Thermal sensation affects peoples’ thermal sensitivity to local cold stimuli——a study based on step changes of metabolic rate

Abstract

To explore the influencing factors on thermal sensitivity to cold stimuli and provide recommendations for design of cooling garments for factory workers, chamber experiments were conducted. The experiments involved two temperature (24 ℃ and 30 ℃) conditions and three activities corresponding to metabolic rate (MR) of 1 met, 2 met, and 3 met. Seven body parts were selected for local cold stimulating. Subjective questionnaires were collected, including cold stimuli sensation (CSS), cold stimuli acceptance (CSA), overall and local thermal sensation vote (TSV and LTSV), and overall/local thermal comfort vote (TCV and LTCV). Physiological parameters of mean skin temperature (MST) and the local skin temperature (Tlsk) of stimulated part were measured. Results showed that subjects became less sensitive and more acceptable to the cold stimuli as MR and air temperature increased. Local stimuli led to significant changes in TSV, LTSV, TCV and LTCV. The MST was not affected by cold stimuli, while the Tlsk declined during stimulating. Comprehensive analysis showed that the TSV before local cold stimuli influenced CSS. The higher the TSV before stimuli, the lower the CSS would be. Cold stimulus on the chest and abdomen led to lower CSS, while stimulus on the upper arm, back and forearm resulted in higher CSS. Stimulating the torso parts caused larger reduction in TSV and TCV than cooling the limbs. Based on the results, the body parts to be cooled were suggested for different TSV ranges, which spread from the torso parts to the limbs with the increase of TSV.