Rubbers and plastics in shoes and flooring: The importance of kinetic friction

experimental retroreflective configurations significantly improved detectability over this configuration. Overall, the most cost-effective configurations were those in which the belt and/or armbands were covered with retroreflective material.

15.2.39 (85837)

Harrison, R., and Malkin, F. On-site testing of shoe and floor combinations. Ergonomics, 1983, 26.1, 101---108. People were filmed walking and running, with shoes and barefooted, wet and dry, against a screen in order to obtain data on the presentation of feet to floors. This information, together with other available data, was used to design a range of machines for measuring the coefficient of friction between shoe and flooring materials. The latest development, the Tortus floor friction tester, measures the coefficient of friction on floors and enables the changes in value to be recorded. A brief description of

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the method of measurement is given, together with typical results. The state of cleanliness of a floor is critical in terms of safety and some of the difficulties resulting from incorrect cleaning procedures are indicated. Floor surfacing materials are usually chosen to meet specified uses. With few exceptions, the specification of particular footwear is only given for some industrial purposes. Optimum accident prevention would require a choice of the most st~itable combinations of these materials.

15.2.40 (85838)

James, D.I. Rubbers and plastics in shoes and flooring: The importance of kinetic friction. Ergonomics, 1983, 26.1, 83-99. Traditionally it has been assumed that static friction and dynamic friction are distinct with static always greater than dynamic. Experimental evidence indicates that rubbers and

plastics show a continuous change of friction with velocity. Walking is safe if friction (slip resistance) increases rapidly as velocity increases, or alternatively if, under all conditions, the coefficient of friction is greater than the maximum H/V value observed in a force plate experiment. If, however, friction decreases as velocity increases then the situation is potentially dangerous since the requirements for stability increase as the stride is inadvertently lengthened. Sometimes a decrease in temperature can change an increasing friction coefficient to a decreasing one and instability in walking may result. Contaminants drastically alter the friction of all materials and mud or other wet slurries are extremely dangerous. Because walking stick ferrules need to have a much higher friction than shoe soles or heels, a level of dry dust which is not dangerous under norm'al conditions may be hazardous to those needing a walking aid. Laboratory assessment of flooring materials should always take account of contaminants and cleaning methods.

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AppliedErgonomics June 1984