Investigation of the physiological response and thermal adaption of environmental sanitation workers in outdoor spaces: A case study in summer

• Thermal comfort and physiological indicators of sanitation workers were investigated in working and resting. • Sanitation workers had a higher tolerance for the thermal environment during rest. • When PET (UTCI) exceeds 53.0 ° C (47.1 ° C), sanitation workers will be very hot. • T a and UTCI are effective reference indicators to prevent heat risks for sanitation workers. The continuous rise in global temperatures has deteriorated the quality of urban environments. Sanitation workers in hot outdoor conditions may face heat-related risks, especially in South China where summers are hot and humid. Therefore, establishing a relationship between sanitation workers’ physiological indicators and outdoor thermal environments is necessary to accurately predict and assess their heat safety in high-temperature working environments. We conducted a field investigation of thermal and physiological parameters in the campus of Guangzhou University and a total of 969 questionnaires (male) were collected. Through the regression equations, the relationships between sanitation workers’ health risks, thermal parameters, and thermal indices were analyzed. The results indicated that sanitation workers had a higher tolerance to the thermal environment at rest than when they were working. The unacceptable T a (air temperature) and T mrt (mean radiant temperature) during work was 31.5 and 41.3 °C, respectively. Except for the blood oxygen level (SpO 2 ), both the heart rate (HR) and auditory canal temperature (T ac ) increased with increasing T a . Compared with PET (physiological equivalent temperature), UTCI (universal thermal climate index) is better in predicting HR levels. For instance, sanitation works’ HR level may be 95 beats/min. When PET exceeded 53.0 °C or UTCI exceeded 47.1 °C, sanitation workers felt extremely hot. Additionally, when the MTSV (mean thermal sensation vote) was close to 3 (indicating feeling hot) and the physiological strain index was > 7, sanitation workers faced a heat risk. Therefore, the findings indicate that management authorities should consider both T a and UTCI to provide appropriate guidance to sanitation workers during their work period to ensure occupational safety and prevent heat-related incidents.