Responses of human perception and skin temperature to directed thermal radiation in hot environments

Abstract Directed thermal radiation (DTR) is a major factor affecting the health of people in hot environments. Understanding the effect of DTR is important for ensuring suitable environmental quality, and for enhancing safety and efficiency. In this study, 96 young healthy subjects (23.31 ± 0.93 years, 172.50 ± 7.21 cm, 62.41 ± 6.32 kg) were exposed to two different air temperatures (34 °C and 37 °C), and a relative humidity of 60% in a climate chamber. During the experiment, three DTR conditions (0 kW/m2, 1 kW/m2 and 2 kW/m2) were chosen, and the subjects were instructed to run on treadmills at a speed of 4.5km/h to stimulate moderately intense labor. Their skin temperatures, comprehensive thermal sensation (CTS), and fatigue perception were recorded during the experiments. The results showed that DTR significantly increases the local and overall skin temperatures. The impact of DTR on the subjects’ skin temperatures was significant at the forehead, back of the hands, and chest, whereas it was insignificant at the tibia and calf. The mean skin temperature was 33.16 °C or 33.35 °C when the subjects experienced a neutral CTS in hot and wet environments under different DTR. The DTR also affected the CTS and fatigue perception of the subjects. The relationships between CTS and mean skin temperature as well as between CTS and the fatigue feeling score were found to be linear. In conclusion, this study suggests that an asymmetrical thermal radiation affects the preferred mean skin temperature and subjective perception. Therefore, reasonable monitoring and improvement measures are recommended for continuous work with moderate intensity in hot environments.