Have you heard of the Wet-Bulb Globe Temperature? Here’s what it’s used for

It’s similar to the heat index, but factors in a few other parameters such as wind and solar radiation

Device used to measure Wet Bulb Globe Temperature. (KSAT 2023)

Throughout the summer, we’ve talked about temperatures and the heat index, but there’s another measurement that’s been used to talk more specifically about heat stress in direct sunlight.

The Wet-Bulb Globe Temperature (WBGT) was originally introduced for the safety of workers inside and outside. OSHA and the International Organization for Standardization recognize this measurement as a standard for occupational environments.

UIL is also recommending coaches use the WBGT to protect their athletes from heat-related illnesses when exercising outdoors.

Here’s why this measurement is used to keep you safe in direct heat:

First of all, what does the WBGT measurement take into account?

According to the National Weather Service, the WBGT measures the heat stress on the body based on four parameters:

  • Temperature
  • Relative humidity
  • Wind
  • Solar radiation

The measurement’s output is a number in degrees (much like the heat index) and is categorized into four danger thresholds: caution, extreme caution, danger, and extreme danger.

Hazard LevelWet-Bulb Globe TemperatureBreak Times from Exercise/Work
Caution80-84.9°F15 minutes each hour
Extreme Caution85-87.9°F30 minutes each hour
Danger88-89.9°F40 minutes each hour
Extreme Danger>90°F45 minutes each hour

How is it different from the heat index?

The heat index is a calculation of what it feels like to our bodies based on the humidity and the temperature in the shade (i.e., not in direct sunlight).

On the other hand, the WBGT takes into account those two parameters while also including the solar radiation and wind speed. The output is then based on how all four parameters affect individuals outside.

We know that hotter temperatures can be more dangerous for those working or exercising outside, but here’s why the other three parameters are also important to consider:

  • Relative humidity is important to the measurement because the greater the humidity, the harder it is for the body to cool down.
  • Wind also helps the body cool down; if there’s no wind, you immediately feel hotter.
  • Solar radiation takes into account how much direct sunlight is present. If clouds are out when measuring the WBGT, the output will be lower because the clouds reflect a portion of the sun’s radiation back into space.

Measuring the WBGT

These days, there are Wet-Bulb Globe Temperature devices that measure all four parameters and produce an output based on the current weather conditions at your location.

As the WBGT increases, so does the risk of heat stroke. Consider taking the recommended amount of break time based on the WBGT thresholds, and visit our article on the symptoms of heat stroke and heat exhaustion to protect yourself and others when working outside.

About the Author:

Leah Mata-Rodriguez is an intern with the KSAT Weather Authority team. She is a rising senior at Texas A&M University majoring in Meteorology. Originally from Pearsall, Leah grew up watching KSAT 12 before and after school. She always looks forward to eating food from Mexican restaurants and bakeries around San Antonio and her hometown.