Development of the equivalent air temperature index (EATI) among male workers under hot and dry and hot and humid climatic conditions

Abstract

Abstract Background Many environmental indices lack a clear association with the parameters under evaluation, making interpretation difficult. As such, using equivalent air temperature as a more comprehensible metric may enhance its precision. Therefore, the present study aimed to develop an equivalent air temperature index (EATI) among male workers in hot-dry and hot-humid climatic conditions. Methods A total of 101 male participants from an industrial facility in a hot and dry region, along with 93 males from another industry in a hot and humid region, voluntarily participated in this cross-sectional study. They rested in a cool environment for 30 min. Then, they returned to their workplace and perform their routine work for 90 min. At the end of the work period, their physiological parameters such as heart rate and auricular temperature were measured. Additionally, the environmental parameters were measured, and metabolic rate and clothing thermal insulation were estimated. Subsequently, a novel index was developed by equating five factors to air temperature. To assess the validity of the index, a linear regression analysis was conducted to examine its relationship with auricular temperature and heart rate. Results Based on the results, the EATI explained 71%, 70%, and 64% of the variation in auricular temperature (°C) in the hot and dry region, hot and humid region, and both region,, respectively (R2 = 0.71, R2 = 0.70, and R2 = 0.64). Additionally, this index explained 72%, 70%, and 70% of the variation in heart rate (beats per minute) in the hot and dry region, hot and humid environment, and both, respectively (R2 = 0.72, R2 = 0.70, and R2 = 0.70). Conclusions The study confirms that the equivalent air temperature index can effectively evaluate thermal strain by considering radiant temperature, humidity, wind speed, and estimated metabolic rate and clothing insulation. This index appears valid for both hot and dry regions as well as hot and humid regions.

Keywords

• Equivalent air temperature index
• Auricular temperature
• Heart rate
• Heat stress
• Heat strain
• Validity