Footwear for cold environments : thermal properties, performance and testing
Sammanfattning: Footwear with various insulation levels was evaluated. Some footwear was manufactured both with and without steel toe cap. Comparative studies between various methods (thermal foot model, human subjects, EN 344) were carried out. Data from subjects and foot model were used in evaluation of thermal properties of footwear. The data was tested in Lotens’ model for foot skin temperature prediction. Field studies were carried out for evaluation of footwear and feet conditions in real wear situation. Heavy winter boots had lowest insulation in toe zone and thin boots had heel zone as the coldest region. Even low sweat rates (3 g/h) can reduce footwear insulation considerably (9-19 %). At higher sweat rates (10 g/h) the reduction could be up to about 36 %. Combined effects of sweating, walking and wind could reduce insulation up to about 45 %. Reduction was bigger in warm winter boots. Minimal amount of moisture evaporates from winter footwear during use. Insulation reduction levelled off over longer period of use. The reduction can be calculated by simple equations. The thermal foot model gave similar insulation values as measured on human subjects in thermal comfort. The results from thermal foot model give more useful information on footwear than does the present standard method. The influence of steel toe cap could be related to the "after effect" that probably depends on the thermal inertia of steel toe cap. Recommendations for footwear choice and use are given.
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