URBANA, Ill. – June has been hot and muggy. Regardless what the thermometer reads, it just feels hotter.
Feels-like temperatures are calculated using the air temperature, relative humidity, wind speed, and an understanding of how the human body responds to heat and cold.
"When the body is hot, it sweats, says Duane Friend, University of Illinois Extension energy and environment educator. "Moisture on the skin surface evaporates, removing heat from the skin surface, which lowers the overall body temperature. If there is already a lot of moisture in the air, the rate of evaporation slows, which slows or stops that cooling. Body temperature continue to increase, placing the person at risk."
When high temperatures are coupled with high humidity, there is greater risk for health dangers, especially when exerting physical activity outside. The body's reaction to the extreme heat can lead to muscle cramps, heat exhaustion, or heat stroke. The individual danger varies based on water vapor, human body volume, skin surface area, clothing, body temperature, temperatures of the skin and clothing, exertion, wind speed, and rate of sweating.
The heat index warns the public of the danger level of outdoor activity. There are four categories: caution, extreme caution, danger, and extreme danger. At extreme caution, temperatures range from 91 to 103 degrees. Heat cramps, heat exhaustion, and sunstroke are possible with prolonged activity, says Friend.
The danger category includes feels-like temperature of 103 to 124 degrees. Under these conditions, the danger of heat exhaustion and sunstroke is extremely high for most people with any physical activity. Seek medical attention if you experience nausea, light headedness, or other symptoms.
"If you’re getting hot, stop what you’re doing and get cooled off," Friend says. "If you start having muscle cramps, get to a cool place and drink some cool water or sports drink that has some electrolytes."
The following references include additional information on the topic:
- Steadman, R.G., 1979: The assessment of sultriness. Part I: A temperature-humidity index based on human physiology and clothing science. J. Appl. Meteor., 18, 861-873
- The Heat Index Equation, Lans Rothfusz.
- Energy Budget: Heat Index and Wind Chill, Iowa State University
- WebMD: Heat Cramps
SOURCE: Duane Friend, University of Illinois Extension Energy and Environment Stewardship Educator
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