Thermal comfort and heat stress indices for outdoor occupations over 15 years: a case study from Iran

The present study aims to assess seasonal trends in thermal comfort and heat stress indices for outdoor occupations over a 15‐year period using the Iranian Meteorological Organization's database for Sari, Iran. Hourly and daily meteorological data including temperature, wind speed, cloudiness, relative humidity and vapor pressure measurements for Sari city from 2000 to 2014 are used. The wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI) are calculated, along with thermal comfort indices including physiological equivalent temperature (PET), standard effective temperature (SET) and predicted mean vote (PMV). The highest and lowest mean monthly air temperature values for the 15‐year period were recorded for August (27.55 ± 0.57°C) and January (7.9 ± 0.68°C), respectively. The highest and lowest mean monthly relative humidity values were observed for December (81.2 ± 2.6%) and August (73.7 ± 1.94%), respectively. The strongest correlations were found between all of the thermal comfort and heat stress indices under study and air temperature (r = 0.97–0.99; P < 0.001), as well as all indices and mean radiant temperature (r = 0.96–0.98; P < 0.001). Strong significant correlations were observed between all heat stress and thermal comfort indices (r > 0.93; P < 0.001). The use of meteorological data can enable the prediction of physiologically stressful conditions via knowledge of the strong positive correlation between heat stress and certain physiological indices, as highlighted in this study. Sari is located around 53°E longitude and 36° N latitude. It ascends to about 43 meters above sea level, on the southern coast of the Caspian Sea and it has a Mediterranean climate (average annual temperature: 15°C and relative humidity: 73%).