Long-Term Physiologically Equivalent Temperature Trends and Climate-Related Occupational Heat Exposure Across Industrial Sectors in Iran

The air we breathe and the heat we feel are not just weather; they are active forces that shape how our bodies function. When the sun beats down, humidity hangs heavy, and the wind dies, our bodies struggle to cool themselves. This struggle is not merely about feeling uncomfortable; it is a physiological battle where the body must work harder to maintain its internal temperature. For people working outdoors or in hot factories, this battle happens every day, and when the conditions are extreme, it can lead to serious health risks. Scientists have long tried to measure this risk, but traditional methods often look only at the air temperature, missing the full picture of how humidity, wind, and radiant heat combine to stress the human body. To understand the true danger, researchers need a way to translate these complex weather patterns into a single number that reflects what a person actually feels. This is where a concept called the Physiologically Equivalent Temperature comes in. Think of it as a universal translator for heat: it takes the messy mix of sun, wind, and moisture and converts it into a simple temperature reading that tells us exactly how hard the human body is working to stay cool.

A team of researchers in Iran set out to use this translator to map the invisible heat burden facing the country's workers. They wanted to know where the most dangerous heat zones were and which industries were most likely to be caught in them. Iran, a nation with vast deserts and high mountains, experiences some of the most intense heat on Earth, making it a critical place to study. The researchers gathered sixty-six years of weather data from forty different stations across the country, stretching from 1959 to 2025. They fed this massive dataset into a computer model that calculated the Physiologically Equivalent Temperature for every location, creating a detailed, long-term map of thermal stress. They then overlaid this map with the locations of Iran's major industries, from oil refineries and metal factories to farms and textile mills. The goal was not just to see where it was hot, but to see where the people who built the country's economy were forced to work in that heat.

The results painted a stark picture of a nation where industry and extreme heat are deeply intertwined. The study found that the vast majority of Iran's industrial facilities are situated in regions where the physiological heat stress is severe or even extreme. In the hottest months, particularly August, most factories and mines sit in zones where the heat feels like a relentless oven, far beyond what is considered comfortable. The researchers identified that industries like mining, metal processing, and the oil and gas sector are overwhelmingly concentrated in these dangerous thermal zones. For example, the massive oil and gas complexes in the south and southwest are almost entirely locked in areas where the heat stress is at its highest level. Similarly, the metal and casting industries, which include steel and pipe manufacturing, are clustered in regions where the heat is so intense that it poses a constant challenge to workers' health. Even the coke-making industry, a specific part of the metal sector, showed a unique pattern, with its facilities almost exclusively located in the most extreme heat zones, creating a highly uniform and intense exposure profile for its workers.

However, the map was not entirely uniform. The study revealed that different sectors face different levels of risk depending on where they are located. While the heavy industries are trapped in the scorching south and central deserts, the agricultural sector showed a slightly different pattern. Although many farms are still located in hot areas, a larger portion of agricultural activity exists in regions with moderate heat stress or even comfortable temperatures, particularly in the northern and western highlands. This suggests that while farmers certainly face heat risks, the intensity and geographic concentration of that risk vary more widely than in the industrial sectors. The textile and leather industries also showed a mix, with many facilities in severe heat zones but some scattered in cooler areas. The paper carefully notes that while these maps show where the environmental heat is most intense, they do not measure the specific health outcomes of individual workers, such as illness or injury. Instead, they provide a clear, nationwide view of the environmental conditions that workers face, highlighting that for many sectors, the job is physically demanding in a climate that is becoming increasingly hostile.

This research offers a new way to look at the relationship between climate and work. By combining decades of weather data with the geography of industry, the study shows that the heat workers face is not random; it is built into the very layout of the country's economy. The findings suggest that as the climate continues to warm, the workers in these specific sectors will face even greater challenges. The study does not claim to have solved the problem of heat stress, nor does it offer a specific fix for every factory. Instead, it provides a solid foundation of knowledge, showing exactly where the heat is worst and which industries are most exposed. This kind of clear, large-scale picture is essential for governments and health officials who need to plan for the future. It allows them to see that protecting workers is not just about checking a thermometer on a single day, but about understanding the long-term, physical reality of working in a country where the heat is a permanent and intensifying feature of the landscape.