What is Wet Bulb Globe Temperature?

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 helpful 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.

Wet Bulb Globe Temperature 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 & 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 People from Exertional Heat Stress Better than Heat Index?

Heat safety starts with monitoring the conditions. WBGT monitoring is the most effective first step in preventing exertional heat stress illness for athletes, military members, and workers. The Kestrel 5400 Heat Stress Tracker automatically calculates accurate WBGT based on onsite environmental conditions. The 5400 is used by safety professionals in major sports organizations such as the NFL, MLS, and USTA as well as by all branches of the US Military for WBGT monitoring.

WBGT & Athletics

When establishing WBGT guidelines for physical activity, the guidelines must be region (geographic) specific. For example, an athlete playing football in Louisiana may be accustomed to warm environmental conditions, unlike a football player from Maine. A football player practicing in 90°F temperatures in Louisiana could be comfortable, whereas a football player practicing in the same conditions in Maine could be experiencing the worst conditions they have felt all year, which would increase the risk of heat illness. Depending on the WBGT reading, there are guidelines for activities and modifications.

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

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

Wet Bulb Globe Temperature Monitoring for Heat Safety

• WBGT has been shown to provide an accurate measure of environmental heat stress.
• WBGT can be used as a preventive measure during exercise in the heat by making activity modifications as WBGT rises.
• When developing guidelines for activity modification using WBGT, it is necessary to include: work/rest ratios, length of activity, hydration breaks, equipment to be worn (if applicable), and a level in which activity is canceled.
• WBGT guidelines must be region (geographic) specific since temperatures fluctuate differently by regions.  People’s response to exercising in heat may vary by the geographic region in which their usual exercise sessions take place.
• WBGT modifications should be fluid, meaning that if the conditions get more restrictive during the day or a particular practice, modifications should be more restrictive. As environmental conditions become more mild, modifications should be less restrictive.
  Source: Korey Stringer Institute (KSI)

WBGT & Military Training

Heat stress can quickly become a dangerous and critical problem if not taken seriously. Through WBGT monitoring, leaders can obtain real-time updates on their work environment conditions, allowing them to act accordingly before things become potentially life-threatening. The United States Military uses WBGT to modify basic training during hot conditions. The chart below shows the modifications that are used during basic training. 

WBGT & Occupational Heat Safety

Heat-related illnesses can be deadly, yet they remain one of the most overlooked safety hazards in the workplace. Occupational heat stress is a condition that frequently affects employees working in extreme or strenuous conditions. Therefore, understanding how to recognize and address heat-related health concerns is vital for employers seeking to create a safe work environment.

Every year, countless workers around the world suffer heat-related illnesses and injuries – putting their health, well-being and livelihoods at risk. That’s why the Occupational Safety and Health Administration (OSHA) launched its National Emphasis Program (NEP) for Heat-Related Hazards to raise awareness of this serious issue. The program aims to prevent workplace heat stress by educating employers about risks associated with overexposure to high temperatures as well as how they can keep their employees safe and healthy during hot working conditions. In addition, OSHA will initiate inspections on heat priority days.  The NEP defines a heat priority day as one where employees are exposed to outdoor heat at or above 80°F with the humidity at or above 40 percent. Employers should expect Increased inspections for targeted industries at both outdoor and indoor jobsites.

WBGT is the most accurate tool for measuring heat hazards for outdoor workers and indoor workers where radiant heat sources are a factor. Monitoring the WBGT conditions where workers are present is key to preventing serious illness and injury.

American Conference of Governmental Industrial Hygienists (ACGIH) provides guidance for maintaining awareness about when workers may be exposed to heat stress so that preventive measures can be taken.

The Kestrel Heat Stress Monitoring System includes the 5400 Heat Stress Tracker and a wall-mounted connected tablet display for at-a-glance visibility on critical jobsite conditions. It’s the ideal WBGT monitoring solution to help safety managers protect workers and comply with OSHA standards. With increased attention on occupational heat stress and more frequent OSHA inspections, it’s imperative for owners and managers to focus on prevention.

Kestrel 5400 Heat Stress Trackers for WBGT Monitoring

Monitoring WBGT is easy and reliable when relying on Kestrel weather meters. With a Kestrel weather meter onsite, 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, easy operation, and reliable readings, rely on Kestrel Heat Stress Trackers for WBGT readings and heat illness prevention.