What is Wet Bulb Globe Temperature?

What is Wet Bulb Globe Temperature?

Monitoring the environment to effectively assess the risk of heat stress during hot weather athletic and occupational activities.

If you've ever been outside on an extremely hot day, you’ve probably felt the impact of heat index—the combination of air temperature and humidity that makes you feel hotter than the temperature of the air itself. While this is a useful indicator for getting a sense of general hot weather conditions, wet bulb globe temperature (WBGT) tells a better story of the effect of heat stress on the human body in a specific environment.

Heat stress is a serious issue for people in a variety of jobs, sports, and recreational activities. Reducing the likelihood of heat stress can save lives. It all starts with monitoring WBGT.

What is WBGT?

WBGT isn't as well-known as heat index but it's a more accurate measure of the heat stress present in the environment. WBGT is a measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle, and cloud cover -- also known as solar radiation. When compared to heat index, WBGT offers a comprehensive picture of how location-specific weather conditions can impact the level of heat stress risk.

wbgt vs heat index

Signs of Heat Stress & Illness

The signs of heat stress should be monitored closely at the earliest stages to prevent serious illness or injury. Even young and healthy people can experience a heat stroke given the right conditions. Typical signs of heat illness and stress include:

  • Dizziness
  • Confusion
  • Nausea
  • Heavy sweating
  • Pale and clammy skin
  • Skin may be cold to the touch
  • Weakness
  • Headache
  • Heat cramps
  • Losing consciousness

WBGT Index & Environmental Monitoring

The concept of WBGT came about in the 1950s. The idea was born when heat illness affected US armed services during the 1940s. After the implementation of WBGT, there were fewer instances of heat illness in basic training moving forward.

"Monitoring the WBGT index is particularly important for soldiers in training, allowing soldiers to train and work safely while factoring in the weather of that day. It is a unit responsibility to record the WBGT Index at your specific training site and implement control measures as necessary."

-WBGT Aids Safe Work, Training, Exercise; Sets Flag Conditions. Army.Mil May 2019; Capt. Matthew Frickey.

WBGT is the preferred method for monitoring heat stress whether it's for work, competitive sports, recreational activities, or training and conditioning.

"The WBGT index encompasses all of these environmental causes of heat stress into one number that is used to characterize the potential effects of hot environments on runners."

-The WBGT Index: A Primer for Road Race Medicine. Endurance and Sports Medicine Fall/Winter 2018; Samuel N. Cheuvront, PhD, RD, FACSM and Yuri Hosokawa, PhD, ATC.

How Will WBGT Protect Athletes from Exertional Heat Stress?

Heat safety starts with monitoring the conditions. WBGT monitoring is the most effective first step in preventing exertional heat stress illness. Following the recommended guidelines for activity modifications helps to protect athletes and workers.

Depending on the WBGT reading, the following actions should be followed:

When determining the correct action to take in correlation with the WBGT reading, a safety chart is useful in many situations.

For example, a high school football team can take the suggested actions and impact preventions in the chart below.

Suggested Actions and Impact Prevention - WBGT

Developing an action plan for preventing heat illness is dependent on the region of the country. Some areas of the country are more susceptible to causing heat illness at different times of the year.

How to Monitor WBGT

Monitoring WBGT is easy and reliable when relying on Kestrel weather meters. Measuring WBGT comes down to the following elements:

    • Humidity
    • Temperature
    • Wind Speed
    • Sun Angle
    • Cloud cover

    With a Kestrel weather meter on-site, like the Kestrel 5400 Heat Stress Tracker, feel confident about keeping heat stress and illness at bay. It also allows for you to keep precautionary measures fluid, as there are different risks of heat stress in the evening vs. mid-day.

    For unbeatable accuracy and reliable readings, rely on Kestrel Heat Stress Trackers for WBGT readings and heat illness prevention.