General Heat Stress Index

relative humidity is routinely computed at many shore stations whenever the air temperature and wet-bulb temperatures are measured. While the effects of moisture in the air affect how people react to temperature by altering the evaporation rate of moisture on the skin, the effects of wind may also alter the evaporation rate of moisture from the skin and affect the temperature of the human body. General Heat Stress Index The General Heat Stress Index (GHSI), also referred to as the apparent temperature, is a measure of how hot the air "feels" to an average person based on the temperature and the humidity. It does not take into account direct sunshine, wind, or the type of clothing a person is wearing. The GHSI value is the "apparent temperature" in National Weather Service public forecasts. The GHSI may be computed from the relative humidity and the air temperature by using figure 1-38. As an example, with an air temperature of 90°F and a relative humidity of 60%, read the apparent temperature at the intersection of the horizontal air temperature line and the vertical relative humidity line. In this case the GHSI or the apparent temperature is 100°F. Interpolate between the lines as necessary. While interpretation of what a given apparent temperature feels like may vary from person to person, the differences among various apparent temperatures are objective and based on physiological research. The General Heat Stress Index uses four categories to relate "apparent temperature" to the probable occurrence of heat-stress-related injury as follows: Apparent Temperature 130°F and up—Category I, EXTREME DANGER—Heatstroke imminent Figure 1-38.—General Heat Stress Index nomogram. 1-56