Whether you work in a hot smelting plant or outdoors in the summer months, heat exposure can be dangerous. Workers who are exposed to extreme heat or work in hot environments may be at increased risk of heat stress. In foundries, steel mills, bakeries, smelters, glass factories, and furnaces, extremely hot or molten material is the main source of heat. For people working outdoors in jobs such as construction, road repair, open-pit mining and agriculture, summer sunshine provides the hot environment. In laundries, restaurant kitchens, and canneries, high humidity adds to the heat burden. In all cases, the cause of heat stress is a working environment which can potentially overwhelm your body's ability to deal with heat.
"Heat stress" is a buildup of body heat generated from a combination of the effort you exert while working, the environment (air temperature, humidity, air movement, radiation from the sun, or hot surfaces/sources), and the clothing and equipment you wear.