Field investigation of the heat stress in outdoor of healthcare workers wearing personal protective equipment in South China.

Since the advent of coronavirus disease 2019 (COVID-19), healthcare workers (HCWs) wearing personal protective equipment (PPE) has become a common phenomenon. COVID-19 outbreaks overlap with heat waves, and healthcare workers must unfortunately wear PPE during hot weather and experience excessive heat stress. Healthcare workers are at risk of developing heat-related health problems during hot periods in South China. The investigation of thermal response to heat stress among HCWs when they do not wear PPE and when they finish work wearing PPE, and the impact of PPE use on HCWs' physical health were conducted. The field survey were conducted in Guangzhou, including 11 districts. In this survey, HCWs were invited to answer a questionnaire about their heat perception in the thermal environment around them. Most HCWs experienced discomfort in their back, head, face, etc., and nearly 80% of HCWs experienced "profuse sweating." Up to 96.81% of HCWs felt "hot" or "very hot." The air temperature had a significant impact on thermal comfort. Healthcare workers' whole thermal sensation and local thermal sensation were increased significantly by wearing PPE and their thermal sensation vote (TSV) tended towards "very hot." The adaptive ability of the healthcare workers would decreased while wearing PPE. In addition, the accept range of the air temperature (T a) were determined in this investigation. Graphical Abstract.

Human thermal physiological response of wearing personal protective equipment: An educational building semi-open space experimental investigation.

With the outbreak and spread of the COVID-19 epidemic, HCWs are frequently required to wear personal protective equipment (PPE) for nucleic acid sample collection in semi-open transition spaces. Wearing PPE causes significant psychological and physical stress in HCWs. In this study, operative temperature (Top) and wet-bulb globe temperature (WBGT) were used to assess thermal conditions through field experiments, while multiple physiological parameters were measured in the subjects. The results indicated that the subjects showed statistically significant differences in thermal perception and physiological parameters with and without PPE. Using observed increases in heart rate (HR), auditory canal temperature (Tac), mean skin temperature (MST), and end-tidal CO2 pressure, subjects were shown to have an increased metabolic rate and heat storage while wearing PPE. Additionally, a decrease in oxygen concentration was also observed, and this decrease may be linked to fatigue and cognitive impairment. Moreover, HR, MST, and Tac showed a significant linear relationship, which increased with temperature and operative temperature, and the HR response was stronger with PPE than without PPE. The neutral, preferred, and acceptable temperatures were significantly lower with PPE than without PPE, and the deviations for neutral Top/WBGT were 9.5/7.1 °C and preferred Top/WBGT was 2.2/4.0 °C, respectively. Moreover, the upper limits of acceptable WBGT, 29.4 °C with PPE and 20.4 °C without PPE, differed significantly between the two phases. Furthermore, the recorded physiological parameter responses and thermal perception responses of the subjects while wearing PPE indicated that they were at risk of thermal stress. Overall, these results suggest that people who wear PPE should focus on their health and thermal stress. This study provides a reference for the development of strategies to counteract heat stress and improve thermal comfort.

Thermal responses of face-masked pedestrians during summer: An outdoor investigation under tree-shaded areas.

During the SARS-CoV-2 (COVID-19) pandemic, most citizens were cooperative towards the face-masking policy; however, undeniably, face masking has increased complaints of thermal discomfort to varying degrees and resulted in potential health hazards during summer. Thus, a thermal comfort survey was conducted under tree-shaded areas generally preferred by pedestrians to explore the thermal response of face-masked pedestrians. Thirty-two subjects, with and without masks, participated in walking experiments, and their thermal parameters and physiological indicators were recorded; moreover, the subjects were asked to fill in subjective questionnaires. The results showed that although tree shades significantly reduced the average radiant temperature, dampness in the mask may cause some discomfort symptoms, among which intense sweating (54.55%) and tachycardia (42.18%) accounted for the largest proportion. Based on thermal indices, it could be concluded that face-masking does not significantly affect the thermal comfort of subjects walking in shaded areas. Notably, a 30-min walk in tree-shaded areas with face masking does not adversely affect human health or quality of life. Thus, the present assessment of the thermal safety of humans in shaded environments provides reference data for determining thermal comfort levels during outdoor walking with face masking.

Comparative analysis on indoor and outdoor thermal comfort in transitional seasons and summer based on multiple databases: Lessons learnt from the outdoors.

In environments with similar physical parameters, thermal comfort and sensation feelings may differ indoors and outdoors. How indoor and outdoor thermal perception differ from each other remains unclear. This study compared and discussed 29,536 field survey data, including 19,191 sets of indoor data, and 10,345 sets of outdoor data, covering five Köppen climate zones during transitional seasons and summer. Indoor data points were collected from two databases: the ASHRAE Global Thermal Comfort II and the SCATs (Smart Controls and Thermal Comfort), while outdoor data points were collected from the RUROS database (Rediscovering the Urban Realm and Open Spaces) and five individual projects executed in Singapore, Hong Kong, Guangzhou, Changsha, and Tianjin. The concepts of neutral rate (NR) and comfort rate (CR) were developed to help categorize "neutral" and "comfort" across different studies. The results of this study show that people are less sensitive to changes in thermal environment outdoors than indoors. Moreover, thermal comfort cannot be simply treated as thermal neutral, particularly for outdoor spaces. Compared with MM (mixed-mode) and NV (naturally ventilated) spaces, outdoor space does not have the highest NR, but its CR is much higher, with a wide range of SET* (Standard Effective Temperature) corresponding to CR over 80 %, from 15.5 °C to 23.4 °C. In the Cfa (humid subtropical) climate zone, significantly higher CR are recorded for outdoor spaces, although the NR are similar or even lower than those of indoors. Natural thermal resources in the outdoor thermal environment may hold the key to extending indoor comfort ranges.

Experimental investigation of the effects of personal protective equipment on thermal comfort in hot environments.

Since the outbreak of COVID-19, wearing personal protective equipment (PPE) has become increasingly common, especially for healthcare workers performing nucleic acid sample collection. A field experiment and questionnaire survey were conducted in a semi-open transition space of a university building in Guangzhou, southern China. Thirty-two subjects wore PPE to simulate nucleic acid sample collection, during which thermal parameters were recorded and subjective questionnaires were completed. The relationship between thermal sensation and thermal index was analyzed to determine the neutral temperature and comfort temperature zones. Subjects had higher requirements for thermal environment parameters when wearing PPE than when not wearing PPE, and were found to have statistically significant differences in thermal perception when wearing and not wearing PPE. Wearing PPE significantly raised the subjects' thermal and humidity sensations and restricted their airflow. Wearing PPE resulted in thermal discomfort for the subjects and a high unacceptability rate for environmental thermal parameters. The subjects wore PPE for an acceptable duration of approximately 1.5 h. The neutral operative temperatures were significantly lower when wearing PPE than when not wearing PPE, and the deviation from the neutral temperature was 9.7 °C. The neutral operative temperature was 19.5 °C and the comfort temperature zone was 17.4-21.5 °C when subjects wore PPE, demonstrating that subjects who wore PPE preferred lower temperatures. These results suggest that people who wear PPE for work, especially outdoors, should receive more attention to ensure thermal comfort and safety.

Investigation into the thermal comfort and physiological adaptability of outdoor physical training in college students.

Over the last few decades, increase in global temperatures have led to a deterioration in the quality of open spaces, urban vitality, and public health. Strenuous physical training under hot conditions outdoors increases the potential for developing heat illnesses. It is therefore necessary to examine the relationships between human physiological indices, psychological responses, and outdoor thermal indices to predict and evaluate human thermal safety in hot environments. A 9-day experiment was conducted in September 2019, which tested the thermal comfort and cognitive ability of 1102 students. Their physiological parameters (Heart rate, Auditory canal temperature) were recorded before and after physical training. Results showed that there were significant differences in the thermal sensation vote before and after physical training. The classification of heat stress was modified based on the MTSV regression model and PET. The maximum acceptable PET was 23.0 °C before physical training and 21.7 °C after physical training. When PET ≥ 40.1 °C, a reduction in physical training intensity is recommended. When PET ≥ 45.7 °C, cessation of physical training should take place and sun exposure should be reduced to avoid health hazards. It is important to use the auditory canal temperature instead of the core temperature to calculate the physiological strain index (PSI). More than 15% of the subjects had a PSI ≥ 7.0 during the test. When the body is in a thermally neutral state (MTSV = -0.5- 0.5), PSI ≤ 2.0. When the MTSV ≥3.2, PSI ≥ 7.0, physical training intensity should be reduced, and warning information should be provided. According to the expected distribution of physical training time and rest time, it is recommended that the time of each physical training session should be within 30 min, with a resting period of more than 30 min in hot environments.

Investigation of the effects of face masks on thermal comfort in Guangzhou, China.

Wearing masks to study and work places has become a daily protective measure during the COVID-19 pandemic. In the summer of 2021, environmental parameters were monitored, and students in a university library in Guangzhou, China, were surveyed to analyze the possible symptoms of wearing masks for a long time, and to assess the sensitivity of various body parts to the environmental parameters. Concurrently, the preference of subjects wearing masks for various environmental parameters was also analyzed. Additionally, the relationship between thermal sensation and thermal index was analyzed to identify acceptable and comfortable temperature ranges. The expected duration of wearing masks was counted. Subjects wearing masks had greater requirements for environmental comfort, and reported increased thermal discomfort of the face and head, compared to those without masks. More than 70% of the subjects wearing masks reported that they experienced discomfort on their faces. Among the subjects who experienced discomfort, 62.7% reported that facial fever was the main symptom; while some reported symptoms of dyspnea (25.4%) and rapid heartbeat (9.1%). More than 75% of the subjects were expected to wear masks for 2.0 h or less. Evaluation of environmental thermal sensation, including overall, facial, and head thermal sensation, differed among subjects who wore and did not wear masks. The indexes of neutral Operative temperature/Standard Effective Temperature (T op /SET*) and preferred T op /SET* were lower among subjects with masks than among those without masks. The neutral T op /SET* deviation was 0.3 °C, and the preferred T op /SET* deviation was 0.5 °C. Additionally, the acceptable and comfortable temperature zones differed between the two cases. The subjects who wore masks preferred colder temperatures. These findings indicated that the environmental parameters should be adjusted to improve the thermal comfort of the human body while wearing masks in work or study places.

Effects of mask wearing duration and relative humidity on thermal perception in the summer outdoor built environment.

During the pandemic, face masks are one of the most significant self-protection necessities, but they also cause heat stress. By using the ERA5 (ECMWF Reanalysis 5th Generation) database and the local weather bureau data, the effect of mask wearing on outdoor thermal sensation has been investigated by a survey conducted in the hot summer and cold winter region of eastern China in the summer of 2020. Results show that wearing a face mask for a longer period result in a higher level of discomfort, and the primary source of discomfort is hot and stuffy feelings. The effect of relative humidity is crucial for mask wearers in warm-biased thermal environments, as mean thermal sensation vote (TSV) peaks when environmental relative humidity reaches the range of 70% to 80% and decreases after this range due to the evaporation within the microclimate created by a face mask. Meanwhile, prolonged mask wearing increases participants' hot feelings, especially in warm environments. Specifically, participants wearing face masks for less than 30 min feel hot at a physiological equivalent temperature (PET) value of 34.4 °C, but those who wear them for over 60 min express hot feelings even at a PET value of 24.7 °C. The participants who wear a face mask while walking slowly outdoors have similar thermal sensations to those who do not wear a mask, but are in a higher activity level. The findings demonstrate that mask wearing has a crucial impact on outdoor thermal comfort assessment in a warm-biased outdoor thermal environment.

Experimental investigation of standard effective temperature (SET*) adapted for human walking in an indoor and transitional thermal environment.

Thermal indices are widely used to predict the human body's thermal sensation indoors and outdoors, with standard effective temperature (SET*) being the most commonly used index. Although SET* has been well-proven in predicting indoor static thermal comfort, it has not yet proven its applicability in thermal comfort and dynamic condition assessments outdoors. Refers to verify the application of SET* in both an indoor and transitional space, experiments were conducted in the badminton hall of Guangzhou University (representing the indoor space) and the overhead floor of the experimental building of Guangzhou University (representing the transition space). Thirty healthy college students were first asked to walk for 20 min at four walking speeds and then to rest for 10 min. During the whole process, environmental parameters and the mean thermal sensation vote (MTSV) were recorded. Thereafter, the relationship between MTSV and the calculated SET* was established; notably, the applicability of the SET* prediction model in the transitional space was significantly better than that in the indoor space during walking. An improved SET* prediction model and the corresponding thermal stress categories are proposed to predict the dynamic thermal sensation, which is suitable for either walking indoors or in transitional spaces. From the linear regression equation in the improved model, it was obtained that the thermal comfort interval (MTSV falling within ±0.5) represented by α SET* is 24-37.5 °C. In addition, through Probit regression analysis, the thermal sensation level corresponding to the improved SET* (α SET*) was determined.

Decreased humidity improves cognitive performance at extreme high indoor temperature.

In this study, we examined the cognitive performance of subtropically acclimatized subjects at an extreme high indoor temperature and the effect of decreased humidity on the cognitive performance at the high temperature. Forty-eight healthy subjects experienced the three exposure conditions: 26°C/relative humidity (RH) 70%, 39°C/RH50%, and 39°C/RH70% in a climate chamber. During 140-minute-long exposures to each thermal condition, they were required to perform cognitive tests that assess the perception, spatial orientation, concentration, memory, and thinking abilities. Meanwhile, their heart rate, core temperature, skin temperature, blood pressure, and body weight were measured and subjective responses, that is, thermal comfort, perceived air quality, and acute health symptoms were investigated. At the relative humidity of 70%, increasing indoor temperature from 26°C to 39°C caused a significant decrease in the accuracy of these cognitive tests. However, when the relative humidity decreased from 70% to 50% at 39°C, the accuracy of the cognitive tests increased significantly. Accordingly, the physiological and subjective responses of the subjects changed significantly with the changes in indoor temperature and humidity, which provided a basis to the variation in the cognitive performance. These results indicated that decreasing indoor humidity at extreme high temperature could improve the impaired cognitive performance.

Investigation into outdoor thermal comfort conditions by different seasonal field surveys in China, Guangzhou.

Outdoor microclimatic conditions strongly affect the thermal comfort of pedestrians. A transversal field survey was conducted in Guangzhou, together with micrometeorological measurements. The outdoor physiological equivalent temperature (PET) varied from 3 to 59 °C. Regression lines were obtained to establish correlations of the mean thermal sensation vote (MTSV) with the PET bins with a width of 1 °C. Furthermore, the thermal comfort range of PET, neutral PET (NPET), and preferred PET was analyzed. The results indicated that, for the young people, thermal comfort range of PET spanned from 19.2 to 24.6 °C. The NPET and preferred PET significantly differed in different seasons. The NPET was higher in the summer than that in the winter and transitional seasons. However, the preferred PET of the summer was lower than that of the winter. The PET limits of different thermal stress categories were also confirmed, which differed from those in other cities. Thus, the impacts of adaptation on thermal comfort range were significant for people in outdoor environment.

Experimental investigation of personal air supply nozzle use in aircraft cabins.

To study air passengers' use of individual air supply nozzles in aircraft cabins, we constructed an experimental chamber which replicated the interior of a modern passenger aircraft. A series of experiments were conducted at different levels of cabin occupancy. Survey data were collected focused on the reasons for opening the nozzle, adjusting the level of air flow, and changing the direction of the air flow. The results showed that human thermal and draft sensations change over time in an aircraft cabin. The thermal sensation response was highest when the volunteers first entered the cabin and decreased over time until it stablized. Fifty-one percent of volunteers opened the nozzle to alleviate a feeling of stuffiness, and more than 50% adjusted the nozzle to improve upper body comfort. Over the period of the experiment the majority of volunteers chose to adjust their the air flow of their personal system. This confirms airline companies' decisions to install the individual aircraft ventilation systems in their aircraft indicates that personal air systems based on nozzle adjustment are essential for cabin comfort. These results will assist in the design of more efficient air distribution systems within passenger aircraft cabins where there is a need to optimize the air flow in order to efficiently improve aircraft passengers' thermal comfort and reduce energy use.