in all slip events to humans, and it applies in the ‘metallurgical’ arena too – all metal surfaces are fabricated. This equation, stereotypically found in expert reports in a slip and fall case, is also of considerable use in auditing slip friction measuring equipment and, in the writer’s own experience*, such auditing is invariably included in the ongoing development of National Standards. Just like impulsive force or vibration landscapes are of concern in the industrial setting, so too their occurrence in a friction test device is to be avoided. These design errors abound. [*The writer sits on the Australian Standard Committee BD094, covering the family of standards on slip resistance of pedestrian surfaces.]
It often relies on the multidisciplinary interaction it has with other disciplines
Because of this breath of application (vehicle, industrial, pedestrian locomotion, etc), the field often relies on the multidisciplinary interaction it has with other disciplines, not all of which are engineering. For example, in medical applications it is often interfacing with biomechanics. For some topographic surface or footwear analyses, one is combining elastomeric material analysis, or even paint lamination, in tandem with a pedestrian’s locomotion and with ergonomics.
Forensic tribology also has much to say on the contact interface in, say, manual handling of an object, or of a patient. In fact, there are few workplace accidents where tribology doesn’t have some input. This is useful to remember if adhering to the ‘basis rule’, for example, the ‘Ikarian Reefer’ case.
From the simplest definition of tribology, being the science of wear, friction and lubrication, the latter two are relatively well developed whereas the former is still in its infancy – at least in the slip and fall arena. An audit of any such interface of interest may well be a tripartite analysis.
‘Legal’ application of tribology is still developing
Because the ‘legal’ application of tribology is still developing, this is reflected in many of the legal-related judgments that one can research. For example, the famous case of ‘Kumho Tire Co V Carmichael, 526 US 137 (1999)’ (United States) an otherwise well-qualified mechanical engineer was deemed to be an inappropriate expert when it came to car tyre analysis due to the true nature of that specific application.
Not just from a scientific perspective, but from a pedagogic perspective, that is an entirely correct decision for a court to make, highlighting their clarity of understanding. It also improves the standing of our profession. In pedestrian analysis, in the case of Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705 (New South Wales), much comment was passed upon the nature of push and drag configuration devices, versus the pendulum friction device, which has a much longer pedigree and, importantly, one not exhibiting a point of inflection in its function. Trolley-style friction test devices are especially prone to this error.
All these avenues of information help our understanding of auditing pedestrian slip and fall accidents. Because it is multidisciplinary, and in particular for pedestrian analysis, tribology also draws on the distinct field of ergonomics. Consequently, and in reverse, we are only now beginning to expand on how the field can assist ergonomics. For example, cognitive ergonomics applies enormously to the initial design specification and concept design stages of road design, just as tribology does, and they can overlap, even for pedestrians.
It is often relevant to, for example, biomechanic legform slip events on a stairwell
So there is much to commend tribology for it is often relevant to, for example, biomechanic legform slip events on say, a stairwell, or to palmar contact errors on a balustrade, as much as it is of benefit to the analysis of indigenous and foreign contaminated, elastomeric footwear on a shopfloor, or on a ladder, or in a farmyard. So, for any consulting engineer the use of experts in this field will allow their clients derive improved return on capital investment. The inverse may otherwise apply.
The current state of the art in footwear analysis, though some of these advances are yet to be appreciated, is of interest. For example, where an item of footwear apparel exhibits a relative softness differential versus that of a harder flooring surface beneath it, means that even new footwear can become, effectively, self-contaminating. Just look at your footwear.
Likewise, when new footwear is worn externally your heels are also subject to an initial and very high, wear rate. This is just the same as that which occurs in the newly in-service ‘metallurgical’ tribological landscape. Again, the consequences of this wear on footwear (for example, Archard’s principle) are very real.
Combining tribology with human factors research can be very helpful
What if the actual footwear in a court case was not needed to comment on it? Well, that’s where forensic tribology is now at. Just as a car’s existence in an accident presupposes four tyres, it is just the same concept with footwear apparel wear. Combining tribology with human factors research can be very helpful and will, one day, make footwear safer and so decrease slip and falls, especially for the eldery, where the consequential links to morbidity are stark.
Finally, lest you think forensic tribology may seem too esoteric, or only serious, it’s not all work and no play. A 2-D topographic analysis, which is heavily visual, and which is generally crucial to tribology in all its facets, is akin to the concept design phase of the engineering cycle, itself something not always relied on in the process/systems specification phase.
Such analysis is very similar to the figure/ground motif used in fine art and in packaging engineering, quite aside from, say, understanding paint* lamination in or upon an interface. [*or varnishes, sealers, waxes, etc.] When, say, one is auditing a wetted rough tile for its subtle topographic characteristics, or a going’s nosing, when both should be slip resistant but test otherwise, or vice versa, perplexion at the hydrodynamics must lead to a solution.
Using such conceptual and applied forms of surface analysis one can audit fine artworks, and discern that, just like the contaminated tile’s unusual hydrodynamics, the ‘landscape’ (the ground as it were) in an artwork is perhaps not just a landscape. So, for example, in one such case, the Alpine landscape turned out to be a religious artwork full of iconographic symbols and figures, largely hidden, and derived from both Bellini’s and Da Vinci’s versions of ‘St Jerome in the Wilderness’.
Copied and jointly intermixed, yet with the UV-audited signature ‘JTurner RA’ upon it, and with the standard Old Germanic typeface hallmark symbol for Wahrheit (Truth) hidden in the clouds, defining it as an example of a Nazarene Turner. It’s his intellectually superior version of JFOverbeck’s ‘Triumph of Religion in the Arts.” So perhaps tribology is neither hermitical nor such a wilderness after all – you may find an old master or two!
Patrick Donohue MA, MED, HDipEd, CEng MIEI, CPE MHFESA, MDIA, is an engineer, ergonomist, designer, artist, art connoisseur, among other fields of studyhttp://www.engineersjournal.ie/2018/04/03/pedestrian-incidents-forensic-tribology/http://www.engineersjournal.ie/wp-content/uploads/2018/04/a-tribe1-1024x643.jpghttp://www.engineersjournal.ie/wp-content/uploads/2018/04/a-tribe1-300x300.jpgMechbiotechnology,mechanical,roads