Wet-bulb globe temperature

(Redirected from Wet Bulb Globe Temperature)
Cryptologic technician checking the Wet Bulb Globe Temperature at the Corry Station Naval Technical Training Center

The wet-bulb globe temperature (WBGT) is a composite temperature used to estimate the effect of temperature, humidity, wind speed (wind chill), and visible and infrared radiation (usually sunlight) 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:

$\mathit{WBGT} = 0.7T_w + 0.2T_g + 0.1T_d$

Where

Indoors, or when solar radiation is negligible, the following formula is often used: $\mathit{WBGT}=0.7T_w + 0.3T_g$

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 U.S. National Weather Service and the humidex used by the Meteorological Service of Canada, along with the wind chill used in both countries, are also measures of perceived heat or cold, but they do not account for the effects of radiation. AccuWeather, a commercial weather forecasting company, offers a product known as the "RealFeel" temperature that purportedly takes radiation into account (presumably by approximation, since American weather observation systems do not measure solar radiation directly); the RealFeel formula is a proprietary trade secret.