Interested in Wet Testing

Slip, Trips and Falls

Interested in Wet Testing?

A majority of slip/fall incidents occur as a result of contact with a spot on the floor surface that is unexpectedly slippery, usually due to moisture. It is important to determine how slip resistant the surface is under dry AND wet conditions because of pedestrian "expectation."

Physics of a Slip

Localized wet spots can create a phenomenon that is very similar to vehicular tire dynamics on wet roads. On surfaces that are not rough enough to dig into the bottom of the shoe as it contacts the surface, a wedge of fluid, known as the "hydrodynamic squeeze film", can build up. This phenomena occurs in many accidents where the heel slips forward. Aside from good housekeeping, the best way to minimize the potential for the buildup of a hydrodynamic squeeze film is to increase the roughness of the floor surface. This measure minimizes the conditions that contribute to the buildup of a hydrodynamic squeeze film.

Sticktion (or Adhesion)

There are currently only two devices with an ASTM F-13 standard for wet testing: the Portable Inclineable Articulated Strut Tribometer (PIAST, aka Brungraber Mark II, or F1677) and the Variable Incidence Tribometer (VIT, aka English XL, or F1679). Numerous independent studies have verified the reliability of these devices for wet testing. From forceplate analysis and roughness measurement to ASTM run round robin testing sessions, the PIAST and VIT have proven to produce repeatable and reproducible results.

Why can these devices more accurately meter wet surfaces than others? They avoid ‘sticktion.’ The outcome of devices subject to sticktion is unrealistically high slip resistance readings on wet surfaces, sometimes producing results higher than the same surface when metered dry. The PIAST and VIT are able to avoid sticktion by applying the horizontal and normal forces simultaneously, thus having no residence time – hence no sticktion.

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