Slips, Trips and Falls – An Evolution in Walkway Safety

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The built environment has changed significantly throughout history and walkways are no exception.  At one point in time, walkways were simply paths worn through the landscape by repeated use.  The more frequent they were used, the nicer they typically became as users would make alterations to improve the convenience and safety of the route.  Fast forward to today (January, 2017) and walkways are considerably different.  Modern walkways are often constructed with intentional surfacing finishes/materials and generally designed to provide the easiest, most hazard-free route possible.  Primarily, the focus has been on controlling or eliminating factors that contribute to trips, slips and falls.

 

Currently, there are a variety of treatises which provide walkway requirements in the interest of pedestrian safety, ranging from third party consensus standards to legally adopted codes.  With regard to tripping hazards, the literature is generally consistent and contains the following requirements: changes in elevation up to 0.25 inches are permitted, changes in elevation between 0.25 and 0.5 inches shall be beveled, and changes greater than 0.5 inches shall be accomplished by means of a ramp or stairway.  These requirements are found in the Americans with Disabilities Act (ADA) which was signed into law by President George H.W. Bush on July 26, 1990, although other provisions existed previously.

 

The allowances for abrupt changes in elevation serve a dual purpose.  From an accessibility aspect, these geometries present little challenge to persons in wheelchairs.  From a pedestrian viewpoint, studies have shown that minimum toe clearance (i.e. the lowest point in the swing of a foot while walking) is typically on the order of 0.5 inches for most pedestrians when walking on an improved surface.  This clearance has been observed to be greater in situations such as hiking where the terrain is uneven and the pedestrian is constantly navigating obstacles.

 

Another important aspect of walkway safety relates to friction characteristics of walkway surfaces.  In the study of walkway surfaces, “coefficient of friction” generally refers to the interaction of two surfaces in the absence of a lubricant.  When a lubricant is present the term “slip-resistance” is often used.  The slip-resistance aspect of walkway safety has also evolved significantly over time, but remains more ambiguous than elevation differentials.  This stems from the number of variables involved in evaluating a surface with respect to slip-resistance. These variables include walkway surface characteristics, footwear selection/material, surface contaminants, and measurement devices and techniques.  Due to the complex nature of slip-resistance, much debate exists as to how to quantify this characteristic of a walkway surface, specifically in the presence of moisture: the most prevalent contaminant.

 

Of importance in measuring walkway surface friction or slip-resistance is the ability to obtain results which are reliable and reproducible, without which the method cannot be deemed scientific.  There are currently several manufacturers of walkway surface friction/slip-resistance measuring devices (“tribometers”), each professing that their device, test foot and measurement technique are the most valid.  Due to slight differences between these devices, testing them side-by-side produces varying results.  Therefore, the results of one device cannot be compared with another.   Further complicating the problem is the lack of any codes or governing regulations providing a quantitative value for floor surface characteristics based on a specific measurement technique.  As an “icing on the cake” element to the chaos, standards offered by various organizations also vary in their proposed requirements.  However, it is our experience that one of these devices has emerged as the front-runner.

 

The English XL Variable Incidence Tribometer (VIT) was originally designed and developed by William English in 1992.  Although the device has undergone scrutiny since its inception, it remains the most widely used tribometer for field testing of walkway surfaces.  Unique to this tribometer’s design is its ability to simulate the heel strike of a pedestrian.  The device incorporates a test foot, sized to replicate the average initial contact area of a heel, as well as a ball joint designed to emulate the flexibility of a human ankle.  The angle at which the test foot strikes the floor is adjusted by the user (lowered from a near vertical position) until a slip occurs.  A protractor on the side of the tribometer provides the angle at which the slip occurred, as well as an associated slip index which is recorded by the user.  The figure below presents an overview of the English XL, provided in the User Guide, identifying key components.

Figure 1 – Overview of English XL VIT

While some debate still exists as to the efficacy of the English XL, the science behind its design is sound and it has been tested and complied with the American Society of Testing and Materials’ (ASTM) standard F2508-13 Standard Practice for Validation and Calibration of Walkway Tribometers Using Reference Surfaces.  Therefore, unless other advancements are made in the field of walkway tribometry, the English XL will remain the preferred apparatus for AKE personnel.