Abstract:

Objective Low temperature working environments significantly increase the risk of hand frostbite and effective hand protection is crucial for maintaining both operational efficiency and personal safety. Current cold protection gloves, however, fail to account for the varying cold sensitivity across different hand regions, limiting their precision in thermal protection. To enhance protection while ensuring work efficiency and safety, this study segmented the hand into 11 anatomical zones based on vascular distribution and conducted localized cold sensitivity tests.

Method Eight healthy male adults participated the hand cold sensitivity experiment. The experiment was conducted in an environment of -10 ℃, no wind, and 30% relative humidity and lasted for 21 min. During the experiment, an infrared imaging device was used to capture thermal images of both hands which maintained an upright position in a natural, motionless state. Besides, the eight participants were asked from time to time for their subjective thermal sensation of the 11 zones based on the 7-point evaluation method. The cold sensitivity at the 11 zones were calculated by dividing the variation of thermal sensation with the variation of skin temperature.

Results Skin temperature experienced a sudden drop within the first minute of exposure to the low-temperature environment, with the temperatures at the upper ends of the little finger, ring finger, index finger and middle finger dropping sharply to 15.3 ℃, 16.7 ℃, 16.4 ℃, 16.8 ℃ and 16.9 ℃, respectively, while the skin temperature decreased slowly from the 1st to 12th min and stabilized from the 12th to 21th min. Skin temperatures across all regions gradually balanced out, and heat loss was stabilized. The thermal sensation votes for each part showed a downward trend over time. The cold sensation rapidly increased within the first three minutes. During this stage, the lowest thermal sensation vote for the hand was at the upper end of the little finger, while the highest vote changed dynamically over time. The highest thermal sensation vote was the thumb after the first minute of exposure, and it changed to the lower end of the ring finger after 2 min of exposure, and further to the inner side of the back of the hand after 3 min of exposure. From the 3rd to 15th minute, the decrease of the thermal sensation vote slowed down. During this phase, the lowest local thermal sensation vote was at the upper end of the little finger. From 3 to 9 min, the highest score was on the inner side of the hand back; from 9 to 15 min, it shifted to the thumb. From 15 to 21 min, the thermal sensation votes gradually stabilized, with the lowest local thermal sensation vote on the hand shifting from the upper end of the little finger to the lower end of the ring finger, and the highest score remaining at the thumb. It revealed distinct spatiotemporal variations in skin temperature and thermal sensation vote. Hand cold sensitivity progressively rose during cold exposure, surpassing 0.40 after 9 min. Cold sensitivity at inner dorsum declined slowly, stabilizing at 0.22 after 9 min, whereas the cold sensitivity at outer dorsum initially increased before decreasing to 0.17 at the 9-minute mark. By averaging the results across the exposure period, the hand was classified into three cold sensitivity areas, i.e., high (>0.4: distal phalanges of index, middle, ring, and little fingers), medium (0.3-0.4: proximal phalanges of the same fingers), and low (<0.3: thumb, inner and outer dorsum).

Conclusion Based on these findings, an optimized glove design was proposed. At the high-sensitivity area, multilayers of thermal insulation materials were integrated, while at the low-sensitivity area, lightweight and breathable fabrics were used. The optimized glove managed to elevate the average skin temperature of the hand by 4.29 ℃ and significantly increased the thermal sensation vote by 1.3 points on average, with no impairment to manual dexterity observed. These findings enriched the theory of thermal-physiological and psychological responses in extreme environments, offering guidance for cold-protection equipment design, demonstrating practical applicability for improving both safety and work efficiency in cold-environment operations. This study has certain limitations in terms of experimental design. The participants lack diversity in terms of gender, age, and physical condition, which may limit the generalizability of the results. The experimental environment of -10 ℃, no wind, 30% relative humidity is not representative of the complex and variable low-temperature conditions encountered in real-world scenarios. The experimental process employed static testing methods, with participants maintaining a relatively fixed posture throughout the cold exposure period, failing to adequately simulate the critical influence of hand movements on experimental outcomes in real-world conditions.

Key words: low-temperature condition, hand cold sensitivity, thermal comfort, protection glove, outdoor textile, infrared thermography