Pain, thermal sensation and cooling rates of hands while touching cold materials

Hand cooling and resulting comfort and pain were studied in 12 subjects, while touching six different materials (polyurethane foam, wood, nylon, rustproof steel, aluminium, and temperature-controlled metal) which were initially at ambient temperature. This was done for three ambient temperatures (-10 degrees, 0 degree and 10 degrees C), after pre-exposure exercise or rest, with bare hands or while wearing gloves. The observed cooling curves were analysed as Newtonian cooling curves. The observed time constants appeared to be significantly related to the materials' contact coefficients, the presence of hand protection, the preceding activity, and the interaction between contact coefficient and the presence of hand protection. These parameters also allowed a good description of the time constant (r2 = 0.8) of the related cooling curves. Thermal and pain sensation could be described in terms of the local skin temperature, ambient temperature and hand protection. Equal pain and thermal levels were associated with lower temperatures of the back of the hand than of the contact side. The slightly painful condition was associated with a skin temperature of 16 degrees C for the back and 19 degrees C for the palm of the hand. The pain level appeared to be inversely related to cooling speed. Skin freezing occurred at higher skin temperatures when touching cold objects than when exposed to cold air as a result of reduced supercooling. The regression equations determined allowed calculations to be made of safety limits for hand cooling while in contact with a wide range of materials.