Understanding the Friction Measured by Standardised Test Methodologies Used to Assess Shoe-surface Slip Risk

This paper discusses standardised mechanical test methodologies that measure dynamic coefficient of friction in order to assess the risk of a pedestrian slip. Currently, two shoesurface contact test methods are specified in British Standards to assess the risk of pedestrian slips during the heel strike phase. A pendulum test device as specified in BS 7976-2:2002 is used to determine the slip resistance of surfaces. Another standard, BS EN ISO 13287:2007 specifies the test method to assess the slip resistance of conventionally soled safety, protective and occupational footwear. Experiments were conducted on six common household surfaces in water contaminated conditions in compliance with the aforementioned standard procedures. The roughness and stiffness of each surface was also found. The results show no statistically significant linear correlation between the dynamic coefficient of friction found via the two standardised test methods. At low levels of roughness, no statistically significant linear correlations were found between the coefficient of friction found via the two standardised test methods and roughness. For flooring with a compliant layer, the contact conditions of the pendulum test device were found to cause friction losses associated with energy dissipated as the surface deforms and recovers during sliding. Differences in sliding velocity and area of contact were found to influence the measurements given by the two test procedures. The higher velocity pendulum is a more appropriate test device to replicate slip in wet conditions as it predicts the worst case scenario. However, it is likely to give misleading results on deformable surfaces as, on such surfaces, as it is not replicating the loading conditions during a real-life heel strike.