This section contains some information about the basic principles of Wet Bulb Globe Temperature measurements. The information is divided in several chapters. Please click on the desired section in the menu.
The Wet Bulb Globe Temperature (WBGT) is a composite temperature. It is used to estimate the effect of temperature, solar radiation and wind speed on the human body. The WBGT is not the same as the ambient (dry) temperature, as it takes into account the levels of radiation, wind movement, humidity and the ambient temperature.
During during training activities at Parris Island (South Carolina) in the early 1950, the US Marine Corps suffered significant casualties due to heat stroke. The WBGT was the outcome of the study commissioned by the US Department of the Navy because of this incident, aiming to find an index which allows to estimate the effects of heat on exercise performance. In 1989, WBGT was suggested as an international standard (ISO 7243).
The WBGT is expressed in °C or in °F. Many public institutions like the American College of Sports Medicine, the US Army, the Japanese Amateur Sports Association, the Japan Society for Occupational Health and the American Conference of Governmental Industrial Hygienists recommend the monitoring of on-field WBGT to prevent heat strokes.
The tables below contain examples of such recommendations.
|WBGT [°C]||Recommended maximum workload|
|Work and rest regimen||Permissible Limits (WBGT [°F])|
|Light work||Moderate work||Heavy work|
|8 h continuous work||
|75% work – 25% rest||
|50% work – 50% rest||
|25% work – 75% rest||90.0||88.0||86.0|
Originally, the WBGT was determined determined based on the measurement of three temperatures with a standard (bulb) thermometer:
The WBGT can then be calculated as follows:
WBGT = 0.7 WB + 0.2 GT + 0.1 DB
If the WBGT is measured inside a building, there is no direct solar radiation. When doing indoor measurements the WBGT is therefore calculated as follows:
WBGT = 0.7 WB + 0.3 GT
Modern portable WBGT Heat Stroke Prevention Meters