When a person works in a hot environment, the body must get rid of excess heat to maintain a stable internal temperature of 97.9ºF to 99.5ºF. The body accomplishes this mainly by circulating warm blood to the skin (thermal convection) and by evaporating fluid off the skin (sweating). This system works quite well until the air temperature approaches body temperature. At that point, blood circulated to the skin cannot lose its heat, so sweating then becomes the main method for the body to cool down. Unfortunately, sweating is effective only if the humidity level is low enough to allow for evaporation and if the lost fluids and salts are adequately replaced. Risks are amplified in workers who: are 65 years of age or older; are overweight; have heart disease or high blood pressure; must wear occlusive, heat-trapping clothing (e.g., Tyvek suit); perform physically strenuous work; or take certain medications (e.g., anti-depressants, diuretics).
If the body cannot rid itself of excess heat, it will store it. When this happens, the body’s core temperature rises and the individual becomes sick. As the body temperature approaches 104ºF., the situation becomes life-threatening. At 106ºF, brain death begins. In 2006, OSHA recorded 24 heat-related deaths.