The technical mistakes in Makita and Sprowles prove why courts needed more expert evidence not less.

Makita and Sprowles

Makita and Sprowles (1999 NSWSC 1239; 2001 NSWCA 305; 2002 HCATrans 274) is a case in negligence about a fall on a stair.  It is – unfortunately –cited as an instructive case on the limits to expert evidence.  For example it gets a reference in Dasreef and Hawchar (2011, HCA 21) and the Crown versus MClelland (2010 ACTSC 40).  However, it is troubling that Makita and Sprowles forms a backdrop for the principles of the use of expert evidence.  The reason is that the case failed to canvass comprehensive technical input on the subject matter.  It is difficult to reconcile how it can be instructive on expert evidence when it is flawed on the same dimension.  Makita and Sprowles is an example where the courts became sidetracked on the one technical issue that appeared important, argued from one court to another about admissibility of evidence about that technical issue, but never worked out that the evidence being argued about was not actually important.  The end result was some thinking about what was admissible evidence but an unfortunate absence of consideration about whether it was useful evidence and subsequently an absence of useful evidence.  Once the expert evidence was put aside the thrust of the proceedings was that the matter under consideration could be viewed through the prism of everyday knowledge.  I do not think that was the right judgment.    The legal system became so concerned about its own procedures, rather than the problem under consideration, that the mechanism of the accident and analysis of relevant design features that should have been the subject of the claim were never properly addressed on my reading.  The judicial commentary of the expert evidence in Makita final judgment (2001 NSWCA 305) included a questionable rationale about empirical proof of safety versus technical assessment (see more below) but the main problem is that the most important technical considerations were never made anywhere in this case.  The matter was about a fall on a concrete stair.  It was called a “slip” so what followed were discussions of slipperiness and this is what the expert evidence was about.  In rejecting an application for leave to appeal to the High Court, Gleeson CJ noted that “The factual issue at the centre of this case was whether the stairs on which the plaintiff/applicant fell were slippery (2002 HCATrans 274).  It might have appeared to be the issue, but I doubt that slipperiness was ever of much importance.  Thinking that slipperiness was important, in fact all-important, presents as being the earliest and largest problem as thereafter examination of the features of the stairs focused on only one element of design and probably the wrong one.  This continued through to the conclusion and was never turned around.  Friction coefficients were investigated and rejected as a result of the big argument about expert evidence.  The decision to reject this aspect might have been right but was arrived at by a debatable example and the most important technical issues that actually mattered were never addressed.  So although the evidence about the slipperiness was rejected, nothing else replaced it and that was the problem.  The courts needed more expert evidence not less.  But they didn’t know what they didn’t know.

The problem began with language and assumptions made about falls.  When people say they” slipped”, often all we really know is that they “fell”.  Terms like slipped should not be used unless there is more detail to confirm with some certainty that mechanism.  Let’s stick with “fall” if that’s all we really know.  That would have perhaps avoided the distractions in this case.  The problem is that the wrong language points all the consideration in one direction, in this case I think the wrong way.  A slip on the tread on descent on a dry concrete stair – or almost any stair actually – would be a reasonably difficult task.  It would take some doing on purpose.  I think it would be some effort to step in such a way that broke friction on the tread (more on that below).

The ultimate decision was to put the expert assessment of friction aside.  This might have been the right call – but for the wrong reason.  The reasoning for rejecting the friction assessment was not via an understanding of stair biomechanics which probably would have made sense but through the following rationale.  More or less the reasoning was that: (a) the stairs had been used for a long time; (b) no one else seemed to have slipped; and (c) so the stairs must be ok.  This possesses a flicker of empirical logic but it is not robust.  Essentially it is saying that “everything is safe until it isn’t”.  For example, it would mean that because the Longford gas plant had not exploded before it exploded then it was safe before it exploded.  Fairly obviously it wasn’t.  So a history of empirical safety is not necessarily a very good method of working out if something is designed well.  To use this observation as a determination of whether something is technically sound is not sufficient.   With proper technical analysis we can say if an industrial plant is designed well without having to wait for it to blow up and the same with stairs.  The problem was that the court failed to be assisted to understand what really needed to be examined.  The assumption was that it was all about friction.  Friction would not be the design issue of interest to me.  But other things would be.

Walking down stairs

The judgment included discussions about coefficient of friction.  This was owed some consideration but was not highly relevant and certainly not the main issue as far as I can see.  Yet it took over the whole matter and was dominant to the end as the comment from the bench in the High Court confirms.  It was of little relevance in that firstly, the stairs were dry.  Almost any dry surface of the kind used for walking will have sufficient friction for walking.  Secondly, stair descent is logically not particularly demanding on friction.  Walking involves applying force to the ground both forward (heelstrike) and backward (pushoff).  It is something of an inefficient arrangement applying forward force when trying to propel oneself in that direction but nevertheless this is what happens.  Slips can be either forward or backward.  Forward slips (pushoff) are usually less troublesome as the fall is interrupted as support can be found as the non-strike foot is swinging forwards (although this is less certain on stairs).  Backward slips (heelstrike) are the more common cause of injuries slips as the person falls backward without finding the support of their other foot and falls onto their elbow, posterior, etc.  Whether forward or back, the slip occurs when the horizontal force applies exceeds the friction characteristic of the surfaces (the slip also must be of sufficient length and this is important – but we will leave it for a moment).  The forward horizontal force is related to the strike angle, stride length and pace.  Could you climb up a ladder with Teflon rungs?  Maybe.  Could you walk on that surface?  With difficulty.  When climbing with near vertical motion and force application on the rung the requirement for friction will be small.  Why is this important?  If we need minimal friction in climbing (up and down motion) and most when we stride out walking (an action with a more horizontal component); what happens on stairs?  Two things.  The stride length is shortened from normal walking according to the geometry of the stairs.  The depth of each step is shorter than a typical step.  If you observe someone walking on something very slippery such as ice you will see that they shorten their stride.  Have a look.  The geometry of stairs achieves this through design thus compelling the user into a gait with lower friction demand (assuming that they are used one at a time).  So we have a normal friction surface (e.g. dry concrete) with a low-friction gait which adds up to a low slip propensity.  Secondly because of the grade of the stairs the motion is increasingly dominated by a vertical motion.  It is for these reasons that the discussion of friction was not owed much space, and that expert evidence was really needed on other matters.  Unfortunately, the irrelevant dominated, and the relevant was absent.

What needed to be discussed?

What needed to be discussed were the factors that relate to stair use which you might call human factors, engineering, design, ergonomics or a combination of these.  Whatever you call it, it is not everyday knowledge.  The design issues that required illumination never received attention.  The factors are such matters as grade, tread depth and height, tread grade or wash (common outdoors), dimensional consistency, distractions, cues, lighting, familiarity (this was the only one that was aired), handrail size, position, relationship with the grade of the nosings, and so on.  The stair geometry for instance is important.  If we wanted someone to mis-locate a foot on a stair, stumble and possibly fall, how would we set it up?  A way to do would be to arrange a highly consistent sequence for several stairs and then one that is a little different.  Why can people walk up irregular outdoor steps and paths and rocky steps carved into hiking tracks?   The answer is that they are obviously irregular.  People can’t walk up them very efficiently because they must concentrate on each step so it is not necessarily a good arrangement for efficient movement.  But it does avoid the trap-effect of seemingly consistent, but actually inconsistent, geometry sometimes found in stairs.  Cues are important.  For instance a seemingly simple handrail serves a number of purposes among those being a grip to aid stability, arrest an out of balance movement or a stumble, etc.  The handrail dimensions, shape and position are important if it is to be useful for these functions.  None of this was discussed.  The handrail is also a cue to the grade of the stair nosings along with the previous sequence and vision of the stairs.  If the handrail follows the nosing grade then it is another cue to foot placement – or alternatively a further element in the trap being set up by a single tread with different geometry.  These are just some aspects.  The quality of the physical arrangements was actually the substance of the claim.  Only one aspect of this was aired (being slipperiness) and it was not the main issue.  The considerations of stair design human factors is technically complex.  In Makita and Sprowles it was not even considered.  The court did not need it.  So they thought.

Conclusion

Everyone has a view on safety and so it is seen as everyday knowledge.  The result could be that courts sometimes think they don’t need advice about design and risk as it relates to safety.  This case consumed a lot of resources much of it about the legal system working out its own rules rather than actually working on the problem at hand.  The problem in Makita and Sprowles looks to have been about the courts “not knowing what they didn’t know” (thank you Donald Rumsfeld).  The formulation of the limit on expert evidence might be neatly worded and even elegant.  But this does not seem sufficient.  Surely, to provide a robust precedent, it must also have been embedded within a case where the principle was applied to useful effect.  It seems ironic, unfortunate and inappropriate that a case which suffers from insufficient technical input supposedly provides an indicator on how technical input should be limited.  If anything it should be used as an example of the danger of insufficient technical input.

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About John Culvenor

Hi, Thank you for taking a look at this blog. I work in engineering, ergonomics, creativity, design, training, etc. Often this is about helping solve legal puzzles through accident analysis. Sometimes it is about thinking up better designs for equipment, workplaces, and systems. This blog is about good design and bad design, accident analysis and how it can be done better, and how we can make a better, safer world by design!
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