Effect of workers' shoe wear on objective and subjective assessment of slipperiness

Subjective rating of slipperiness tests were conducted for 12 male industrial workers on three slippery surfaces, with poor or good lighting conditions, and with new or workers' own old shoes. A strain gauge force platform was used to evaluate dynamic coefficient of friction (COF) of shoes for the same surface conditions representing objective measurements. The shoe wear, available tread pattern, and hardness of old shoes were determined by instruments including a digital caliper, a digitizer, and a durometer, respectively. The surface effect was found to be highly significant on subjective ratings as well as dynamic COF (p < 0.0001). The correlation between dynamic COF values and subjective ratings was significant only for old shoes under medium oily conditions (r = 0.55, p < 0.04). For a slightly oily surface, decreasing the percent of tread available significantly increased dynamic COF values (p < 0.016). In addition, the effect of increased shoe hardness significantly increased the available tread pattern when only the data from the most deteriorated old shoes were included in the analyses (p < 0.004). These results emphasize the need to consider subjective assessment of slipperiness as a valid way to evaluate floor slipperiness. Further study is needed to (1) evaluate the effects of physical fatigue due to workload on subjective assessment of slipperiness and workers' ability to assess slipperiness during task performance; (2) consider the effect of available shoe tread on COF values and slip potential; and (3) determine if guidelines should be developed regarding when work shoes should be replaced to reduce slip and fall injuries.