What is Wet-bulb Globe Temperature?
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).
History and Development
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.
How WBGT is Calculated
A WBGT meter combines three sensors: a dry-bulb thermometer, a natural (static) wet-bulb thermometer, and a black globe thermometer (for radiant heat). These sensors measure environmental conditions and calculate a single value representing overall heat stress. For outdoor environments, the meter uses all sensor data inputs to calculate WBGT as:
WBGT = 0.7T_w + 0.2T_g + 0.1T_d
Where:
- Tw = Natural wet-bulb temperature (combined with dry-bulb temperature indicates humidity)
- Tg = Globe thermometer temperature (measured with a globe thermometer, also known as a black globe thermometer)
- Td = Dry-bulb temperature (actual air temperature)
- Temperatures may be in either Celsius or Fahrenheit
For indoor environments, a different formula is used:
WBGT = 0.7T_w + 0.3T_d
Importance and Applications
WBGT is used to determine the risk of heat-related illnesses and to assess the need for heat stress prevention measures. It is commonly used in industries that involve physical labor, such as construction, manufacturing, and agriculture, as well as in sports and military training. WBGT is also used in urban planning and architecture to design buildings and cities that are resilient to heat stress.
Calculating WBGT without a Meter
If a meter is not available, WBGT can be calculated from current or historic weather data. A clothing adjustment may be added to the WBGT to determine the "effective WBGT", WBGTeff.
Examples and Case Studies
WBGT has been used in various contexts, including:
- Military training: The US military uses WBGT to determine when to stop training due to heat-related risks.
- Sports: WBGT is used to determine the safety of outdoor sports events, such as marathons and football games.
- Industrial settings: WBGT is used to monitor heat stress in workers in industries such as construction and manufacturing.
Relation to Apiary Mission
While WBGT is not directly related to bee conservation or self-governing AI agents, it can be used as a tool to assess the heat stress of bees in outdoor environments. Bees are sensitive to high temperatures and humidity, and WBGT can be used to determine when bees are at risk of heat-related stress.
FAQ
What is the difference between WBGT and dry-bulb temperature?
WBGT takes into account not only dry-bulb temperature but also humidity, heat radiation, and air movement, making it a more comprehensive measure of environmental heat.
How is WBGT used in military training?
WBGT is used by the US military to determine when to stop training due to heat-related risks. When WBGT exceeds a certain threshold, training is halted to prevent heat-related illnesses.
What is the difference between WBGT and WBGTeff?
WBGTeff is the effective WBGT, which takes into account the clothing worn by individuals. It is used to determine the actual heat stress experienced by individuals in different clothing conditions.
What is the formula for calculating WBGT indoors?
The formula for calculating WBGT indoors is WBGT = 0.7T_w + 0.3T_d.
Can WBGT be calculated from weather data?
Yes, WBGT can be calculated from current or historic weather data. A clothing adjustment may be added to the WBGT to determine the effective WBGT, WBGTeff.