The surface roughness of a rubber soling material determines the coefficient of friction on water-lubricated surfaces

For more than a decade, evidence has been accumulating that points to the f act that the microscopic roughness of the footwear soling surface is a majo r determinant of slip-resistance on lubricated surfaces, but conclusive exp erimental proof has been lacking. This article describes an experiment in w hich five pairs of shoes were soled with the same rubber compound. Four of the pairs were abraded by different grades of grit to produce a range of ro ughness values. The coefficient of friction (CoF) of the five solings was t hen measured repeatedly by the walking traction method on wet surfaces incl uding glazed wall tiles, vinyl asbestos coated with the wax floor polish, a nd both sides of a sheet of float glass. The Kruskal-Wallis statistical tes t proved beyond doubt that the soling roughness is a major factor in determ ining the CoF of this rubber soling material; p < 10(-5). Nearly all of the grip was due to surface roughness of the soling material on these atypical ly smooth floors, although the surface roughness of the floors also had a s ignificant effect on CoF; p < 0.003. Float glass is shown to be a promising reference floor material for the measurement of CoF of footwear; there was no statistical difference between results for the two sides of the glass s heet. Float glass could be used in the development of a standard CoF test m ethod because new sheets of glass from the same manufacturer are identical and extremely smooth. The specification of CoF values for solings/floors co mbinations in lubricated conditions is of Little value unless associated wi th roughness measurements and knowledge of how wear will affect the surface roughness of the sole. This article reports the first evidence that any sp ecification of flooring by measuring CoF based on dry surfaces could lead t o an increase in the number of injuries caused by slipping on the wet surfa ces. Published by Elsevier Science Ltd.