Influence of Indian Footwear Tread Wear on Friction at the Shoe-Floor Interface During Slips

Accidental injuries sustained due to slipping and falling incidents are very common in the workplace. The major reason for these accidents is the inadequate friction available at the shoe-floor interface. Furthermore, the presence of slippery contaminants (i.e., water or oil) over the flooring significantly increases the slipping hazards. In addition to the existence of slippery pollutants, wearing of outsole treads over time is one of the key reasons that can lead to a large reduction in friction. Although footwear-based slip risk assessment has been performed extensively on a variety of floorings and pollutants, limited studies have examined the influence of worn shoes on slipping. In the current work, five high-selling footwear from popular Indian brands were considered to study their slip severity in new and worn conditions. The topographical features of the outsoles were modelled, progressively worn, and slip-tested using a customised tribometer (i.e., British pendulum skid tester) across three types of contaminant situations (i.e., dry, water, and canola oil) and three different floorings (i.e., laminate, ceramic, and anti-skid). All the outsoles were measured for their available coefficient of friction (ACOF). Reduction in the ACOF values ranged from 40 to 90% as the outsoles were worn progressively. Outsoles consisting of oblique tread design were found to produce high friction as compared to other tread geometries. An increase in worn area was found to strongly correlate (R2 = 0.95) with the decrease in friction. The economical modelling methods and the study results are anticipated to provide guidelines for footwear manufacturers in the selection of appropriate tread designs and suggest replacement thresholds.