National Usage of Wet Bulb Globe Temperature in Athletics
A brief guide to wet bulb globe temperature and complete list of every state and their stance on its usage in place of heat index for heatstroke prevention in athletes.
On July 31st, 2001, in Mankato, Minnesota, heat sweltered around a group of Vikings Football players as they conducted their preseason trainings. One athlete, in particular, Korey Stringer, was intensely affected by the heat. He experienced nausea and exhaustion due to the heat index reaching 99°. In an effort to continue to show up for his teammates, Korey pushed through practice the next day in full padding before feeling extremely weak and eventually collapsing. He passed away only a few hours later from heatstroke that induced organ failure.
The truth is: Korey's death was preventable.
Following his passing, the Korey Stringer Institute was established in his honor. The institute's founding helped, and continues to help, spread awareness regarding the dangers of exertional heat stroke in athletes. The original methodology of calculating the risk of heat stroke, utilizing heat index, began to be challenged. Wet Bulb Globe Temperature (WBGT) emerged as the gold standard heat stress measurement tool utilized to calculate heatstroke risk. It employs a combination of wind speed, temperature, and humidity to provide the most accurate assessment of heatstroke risk.
Nielsen-Kellerman Co. has emerged as the leading producer of this WBGT technology with our very own Kestrel heat stress meter.
Across the United States, state athletic associations and governing bodies are adopting WBGT to protect their athletes. Below is a list of all fifty states and the District of Columbia and where they stand on the usage of WBGT.
Alabama - strict heat acclimatization protocols, activities must be adjusted based on the Wet Bulb Globe Temperature (WBGT).
- Alabama High School Athletic Association describing how WBGT is the first choice before heat index for assessing environment
Alaska - focus on just monitoring, just general awareness encouraged
Arizona - strict monitoring of the WBGT
Arkansas - require to monitor WBGT
California - requires schools to monitor environmental conditions using the WBGT
Colorado - advised monitoring based on WBGT
Connecticut - advised monitoring based on WBGT
Delaware - advised monitoring based on WBGT
Florida - mandatory to monitor WBGT
Georgia - advised monitoring based on WBGT
Hawaii - advised/encouraged to monitor based on WBGT
Idaho - advised/recommended usage of WBGT
Illinois - mandated use of WBGT
Indiana - uses heat index to guide
Iowa - recommended use of WBGT
Kansas - recommended use of WBGT
Kentucky - required use of WBGT
Louisiana - recommended use of WBGT
Maine - recommended use of WBGT
Maryland - required to monitor WBGT
Massachusetts - required to monitor using WBGT
Michigan - utilizes heat index
Minnesota - required to monitor WBGT
Mississippi - required to monitor WBGT
Missouri - recommended/guided use of WBGT
Montana - no formal standardized monitoring of either, just awareness
Nebraska -recommended/monitoring use of WBGT
Nevada - required/mandated use of WBGT
New Hampshire - recommended use of WBGT
New Jersey - required use of WBGT
New Mexico - recommended use of WBGT
New York - monitoring of WBGT, uses both heat index and WBGT
North Carolina - required monitoring of WBGT
North Dakota - no required heat index or WBGT monitoring
Ohio - mandated WBGT monitoring
Oklahoma - recommended WBGT monitoring
Oregon - recommended WBGT
Pennsylvania - required WBGT monitoring
Rhode Island - required WBGT monitoring
South Carolina - required WBGT usage to guide
South Dakota - recommended WBGT usage to guide
Tennessee - enforced/required WBGT usage to guide
Texas - required WBGT usage
Utah - recommended/emphasized importance
Vermont - encouraged to monitor using WBGT
Virginia - mandated WBGT monitoring
Washington - uses heat index
Washington D.C. - WBGT monitoring is basis of policy
West Virginia - required WBGT monitoring
Wisconsin - WBGT monitoring is encouraged
Wyoming - no monitoring using either system required
FAQS
What is Wet Bulb Globe Temperature and how is it measured?
Wet Bulb Globe Temperature (WBGT) combines three environmental measurements: evaporative cooling, radiant heat, and air temperature. Unlike a standard thermometer or heat index, WBGT reflects how the human body truly experiences heat. Devices like the Kestrel heat stress meter are intentionally built to calculate WBGT accurately and quickly to assess exertional heat stroke risk in athletes and workers.
What are WBGT regulations in the United States?
WBGT regulations in the United States vary by state. Across the country, state athletic associations and governing bodies have begun replacing the traditional heat index with WBGT-based guidelines to protect athletes from exertional heat stroke. Many states now require or recommend that schools, athletic programs, and sports organizations use WBGT measurements to make decisions about practice modifications, rest periods, and activity cancellations during hot weather.
Why is WBGT better than the heat index for athlete safety?
The traditional heat index only accounts for temperature and humidity, which underestimates heat stress in the sunny, low-wind outdoor conditions common in sports settings. WBGT also incorporates solar radiation and wind speed, providing a more complete picture of how the environment affects the active human body. Research and tragic events, like the heat stroke death of Minnesota Vikings offensive lineman Korey Stringer, have shown that relying on the heat index alone is insufficient for protecting athletes during intense outdoor physical activity.
