Frictional Characteristics of Progressively Worn Footwear Outsoles on Slippery Surfaces

Slip and fall related injuries are common in workplaces and sufficient shoe-floor friction is required to prevent such incidents. Besides the presence of slippery contaminants, shoe wearing over time is one of the key factors which may lead to significant reduction in shoe-floor friction. While footwear-based slip testing has been conducted widely across floorings and contaminants, limited studies have focused on the effect of worn shoes on slipping. In this work, twelve formal shoes from common brands were tested through modelling of their outsoles in normal and different degrees of progressively worn conditions. Mechanical slip testing was conducted to quantify the available coefficient of friction (ACOF) of the outsole models across dry and two common contaminant conditions (i.e., floor or surface cleaner, and canola oil), and on three commonly available floorings. The effect of flooring, contaminant, and worn area, on the ACOF were characterized extensively. Progressively worn outsoles were found to lead to reduction in ACOF in the range of 28-97%. Outsoles having tread channels oriented at different angles with respect to the direction of footwear motion, were found to generate higher ACOF, than ones with horizontal tread patterns. Outsoles which had larger treads but with lesser intervals (i.e., large tread surface area) showed lower ACOF values. These outsoles experienced less reduction in the ACOF in the following cycles of wear. For safety against slips, outcomes from this work are expected to provide essential information for buying or replacing the formal shoes in its new or worn condition.