Subjective assessment of floor slipperiness

Measured coefficients of friction of floor surfaces have not been shown to be consistent predictors of slipping and falling. However, human subjects appear to be able to perceive the slipperiness of a floor surface, and to modify their gait to mitigate the effects of slippery surfaces. This study investigated subjective rankings of floor surfaces (ceramic, steel, vinyl, plywood, and sandpaper) and the measured coefficients of friction. In addition, subjects reported a confidence rating on the occurence of a slip at "heel down". The floor surfaces were selected a priori, to provide a range of slipperiness and subjects appeared to be able to reliably discriminate between those surfaces. Ceramic tile was the most frequently determined as the slippery floor with the high level of confidence ratings, CERTAIN and ALMOST CERTAIN. In other words, the confidence ratings were closely related to the subjective rankings. The higher the subjective rankings were, the higher the confidence ratings were. To prove subjective rankings by the quantitative measure, static coefficients of friction were measured and it appears that subjects were able to relate their sensations to a function of the static coefficient of friction.