thumb|Electronic WBGT meter

thumb|Analog WBGT meter consisting of three thermometers and a [[slide rule to compute WBGT]]

The wet-bulb globe temperature (WBGT) is a measure of environmental heat as it affects humans and animals. Unlike a simple temperature measurement, WBGT accounts for air temperature, humidity, heat radiation (from hot objects like the Sun or a furnace), and air movement (wind or ventilation). WBGT was developed in the 1950s as a part of an effort to reduce heat related illness and death during US military training. Today, it is used by industrial hygienists, athletes, sporting events, and militaries to determine appropriate exposure levels to high temperatures.

A WBGT meter combines three sensors, a dry-bulb thermometer, a natural (static) wet-bulb thermometer, and a black globe thermometer (for radiant heat), which together measure environmental conditions and calculates a single value representing overall heat stress

In hot areas, some 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. The University of Georgia adapted these categories for use in college sports as a guideline for how strenuous practices can be.

:{| class="wikitable"

!Category||WBGT (°F)||WBGT (°C)||Flag color

|-

|1||≤ 78–81.9||≤ 25.6–27.7||style="background:white;color:black"|White

|-

|2||82–84.9||27.8–29.4||style="background:limegreen;color:black"|Green

|-

|3||85–87.9||29.5–31.0||style="background:yellow;color:black"|Yellow

|-

|4||88–89.9||31.1–32.1||style="background:red;color:white"|Red

|-

|5||≥ 90||≥ 32.2||style="background:black;color:white"|Black

|}

Safety considerations

Often used by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the American Conference of Governmental Industrial Hygienists (ACGIH) WBGT serves as a basis for standards and regulations in order to prevent heat related illnesses, such as heat stress, in the workplace.

WBGT meters, such as data logger heat stress monitors, are designed to help employers assess heat exposure by combining measured humidity, temperature, air movement, and direct or radiant sunlight into a single value that represents accurate heat stress conditions for workers. These meters are used in workplace safety monitoring, environmental/occupational assessments, and preventing heat related illnesses for workers in intense heat environment.

Vulnerable populations

Outdoor and industrial workers are most at risk for health problems due to overheating when working in an ambient temperature over 38 °C (100.4 °F). Heatstroke often results from factors such as increasing ambient temperature, high humidity, heavy physical workloads, prolonged sun exposure, improper clothing, and inadequate hydration. These concerns increase as factors such as a country's greenhouse gas emissions, population size, and socioeconomic status are considered. These risks are notably higher in mid-latitude, tropical climates, where populations receive year round heat exposures because of their geographic location.

Global impacts

Global heat stress management strategies prompted by the World Health Organization emphasized the importance of reducing greenhouse emissions to protect worker health. Data from 2019 shows that in the past 10 years, 41.9% of worker deaths were linked to extreme heat exposure while working. WBGT is increasingly being used in safety research and in forecasting early warning systems to help guide public health responses.

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.

The NWS office in Tulsa, Oklahoma, in conjunction with Oral Roberts University's mathematics department, published an approximation formula to the WBGT that takes into account cloud cover and wind speed; in limited experimentation (four samples), the office claimed the estimate was regularly accurate to within , even with a simplification that reduces the equation from a four-degree polynomial to a linear relationship (the authors noted that the linear approximation was not tested for air temperatures under since the WBGT is designed to measure heat stress, which seldom occurs below that threshold).

See also

  • Hygrometer

References

Further reading

  • Air Force Pamphlet 48-151
  • U.S. Army Technical Bulletin Medical 507/Air Force Pamphlet 48-152
  • Zunis Foundation background article
  • Thermal Comfort observations from the Australian Bureau of Meteorology
  • Extreme Hot or Cold Temperature Conditions from the Canadian Centre for Occupational Health and Safety
  • OSHA Technical Manual: Heat Stress from the U.S. Occupational Safety and Health Administration