Heat Index vs. Wet bulb globe temperature
Tools like the Wet-Bulb Globe Temperature (WBGT) and Heat Index help assess environmental heat risks, but they serve different purposes and vary in accuracy. Understanding these tools and the guidelines associated with them is essential for preventing heat-related illnesses.
Wet-Bulb Globe Temperature (WBGT)
WBGT is a comprehensive measure of heat stress that accounts for air temperature, humidity, wind speed, sun angle, and solar radiation. It is calculated using specialized devices designed to factor in these variables, providing a more precise assessment of heat risk for outdoor activities.
WBGT is widely used in athletic guidelines, with thresholds that dictate activity modifications or cancellations.
Outdoors with sunlight, the formula for WBGT is:
WBGT = (0.7×Twb)+(0.2×Tg)+(0.1×Tdb)
- Tdb - The dry-bulb temperature is the ambient air temperature, measured with a standard thermometer in the shade. It provides the baseline
- Twb - The wet-bulb temperature represents the cooling effect of evaporation, reflecting humidity and air movement. It is measured using a thermometer covered with a moistened wick, allowing evaporation to cool the sensor.
- Tg - The globe temperature captures radiant heat from the sun or other heat sources. It is measured with a thermometer inside a black sphere that absorbs radiant energy.
Learn more about your region and the different limits and guidelines for WBGT
Heat Index
The Heat Index combines air temperature and relative humidity to calculate how hot it feels to the human body. Unlike WBGT, it does not account for factors like wind speed or direct solar radiation, making it less comprehensive.
While the Heat Index is commonly used for public health warnings, it is not as effective for assessing heat risks during sports, where athletes are exposed to more dynamic environmental conditions.
Heat Index is limited in its ability to help understand heat stress because it does not account for wind speed, direct sunlight, or radiant heat. Said differently, the Heat Index assumes you are in the shade.
Why WBGT Is Used in Sports
WBGT is the preferred tool in sports because it provides a detailed and accurate evaluation of heat stress, considering factors that directly impact athletes' safety. Organizations like the NCAA and high school athletic associations rely on WBGT thresholds to set activity guidelines, ensuring that decisions are based on precise environmental data. This comprehensive approach helps protect athletes from heat-related illnesses and creates safer conditions for training and competition.