Floor slipperiness measurement: friction coefficient, roughness of floors, and subjective perception under spillage conditions

Measurement of the coefficient of friction (COF) between the shoe/sole and the floor is essential in understanding the risk of slipping accidents. In this research, the COF of five floor materials commonly used on a university campus, under five surface conditions including dry and four liquid spillage conditions, were measured. The COF measurements were conducted using a Brungraber Mark II slip tester with four footwear materials: leather, neolite, ethylene vinyl acetate, and blown rubber. The results of the COF measurements showed that floor tile, footwear material, and surface conditions were all significant factors affecting the COF. Interactions between these factors were also significant. Four surface roughness parameters ( R a, R tm, R pm, R q) of the five tiles selected in the friction measurement were measured using a profilometer. The roughness of the two ceramic tiles was significantly higher than the three non-ceramic tiles. The correlation between the four roughness parameters and the measured COF was very high ( r=0.932 to 0.99) under both wet and water–detergent conditions. The tile and surface conditions in the friction measurements were presented to 24 subjects and the subjective evaluation of floor slipperiness was determined. The differences of the scores from the five surface conditions were statistically significant. The difference under floor tile conditions with the same spillage condition was, however, not significant. Spearman's rank correlation coefficients between subjective score and measured COF using neolite footwear were in the range of 0.8–0.975 for the five floors under all the surface conditions. This implies that subjective scores may reasonably reflect floor slipperiness measured with the Brungraber Mark II slip tester using neolite footwear pad.