In this study, 30 subjects were exposed to different combinations of air temperature (T a : 24, 27, and 30°C) and CO 2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to T a = 24°C, exposure to 30°C at all CO 2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported.However, no significant effects of T a on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO 2 from 8000 to 12 000 ppm at all T a caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/ stress. No significant interaction effect of T a and CO 2 concentration on human responses was identified.

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Due to insufficient ventilation and absence of daylight, underground confined environment will be dim and occurred with high CO2 concentration. It is essential to clarify the combined effects of high CO2 concentration and illuminance on human responses in confined spaces. Twenty-four subjects were exposed to different combinations of illuminance and CO2 concentrations in an underground climate chamber, with thermal responses, physiological responses and acute health symptoms being investigated. Results show that: at CO2 level of 12,000ppm, heart rate (HR), diastolic blood pressure (DBP) and ratings of acute health symptoms (dizziness, agitation and depression) increased significantly when illuminance level was up to 500 lux. However, no similar results were observed at a CO2 concentration of 8000 ppm. Additionally, thermal sensation votes (TSV) increased significant with increasing illuminance level, regardless of CO2 concentration being 8000 or 12,000 ppm. Similar result was obtained for the change of thermal comfort votes (TCV) at CO2 level of 12,000 ppm. However, TCV result for illuminance level of 100 and 500 lux did not show a significant difference at CO2 concentration of 8000 ppm. This indicated that the combined effects of illuminance and high CO2 concentration lead to different human responses.