WBGT Policies

A Wet Bulb Globe Temperature (WBGT) is defined as the temperature at which water, by evaporating into air, can bring the air to saturation at the same temperature and is measured by a wet–bulb psychrometer. The WBGT was created to prevent heat illness in the United States Army and Marine Corps, and is now the most widely used index of heat stress. It will give the Athletic Trainer or medical staff the necessary information to modify a practice or event based on three temperature values combined.

Heat illness is among the top causes for sudden death in sport, and the WBGT is an effective way to determine if the outside environment is safe to continue physical activities. Modifications need to be made if the environment is putting athletes at a greater risk for heat illness. All factors must be considered. The Korey Stringer Institute along with the NATA have established a list of recommended guidelines for each state to implement and execute. By not adhering to these guidelines, states are being careless in their efforts to prevent heat illness and sudden death in their athletes.



The Korey Stringer Institute recommends the following guidelines:

  1. State requires all schools to have a heat modification policy for any sanctioned activity.
  2. The recommended heat policy is based off of WBGT (not heat index or any other methods) Heat Index is only acceptable for schools without funding for WBGT and the state is actively petitioning for funding to supply a WBGT.
  3. The WBGT temperature guidelines are based off of epidemiological data specific to that state/region (for bigger states a more comprehensive analysis may be needed). State required to seek alternative ways to obtain WBGT for their area via weather station WBGT or other valid local sources.
  4. The heat policy has at least 4 step progression of modifications (does not include the limit that dictates normal practice).
  5. Policy includes modification of equipment (if applicable to the sport).
  6. Policy includes specific modification of work:rest ratios.
  7. Policy includes specific modification of total practice time.
  8. Policy includes specific modification of water breaks.
  9. Policy mentions the use of a shaded area for rest breaks.

If any of this information is incorrect, has changed, or should be updated, please contact KSI.

Binkley HM, Beckett J, Casa DJ, Kleiner DM, Plummer PE. National Athletic Trainers’ Association Position Statement: Exertional Heat Illnesses. J Athl Train. 2002;37(3):329–343.

Budd GMWet-bulb globe temperature (WBGT)—its history and its limitations. Heat Stress in Sport. J Sci Med Sport. 2008;11(1):20–32.