Wet-bulb globe temperature
The Wet Bulb Globe Temperature (WBGT) is a composite temperature used to estimate the effect of temperature, humidity, wind speed (wind chill) and solar radiation on humans. It is used by industrial hygienists, athletes, and the military to determine appropriate exposure levels to high temperatures. It is derived from the following formula:
Where
- Tw = Natural wet-bulb temperature (humidity indicator)
- Tg = Globe thermometer temperature (measured with a globe thermometer, also known as a black globe thermometer, to measure solar radiation)
- Td = Dry-bulb temperature (normal air temperature)
- Temperatures may be in either Celsius or Fahrenheit
Indoors, or when solar radiation is negligible, the following formula is used:
The WBGT index was developed in 1956 by the United States Marine Corps at Parris Island to reduce heat stress injuries in recruits; it has been revised several times.[citation needed]
Uses
The American Conference of Governmental Industrial Hygienists publishes threshold limit values (TLVs) that have been adopted by many governments for use in the workplace. The process for determining the WBGT is also described in ISO 7243, Hot Environments - Estimation of the Heat Stress on Working Man, Based on the WBGT Index. The American College of Sports Medicine bases its guidelines on the intensity of sport practices based on WBGT.[1]
In hot areas, some[specify] US military installations display a flag to indicate the heat category based on the WBGT. The military publishes guidelines for water intake and physical activity level for acclimated and unacclimated individuals in different uniforms based on the heat category.
| Category | WBGT °F | WBGT °C | Flag color |
|---|---|---|---|
| 1 | <= 79.9 | <= 26.6 | White |
| 2 | 80-84.9 | 26.7-29.3 | Green |
| 3 | 85-87.9 | 29.4-31.0 | Yellow |
| 4 | 88-89.9 | 31.1-32.1 | Red |
| 5 | => 90 | => 32.2 | Black |
The heat index used by the National Weather Service and the humidex used by the Meteorological Service of Canada are also measures of perceived heat, but they do not account for the effects of radiation.
See also
Citations
 | This article includes a list of general references, but it lacks sufficient corresponding inline citations. (February 2012) |
Specific references:
- ^ "Deaths Triple Among Football Players, Morning Temperatures Thought to Play a Role". Science Daily. February 27, 2012. Retrieved 2012-02-28.
General references:
- Air Force Pamphlet 48-151
- U.S. Army Technical Bulletin Medical 507/Air Force Pamphlet 48-152
- Zunis Foundation background article