Floor slipperiness and load carrying effects on the biomechanical study of slips and falls
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Biomechanical and tribological studies have been the main approaches for investigating slips and falls. The commonly used dynamic coefficient of friction (DCOF), a tribological approach, is based on limited biomechanical studies. Therefore, a study was conducted to find the floor slipperiness effect, load carrying effect, and contaminant effect with slip distance, heel velocity, and stride length using a broader variety of floors and levels of slipperiness than has been used before. Slip distance was hypothesized as being a superior parameter over DCOF in differentiating floor slipperiness. Heel velocity was measured to find its significance m a biomechanical approach, since it is the most important factor in tribological DCOF measures. Stride length was measured to find the gait pattern changes for different levels of floor slipperiness and load carrying levels. Four different floor surfaces covering the full range of safety standards for slipperiness (with and without an oil contaminant) were prepared for ten subjects with each walking at a fixed velocity while carrying five different loads. A programmable slip resistance tester was used to measure DCOF with conventional setup values for heel velocity and vertical force. The results showed that the floor slipperiness effect and load carrying effect were very significant. The effect of the contaminant was highly significant and even overpowered the floor slipperiness and load carrying effects. Slip distance and heel velocity increased while stride length decreased as floor slipperiness and load carrying levels increased. The inconsistency of steel DCOF showed that slip distance was a comparatively stable measure because it was measured directly from human reactions and resulted in as good as DCOF in differentiating floor slipperiness. In measuring DCOF in the past, the selection range of heel velocities and load carrying levels were chosen at levels seen with a normal waDcing gait in non-slippery conditions. However, a normal gait could not be maintained on contaminated floors because stride length decreased so that a faster transfer of the body weight could be accomplished. Therefore, faster heel velocities and heavier load carrying levels should be applied for realistic DCOF measures on contaminated floors.