Human responses to high air temperature, relative humidity and carbon dioxide concentration in underground refuge chamber

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In underground confined spaces with a crowded population, the thermal environment will be hot-humid and occurred with high CO2 concentration. Investigating the combined effect of increased temperature, relative humidity and CO2 concentration on human responses is important for confined spaces. In this paper, 32 subjects were exposed to different combinations of air temperature (Ta), relative humidity (RH) and CO2 concentrations in an underground climate chamber, with thermal response, physiological response and acute health symptoms being investigated. Results show that: at a Ta of 28 °C, RH of 65% and CO2 level of 12,000 ppm, thermal sensation votes (TSV) and thermal acceptability (TA) did not significantly changed, while a significant change was recorded with a RH of 85%. When CO2 concentration increased to 8000 ppm, the subjects' perceived air quality acceptability significantly decreased at Ta of 33 °C, however it did not significantly change at Ta of 28 °C and RH of 65%. Maximum mean skin temperature and wetness difference did not exceed 0.3 °C and 0.15 units between the different exposure conditions, respectively. Significant changes of headaches were observed when CO2 concentrations increased to 12,000 ppm at a RH of 85%, but the difference was not statistically significant at a RH of 65%. This indicated that the combined effects of high Ta, RH and CO2 concentration lead to different human responses.