- Ueno, Satoru, et al.
Thermal insulation of occupational footwear used in Japan
- Introduction Many kinds of footwear are used for various purposes in the workplace in Japan. Careful selection of footwear is needed to protect workers from coldness and to keep the performance of workers in cold workplace where employees have to work under -20℃. On the other hand, safety boots with high heat conductivity from foot to outside are needed for the workers in hot environments. But thermal characteristics are not shown for each boots. We measured the thermal insulation values of various kinds of footwear by thermal foot manikin. Materials and methods We tested 14 kinds of Japanese protective footwear (Midori Safety) with a thin or a thick sock in climate chamber by thermal foot manikin having 8 zones. The footwear included cold protective boots(2), long rubber boots(1), safety boots(4), safety shoes(2), business shoes(1), work sneakers(1), anti-electrostatic aerated shoes (2) and sandals (1). The ambient temperature of climate chamber was 4.6±0.5℃. The air velocity near boot was 0.27±0.5m/sec. The boots were placed on a copper/zinc alloy plate in the climate chamber. When upper parts of foot manikin were not covered by footwear, muffler was wound around the foot manikin to avoid the unnecessary heat dissipation from manikin. The manikin skin temperature of each zones were set at 34℃ on the control software. Each test was run for about 80 minutes to reach steady state. The data registered during the last 10 minutes on PC were used to calculate the thermal resistance. In boot toe to L Calf data were used, in shoe foot and ankle data were used. We conform to ISO 15831 about the test methods. When the thermal resistance of the second measurement was not within the 4% difference of that of first, the third measurement was done. The temperatures on the sock at the toe tip, the mid-sole, the dorsal foot, the guard front were measured by thermocouples which were fixed by surgical tape. Results and discussion In boots, thermal insulation with thick sock was larger than that with thin sock by 0.014-0.0033 m2℃/W. The cold protective boot which had the inner sock with thick sock had the largest insulation, which was about 0.45 m2℃/W. The other kind of cold protective boot was 0.325 m2℃/W. Though the thermal resistances of normal safety boot were the same values of 0.26-0.27 m2℃/W, safety boot whose material was fibrous leather made by cutting outer layer from normal leather was relatively lower value. Common rubber boot made of polyvinyl chloride (PVC) was lowest, 0.215 m2℃/W. In shoes, the thermal insulation of work sneaker was 0.28 m2℃/W, which was larger than business shoe, aerated shoe and sandal. The larger the aeration the shoes had, the smaller the temperature insulation. Temperature on sock in toe tip was smaller in sandal and aerated shoe than non-aerated work sneaker.