A method of ranking the grip of industrial footwear on water wet, oily and icy surfaces

Abstract

A recently invented walking traction test method was chosen to measure the coefficient of friction (c.o.f.) of thirteen pairs of discarded working footwear. Floor surfaces were lubricated with a water-based wetting agent and four grades of mineral oil. The footwear were also tested on wet and dry ice. The maximum c.o.f. attained prior to each slip was recorded whilst walking forwards and again whilst walking backwards on the heels. Results for the thirteen footwear samples were ranked in descending order of c.o.f. for each floor and lubricant combination, and rank orders for the seven most slippery surfaces were compared. Kendall's coefficient of concordance W = 0.73 for walking forwards and 0.79 for walking backwards; P < 0.001. Rank orders for each of the seven surfaces were also compared with mean rank orders. Correlation coefficients r, all reached or exceeded 0.92 ( P < 0.005) on rough plastic and stainless steel coated in 121.4 or 88.2 cSt oil (at 17.5°C) and on water lubricated glazed white tiles. On dry ice, r = 0.49; P < 0.05. The correlation between mean rank orders of footwear on forward and backward walking was 0.95; P < 0.005. The c.o.f. recorded whilst walking backwards was 37.7% lower than the forward walking c.o.f., supporting the hypothesis that dangerous slips are likely to occur on heel strike. There was also a significant correlation between roughness of soling and c.o.f.; P < 0.01. This method of measuring c.o.f. is now being applied to eliminate the most slippery footwear with the long-term aim of selecting the safest solings for specific environments.