Detecting and eliminating slippery footwear.

A recently developed walking traction test has proved to be a reliable and rapid method of measuring coefficient of friction (c.o.f.) of floor surfaces and footwear, and is a suitable method for ranking the grip of footwear solings on slippery floors. This paper describes four new experiments in which footwear samples were ranked. The first experiment compared mean rank orders on water wet (wet) and oily surfaces of seven flat solings. Spearman's rank correlation coefficient rs was 0·893, P < 0·005. In the second experiment, five pairs of women's shoes were ranked on wet and oily surfaces. On the wet surfaces, three samples recorded maximum attainable c.o.f. but rank orders on two oily surfaces were identical, rs = 1·0, P < 0·01. In the third experiment, thirteen pairs of discarded footwear were ranked using three different test methods. The test surfaces were oily stainless steel plates cut from the same sheet. Rank orders of the three test methods were significantly similar. Kendall's coefficient of concordance w = 8·68, P < 0·001. In another experiment samples of commercially available footwear were issued to factory workers and recalled for c.o.f. measurements at intervals. Their rank orders on wet and oily surfaces were not statistically similar but when wet surface results obtained at 4 months, were compared with those at 10 months, rank orders were significant; rs = 0·994, P < 0·01. Also on oily surfaces, rank orders of two measurements were significant, rs = 0·982, P <0·01. Although most experiments have revealed significant correlations between footwear samples on wet and oily surfaces there are examples where a soling performs well on wet surfaces but is at the lower end of rank order on oily surfaces. It is concluded that rank orders on wet, oily and icy surfaces should be calculated but also it is necessary to examine rank orders on each surface-lubricant combination, by comparing results obtained at intervals during the useful lives of the solings. In future, samples at the lower end of the rank orders of c.o.f. will be eliminated from the varieties available to workers.